WINTER 2018VOLUME LIV

THE QUARTERLY JOURNAL OF THE GEMOLOGICAL INSTITUTE OF AMERICA

Characterization of Natural-Color Pink Diamonds
The Allure of the Amber RoomColor Origin of Gem Diaspore
Diamond Inclusions Chart

Winter 2018VOLUME 54, No. 4

EDITORIAL
351

Pink Diamonds, Russia’s Amber Room, and More...
Duncan Pay

FEATURE ARTICLES
352

Natural-Color Pink, Purple, Red, and Brown Diamonds: Band of Many Colors
Sally Eaton-Magaña, Troy Ardon, Karen V. Smit, Christopher M. Breeding, and James E. Shigley
Summarizes data collected by GIA on more than 90,000 natural diamonds in this color range
and presents their gemological and spectroscopic properties.

pg. 358

378

The History and Reconstruction of the Amber Room
Russell Shor
Chronicles the history of this cultural landmark, originally assembled for the Prussian kingbetween 1701 and 1714, and its reconstruction by the Soviet Union starting in 1979.

394

The Color Origin of Gem Diaspore: Correlation to Corundum
Che Shen and Ren Lu
Examines the color origin of color-change diaspore, known commercially as Zultanite, andcompares the effectiveness of the chromophores it shares in common with corundum.

404

Corundum with Spinel Corona from the Tan Huong–Truc Lau Area inNorthern Vietnam
Nguyen Ngoc Khoi, Christoph A. Hauzenberger, Chakkaphan Sutthirat, Duong Anh Tuan,
Tobias Häger, and Nguyen Van Nam
Explains the reactions responsible for the formation of a well-developed reaction rim of spinelthat surrounds the corundum core in some specimens from this deposit.

pg. 389

NOTES & NEW TECHNIQUES
418

The Gemological Characteristics of Pipi Pearls Reportedly from
Pinctada maculata
Nanthaporn Nilpetploy, Kwanreun Lawanwong, and Promlikit Kessrapong
Reveals the internal features and spectroscopic data of these small natural pearls and offers themeans of separating them from pearls of related mollusk species.

CHARTSpg. 419428

Inclusions in Natural, Synthetic, and Treated DiamondNathan D. Renfro, John I. Koivula, Jonathan Muyal, Shane F. McClure,
Kevin Schumacher, and James E. Shigley
Provides a visual guide to the internal features of natural, synthetic, and treated diamonds.

REGULAR FEATURES
430

Lab Notes
Natural diamond mistaken as HPHT-grown diamond • Manufactured gold-in-quartz• Freshwater pearls with host shells • Montana ruby • Pargasite inclusions in Kashmir
sapphire • Irradiated CVD-grown melee diamond • Lightbox CVD-grown “white”
diamonds • Cat’s-eye Paraíba tourmaline from Brazil

pg. 432

440

Diamonds from the DeepAn examination of how diamonds form in the deep earth.

446

G&G Micro-World
Flower in demantoid • Lepidocrocite in boulder opal • Prismatic rutile in quartz • Heated
Burmese pink sapphire • Sillimanite in ruby • Gilson cat’s-eye synthetic emerald • Zircon
cluster in Ethiopian sapphire • Quarterly crystal: Bubble in fluorite

pg. 447

452

Gem News International
Emerald with inclusions along three directions • Type IaB diamond with boron • “Guizhou
Jade” from Qinglong, China • HPHT-grown diamond found in ring with diamond melee• Blue sapphires treated with heat and pressure • DiamondView observation of epoxy resin
filling in emeralds • Coated synthetic moissanite, rough and cut • Conference reports• Announcement: Crowningshieldite

470

2018 G&G Challenge Winners

Editorial Staff
Editor-in-Chief

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About the CoverNatural-color pink diamonds are exceptional treasures. The lead article in this issue, based on GIA’s database of
more than 90,000 diamonds in the pink, orangy pink, purple, red, and brown color continuum, summarizes theirgemological and spectroscopic characteristics. Shown on the cover is the 18.96 ct Winston Pink Legacy, a Fancy
Vivid pink emerald-cut diamond that recently sold at auction for more than $50 million. Winston Pink Legacy courtesy of Harry Winston, Inc. © 2018 Christie’s Images Limited.
Printing is by L+L Printers, Carlsbad, CA.
GIA World Headquarters The Robert Mouawad Campus 5345 Armada Drive Carlsbad, CA 92008 USA© 2018 Gemological Institute of America
All rights reserved.
ISSN 0016-626X

Pink Diamonds, Russia’s Amber Room,and More…
The beauty and desirability of pink diamonds is exemplified by the Winston Pink Legacy, astunning 18.96 ct Fancy Vivid pink diamond that realized US$50 million at auction in November
2018. Such sought-after diamonds are the subject of the third installment of our coloreddiamonds series. GIA researchers Sally Eaton-Magaña, Troy Ardon, Karen Smit, Christopher
Breeding, and James Shigley
An unprecedented characterization of naturally
summarize the current
science on natural-color
colored pink to red diamonds…
pink to red diamonds anddetail the cause of their color. The authors provide an unprecedented gemological andspectroscopic characterization by presenting absorption and luminescence spectra drawn from a
representative sample of 1,000 diamonds from GIA’s database.
Our second paper, by GIA’s Russell Shor, surveys the history of the legendary Amber Room. Originally commissioned
for Prussia’s King Frederick I in the early 1700s and presented to Czar Peter I of Russia in 1716, the amber panels
disappeared from St. Petersburg during the Second World War. In 1979, the Soviet Union initiated a painstaking
reconstruction of this cultural treasure. Besides its rich history, the author provides firsthand accounts from those who
participated in its recreation.
Next, Che Shen, a graduate student at the Gemmological Institute of China University of Geosciences in Wuhan, and
Ren Lu investigate the color origin of gem-grade diaspore using LA-ICP-MS spectrometry.
A reaction rim or “corona” results from alteration of a crystal’s exterior after its formation due to changes in geologicalconditions. In our fourth paper, researchers led by Nguyen Ngoc Khoi, from the Hanoi University of Science, provide
a study on corundum with spinel corona from northern Vietnam. The authors explain the genesis of the corona by
examining its reaction textures, chemical composition, and mineral inclusions and applying thermodynamic phaseequilibria calculations.
Our fifth paper offers a gemological characterization of pipi pearls from the bivalve mollusk Pinctada maculata.
Authors Nanthaporn Nilpetploy, Kwanreun Lawanwong, and Promlikit Kessrapong detail the internal structures andfurther investigate these small, sometimes strongly colored natural pearls using microradiography and UV-Vis, Raman,
and photoluminescence spectroscopy.
Our final article is a brief summary of diamond inclusions by GIA’s Nathan Renfro, John Koivula, Jonathan Muyal,
Shane McClure, Kevin Schumacher, and James Shigley. A foldout wall chart with photomicrographs showcasing
remarkable inclusions in natural, synthetic, and treated diamonds accompanies this article.
Besides our six articles and the chart, there’s plenty to enjoy in our regular features: Lab Notes offers analysis of threefreshwater blister pearls attached to their host shells, De Beers’ Lightbox CVD-grown diamonds, and an exceptionallyrare Montana ruby. Our new Diamonds from the Deep section provides an examination of how diamonds form in the
deep earth. Micro-World serves up an array of internal features observed in gem materials, while Gem NewsInternational reports on sapphire treated with high pressure and high temperature, coated rough and faceted synthetic
moissanite, and gemological conferences around the world.
Finally, don’t forget to check our listing of the 2018 G&G Challenge winners, and please do remember to cast yourvote for the Most Valuable Article of 2018 by mailing in the enclosed ballot card or by scanning the QR code to castyour vote online.

Duncan Pay | Editor-in-Chief | dpay@gia.edu

EDITORIALGEMS & GEMOLOGYWINTER 2018351

FEATURE ARTICLESNATURAL-COLOR PINK, PURPLE,
RED, AND BROWN DIAMONDS:
BAND OF MANY COLORSSally Eaton-Magaña, Troy Ardon, Karen V. Smit, Christopher M. Breeding, and James E. Shigley
Among fancy-color diamonds, naturally pink to red stones are among the rarest and most valuable. The color
origin for natural pink diamonds is due to either absorption from the as-yet-unidentified “550 nm” defect(s)that are correlated with shear stress and natural plastic deformation or, very rarely, the NV0/– centers (nitrogencombined with a vacancy). In this article we summarize prior research as well as the physical characteristics ofmore than 90,000 natural pink, orangy pink, red, purple, and brown diamonds from the internal GIA database.
(Browns and purples are included here, as they coexist on a color continuum with pink diamonds.) We alsopresent absorption and luminescence spectra on a representative subset of 1,000 diamonds to provide an unparalleled gemological and spectroscopic description of these rare gemstones. For pink diamonds, the gemological observations closely correlate with diamond type and the extent of nitrogen aggregation (i.e., type IaA<B,
type IaA>B, and type IIa pinks show distinct characteristics). Since type IaA<B diamonds are predominantly
sourced from the Argyle mine, which is scheduled to close in the next few years, we distinguish the propertiesof these pink diamonds from the others studied.

Diamond is one of Earth’s most extraordinarymaterials. It represents the pinnacle for several material and physical properties. As agem, however, it is the near-perfect examples—diamonds attaining the D-Flawless distinction—and
those with imperfections resulting in a vibrant or
surprising color that create the most enduring impressions. Fancy-color natural diamonds are among
the most highly valued gemstones due to their attractiveness and great rarity. The 18.96 ct Winston
Pink Legacy, with a color grade of Fancy Vivid pink,recently made history by selling at over $50 million,
its $2.6 million per carat price an all-time high for apink diamond (Christie’s, 2018).
This article is the third in a series of studies onnatural colored diamonds: Breeding et al. (2018) discussed the color origin of green diamonds, and EatonMagaña et al. (2018) dealt with blue/gray/violet
diamonds. Here we summarize the color origin oforangy pink, purplish pink to pinkish purple, brown-

ish pink to pinkish brown, pink, red, purple, and unmodified brown diamonds. Although this article cov-

In Brief• Almost all pink/purple/red/orangy pink diamonds owe
their color to the presence of an as-yet-unidentified
550 nm absorption band. Minor differences in bandcharacteristics along with the presence of other defects(such as N3 and H3) lead to differences in hue andsaturation.
• Among “pink” diamonds colored by the 550 nm band,
distinctions in color distribution and observed strain
can be correlated with their diamond type.
• A sizable percentage of the “pink” diamonds studied,particularly those with saturated colors, are consistent
with material found at the Argyle mine, scheduled toclose in 2020.

See end of article for About the Authors and Acknowledgments.
GEMS & GEMOLOGY, Vol. 54, No. 4, pp. 352–377,
http://dx.doi.org/10.5741/GEMS.54.2.352© 2018 Gemological Institute of America

ers a wide variety of color descriptions compared to,for example, the first article in the series, which was
limited to natural diamonds with only green as the352

GEMS & GEMOLOGY

NATURAL-COLOR PINK DIAMONDSWINTER 2018

Figure 1. The 34.65 ct Princie (center, photo courtesy of Christie’s) is a famous example of a pink diamond coloredby NV0/– centers. It is flanked by an array of natural brown, brown-pink, orangy pink, purple-pink, and pink diamonds with the far more common cause of color—the 550 nm absorption band. These examples span the diverse
color range of pinks submitted to GIA. The photos in this compilation are not imaged to scale.

dominant description, the color descriptions arejoined here, as the vast majority of them (which will
be quantified below) contain the 550 nm band as aprevalent absorption feature. For the sake of simplicity, this broad range of color descriptions (e.g., figures
1 and 2) will generally be shortened to “pink” in thisarticle.
Previously, several aspects of gem-quality “pink”
diamonds have been addressed, such as their gemological characteristics (e.g., King et al., 2002); theirdefects and associated spectroscopic features (e.g.,
Titkov et al., 2008; Deljanin et al., 2008; Fisher et al.,2009; Gaillou et al., 2010; Stepanov et al., 2011;
Byrne et al., 2012a,b; Titkov et al., 2012; Gaillou etal., 2012; Howell et al., 2015); and reports on notable“pink” diamonds (Smith and Bosshart, 2002; King etal., 2014). Here we review the published literatureand supplement it by compiling results obtained
from 90,000+ natural diamonds recorded in the GIAinternal database.
Our purpose is to provide a detailed account of thegemological and spectroscopic characteristics of natu-

ral “pink” diamonds, principally colored by an as-yetunidentified “550 nm” absorption band, in order tohelp the trade better understand how these beautiful
diamonds with extremely valuable colors originate.

NATURAL-COLOR PINK DIAMONDSGEMS & GEMOLOGYCAUSES OF COLOR
All colored diamonds submitted to GIA are subject
to a variety of spectroscopic analyses. The analyticaltechniques and specific details of the instrumentation and methods used are summarized in Breeding
et al. (2018; see supplementary table S-1 athttps://www.gia.edu/gems-gemology/spring-2018natural-color-green-diamonds-beautiful-conundrum).
“Pink” color in diamonds spans a wide range in
the GIA color description terminology (figure 2; Kinget al., 1994; King, 2006). In this article, we include all
natural fancy-color diamonds with pink, purple, or
red as the dominant hue (i.e., the final name in thecolor description) in addition to unmodified brown.
Diamonds with yellow-brown or orange-brown color
will be discussed in an upcoming article. In the full
dataset of 90,000+ “pink” diamonds seen at GIA be-

WINTER 2018353

Increasing Saturation

Very Light pink

Light pink

Fancy Light pink

Fancy pink

Fancy Intense pink

Increasing Brown

Fancy brown

Fancy Deep pink

Fancy red

Increasing Orange

Fancy pink-brown

Fancy brown-pink

Fancy brownish
orangy pink

Fancy Intense orangy
pink

Fancy Vivid pinkishorangeIncreasing Purple

Fancy Vivid purplish pink

Fancy Intense purplepink

Fancy pink purple

Fancy Vivid pink purple

Fancy Vivid purple

Figure 2. These examples of diamonds with varying hues and color saturations represent the “pink” color ranges.
Photos by GIA staff. The photos in this compilation are not imaged to scale.

tween January 2008 and December 2016, the highest
percentage were unmodified pink (40%), followed bypinkish purple to purplish pink (28%), brownish pink
to pinkish brown (17%), and orangy pink (10%); see
the color distribution in figure 3. The rarest colors
were unmodified brown (3%); purple with brown orgray modifiers (1%); unmodified red (0.5%); red withbrown, purple, or orange modifiers (0.4%); and, leastof all, unmodified purple (0.05%).
In the description of color grades, it is more difficult
for the eye to interpret subtle hue differences for very
light-colored diamonds than it is for more saturated diamonds (King et al., 1994; King, 2006). For the lightest
color grades, therefore, fewer hue names are used andthe color description spans a wider portion of the hue
wheel. Among unmodified pink diamonds, 54% wereFaint, Very Light, or Light in color (figure 3, right).
Below we chronicle the main causes of color in theform of various structural defects, through which“pink” diamonds can be divided into different groups.

Colored Deformation Lamellae. In many brown,
pink, and purple diamonds, the color is concentrated
within parallel narrow bands (referred to as “brown
graining,” “pink graining,” or glide planes, or alternatively as a more generalized term of colored lamellae).
When manufactured as cut stones, these are typicallyoriented to minimize the face-up appearance of thelamellae, resulting in an apparent even color distribution through the table facet. Since the lamellae arealong the {111} plane, these pink diamonds are generally oriented such that the table facet is {100} (J. Chapman, pers. comm., 2018). Microscopic observation of
the lamellae is best accomplished looking throughthe pavilion facets of the diamond.
These colored lamellae are caused by shear stressand natural plastic deformation (figure 5, A and B).
Deformation to form these lamellae only occurs dur-

354

GEMS & GEMOLOGY

NATURAL-COLOR PINK DIAMONDS

Various colors and representative visible-near infrared
spectra are shown in figures 2 and 4, respectively.

WINTER 2018

Brownish pink
to pinkishbrown, 17%

Brownish orangy
pink to orangy
pink,10%

Pinkish purple topurplish pink, 28%

Brown, 3%
Purple/brownpurple/graypurple, 1%
Pink, 40%

Red/brown-red/orange-red,
0.9%

DISTRIBUTION OF TONE/SATURATION
IN "PINK" DIAMONDSCOLOR DISTRIBUTION
35%

Unmodified pink diamonds
All others (including purplepink, orangy pink, brownpink, etc.)

30%

25%

20%

15%

10%

5%

0%
Faint

Very
Light

Light

Fancy
Light

Fancy Fancy Fancy Fancy
Intense Vivid Deep

Fancy
Dark

Figure 3. Color distribution of 90,000+ pink, purple, brown, orangy pink, and red diamonds graded at GIA between
2008 and 2016. Left: Unmodified pink and purplish pink diamonds dominated within this color range, while diamonds with a brown color description were submitted in lower quantities. Right: Saturation distribution of unmodified and modified pink diamonds. A majority of the unmodified pink samples (54%) are in the Faint to Light
color range.

ing a diamond’s extended residency at high temperature (>900°C; DeVries, 1975; Brookes and Daniel,
2001), either in the mantle or during kimberlite eruption to the earth’s surface. These deformation lamellae have been attributed to slip/glide planes(dislocation movement) and to micro-twins (Mineeva
et al., 2009: Gaillou et al., 2010; Titkov et al., 2012;

Howell et al., 2015). In many diamonds these deformation lamellae are closely associated with brown,
pink, or purple color; these colors can also appear
evenly through the entire diamond or irregularly as
distinct patchy areas (figure 5, C and D). The structural defects responsible for the different color contributions in pink, brown, and purple diamonds (i.e., the

VIS -NIR SPECTRA

N3 (415 nm)
550 nm band
H3 (503 nm)

ABSORBANCE

A: Fancy pink

B: Fancy Light purple-pink

C: Light brown-pink

NV0 (575 nm)

D: Fancy Dark brown

NV– (637 nm)

E: “Golconda” Fancy Light pink
400

450

500

550

600

650

700

750

WAVELENGTH (nm)

NATURAL-COLOR PINK DIAMONDSGEMS & GEMOLOGY

800

Figure 4. The vast majority of “pink” diamonds
owe their color to the 550
nm absorption band (A–C). Spectrum A shows adiamond with the 550
nm band along with pronounced N3 and H3 centers. Spectrum D is for abrown diamond with a
gradually increasing absorption toward lower
wavelengths that creates
the brown color; a very
shallow 550 nm absorption band has little effecton the color. Spectrum E
is for a “Golconda pink,”
which shows absorption
by NV0/– centers. The
spectra are offset vertically for clarity.

WINTER 2018355

Slip/Glide planesA

Graining
B

UniformC

PatchyD

Figure 5. A: These pink type IaA>B diamonds show the color concentrated within pink lamellae (identified as“slip/glide planes” by GIA), while the remainder of the diamond is comparatively colorless. B: These typeIaA<B pink diamonds show more subtle concentrations of color compared to A—the red arrow indicates thebest example of this graining. C: These type IIa pink diamonds show uniformly distributed color. D: An unusual
example of a rough pink diamond with radiation stains and irregular or “patchy” distribution of color.

“brown absorption continuum,” the 550 nm absorption band, and NV0/– centers) are discussed in later
sections.
Viewed with a microscope, the two types oflamellae appear distinct, and at GIA these are referred to as either slip/glide planes or graining. They
also appear to correspond with the ratio of A centers(nitrogen pairs) and B centers (four nitrogen atoms
around a vacancy) in the diamond (Gaillou et al.,2010). As diamonds reside in the mantle, or are exposed to higher temperatures, the A-aggregates decrease as they combine to form B-aggregates (Taylor
et al., 1990). “Pink” diamonds where A-aggregates
outnumber B-aggregates (i.e., type IaA>B, such as
some Siberian diamonds; Titkov et al., 2008) show
colored lamellae that appear distinctly different
from “pink” diamonds where B-aggregates are
greater than A-aggregates (i.e., type IaA<B, such as
Argyle diamonds; Howell et al., 2015). In type IaA>B“pink” diamonds (designated below as Group 2), thecolored lamellae appear distinct and straight alongthe {111} planes, and the pink color is restricted tothese colored lamellae (Gaillou et al., 2010). Between these lamellae, the diamond is colorless (e.g.,
figure 5A). GIA often refers to these lamellae as“slip/glide planes” to distinguish them from theother type of colored lamellae. In type IaA<B “pink”
diamonds (designated below as Group 1; figure 5B),
the pink color is not restricted to the lamellae anddoes not appear as straight lines. GIA commonlyrefers to this as “graining,” although these distinctions in terminology have not been defined within
the gemological literature.
In faceted diamonds, the colored lamellae of typeIaA<B “pink” diamonds can appear more subtle than
the apparent contrast in color within type IaA>B“pink” diamonds (compare figure 5A with 5B). Recent research (see box B) shows that these classifications are not quite so distinct for diamonds that are
low in nitrogen, and the visual distinction between
colored “graining” and “slip/glide planes” becomeschallenging.
In contrast, the majority of type IIa “pink” diamonds, and some pure type IaB diamonds, do notshow visible evidence of colored lamellae (either as“graining” or “slip/glide planes”), and the “pink”
color is uniformly distributed. However, type IIa“pink” diamonds do occasionally exhibit graining (appearing as colorless, brown, or pink) similar to thatseen in type IaA<B diamonds.

356

GEMS & GEMOLOGY

NATURAL-COLOR PINK DIAMONDSWINTER 2018

Brown General Absorption. Brown color is quite
common in natural diamonds, and a brownish tingeis reportedly observed in 98% of all as-mined diamonds, whether or not they are deemed gem-quality(Dobrinets et al., 2013). While brown diamonds areabundant, most are either not faceted or not submitted for grading reports unless there is another contributing color such as pink, orange, or yellow or ifthey can be faceted in such a way as to receive a gradeon the D-to-Z scale (King et al., 2008). As mentioned
previously, only 3% of the 90,000+ samples studied
here had an unmodified brown color.
The vast majority of brown diamonds have theircolor ascribed to vacancy clusters (i.e., clusters of vacant carbon-atom positions; see Hounsome et al.,2006; Fisher et al., 2009) that are created through natural plastic deformation. These clusters are generally
thought to contain approximately 40–60 vacancies,
and the dissociation (generally through high-pressure,high-temperature HPHT annealing) of these vacancy
clusters leads to the removal of brown color. These
vacancy clusters create a so-called brown absorption
continuum (Fisher et al., 2009; Dobrinets et al., 2013)that causes a gradually increasing absorption acrossthe visible spectrum toward lower wavelengths (figure 4, spectrum D). This brown absorption continuum can coexist with other color centers (e.g., figure
4, spectrum C).
Brown coloration (by itself or in combination withother color centers) can also have other origins, including high concentrations of isolated substitutional
nitrogen, CO2, and micro-inclusions (Hainschwang etal., 2008; Dobrinets et al., 2013). However, these are
not as commonly observed as those diamonds withthe brown absorption continuum.

additional absorption at lower wavelengths (figure 4,
spectrum A) that can alter the observed color.
Nitrogen-Vacancy Centers. “Pink” diamonds naturally colored by NV0/– centers are extremely rare;
however, these centers are almost exclusively thecause of color in treated and synthetic “pink” diamonds. Absorption by the nitrogen-vacancy centers(the ZPL for the neutral NV center is at 575 nm,
while the negative NV center is at 637 nm) alongwith their sidebands creates the absorption that produces the pale, uniform “pink” color in these veryrare type IIa diamonds (figure 4, spectrum E). They
are often referred to as “Golconda pink” diamonds(Fritsch, 1998). The 34.65 ct Fancy Intense pink Princie is a famous example of “Golconda pink,” and it
sold for more than $39 million at auction in 2013
(Christie’s, 2013). While the Princie originates fromthe historical mining region of Golconda in India,
today the term “Golconda” is generally associatedwith this cause of color and not with any geographical link to the ancient mining region.

OCCURRENCE AND FORMATION
The formation mechanism for “pink” diamonds inthe earth varies significantly depending on the defects
responsible for the color. Historical sources include
India, Brazil, Indonesia (Borneo), and southern Africa.
But before the Argyle mine in Australia opened in
1983, there was no stable supply of “pink” diamonds,
and many of those currently available come from Argyle (figure 6; Hofer, 1985; Shigley et al., 2001; Shirey
and Shigley, 2013). More recently, mines in the Siberian and Arkhangelsk regions of Russia have been documented as producing pink to purple-pink diamonds(Titkov et al., 2008; Smit and Shor, 2017). Finding new
deposits with “pink” diamond production is important to the trade, since the final year of planned operation at the Argyle mine is 2020 (Shor, 2018).

550 nm Visible Absorption Band. The most common
cause of “pink” color is a broad absorption band centered at around 550 nm (Orlov, 1977; figure 4, spectrum B). The defect responsible for this visible
absorption band has not yet been identified, but it
has been correlated with plastic deformation (Gaillou
et al., 2010; Howell et al., 2015). In conjunction withthe 550 nm band is a smaller, narrower band within
the UV range centered at ~390 nm (Fisher et al., 2009;
Byrne et al., 2012a).
In “pink” type Ia diamonds, nitrogen often creates
other visible absorption features that are detected in
the visible absorption spectra and can affect the observed color. The N3 defect (zero phonon line, or ZPL,
at 415.2 nm) and the H3 defect (ZPL at 503.2 nm)
along with their vibronic structure (sidebands) create“Pink” Diamonds with 550 nm Absorption Band.
Occurrence. Nitrogen content and the extent of nitrogen aggregation in the atomic structure, and by inference the diamond’s geographic origin, leads to very
different observations of how “pink” color due to the
550 nm band is distributed within the diamond.
Sources for Group 1 “pink” diamonds (type IaA<B,
with wavy graining) include the Argyle mine in Australia and alluvial deposits in Venezuela. Group 2“pink” diamonds (type IaA>B, slip/glide planes) are
principally mined in southern Africa, Canada, andRussia (Howell et al., 2015).

NATURAL-COLOR PINK DIAMONDSGEMS & GEMOLOGYWINTER 2018357

or could only form, under high-pressure conditions)have been documented in GIA’s New York laboratory,
but their geographic source location is unknown. Oneof the few superdeep IIa “pink” diamonds for which
GIA does have locality information is a 23 ct roughpink type IIa diamond found at the Williamson mine(Tanzania) in November 2015 (Smith et al., 2017;
Petra Diamonds, https://www.petradiamonds.com/
about-us/our-heritage). Fisher et al. (2009) also citedthe Williamson mine as a source of type IIa pinks,
though production numbers are unknown. The
Williamson mine has also been a source of highnitrogen type Ia “pink” diamonds (Gaillou et al., 2012).
Although “pink” diamonds are known from several deposits around the world, they remain a verysmall percentage of the overall production from any
particular deposit. The Argyle mine is well known
as a source for “pink” diamonds, but these accountfor much less than 0.1% of the overall production,
where 72% of the production is brown and 27% iscolorless to yellow (Shigley et al., 2001; figure 6). At
the Lomonosov deposit in northwestern Russia, only
0.04% of production is fancy-color diamonds (purple,
pink, violet, green, yellow, and brown; Smit and Shor,2017). Some parcels from the Mir deposit in Siberia
contain 1–6% pink to purple diamonds, although nooverall production data were available (Titkov et al.,2008 and references therein).

An abundance of locality data is available on typeIa “pinks” but not for type IIa “pink” diamonds.
There are several observations of type IIa “pinks” thatcoincide with Argyle “pinks” such as color range, thepresence of wavy graining in some type IIa diamonds,
and some photoluminescence peaks that appear in
type IIa, IaB, and IaA<B “pinks.” However, reports regarding the output of the Argyle mine largely exclude
type IIa diamonds (J. Chapman, pers. comm., 2018).
Type IIa pink-brown diamonds are known from localities that also yield so-called superdeep diamonds
from >250 km in the earth’s mantle (Smith et al.,2017). Pink-brown type IIa diamonds with superdeep
mineral inclusions (i.e., minerals that are only stable,

Formation. Pink-brown color is often associated with
deformation lamellae in the diamond, and the geological process responsible for this deformation is often
mountain building (Stachel et al., 2018). A geologicallymodern example of mountain building is the Himalayan range in Asia, which is increasing in elevation due to collision between the Eurasian and Indian
tectonic plates. The remnants of mountain ranges thatdeveloped during collisional processes millions to billions of years ago, and have since been eroded away,
are called “orogens.” During continental collision,
rocks become highly deformed with such severe mineral recrystallization that any diamonds and otherminerals in the rock can take on a “flow” texture.
The Argyle mine, the most famous supplier of occasional pink and red diamonds, occurs in one sucharea that experienced ancient continental collision,
the Proterozoic Halls Creek orogen (1.8 Ga; Tyler andPage, 1996). Argyle diamonds formed in close association with these collisional processes (Richardson
et al., 1985), and after their formation resided near
the base of the lithosphere (Stachel et al., 2018). It isin this high-temperature, high-deformation environ-

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GEMS & GEMOLOGY

Figure 6. The Argyle mine is well known as a sourcefor pink diamonds, although these account for muchless than 0.1% of the overall production. Photo ©
Rio Tinto.

NATURAL-COLOR PINK DIAMONDSWINTER 2018

ment near the convecting mantle that the pinkbrown-red color in these diamonds likely originated.
The Lomonosov mine, which produces pink-purple-brown diamonds, also lies within an area that experienced ancient subduction and continental
collision—around 1.9 billion years ago—and is
known as the Lapland-Kola orogen (Daly et al., 2006).
Although the Lomonosov diamonds have not been
dated, it is very possible that they formed in association with subduction, or experienced deformation related to the subduction-collision events, during theirresidence at depth in the lithospheric mantle (Smitand Shor, 2017).
Diamonds’ presence within an orogenic belt does
not necessarily imply high deformation that could result in pink-brown colors. The Ellendale mine is in
the King Leopold orogen, a geologic region that experienced mountain building 545 million years ago along
the southwest margin of the Kimberley craton in Australia. Although diamonds from this deposit are famous for their fancy colors, they are yellow (not thepink-brown colors typically associated with deformation) and the defects responsible for their yellow color
are the very common “cape” absorption series (N3and N2 defects). Additionally, cathodoluminescence
images of the internal growth features in these diamonds are not dominated by deformation lamellae(Smit, 2008). Together, the bodycolor and lack of deformation features suggest that the 1.4 billion-yearold Ellendale diamonds survived in the lithosphericmantle through the Proterozoic orogenic event (until
their eruption at 20 Ma) without being significantly
deformed, implying that the King Leopold orogenic
event was limited to the earth’s crust.

Formation. The combination of geologic conditions
necessary to create and preserve NV0/– centers in natural diamonds is exceedingly uncommon. NV0/– centers form when vacancies in the diamond lattice aretrapped next to isolated substitutional nitrogen. Although these defects are rarely preserved in nature,they are relatively easy to create in a laboratory.
Three rare conditions are needed to produce natural“Golconda pink” diamonds.
First, these diamonds need low nitrogen concentrations such that when any nitrogen present in thelattice combines with vacancies upon eventual annealing, no infrared-active nitrogen is detected. This
would classify the diamond as rare type IIa, whichaccording to a recent survey make up only 1.3% of
diamonds submitted to GIA for grading (out of 3.5
million diamonds; Smith et al., 2017).
Secondly, vacancies need to be present in the diamond lattice. Vacancies in the lattice are created either through irradiation or deformation. Radiation
exposure is rare in the mantle, and typically only occurs once the diamond is erupted to the earth’s surface and has been in contact with crustal rocks or
fluids that contain sufficient concentrations of elements such as uranium, thorium, or potassium(Breeding et al., 2018). Since high temperatures above
600°C are needed to combine vacancies with nitrogen, it is more likely that deformation processes in
the mantle are responsible for vacancy creation. For
example, brown coloration due to vacancy cluster
formation often originates from deformation of diamond in the mantle (Fisher et al., 2009).
Thirdly, in order to preserve isolated nitrogen forannealing, and prevent any NV centers from annealing further to form A and B nitrogen centers, the diamonds must not have experienced high temperaturesof greater than 900°C for more than a few million
years (Smit et al., 2016, 2018).
The exact geological environment in the deep
earth where all these conditions are met is not clear.
It is possible that some “Golconda pink” diamonds
are superdeep, since type IIa diamonds often have asublithospheric origin (depths >300 km; Smith et al.,2016, 2017), and these superdeep diamonds often exhibit deformation features. For example, brittle fractures along the {110} crystallographic planes as wellas polygonized dislocation networks have been observed in deformed superdeep diamonds (Smith et al.,2016, 2017). Deformation processes responsible forthese features could be related to mantle convection
or deep subduction processes. However, sublithospheric mantle temperatures are in excess of 1400°C,
and it is not clear how isolated nitrogen and NV0/–
would survive at these temperatures without being
annealed to more aggregated nitrogen, which is common in superdeep nitrogen-bearing diamonds.

NATURAL-COLOR PINK DIAMONDSGEMS & GEMOLOGY

Pink Diamonds with NV0/– Centers. Occurrence. Although pink diamonds colored by NV0/– centers (i.e.,“Golconda pinks”) are associated with the ancient diamond mining and trading center of Golconda in India(now Hyderabad), there are no known reliable modern
sources in this region. Natural diamonds with sufficient concentrations of NV0/– absorption to contributeto the pink color are extremely rare. The “Golcondapink” diamonds examined in GIA laboratories (0.6%
of 1,000 randomly selected “pink” diamonds; see theAbsorption Spectroscopy section for further details) do
not have any geographic source information.

WINTER 2018359

WEIGHT DISTRIBUTION OF “PINK” DIAMONDSPERCENTAGE OF DIAMONDS IN WEIGHT RANGE

14%

Pink
Purple-pink

12%

Figure 7. Histogram
showing the weight distribution of the 90,000+
diamonds graded by
GIA from 2008 to 2016
in the pink, purple,
orangy pink, brown,
and red color range.
The histogram is divided into 0.1 carat increments between 0
and 5 carats. Also
shown are the remaining 2% that weighed
more than 5 carats.

Brown-pink
Orangy pink
10%

Brown
Purple
8%

Red
6%

4%

2%

0%
0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

>5

CARAT WEIGHTLABORATORY GRADING
Stones weighing less than 1.0 ct comprised 83% of
GIA intake of the 90,000+ natural “pink” diamondsin this study, and more than half (56%) weighed lessthan 0.5 ct (figure 7). This chart clearly shows thatwhile the total number of “pink” diamonds appears
to be quite large—compared to 15,000+ in theblue/gray/violet group (Eaton-Magaña et al., 2018)
and 50,000+ in the green group (Breeding et al.,2018)—all colored diamonds submitted to GIA annually represent approximately 3% of overall intake.
The vast majority are also quite small. Noticeable
spikes in quantity are observed near important caratweight thresholds (1.0, 1.5, 2.0, 3.0 ct, etc.), and many
have a light color (figure 3, right).
This chart also serves to illustrate that while cutters make faceting and polishing decisions to maximize the face-up color and appearance, weightthresholds are often important considerations as
well. Diamonds with purplish pink coloration aremuch more prevalent at weights below 1 carat, while
those with brown coloration are much more prevalent above 1 carat (figure 7), likely because it is only
worthwhile to submit brown diamonds in larger
sizes.
Although colored diamonds are often fashioned
as fancy shapes to enhance their face-up color, rounds
represent a slight plurality (24%) of the 90,000+“pink” diamonds (figure 8), followed by pears (20%),
rectangles (16%), and cushions (13%) and others.

360

NATURAL-COLOR PINK DIAMONDS

While the fancy shapes are generally evenly distributed across the range of weights and color saturations, the rounds are predominantly seen among thesmaller and lighter-color diamonds. Of all fancycolor “pink” rounds, 90% are less than one carat and
42% are Faint, Very Light, or Light.

ABSORPTION SPECTROSCOPY
To investigate the distribution of the major causes ofcolor, we studied the visible absorption and IR ab-

Figure 8. The shape distribution of the 90,000+ “pink”
diamonds graded by GIA from 2008 to 2016.

Heart, 6%Oval, 9%Marquise, 5%
Cushion, 13%
Square, 3%
Other, 2%
Emerald, 2%

Rectangle, 16%

Round, 24%
Pear, 20%

GEMS & GEMOLOGYWINTER 2018

sorption spectra of 1,000 natural brown, pink, purple,
and orangy pink diamonds. These were randomly selected as representative of the 90,000+ samples in ourinternal GIA database. This subset of data was used
to generate the charts provided in figures 9–15.
Absorption spectroscopy measurements are nondestructive and indicate the major defects and impurities within a diamond by passing light through thestone and measuring the wavelengths (energies) absorbed by the impurities and defects present. Defects
that cause absorption within the visible spectrum(between 400 and 700 nm) contribute to the bodycolor of the diamond. Other defects that are detected
only through infrared (IR) absorption spectroscopy do
not give information about the color-contributing defects but provide an indication of whether a diamondis natural, synthetic, or treated.
For this 1,000-diamond subset, we observed that
992 (99.2%) contained the 550 nm band. Six were colored by NV0/– defects (0.6%); this percentage indicatesthe extreme rarity of “Golconda pink” diamonds evenamong this restricted population of “pink” diamonds.
The remaining two of the 1,000 diamonds in this subset were unmodified brown diamonds that did notshow an observable 550 nm band, while the otherbrown diamonds showed a slight 550 nm band that
did not cause sufficient absorption to affect the color(figure 4, spectrum D). The majority of this section
will focus on the optical and infrared absorption spectra of diamonds colored by the 550 nm absorption
band, and the diamonds containing NV0/– defects will
be briefly discussed at the end.
Vis-NIR Absorption Spectroscopy of 550 nm “Pink”
Diamonds. As the vast majority of these diamonds
were principally colored by the 550 nm band, we
looked for subtle distinctions between the Vis-NIR
absorption spectra to chronicle their differences. As
such, the Vis-NIR absorption spectra of most diamonds were distinguished by the presence or absenceof the N3 and H3 centers, so we could gauge whether
these had any effect on the resulting color grade. Figure 9 shows the effect of these various Vis-NIR absorption spectral features on the resulting hue andtone. Figure 9A indicates that the addition of N3 andH3 does not appear to correlate with the observed hue(that is, the proportion of diamonds with H3 and/or
N3 does not significantly change between those withbrown-pink, pink, and purple-pink designations). Unmodified purple and red diamonds deviate from thisobservation and are discussed in box A. Additionally,orange-pink diamonds showed a slightly higher per-

NATURAL-COLOR PINK DIAMONDS

centage with H3/N3 centers; when these were present, the increased absorption of blue light shifted theperceived color to orange. However, the presence ofN3 and H3 centers did have a dramatic effect on thetone of the color (figure 9B). In most cases, those diamonds with faint colors only have a detectable 550
nm band. For the majority of diamonds with a fancy
or deeper tone, the 550 nm band is enhanced by theaddition of the N3/H3 center (or the presence of bothfeatures).
The spectra of 50 “pink” diamonds with the 550
nm band were analyzed to determine the full widthat half maximum (FWHM) of the band and the center
wavelength, as minor variations in the peak widthand position of this band can affect the color. The
center wavelength of the absorption band is nominally at ~550 nm, but performing peak fitting using
a mixed Gaussian/Lorentzian equation shows thatthe center wavelength can vary from 545 nm to 565
nm. Meanwhile, the width of the absorption band
can vary from 60 nm to 100 nm. Fitting the 550 nm
absorption bands from diamonds of various hues
showed that the orangy pink to pink diamonds generally had a lower center wavelength (545–550 nm)
and a narrower width (60–80 nm) than purple-pink
diamonds (555–560 nm and 70–100 nm, respectively); for example, figure 9C compares the Vis-NIR
absorption spectra of a purple and pinkish orange diamond. The slight shift of the 550 nm band awayfrom the orange to red portion of the visible spectrum (for orangy pink diamonds) or away from theblue (for purple-pink to purple diamonds) can contribute to the transmission window that leads to theresulting bodycolor. A notable percentage of pink topurple-pink (~20%) also show a series of oscillations
overlaid on the 550 nm band at ~600 nm (figure 4,
spectra B and C; box B).
Fourier-Transform Infrared (FTIR) Absorption Spectroscopy of 550 nm “Pink” Diamonds. Nitrogen Aggregation. Within the 1,000-diamond subset, 992
contained the 550 nm band, as stated above. Of
these, 243 (24%) were type IIa based on IR absorption
spectra along with the six diamonds colored by NV0/–
centers (i.e., “Golconda pinks”), for a total of 249
type IIa diamonds. The remaining 751 diamonds all
contained aggregated nitrogen (figure 10A shows avariety of the IR spectra obtained for “pink” diamonds along with the corresponding A and B nitrogen aggregate concentrations, and figures 10B and
10C show the overall distribution of diamond type
along with the origin of color and color description).

GEMS & GEMOLOGYWINTER 2018

361

BOX A: PURPLE AND RED DIAMONDS
Purple Diamonds. Unmodified purple diamonds areamong the rarest of all natural diamonds (figure A-1,
inset). Due to their extreme rarity, none were randomly
chosen for the 1,000-diamond subset. Nevertheless, wesummarize here the properties of ~50 submitted purple
diamonds. Among these purple diamonds, 69% wereless than 1 carat, and 91% were less than 2 carats. Additionally, 42% had a color grade of Vivid or Intense
purple.
Pinkish purple to purplish pink diamonds span
across almost all diamond types, and about half containsufficient quantities of H3 and/or N3 in their Vis-NIR
absorption spectra to affect the color (figure 9A). In contrast, the vast majority (98%) of the approximately 50
unmodified purple diamonds did not show a significant
H3 or N3 peak (figure A-1). In these samples, more blue
light is then transmitted, giving rise to the purple tint.
Additionally, as shown in figure 9C, the purple-pink topurple diamonds have the center of the ~550 nm band
shifted slightly toward longer wavelengths, further increasing the blue light transmission. Additionally, thevast majority (96%) were either type IaA>B or IaA withtotal nitrogen greater than 150 ppm or showed a saturated type Ia spectrum, consistent with prior reports(Titkov et al., 2008). Among these, the color saturation(Very Light to Vivid) did not appear affected by nitrogenconcentration. Instead, the color saturation appeared to
be derived more from an increase in absorption of the
550 nm band.
The few samples deviating from the vast majority of
purple diamonds were a Fancy purple low-nitrogen typeIaA<B sample that had H3 and N3 centers, and a Light
purple type IIa diamond. For the set of purple diamonds,
33% showed no fluorescence to long-wave UV, 33%
showed blue fluorescence (most were very weak to
Figure A-1. These three Vis-NIR absorption spectra arefrom a 0.67 ct Light purple, a 0.83 ct Fancy purple, and a
0.81 ct Fancy Vivid purple. The diamond shown in theinset was identified as type IaA with 250 ppm of nitrogen(Darley et al., 2011).

weak), and 33% showed yellow fluorescence (most werevery weak to weak).
Red Diamonds. Unmodified red diamonds are some of
the most sought after gems (e.g., figure A-2, inset), andfor decades it was uncertain whether any diamond would
achieve this color description. To study these diamonds
in more detail (as only five unmodified red and six withorange or purple modifiers were randomly selected for the
1,000-diamond subset), we looked at the spectra of 100
Fancy red diamonds colored by the 550 nm band. Unlike
most hue groups, red diamonds do not show any distinction in tone—a “light red” diamond would be designatedas pink instead. Among these 100 diamonds, 80 were lessthan 1 carat and all were less than 2 carats.
From examination of the Vis-NIR absorption spectra,
all showed very similar spectra in that they were coloredby the 550 nm band in combination with the H3 centerand its sideband (figure A-2).
Almost all of the Fancy red diamonds were type IaA<B(96), with the balance including a saturated type Ia, IaA,
IaA>B, and IaB. Of the type IaA<B diamonds, most had
low to moderate amounts of nitrogen (20–100 ppm total
nitrogen), with a few showing very low (<10 ppm) or comparatively high amounts of nitrogen (>150 ppm).
For these 100 Fancy red diamonds, all showed fluorescence to long-wave UV and most (95) showed blue fluorescence; the majority showed weak (30) or medium(53) intensity. Of these 100, the remaining five showed
yellow fluorescence (weak to medium).
As the vast majority of Fancy red diamonds are typeIaA<B, a diamond type principally sourced from the Argyle mine in Australia (e.g., Howell et al., 2015), this rarecolor will likely become even more so with the planned
closing of the mine in a few years.

Figure A-2. The Vis-NIR absorption spectra are from three
Fancy red diamonds (from top: 1.01 ct, 0.48 ct, and 0.67ct) that show similar features.

VIS -NIR ABSORPTION SPECTRAVIS -NIR ABSORPTION SPECTRA
N3

N30.83 ct Fancy purple

H3
H4

0.81 ct Fancy Vivid purple

400

450

500

550

600

650

700

750

800

850

H4 H3

ABSORBANCE

ABSORBANCE

0.67 ct Light purple

450

362

NATURAL-COLOR PINK DIAMONDS

500

550

600

650

700

750

800

WAVELENGTH (nm)WAVELENGTH (nm)GEMS & GEMOLOGYWINTER 2018

VIS -NIR ABSORPTION FEATURES IN “PINK” DIAMONDS
100%

100%

A

B

Optical absorption
spectral features

90%

PERCENTAGE OF DIAMONDSPERCENTAGE OF DIAMONDS

90%
80%
70%
60%
50%
40%
30%
20%
10%

NV
80%

Other
N3/H3/550 nm band70%

N3/550 nm band60%

H3/550 nm band
50%

550 nm band

40%
30%
20%
10%

0%

0%
Brown
(28)

Brown-pink Orangy pink
(212)
(63)

Pink
(410)

Purple-pink
(276)

Red
(11)

Faint
(89)

Very
Light
(69)

Light
(109)

HUE OF DIAMOND

Fancy
Light
(116)

Fancy
(325)

Fancy
Intense
(166)

Fancy
Vivid
(32)

Fancy
Deep
(63)

Fancy
Dark
(31)

SATURATION/TONE OF DIAMONDABSORBANCE

C
N3(415 nm)H3(503 nm)0.22 ct Fancy Vivid purple
550 nm band

1.49 ct Fancy Deep
pinkish orange
400

450

500

550

600

650

700

750

800

WAVELENGTH (nm)Figure 9. Natural “pink” diamonds submitted to GIA over the last decade are predominantly colored by the 550
nm band. A: When a subset of 1,000 diamonds are analyzed by hue, they show minor differences in thepresence/absence of H3/N3 centers, indicating that intensity differences in peak characteristics, and not the presence/absence of these features, generally create the differences in hue. B: The addition of the N3 and/or H3 centers
leads to an increase in overall absorption, creating more saturated colors. C: A comparison of the Vis-NIR absorption spectra between a 0.22 ct Fancy Vivid purple and a 1.49 ct Fancy Deep pinkish orange diamond. While bothhave a ~550 nm absorption band, differences in this band and the presence of other centers lead to vastly different
colors. The pinkish orange diamond shows pronounced H3 and N3 centers that are lacking in the purple diamond.
For the pinkish orange diamond, the 550 nm band is centered at 548 nm with a width of 62 nm. For the purple diamond, the center is located at 556 nm and the peak width is much wider, 105 nm. The vertical line indicates thecenter point for each of these bands.

Those 170 termed as type Ia (17%) had saturated nitrogen concentrations in their IR absorption spectra,
and the specific A and B nitrogen aggregates were too
great to be resolved with our instrumentation andthus could not be calculated. The remaining 581 diamonds had sufficiently low nitrogen to determine
the aggregate concentrations (Boyd et al., 1994, 1995).
Of those, 396 were type IaA<B (40%) followed by 125
type IaA>B (13%), 31 pure type IaA (3%), and 29 puretype IaB (3%).

Figure 10B shows that the type IIa “pink” diamonds were overwhelmingly colored by the 550 nm
band alone and generally did not include the additional H3 and N3 centers. This is not surprising, as
type IIa diamonds do not have sufficient nitrogenconcentration to generate nitrogen-related defects
that could be detected by visible absorption and affect the color.
Among the diamonds with nitrogen aggregates,
many were colored by H3 and/or N3 that appeared

NATURAL-COLOR PINK DIAMONDSGEMS & GEMOLOGYWINTER 2018363

IR SPECTRA AND DIAMOND TYPE DISTRIBUTION

A

Intrinsic diamondfeatures

3107

Fancy Intense purple-pink; saturated nitrogen
Type Ia

ABSORBANCE

Nitrogenaggregates

Fancy pink; A = 83 ppm; B = 238 ppm
Type IaA<B
Fancy purple-pink; A = 220 ppm; B = 26 ppm
Type IaA>B
Fancy pink; A = 20 ppm; B = 46 ppm
Type IaA<B
Fancy Light pink
Type IIa
4000

5000

3000

2000

1000

WAVENUMBER (cm–1)
100%

B

Other
NV

NUMBER OF DIAMONDS

350

N3/H3/550 nm band300

N3/550 nm band
H3/550 nm band250

550 nm band

200
150
100
50

C

Red

90%

PERCENTAGE OF DIAMONDS

400

Purple-pink
Pink

80%

Orangy pink
70%

Brown-pink
Brown

60%
50%
40%
30%
20%
10%

0

0%
Ia
(170)

IaA
(31)

IaA>B
(125)

IaA<B
(396)

IaB
(29)

IIa
(249)

Ia
(170)

DIAMOND TYPE

IaA
(31)

IaA>B
(125)

IaA<B
(396)

IaB
(29)

IIa
(249)

DIAMOND TYPE

Figure 10. A: Five representative IR spectra of “pink” diamonds show the variety of possible nitrogen concentrations and ratios of A/B aggregates. B: The distribution of diamond type for these 1,000 “pink” diamonds is distinguished by features in their Vis-NIR absorption spectra. Type IIa and type IaA diamonds are almost always
colored by the 550 nm band only. As more B centers develop, the percentage of diamonds with a contribution
from H3 and/or N3 increases. Diamonds designated as type Ia have IR spectra with a saturated nitrogen region
and very high nitrogen concentration; the A/B ratio of aggregates cannot be reliably determined in those cases. C:
The distribution of the diamond type for these 1,000 “pink” diamonds and the color description.

to impact the color saturation more than the hue, as
indicated by comparing figure 9A and 9B. Amongtype IaA diamonds, very few showed either H3 or N3
centers. In contrast, a majority of type IaA<B diamonds had both the N3 and the H3 in addition to the
550 nm band.
The observation that diamonds with higher
amounts of B-aggregates also showed a higher incidence of H3 and N3 centers is not surprising given
the evolution of these various defects within diamond. A very young diamond will show only isolated nitrogen. As time progresses, these nitrogenatoms combine to create more and more complex de-Concentrations of A and B Nitrogen Aggregates. The
ratio between A and B nitrogen aggregates can beused to assess the time and/or temperature of a diamond’s residence deep within the earth (Leahy and

364

GEMS & GEMOLOGY

NATURAL-COLOR PINK DIAMONDS

fects. The A-aggregates are composed of two nitrogenatoms; the H3 defect contains two nitrogen atoms
plus a vacancy; the N3 defect includes three nitrogenatoms with a vacancy; and the B-aggregate includes
four nitrogen atoms plus a vacancy. As the A-aggregate/B-aggregate ratio shifts toward higher amountsof B, other defects (such as H3 and N3) will be produced as well (Dobrinets et al., 2013).

WINTER 2018

DISTRIBUTION OF A- AND B-AGGREGATES
200

400

A=

A=

Type IaA<B

B-AGGREGATES (ppm)

B-AGGREGATES (ppm)

500

B

Known Argyle diamonds
Known Siberian diamonds
Pink
Purple-pink
Brown-pink
Orange-pink

B

600

300

200

150

Type IaA>B

100

50

100

0

0
0

100

200

300

400

500

600

0

50

A-AGGREGATES (ppm)

100

150

200

A-AGGREGATES (ppm)

Figure 11. The A and B nitrogen aggregates for 581 type IaAB diamonds are plotted against each other along with
A/B concentrations for 62 known Argyle diamonds and a pair of known Siberian diamonds (most IR spectra of the
known Siberian samples had saturated spectra, thus reducing number of plottable datapoints). Also shown is a diagonal line designating where A- and B-aggregates are equal and a green slope line in the inset showing where thevast majority of data are clustered.

Taylor, 1997). Even if the total nitrogen concentration is different between diamonds, the transition
from A-aggregates to B-aggregates increases at higher
temperatures and longer timescales. If a populationof diamonds has similar A-to-B ratios, they likely
resided under similar time and temperature conditions, increasing the likelihood that they originatedfrom the same source.
As mentioned previously, 581 of the “pink” diamonds from the 1,000-diamond subset had IR spectrafrom which the concentrations of A- and B-aggregates could be calculated (in atomic parts per million,
or ppma; figure 11). These were calculated individually by baseline correcting each spectrum, and thencalculating A- and B-aggregates using a spreadsheet
provided by Dr. David Fisher (DTC Research Center,
Maidenhead, UK) using absorption coefficients fromBoyd et al. (1994, 1995). The majority of the 581 diamonds contained more aggregated nitrogen as B centers (type IaA<B; figure 11).
In the inset of figure 11, most of the datapoints are
clustered near the green guide line (i.e., the calculated
best-fit line for type IaA<B diamonds), indicating that
A/B concentrations generally lie along that slope. Although the total nitrogen concentrations vary from a
few ppm to a few hundred ppm, the conversion of Aaggregates to B-aggregates is roughly consistent for all
values near the green slope line. This consistency

strongly suggests that all of these diamonds experienced similar time/temperature conditions within theearth and potentially from the same mine. The sheer
quantity of diamonds plotted here (compared withthose scattered among the rest of the graph) imply thatthey come from the most abundant source—the Argyle mine—although they could also be from Namibia
or Venezuela. Also plotted are the data of 67 diamonds, unrelated to this study, that are known to besourced from the Argyle mine (unpublished GIA data,
2007). In contrast, pink to purple diamonds sourced
from Siberia are predominantly type IaA>B, and two
known Siberian samples with unsaturated IR spectra(Titkov et al., 2008) are also shown alongside the datafrom this study. This geographical distinction basedon nitrogen aggregation has been documented before(Gaillou et al., 2010; Howell et al., 2015), and a good
hypothesis of origin is possible, though not with any
reliable certainty, as “pink” diamonds originate fromvery few sources.
Although this plot cannot include type IIa or saturated type Ia diamonds, it is consistent with priorreports (e.g., Howell et al., 2015) that “pink” diamonds clustered around the green slope line aremainly sourced from the Argyle mine, and these encompass a significant percentage of “pink” diamonds
submitted to GIA. If we assume that the type IaB and
IaA<B diamonds are generally from the Argyle mine

NATURAL-COLOR PINK DIAMONDSGEMS & GEMOLOGYWINTER 2018

365

BOX B: PL FEATURES OF PINK TYPE IIA TO TYPE IAAB DIAMONDS
Photoluminescence Band Associated with 550 nm Absorption Band. As part of our identification procedure
for pink diamonds, GIA routinely collects their PL spectra (e.g., using 514 nm excitation). One interesting andconsistent feature in the PL spectra of these pink diamonds is a wide emission band extending from ~600 to
750 nm, with a series of smaller oscillations overlaid on
the larger emission band (e.g., the black trace in figureB-1). This emission band is consistently seen in diamonds colored by the 550 nm absorption band; the absorption band often, but not always, shows similar
oscillations at ~600 nm (e.g., the red trace in figure B-1;
see also figure 4, B and C). The oscillations in the 550
nm absorption band are most often detected in saturated
pink to purple-pink diamonds. While this feature is only
rarely detected in light pink diamonds with a weak 550
nm absorption band, the 600–750 emission band may
still be detected in their PL spectra. Although this emission band appears qualitatively similar to the PL bandassociated with the 480 nm band (figure 21C), the two
are dissimilar in overall band width and the spacing between the oscillations.
Additional interesting observations about this 600–
750 emission band include:

2. After exposure to the high-energy UV of the
DiamondView, the intensity of the emission banddecreases and shows a bleaching behavior similar
to that of the 550 nm absorption band. When thepink diamond returns to its stable color, so does
the intensity of the emission band.
3. In diamonds with pink and brown graining, the intensity of the emission band is lower in the brown
graining than in the pink graining.
4. This emission band is absent from diamonds that
do not show a 550 nm absorption band.
5. This emission band is similar to one previously documented by Gaillou et al. (2010), appearing only
within photoluminescence spectra obtained frompink lamellae and absent from colorless portions.
Photoluminescence Maps of Type IIa and Type IaAB Diamonds. We wished to study this emission band in moredetail, and therefore 455 and 532 nm photoluminescencemaps were analyzed to examine several features in pinkdiamonds. These included H3, H4, the 600–750 nm
emission band, and several other common features seenin PL spectra (e.g., figure 14). These results will be discussed in an upcoming paper.
Gaillou et al. (2010) performed PL spectra line scans
across a series of flat plates containing pink lamellae. In
addition to finding this 600–750 nm emission band

1. The spacing of the oscillations between the 550
nm absorption band and the emission band show
a pronounced similarity.

7 nm

20 nm
14 nm

ABSORBANCE

VIS -NIR ABSORPTION AND PL SPECTRA

Vis-NIR absorption spectrum of type IIa
Fancy purple-pink diamond500

2nd order
Raman

550

600

GR1

20 nm
14 nm
7 nm

Raman

PL INTENSITY

514 nm PL spectrum of same diamond

650

700

750

800

850

Figure B-1. The Vis-NIR
absorption spectrum (redtrace) for a purple-pink diamond is shown alongwith its 514 nm PL spectrum (black trace). Bothspectra were collected at
liquid nitrogen temperature and show an interesting symmetry in theoscillations observed
within the 550 nm absorption band and the emission band.

900

WAVELENGTH (nm)366

NATURAL-COLOR PINK DIAMONDSGEMS & GEMOLOGYWINTER 2018

High-nitrogen type IaA>B pink diamondwith visible slip/glide planes

PL map of 600–750 nm emission band
(normalized using area of diamond Raman peak)PL map of H3 peak width (nm)

100

1.5

0

0.5

Figure B-2. Photoluminescence maps of the 600–750 nm emission band and H3 peak width show excellent agreement with the visual observation of pink color along deformation lamellae in this type IaA>B pink diamond. The
intensity bars show the range of values.

solely within the pink lamellae, they observed that the
Raman width noticeably increased as well. They wereunable to produce the PL maps that are possible withtoday’s technology, and they did not have type IIa pinkdiamonds available for comparison.
As PL is a very sensitive method capable of collecting
information on defects at the parts-per-billion (ppb) level,
it can detect subtle variations in diamond far better thanthe eye can distinguish pink color. Additionally, we are unable to perform visible absorption spatial mapping on thesepink diamonds, so we cannot map the distribution of the
550 nm band in pink diamonds. We can collect PL spectral
maps at liquid nitrogen temperature, however. Based on
the observations of this 600–750 nm emission band, it ismonitored as a proxy of the 550 nm absorption band.
Here we performed PL mapping on type IIa and type
IaAB diamonds. In type IaAB pink diamonds, these data
will show the spectral differences between the coloredlamellae (either as graining or slip/glide planes), and also
demonstrate that the PL spectra of type IIa diamonds areas spatially uniform as their pink color. We paid particularattention to low-nitrogen type Ia diamonds to examine
the progression from the homogeneity of type IIa diamonds to the color segregations seen in type Ia diamonds.
For moderate-nitrogen type IaA<B diamonds (i.e.,
Group 1 pink diamonds; Gaillou et al., 2010), the distri-

NATURAL-COLOR PINK DIAMONDS

bution of the 600–750 nm emission band is consistent
with its color distribution, with wavy-appearing concentrations of color that are slightly more saturated than thesurrounding diamond. For higher-nitrogen type IaA>B diamonds (i.e., Group 2 pink diamonds) that have pronounced slip/glide planes, there is a distinct change inspectral properties within the pink slip/glide planes (figure B-2); these changes include a pronounced increasedin the 600–750 nm emission band, along with other features such as H3 peak width. In contrast, the PL mappingof type IIa diamonds showed that the spatial distributionof the 600–750 nm emission is nearly uniformly distributed, as is the distribution of the pink color.
Low-nitrogen “pink” diamonds generally show a
mixture of spectral features, with some exhibiting a
combination of traits seen in the uniform color distribution of type IIa pinks, the irregular graining seen in typeIaA<B pink diamonds (i.e., Group 1 diamonds; Gaillou
et al., 2012), and the sharply defined, distinct, and parallel lamellae seen in type IaA>B (i.e., Group 2). Diamondswith low nitrogen concentrations generally show a combination of features seen in type IIa and Group 1 diamonds such as a uniform pink color distribution, though
there are some instances of visible pink graining or a uniform distribution of the 600–750 nm emission band, as
well as wavy graining when plotting the H3 peak width.

GEMS & GEMOLOGYWINTER 2018367

and the other types, including the saturated type Ia
diamonds, are sourced from other mines, then 425 of
the 992 diamonds with the 550 nm band, a total ofat least 43%, originated from Argyle.
The nitrogen aggregation results for these diamonds, shown in figure 11, are also split according
to the color description of the “pink” diamond. This
indicates several interesting trends. Among the typeIaA<B diamonds (i.e., the left side of the diagonal infigure 11), most purple-pink to pink-purple samples
are congregated in the portion that indicates low nitrogen. Also, the orangy pink diamonds are almost
exclusively contained among the type IaA<B population, while a single orangy pink type IaA sample isrepresented elsewhere on the plot (see also figure
10C).
Among type IaA>B diamonds (i.e., the right sideof the diagonal in figure 11), the nitrogen concentrations are higher, with many showing A-aggregate
concentrations of 300 ppm or more. Also, many of
the unmodified pink diamonds are nearly pure type
IaA, while the purple-pink diamonds have a greater
concentration of B-aggregates, consistent with previous reports by Titkov et al. (2008).

increases the overall absorption in these diamonds,
leading to more saturated colors.

Effect of Total Nitrogen Concentration. To visualize
the effect that nitrogen concentration had on color
hue, tone, and spectral features (figure 12), we grouped
the A<B and A>B data of all 581 “pink” diamonds
shown in figure 11 by the total aggregate concentration into five different ranges. The concentration
range of each group was determined in order to create
roughly equal groups.
With increasing nitrogen, we generally saw adecrease in purple-pink to pink-purple diamonds(figure 12A); this is likely due to a greater absorption of the H3 and N3 centers that reduced transmission of blue light. Additionally, among typeIaA<B with increased nitrogen there was a greater
proportion of unmodified brown diamonds. The
other hues showed fluctuations with increasing nitrogen, but no clear trends. Again, orangy pink diamonds are essentially seen only among diamondswith A<B aggregates.
Across the range of total nitrogen, type IaA<B diamonds show more saturated colors (figure 12B) thantype IaA>B that appears due to the higher incidenceof the N3 and H3 centers (figure 12C and consistent
with figure 9). For the highest range shown in figure
12C (>250 ppm total nitrogen), more than 80% of thetype IaA<B diamonds show one or both of these centers. The additional absorption of the N3/H3 centers

Other IR Features. Of the 1,000-diamond subset, half
were randomly selected and surveyed for the presence in their spectra of the N3VH defect (3107 cm–1
center), the platelet feature, and “amber” centers.
The 3107 cm–1 peak was designated for many
years as a “hydrogen-related defect,” and only recently was it ascribed to N3VH by Goss et al. (2014).
N3VH was frequently observed in our sample suite,
occurring in 74% of the “pink” diamonds surveyed.
Of the diamonds without N3VH visible in the infrared spectrum, 87% were type IIa. The saturated
type Ia group contained 80% of the diamonds thatwere rated as having a strong 3107 cm–1 peak. The
type IaA>B and IaA<B groups showed no significant
difference in occurrence of the N3VH defect or in thestrength distribution.
The platelet feature is comprised of extended defects involving carbon interstitials (i.e., clusters ofcarbon atoms not in normal positions in the lattice)and nitrogen in thin layers thought to form as A-aggregates transition into B-aggregates (Humble, 1982;
Speich et al., 2017). The position of the peak can varyfrom 1358 to 1380 cm–1 depending on the diameterof the platelet, where the lower wavenumber value
corresponds to a higher platelet diameter (Speich etal., 2017). None of the type IIa and IaB stones in ourdataset had a platelet peak present in the IR spectrum, which is to be expected due to their lack of A
centers (Humble, 1982). The IaA, IaA>B, IaA<B, andIa groups all showed a platelet peak occurrence morethan 50% of the time, with the Ia group having an
occurrence of 96%. The strength of the platelet peakcorrelated best with the concentration of B-aggregated nitrogen, consistent with previous studies(Woods, 1986; Speich et al., 2017). The type Ia diamonds had the highest average peak position (andtherefore the smallest average platelet diameter) at
1369 cm–1, and the IaA<B group had the lowest average peak position (and therefore the largest average
platelet diameter) at 1362 cm–1.
The “amber” centers are a series of broad bands
related to diamonds with brown coloration and/orcolored graining, occurring between 4000 to 4400
cm–1. It has been suggested that the “amber” centers
are defective A-aggregates formed along plastic deformation planes (Massi et al., 2005). Two specificbands were surveyed for this study: the “amber” centers at 4065 and 4165 cm–1. The 4065 cm–1 “amber”
center has been observed to be stable up to 1700°C,

368

GEMS & GEMOLOGY

NATURAL-COLOR PINK DIAMONDSWINTER 2018

HUE: A<B

A

HUE: A>B

100%

100%

80%

80%

60%

60%

40%

40%

20%

20%
0%

0%
0–40 ppm

40–70 ppm

Brown

Brown-pink

70–150 ppm

150–250 ppm

Orangy pink

Pink

> 250 ppm

0–40 ppm

40–70 ppm

Purple-pink

Brown

Brown-pink

TONE/SATURATION: A<B

B

Orangy pink

> 250 ppm

Pink

Purple-pink

TONE/SATURATION: A>B

100%

100%

80%

80%

60%

60%

40%

40%

20%

20%
0%

0%
0–40 ppm

40–70 ppm

Faint to Fancy Light

70–150 ppm

Fancy

150–250 ppm

Fancy Intense to Vivid> 250 ppm

0–40 ppm

Fancy Deep to Dark

40–70 ppm

Faint to Fancy Light

70–150 ppm

Fancy

150–250 ppm

Fancy Intense to Vivid> 250 ppm

Fancy Deep to Dark

VIS-NIR ABSORPTION FEATURES: A>B

VIS-NIR ABSORPTION FEATURES: A<B

C

70–150 ppm 150–250 ppm

100%

100%

80%

80%

60%

60%

40%

40%

20%

20%
0%

0%
0–40 ppm

40–70 ppm

550 nm band

70–150 ppm

H3/550

150–250 ppm> 250 ppm

N3/550N3/H3/550

0–40 ppm

40–70 ppm

550 nm band

70–150 ppm

H3/550

150–250 ppm

N3/550> 250 ppm

N3/H3/550

Figure 12. Type IaAB diamonds were split into two groups, IaA<B and IaA>B, and sorted based on total nitrogenconcentration. A: The effect of total nitrogen concentration on hue. B: The effect of increasing nitrogen on the toneof the diamond. C: The effect of total nitrogen concentration on features present in Vis-NIR absorption spectra.

while the 4165 cm–1 “amber” center can survive
heating until 1900°C (Eaton-Magaña et al., 2017). As
these two features are stable to different temperatures, they are likely different centers. Previous reports have shown that the 4065 cm–1 “amber” center
is more prevalent in diamonds of type IaA>B (Gaillou
et al., 2010).
The IR spectra were categorized as having neither
peak, one of these peaks, or both (figure 13). None of
the type IaB stones and very few (14%) of the type IIa
diamonds showed either the 4065 or the 4165 cm–1
peak, consistent with the model of the “amber” cen-Diamonds Colored by NV0/– Centers. Only six of the
1,000-diamond subset were colored by NV0/– centers,
thus rendering a very small sample size and provide

NATURAL-COLOR PINK DIAMONDSGEMS & GEMOLOGY

ter being a defective A center (Massi et al., 2005). As
the concentration of A-aggregates increased, the likelihood of one or both “amber” peaks increased aswell; the type Ia diamonds showed a high percentage
of “amber” centers, likely corresponding to the highconcentration of A-aggregates within them (although
the saturated spectra do not allow us to accurately
make that determination).

WINTER 2018

369

AMBER CENTER OCCURRENCE
100%

PERCENTAGE OF DIAMONDS

90%

80%

70%

Figure 13. IR absorption
peaks related to“amber” centers areplotted based on diamond type. The numberof samples tested withineach diamond type isshown in parentheses.

60%

50%

40%

30%

20%

10%

0%
IIa (128)IaB (15)

IaA<B (207)

IaA>B (57)

IaA (18)

Ia (75)

DIAMOND TYPE
Neither

Only 4065 cm–1

Only 4165 cm–1

little more to illuminate beyond what has alreadybeen discussed in the Causes of Color section. As expected, all six showed type IIa IR absorption spectrathat were featureless except for intrinsic diamondfeatures. In the Vis-NIR absorption spectra, the six
diamonds (three orangy pink, two pink, and one
brownish pink) had NV0/– centers at 575 and 637 nm
along with their accompanying sidebands, with themost prominent of those centered at ~520 and 620
nm (figure 4, spectrum E). Of these, four had detectable GR1 peaks and four showed the 595 nm center commonly seen in irradiated diamonds (Breeding
et al., 2018). The presence or absence of these radiation-related peaks did not correspond with the gradedcolor.

Both

Diamonds Containing the 550 nm Absorption Band.
The PL spectra of diamonds colored by the 550 nm ab-sorption band often show features that either containvacancies or correlate with plastic deformation. For
example, the 566 nm triplet is seen in pink to brown
diamonds of both type Ia and IIa (i.e., those with andwithout colored graining; GIA unpublished data).
Common vacancy-related peaks include the H3(NVN0 at 503.2 nm), H4 (NVN– at 496 nm), GR1 (V0at 741.2 nm), and NV centers (NV0 at 575 nm, NV–
at 637 nm; figure 14). The NV0/– centers are often
present in diamonds containing the 550 nm band but
not in sufficient concentrations to be detected in the
Vis-NIR absorption spectra, and therefore they do notaffect the color. Peaks at 657, 661, and 668 nm areoften seen together in type IIa, IaA<B, and IaB “pink”
diamonds; however, the defect structure of thesepeaks has not been identified. Box B further discusses
the photoluminescence features within the graining
and slip/glide planes that are observed in type IaAB
diamonds.
The peak width of the diamond Raman line is affected by the local strain environment, and an increase in crystallographic strain leads to a broadeningof the peak width (Grimsditch et al., 1978). The diamond Raman line has been shown to increase inwidth on pink grain lines in type Ia diamonds,
demonstrating that the pink lamellae lie in planes ofplastic deformation (Gaillou et al., 2010).
In contrast, type IIa “pink” diamonds rarely show
colored lamellae and instead are evenly colored. In

370

GEMS & GEMOLOGYPHOTOLUMINESCENCE SPECTROSCOPY
Photoluminescence (PL) uses lasers of different wavelengths to produce emission spectra that reveal the
optical defects present in a diamond. PL analysis is
one of the most useful and sensitive techniques fordefect characterization. Using PL spectroscopy, defects occurring at parts per billion (ppb) concentrations (and therefore not necessarily contributing to
the diamond’s bodycolor) can easily be detected(Eaton-Magaña and Breeding, 2016).

NATURAL-COLOR PINK DIAMONDSWINTER 2018

PL SPECTRUM
552 nm saturated diamond Raman line
741 nmGR1

PL INTENSITY (COUNTS)

20000

Figure 14. A typical 514
nm photoluminescence
spectrum from a 550
band pink type IIa diamond. The 566 nm
triplet, NV0/– centers,
657 nm peak, and GR1
are all shown. The diamond Raman line at
552 nm is saturated.

2nd order
diamond Raman
15000
637 nmNV–
657 nm

575 nmNV0

10000

566 nm
5000

0
550

600

650

700

750

WAVELENGTH (nm)type IIa diamonds showing a uniform pink coloration, this relationship of strain versus pink color
is not so easily visualized. Therefore, we plotted theGR1 width (i.e., increasing strain) of 239 type IIa“pink” diamonds from the 1,000-diamond subset
against pink color intensity (figure 15). This plotshows that in type IIa diamonds, an increase in strain(represented by the peak width of the GR1 center)

Figure 15. Among type IIa “pink” diamonds, the color
is generally uniform rather than concentrated within
graining. We see that among type IIa “pinks,” an increase in GR1 full width at half maximum (functioning as a proxy for the strain measurement) correspondswith more saturated pink color. The individual points
are shown along with the average values.

COLOR INTENSITY VS. GR1 WIDTH
2.5

corresponds to an increase in pink color saturation
in type IIa diamonds, despite the lack of easily distinguishable strained regions.
Diamonds Colored by NV0/– Centers. Diamonds colored by NV0/– centers (i.e., those with NV0/– centersin sufficient concentrations to be detected by VisNIR absorption spectroscopy) will have high-intensity NV0/– peaks in their PL spectra (figure 16). Dueto this high intensity of the NV0/– centers and theirassociated vibronic structures, it can be difficult to
detect other peaks that may be present at lower PL
intensities. A peak at 561 nm is commonly seen, but

Figure 16. A typical 514 nm photoluminescence
spectrum from a “Golconda pink” diamond. The
NV0/– centers (and their vibronic structure/sidebands) and the diamond Raman line (R) are the only
features detected.

PL SPECTRUM

2.0

PL INTENSITY (COUNTS)

GR1 PEAK WIDTH (mm)Individual Values
Average

1.5

1.0

0.5

0
Faint

Very Light
to Light

Fancy
Light

Fancy

Fancy Intense
to Vivid

60000

575 nm
NV0

40000

20000
Raman
0
550

600

650

700

750

WAVELENGTH (nm)TONE OF DIAMOND

NATURAL-COLOR PINK DIAMONDS

637 nmNV–

GEMS & GEMOLOGYWINTER 2018371

the structure of this defect is still unknown. Common vacancy-related defects seen in diamonds with
NV0/– centers include H3 (NVN0), H4 (4N-2V), andGR1 (V0).

A

Brown graining

GEMOLOGICAL OBSERVATIONS
Physical Characteristics. Pink and brown color isoften associated with plastic deformation lamellae(“graining” or “slip/glide planes”). These are often
observed as visible lines on the polished surface ofthe diamond, known as surface graining, which result from differential polishing rates along the deformation lamellae relative to the surrounding
diamond. This leaves visible lines on the surface; unlike polishing features, these can cross multiple
facets (figure 18, right).
The graining usually has a hue similar to the diamond’s bodycolor, though in some cases diamondcan exhibit both pink and brown graining (figure
17A). Additionally, graining and slip/glide planes canappear more pronounced when the diamond is put
between crossed polarizers to show the strain (i.e.,
anomalous birefringence; figure 17B). The disruption
in the strain pattern apparent at a slip/glide plane
provides further evidence that these planes are a disruption of the diamond lattice (figure 17C).
Trigons can be etched where deformation lamellae
intersect the surface of a rough diamond (figure 18,left). Where two of these deformation lamellae intersect, it is common to see an etch channel or thin needle-like structure (Wang et al., 2006). Diamonds are
etched by fluids during their mantle residency or during kimberlite ascent (Fedortchouk et al., 2005; Fedortchouk and Zhang, 2011), and these fluids first
exploit preexisting weaknesses in a diamond. Hollow
channels known as Rose channels can also occur alongintersecting twin lamellae (Schoor et al., 2016; figure
18, right). First described by Gustav Rose in 1868, theseare formed by the intersection of twin lamellae, where
the twinning action can result in a straight, hollow
channel with a prismatic opening (Rose, 1868).

Pink graining

B

C

Figure 17. A: These two pink diamonds are rare examples exhibiting both pink and brown graining. B: Thisdiamond shows slip/glide planes that are readily
viewed through crossed polarizers (right), indicatingthat the lattice has been strongly distorted due toplastic deformation. C: This 5.09 ct Fancy pink-purple
sample with obvious slip/glide planes (left) will show,
when viewed at the proper angle and with proper illumination (right), that light is reflected from plastic
deformation lamellae, indicating a physical discontinuity or a damaged zone of the diamond’s lattice
structure. Photomicrographs by GIA staff.

medium (53%) to strong (25%) intensity and had a diamond type of IaA<B (70%). Those with reported yellow fluorescence to long-wave UV generally had very
weak to weak intensity (88%) and were either saturated type Ia (42%) or IaA>B (36%). Those with fluorescence reported as none generally were either
saturated type Ia (67%) or IaA>B (29%).

UV Fluorescence. 550 nm Band. Of the 992 “pink”
diamonds colored by the 550 nm band that were randomly selected for detailed spectroscopic analyses,
786 had observations of long-wave (365 nm excitation)and short-wave UV (254 nm excitation) reported in the
database. Among those with fluorescence observations, 571 (73%) showed blue fluorescence to longwave excitation; 89 (11%) exhibited yellow
fluorescence and 113 (14%) no fluorescence. Thosewith reported blue fluorescence generally showed

NV0/– Centers. The rare “Golconda pink” diamonds(six out of the subset of 1,000 samples, or 0.6%) all
showed yellow-orange-red fluorescence colors causedby NV0/– centers. Although all colored diamonds
should be submitted to a laboratory to determine the372

GEMS & GEMOLOGY

NATURAL-COLOR PINK DIAMONDSWINTER 2018

Deformation
lamellae
Rose channel

Figure 18. Left: Etching as trigons along plastic deformation lamellae in Light purplish pink type Ia diamonds, captured in differential interference contrast lighting to help improve image contrast. Photomicrograph by Nathan
Renfro; field of view 1.24 mm. Right: Hollow channels (called Rose channels and indicated by the red arrow) havedeveloped at the intersections of deformation lamellae in a 0.98 ct Fancy brownish pink diamond. Photomicrograph by Wuyi Wang; field of view 1.30 mm.

Bleaching. Many type IIa diamonds, including thosecolored by the 550 nm band and “Golconda pink” diamonds, change color after exposure to UV light. Although typically observed following exposure to thehigh-energy light of the DiamondView instrument(with wavelengths <225 nm), bleaching can be observed following exposure to longer-wave UV but theeffect is lessened at lower-energy, higher wavelengths(Fisher et al., 2009; Byrne et al., 2012b, 2014). After
exposure to UV, “pink” diamonds can change color
to yellow, brown, or near-colorless, and thesechanges are due to several charge-transfer processes
that have been associated with the vacancy clusters
present in brown diamonds (Byrne et al., 2014).
Bleaching has also been observed during polishing ofpink diamonds (Chapman, 2014).
The diamond’s color always reverts back to“pink,” though this can take anywhere from several
minutes to more than a day depending on the colorand intensity of the light (Byrne et al., 2014). Exposure to bright light (such as placing the diamond ina microscope light well) accelerates the process. As
a precaution, GIA gemologists generally do not collect DiamondView images on “pink” diamonds unless other data indicate potential treatment, andDiamondView images are always collected after color

NATURAL-COLOR PINK DIAMONDS

grading. Any “pink” diamonds that require DiamondView imaging are returned to their stable color before
leaving the laboratory.
Figure 19 shows the photos and spectra of a type
IIa Fancy Intense pink diamond that was exposed to

Figure 19. This 9.35 ct Fancy Intense pink type IIa diamond showed a dramatic color change to Fancy Intense brownish yellow following exposure to thehigh-energy UV of the DiamondView. The UV exposure caused a decrease in the ~390 and ~550 nm
bands, and the original color was completely restored
after 30 minutes of exposure to bright visible light.

UV-VIS -NIR ABSORPTION SPECTRA
390 nmband
N3

ABSORBANCE

origin of their color, any “pink” diamond with yellow-orange-red fluorescence colors should be given
special attention.

H3
Stable color:
Before UV bleaching

550 nmband

GR1

After UV bleaching

350

400

450

500

550

600

650

700

750

800

WAVELENGTH (nm)GEMS & GEMOLOGYWINTER 2018

373

VIS-NIR ABSORPTION SPECTRUM

ABSORBANCE

high-energy UV in the DiamondView. Its color dramatically and temporarily changed to Fancy Intensebrownish yellow, which was accompanied by a decrease in the 390 nm and 550 nm absorption bands,
while the intensities of the other centers (e.g., N3,
H3, and GR1) remain unchanged.

IDENTIFICATION CONCERNS

Type IIa and Type IaB “Pinks.” As with the high-pressure, high-temperature (HPHT) decolorizing treatment, type IIa and type IaB pinkish brown diamonds
can be HPHT-treated to remove the brown component (Hainschwang et al., 2003; Fisher et al., 2009). If
the 550 nm band is present in these diamonds, thepink color will be accentuated by HPHT treatment,
as the brown color is reduced. Diamonds that are
HPHT-treated to pink are generally subjected to lower
temperatures (1700–1800°C) than those that are
HPHT-treated to colorless (2000–2300°C; Fisher et al.,2009; Dobrinets et al., 2013). As with colorless diamonds, these “pink” diamonds should be assessed byphotoluminescence spectroscopy, which shows emission peaks that reliably distinguish between naturaland treated diamonds. Additionally, a few “pink”
CVD diamonds appear pink due to an absorption bandat ~520 nm (Wang et al., 2007); therefore, careful assessment is needed to verify that the color-causing visible absorption band in type IIa “pink” diamonds iscentered at ~550 nm. The cause of the ~520 nm bandin CVDs is also unknown.

400

450

500

550

600

650

700

750

800

750

800

850

WAVELENGTH (nm)

PL SPECTRUM
PL INTENSITY (COUNTS)

Type Ia “Pinks.” There is no known method of treatment to create the 550 nm absorption band in thelaboratory. Except for the rare type IaB diamonds discussed below, the majority of type Ia diamonds cannot be treated to appear pink. Additionally, thecolored graining common in type Ia “pinks” cannot
be artificially created.

140000120000100000
80000
60000
40000
20000
0
500

550

600

650

700

850

WAVELENGTH (nm)Figure 20. This 5.71 ct Fancy red-brown diamond derives its color from the 480 nm band, as shown by its
Vis-NIR absorption spectrum (top). The presence ofthe sometimes subtle 480 nm band is unambiguously
identified by a distinctive emission band determinedby PL spectroscopy (bottom), such as this spectrum
collected with 488 nm excitation.

ment of absorption, luminescence (such as mapping
the spatial distribution of defects; D’Haenens-Johansson et al., 2017), and gemological data should always
be collected and carefully evaluated.

Type IIa “Golconda Pinks.” Any diamond colored by
NV0/– centers must be examined extremely carefully.
Both treated naturals and treated synthetics are altered to a pink color by generating NV0/– centers.
Eaton-Magaña and Shigley (2016) provide a comparison table contrasting the distinguishing characteristics of natural, treated, and synthetic “pink”
diamonds that are colored by NV0/– centers. Natural“Golconda pink” diamonds typically have pale colors, while treated “pink” diamonds have much moresaturated colors. Although the separation of synthetic diamonds is generally less complicated than
the separation of treated diamonds, a full comple-

A small number of brown-red to red-brown diamonds
owe their color to a combination of a slight 550 nm
band with a 480 nm band (figure 20). The defect responsible for the ~480 nm absorption band also has
a luminescence band centered at ~700 nm that is extremely broad with a unique wavy shape (figure 20,
bottom). The combination of these two broad bands(the 480 and 550 nm absorption bands) leads tostrong absorption from the orange to blue color regions. This combination of absorption features not
only induced the common brown color but also cre-374

GEMS & GEMOLOGY

NATURAL-COLOR PINK DIAMONDSUNUSUAL EXAMPLESWINTER 2018

Figure 21. These diamonds are from the 2016 Argyle Pink Tender in New York City. Left to right: 0.64 ct Fancy
Deep pink oval, 0.75 ct Fancy Intense purplish pink trilliant, 0.91 ct Fancy Vivid purplish pink oval, 1.30 ct Fancy
Intense pink heart, 1.35 ct Fancy Intense purplish pink cushion, 0.80 ct Fancy Vivid pink pear, and 0.45 ct Fancy
Vivid purplish pink emerald cut. Photo by Robert Weldon; courtesy of Argyle Pink Diamonds.

ated a “transparent window” in the red region. The
result is a red-brown coloration.

CONCLUSIONS
Most colored diamonds receive the ingredients forcolor deep within the earth as they are created—nitrogen, boron, nickel, and hydrogen impurities produce yellow, yellowish green, violet, and blue colors,
while abundant micro-inclusions can create whiteand black colors. After reaching the earth’s surface,diamonds can be exposed to radiation to create blue
to green colors. However, the vast majority of natural“pink” diamonds colored by the 550 nm absorption
band are produced through deformation processes
deep within the earth.
Many source locality reports have been written
about type Ia “pink” diamonds from Australia andRussia (Iakoubovskii and Adriaenssens, 2002;
Titkov et al., 2008, 2012; Gaillou et al., 2010, 2012;
Howell et al., 2015), yet very little has been written

ABOUT THE AUTHORS
Dr. Eaton-Magaña and Dr. Breeding are senior research scientists, Mr. Ardon is a research associate, and Dr. Shigley is a distinguished research fellow, at GIA in Carlsbad, California. Dr. Smit isa research scientist at GIA in New York.

NATURAL-COLOR PINK DIAMONDS

about type IIa “pinks,” and we could find no studies
of a mine that regularly produces type IIa “pinks.”
Therefore, one enduring question is the source locality of the type IIa “pink” diamonds colored by
the 550 nm absorption band. Of the 992 diamonds
colored by the 550 nm band that were randomly selected and studied in detail, almost one-fourth (243)were type IIa. Although this is a comparatively highpercentage, little has been written about theirsource localities (e.g., Fisher et al., 2009; Smith etal., 2017).
Today, the Argyle mine produces a sizeable percentage of the world’s “pink” diamonds (e.g., figure21), although pink to purple diamonds also comefrom countries such as Brazil, South Africa, and Russia. Since the Argyle mine is set to close within thenext few years, the supply of “pink” diamonds, particularly those with saturated colors or those with
red color descriptions, will decline unless the supply
from other producers becomes more substantial.

ACKNOWLEDGMENTS
Discussions with GIA’s Dr. Evan Smith and John King contributed
to some ideas presented here. John Chapman (Gemetrix, Perth,
Australia) and Sergey Titkov provided helpful insight.

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375

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FEATURE ARTICLESTHE HISTORY AND RECONSTRUCTION OF
THE AMBER ROOM
Russell Shor
The Amber Room was constructed for King Frederick I of Prussia in Danzig (modern-day Gdansk, Poland) between 1701 and 1714. The amber panels making up the room were presented to Czar Peter I of Russia in 1716
and eventually installed in the Catherine Palace near St. Petersburg. They remained there until the outbreak ofWorld War II, when a German army unit looted the room. The Soviet government, which deemed the room acultural treasure, mandated its reconstruction in 1979, beginning a 24-year process that culminated with its reopening in 2003. This article offers a history of the original room drawn from the published writings of historians,
accounts of the looting and subsequent disappearance of the amber panels, and detailed firsthand accounts of
the reconstruction from those who participated in its planning, design, and execution.

T

he Amber Room (figure 1), located in theCatherine Palace in the Russian town of
Pushkin (previously Tsarskoye Selo), is considered by many historians the pinnacle of amber craftsmanship. The chamber is a reconstruction of the firstAmber Room, which was begun in 1701 by order ofFrederick I of Prussia and was actually a series oflarge panels designed to be mounted onto walls
within Berlin’s Charlottenburg Palace. The original
project took 13 years to complete. Once it was finished, Frederick’s son, William I, presented the amber
panels to Peter the Great of Russia to commemorate
a treaty between the two rulers against Charles XIIof Sweden. The panels were installed in the Winter
Palace in St. Petersburg and in 1755 moved to theCatherine Palace, where they remained for nearly
200 years.
In 1941, Nazi Germany invaded Russia. After surrounding St. Petersburg (called Leningrad between
1924 and 1991), they occupied Pushkin. Just before
the invaders reached the palace, its caretakers removed the smaller amber objects from the Amber
Room and attempted to hide the panels behind wallpaper. The invading German officers, however, knewof the room and confiscated the panels before destroying most of the palace. After the war, the panels
were never seen again.
See end of article for About the Author and Acknowledgments.
GEMS & GEMOLOGY, Vol. 54, No. 2, pp. 378–393,
http://dx.doi.org/10.5741/GEMS.54.4.393© 2018 Gemological Institute of America

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HISTORY OF THE AMBER ROOM

In 1979, Russian craftsmen began the long processof recreating the Amber Room. This was extremely
challenging because there was little documentationof the original room. Many of the amber working
skills of the eighteenth-century craftsmen had been
lost, and the materials used in adhesives and dyes
were no longer known. With the work less than half

In Brief• The original Amber Room panels were constructed inPrussia from 1701 to 1714, presented to Peter theGreat of Russia, and installed in the Catherine Palace.
• The panels were looted by the advancing Germanarmy in 1941 and are presumed lost.
• Reconstruction began in 1979, but there was scantphotographic evidence of the original room and little
documentation of the materials and techniques used.
• After 24 years of work, the craftsmen in the amber studio achieved an accurate reconstruction of the room.

completed, political changes nearly forced the project’s end. From initial research to the reopening of
the room before heads of state in 2003, the reconstruction took 24 years to complete.

BALTIC AMBER
Baltic amber, or succinate, is fossilized resin from
Pinus succinifera. This tree grew in abundance

GEMS & GEMOLOGYWINTER 2018

Figure 1. Detail showing the upper portions of the reconstructed room, including the gilded sculptures and the imitation amber painting above the cornice. Photo courtesy of Amberif.

HISTORY OF THE AMBER ROOMGEMS & GEMOLOGYWINTER 2018379

throughout Scandinavia and northern Europe morethan 20 million years ago (Kosmowska-Ceranowicz,2009). The vast Baltic area deposits were formed
when resin-bearing sediments flowed from Scandinavia to the Sambia Peninsula (figure 2), transforming
those resins over millions of years into amber.
Streams and rivers and glaciers carried large amountsof amber throughout northern Europe as secondary
deposits (Gaigalas and Salas, 2009). The primary deposits of the southern Baltic region—particularly the
Sambia Peninsula, where Kaliningrad, Russia, is situated—are the world’s most prolific sources of amber
and among the oldest gem deposits still in production, dating back to before recorded history. While
there are no ancient accounts of amber mining, mostof the material was probably collected on beaches following storms—a method still used today by amateurcollectors. Amber objects and carvings dating back toprehistoric times have been found in Great Britain(9000 BCE) and in the southern Baltic region (6000
BCE) (Langenheim, 1990).

THE AMBER ROADS
Collection and trade of amber in the Baltic region for
ornamental uses is believed to have begun some 6,000
years ago, during the Neolithic period. Amber was regarded as a valuable trading commodity for its deco-

Figure 2. The southern Baltic region and Sambia
Peninsula are the source of a vast amber deposit thathas been producing since before recorded history. The
most prolific area of the deposit is located near Kaliningrad. The city of Danzig (now Gdansk) on the western portion of the map has been a center of amber
craftsmanship for more than 1,000 years and was thehome of the designers and builders of the originalAmber Room.

ESTONIA
Gulf of
Riga
SWEDEN
Riga

ic

Se

a

LATVIABa

lt

LITHUANIA
VilniusRUSSIA

Malmö

Kaliningrad

POLAND380

ElblagHISTORY OF THE AMBER ROOM0

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Gdanskrative qualities and for its use as fuel for fires. Amber
trade routes extended from the Baltic through the continent to southern Europe and the Arabian Peninsula;some routes dating back to the Neolithic have been
documented (Butrimas and Jovaiša, 2013). Among thebest documented were the amber trade routes extending from the Baltic Sea to the Mediterranean. These
were established around 3000 BCE, based on archeological finds of beads and carvings in various locations
in Eastern Europe (Mazurowski, 2011). In addition, atrove of 850 amber ornaments, estimated to have beencreated about 3000 BCE, were found in present-day
Lithuania, and evidence of an amber carving enterprise was discovered in what is now Latvia (Grimaldi,
1996; Czebreszuk and Szmyt, 2013).
Amber’s origins were known by the first century
CE. Pliny the Elder, a contemporary of Roman Emperor Nero (37–68 CE), wrote in Natural History thatthe material “is formed from the liquid that exudes
from a type of pine tree” but noted it was generally
useless except as an adornment for women (Clark,
2010). The Roman historian Tacitus described the
trading of Baltic amber with Germanic tribes thatcollected and bartered the material (Clark, 2010).
Pliny noted the high value Romans placed on amber
and wrote that Nero’s chief gladiator, Julian, dispatched a mission to the north to bring back large
quantities of it. Upon their return, the Romans used
the amber to decorate the arena for gladiator games.
Because it was believed to have protective qualities,
the material was sewn into the nets separating thespectators from the wild animals in the area.
Trade routes originated at the southern Baltic
coast near the site where Danzig (now Gdansk,
Poland) was founded. The best-known route wasdown the Vistula River and over land to the Danube,
to the Roman port of Aquileia on the Adriatic Sea.
This was generally known as the Amber Road. However, archaeological evidence indicates many socalled Amber Roads that wound through Europe, allleading from Danzig or Königsberg (now Kaliningrad),about 120 km (75 miles) east from Danzig, toAquileia, or ports on the Mediterranean as far west as
Massalia (now Marseille; Clark, 2010).
One of the most important amber trading centers
was the Viking village of Truso, located near themodern-day city of Elblag in Poland. Excavations
conducted over the past 120 years have found remains of amber workshops and objects from Viking
and Celtic civilizations (Mazurowski, 2011). By thetime Danzig, about approximately 60 km (37 miles)
from Truso, was founded around 980, amber working

GEMS & GEMOLOGYWINTER 2018

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Eastern route

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Figure 3. Amber has
been collected andtraded throughout
Europe and as far as theMiddle East for at least
6,000 years. Archaeological finds show anumber of early traderoutes from the Baltic
to the Adriatic andMediterranean Seas;
these roads were highly
developed by the timeof ancient Greece andRome.

was a recognized skill among its inhabitants (City ofGdansk, 2017; see figure 3).
Up to this point, most amber had been collected by
Baltic tribes inhabiting the southern coastal areas andthe Sambia Peninsula. After the religious order known
as the Teutonic Knights returned from the Crusades in
1211, the Duke of Masovia (which encompassed modern-day Warsaw) enlisted their help in conquering thetribes. The Knights completed their conquest of theBalts in 1283 and in 1312 assumed a monopoly over
the amber trade, even forbidding its collection on thebeaches. Despite the restrictions, amber remained awidely traded commodity in the southern Baltic region
in the Prussian states, especially between Danzig andother cities that were members of the Hanseatic
League, a Baltic-centered trading alliance (Grimaldi,1996). Because of the Knights’ iron rule over trade in
the region, craft guilds specializing in amber formed incities outside their jurisdiction, even as far away as
Bruges, Belgium, where craftsmen carved the material
into rosaries (Grimaldi, 1996).
By the end of the fifteenth century, the Knights’
centuries-long grip over amber mining and trade had
weakened. In 1533, the Duke of Prussia granted control over much of the raw amber supply to a syndicate
of traders led by Paul Koehn von Jaski. This syndicate
established workshops in Livorno, Italy, Vienna,
Berlin, Paris, and Persia, and their monopoly endured
until 1642 (Netzer, 1993). As supply increased andtrade became freer, amber workers formed guilds. The
first was in Danzig in 1477, followed by Stolp (nowSłupsk) and Kolberg (now Kołobrzeg), both in 1480

(Netzer, 1993). The Danzig guild produced mainly religious items such as altars, shrines, and images ofsaints. The others created an array of amber goods:
small furniture pieces, game boards, mythological figures, lidded tankards, and decorative objects(Grimaldi, 1996). The Königsberg guild was foundedmuch later (1641), when the elector of Brandenburg
permitted it to set up in his residence (Netzer, 1993).
Through the guilds, amber craftsmanship evolved
to a high art in Prussia over the following two centuries. Workshops developed techniques beyond
carving to create large furniture pieces, sculptures,and other commissions from the Brandenburg Court,
which ruled the region from 1618 to 1701. By the endof the seventeenth century, many prominent amber
craftsmen had assembled in Danzig and Königsberg
because the Brandenburg Court had begun commissioning major amber works as gifts to foreign rulers
to seal diplomatic pacts (Netzer, 1993). One of themost renowned workshops in Danzig, where manysuch works were made, was operated by the head of
the guild, Gottfried Turau, and his partner, Ernst
Schacht. These men would figure prominently in theconstruction of the Amber Room (Grimaldi, 1996).

HISTORY OF THE AMBER ROOMGEMS & GEMOLOGYTHE ORIGINAL AMBER ROOM
The idea of the Amber Room was first raised byFrederick III, elector of Brandenburg, then a principality within the Holy Roman Empire and today aprovince that surrounds Berlin. Frederick III (later
Frederick I of Prussia) inherited the title of elector
in 1688 at the same time he was named Duke of

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381

Figure 4. The Amber
Room was designed fora chamber in the Charlottenburg Palace inBerlin but was neverhoused there. Courtesyof Tsarskoye Selo
Amber Workshop.

Prussia, which encompassed the southern Baltic
coast and the Sambia Peninsula. During this period,
Frederick commissioned three large mirror frames
made from natural-color and dyed amber with ivory
accents. The mirrors measured 142 × 120 cm, 156 ×
116 cm, and 156 × 116 cm at their outer dimensions,and each frame was 13 cm wide (Gierlowski, 2006a).
These mirror frames would be incorporated into theAmber Room during its construction some 20 years
later.
Upon his elevation to King of Prussia in 1701,
Frederick decided to commemorate his rule by creating a room fully lined with amber in the Charlottenburg Palace in Berlin (figure 4). That room, hebelieved, would surpass the opulence of Louis XIV’spalace at Versailles (Gierlowski, 2006a).
At that time, large stocks of uncut amber, including many very large pieces, had accumulated in warehouses in Danzig, about 480 km (300 miles) east of
Berlin. The excess supplies were a result of increased
mining activities in the Sambia Peninsula and theCuronian Spit, a sand barrier separating Königsberg
from the Baltic Sea (Grimaldi, 1996).
To design the room, the monarch appointed Andreas Schlüter, director of royal construction in
Danzig and one of the architects of the City Palacein Berlin. He selected a cabinet room meant for Frederick I’s private audiences, located in a corner of thepalace. The room measured more than 74.25 square
meters and stood about 5 meters high from floor toceiling (Gierlowski, 2006a).
The plan was to create the appearance of amber
walls through a series of large wood-backed mosaic

panels, on which were glued amber slices of varied
hues. The design called for 12 main panels measuring
over 3.5 meters high, with most nearly 56 cm wide.
Several narrower panels, each approximately 25 cm
wide, were fitted near the corners and windows. Eachpanel was separated by mirrored pilasters decorated
with candelabras and gilded wood carvings. Below
the main panels were wainscot panels of equal width,
approximately three feet high and separated from themain pieces by a chair rail, also made from assembled
amber pieces, and supported by a plinth all the way
around. The design called for the craftsmen to add
bas-relief decorative elements such as frames,
wreaths, and garlands to the amber mosaic panels.
The completed panels would then be mounted on
the walls. Other decorative elements carved fromamber, including garlands, fruit clusters, and sculptured figures carved from wood and gilded with gold
foil, would then be mounted on top of the panels.
Mounted on the cornice around the room, just below
the ceiling, was a series of carved amber pieces withrose, tulip, and other motifs, approximately 20 to 25
cm high. The design called for the completed amber
works to cover 80% of the wall surface (Gierlowski,
2006a; Owen, 2009).
In addition, there were to be large mirrors on eachof the four walls surrounded by the amber frames
manufactured in Dresden 25 years earlier. These mirrors would be replaced by stone mosaics after thepanels were relocated to the Catherine Palace.
The task of executing the design fell to Gottfried
Wolfram, who had worked in the Danish court as amaster amber and ivory carver and was renowned for

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his skill in executing intricate, artistic designs. In
1701, Frederick IV of Denmark recommended Wolfram to Frederick I of Prussia to supervise the work
(Hein, 1991). In constructing the panels, Wolfram
first lined the oak panels with bronze foil, having discovered when making amber-covered furniture thatthe subtle expansion and contraction of wood due totemperature and humidity caused the amber tocrack, fall off, or separate (Gierlowski, 2006a). The
slightly reflective bronze backing also enhanced thecolor of the translucent amber. Wolfram’s workmen
laid the large oak panels flat and fastened bronze foil
to them using iron clasps. They prepared the piecesof amber by sawing them into strips, approximately
5 mm thick, to be mounted in a mosaic onto thebronze foil (Gierlowski, 2006a).
The adhesive was a mixture of pine resin andbeeswax with a low melting point so craftsmen could
easily remove or replace broken or ill-fitting slices.
The amber carvings were assembled by mortise-andtenon joints (similar to tongue and groove) and fixed
to the panel by ivory pegs. The design elements on
the main wall panels, cartouches, and cameos andthe Dresden frames for the four mirrors were also
made of amber and attached by either method. The
frames also served as a structural element tostrengthen the panels.
After six years, Wolfram’s shop had completed onefourth of the panels, frames, and carvings. In 1707,
however, Schlüter fell out of favor with the court andwas abruptly dismissed from his post, with the captainof the guards, Eosander von Goethe, appointed in hisplace. In turn, Goethe dismissed Wolfram over a payment dispute and ordered the guards to remove theamber panels and carvings from his workshops—barring Wolfram in the process—and transport everything
to Charlottenburg. Wolfram spent a number of years
trying to recover his workshop and payment, but heeventually fled to Copenhagen after being threatenedwith arrest (Hein, 1991; Gierlowski, 2006a).
Schlüter also left Prussia for Saxony and eventually moved to St. Petersburg at the invitation of Peter
the Great. Goethe did not modify Schlüter’s original
design and eventually hired Gottfried Turau andErnst Schacht to complete the project. An inventory
taken six years later, in 1713, indicated that the twocraftsmen had completed a majority of the carvings,
four of the 12 pilasters, and most of the panels thatwould cover about 95% of the walls in the room
(Gierlowski, 2006a).
The death of Frederick I in 1713 brought his successor to the Prussian throne. Frederick William I

disdained the extravagance the Amber Room represented and promptly ordered all work on it to stop,with the materials packed up and deposited in the
Berlin armory. The new monarch also halted payments to Turau and Schacht (Gierlowski, 2006a). The
panels and carvings remained hidden in the Berlin armory until 1716, after a visit to the Prussian court
by Czar Peter I. Frederick William I took the occasion to present the still-unfinished panels to theRussian monarch in exchange for a company of 40
grenadiers, on November 17, 1716. The exchange
sealed a valuable alliance of the two states to end
Swedish occupation of large sections of Russia’s
Baltic coast.
The presentation of the amber panels to Peter I
was not an impulsive decision. Prussian royalty had
regarded amber as their national treasure for at leasta century and had established a tradition of sealing
diplomatic agreements with objects such as furniturepieces, chandeliers, and large mirror frames fashioned from the material. The panels for the Amber
Room were the largest such gifts (Netzer, 1993). On
January 13, 1717, workmen packed the pieces into
eight large crates and dispatched them to St. Petersburg. The journey proceeded by road through Königsberg and Klaipeda (in modern-day Lithuania) andtook nearly six months. A report from Alexander
Menshikov, St. Petersburg’s first governor general,
noted that “there was practically no damage to theamber cabinet” (Gierlowski, 2006a).
After the shipment’s arrival in St. Petersburg, it
was discovered that the amber panels, which had
been designed for a specific cabinet room in the Charlottenburg Palace, did not conform to any rooms in
the Russian palace. Several panels remained unfinished, as did the mirrored pilasters, and no local
craftsmen had the skills to complete them andmount the elements to the walls. Neither Peter I,
who died in 1725, nor his wife Catherine (r. 1725–7)
or grandson Peter II (r. 1727–30) made any decision
about where to install the amber panels.
After the death of Peter I, his daughter, Elizabeth,
in 1730 ordered the large panels to be displayed in the
St. Petersburg Summer Palace, where they remainedpropped against the walls in various function rooms
for 13 years. In 1743, Elizabeth, who had taken thethrone two years earlier, ordered her staff to transport
the amber elements to the much larger third Winter
Palace. She appointed Italian craftsman Alexander
Martelli to oversee the mounting of the amber panels
in a suitable room. Martelli, who served the Russian
court as a monument conservator, also had some skill

HISTORY OF THE AMBER ROOMGEMS & GEMOLOGYWINTER 2018383

in amber working and the techniques employed by
the original Danzig craftsmen (Gierlowski, 2006a).
Francesco Bartolomeo Rastrelli, senior court architect, was appointed to redesign the amber elements
to fit the new room, which was a much larger ceremonial hall. Other problems presented themselves.
When Martelli’s workers could not replicate the intricate amber engravings and bas-relief on the remaining eight pilasters, Rastrelli replaced the amber
elements with mirrors mounted in gilded frames tofill the remaining space. This solution created another problem. Russia had no glassmaker capable ofmaking one-piece mirrors more than 3.65 meters inheight. This delayed the project for nearly three years,
until a French company delivered the mirrors in oak
frames at the end of 1745. Martelli also replaced themirrors in the Dresden frames with oil paintings by
Dutch artist Johan van Groot (Gierlowski, 2006a).
The Winter Palace room also required an additionalamber window frame, so Martelli had to commission
an amber workshop in Königsberg to create one.
When the window frame arrived, two months before
the mirrors, it was discovered that the makers hadmeasured it incorrectly. It took another six weeks tocorrect the problem (Gierlowski, 2006a).
The Amber Room was completed in late 1745 but
was moved again and reassembled in other rooms
within the Winter Palace several times before August
1755, when Empress Elizabeth I ordered the entire
room to be dismantled a final time and moved about
24 km (15 miles) out of the city to Tsarskoye Selo, a
royal preserve that held the newly constructed palace(also designed by Rastrelli) named for Elizabeth’s
mother, Catherine I.
The Catherine Palace was one of the largest in Europe. The square chamber selected for the Amber
Room was even more spacious than the Winter
Palace site and nearly three times the size of the original Prussian cabinet room, despite the fact that one
wall consisted mainly of three very large arched windows. The 12 amber panels covered 68.5 square meters and the other elements an additional 5.57 square
meters. The wall space of the square room in theCatherine Palace, whose ceiling stood nearly twice
as high as the original room, was approximately 216
square meters. And no amber craftspeople who
resided in the region possessed the skills to create additional panels.
Rastrelli’s goal was to convey the impression thatthe three walls were composed almost entirely ofamber. To occupy the additional space, Rastrelli
added 18 mirrored pilasters to separate the amber

panels. To account for the ceiling height, he raised
the amber panels onto a stone base and placed anelaborate gilded cornice above them. The decorations
on the cornice were wreath patterns carved in relief,
all coated with gold foil. Above the cornice, Rastrelli
commissioned artist Ivan Belsky to paint a simulated
amber mosaic on a 30 × 2.68 meter canvas. The canvas was mounted over the three non-windowed walls
to fill the space between the top of the cornice andthe ceiling, creating the illusion that this upper portion was also lined with amber. He painted imitationamber panels to fit in the narrow strips between the
double pilasters. Rastrelli also mounted gilded figures, carved reliefs, and gilded bronze candelabras on
top of the painting, further obscuring the facade. The
wooden panels over the double doors were painted
white and covered by gilded reliefs (Gierlowski,
2006a).
To replace the van Groot oil paintings from theWinter Palace amber panels, Rastrelli commissioned
Florentine artist and printer Giuseppe Zocchi to create four mosaics depicting the five human senses(sight, hearing, touch, smell, and taste) that would be
mounted in the same amber frames as the oil paintings. Craftsmen also created a parquet floor containing 15 different varieties of wood, each a different
shade, set in circular motifs (Gierlowski, 2006a).
The basic design was completed in 1756, and Empress Elizabeth began using the room for official
functions. However, the many moves had damaged
some of the original amber pieces, and she wanted to
add amber furnishings to complement the room.
Much work was needed before the panels would becompleted to her satisfaction.
In 1758 the empress appointed Friedrich Roggenbucke, a noted amber craftsman in Königsberg, toserve as the room’s curator and to create amber-covered tables, chests, and bureaus for it. Roggenbuckeestablished an on-site workshop and brought inamber workers from his native city to train local
workers, who were mostly recruited from nearby villages. These craftsmen added an amber section overthe middle door, replacing a wooden section, and set
amber mosaic strips in the narrow sections between
the mirrored pilasters and in other small spaces
throughout the room (Owen, 2009).
Contemporary reports said that the staff worked
long hours (for 12 rubles yearly) because continual
repairs were necessary. The palace was not occupied
and not heated during the cold Russian winters.
When it was occupied, the heat from the 550 wallmounted candles could make the room very warm.

384

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Figure 5. The only
known color photographof the original Amber
Room, taken inTsarskoye Selo in 1937.
This photograph helped
researchers establish thedesign and color schemeof the reconstructed
Amber Room. Photo
courtesy of Amberif.

The Amber Room remained in the Catherine Palace
relatively unchanged, except for restorations in 1833,
1865, and 1890. After the Russian Revolution of
1917, the palace was turned into a museum. The
room remained intact, though not on public display.
Conservation efforts were minimal. In 1937, the Soviet government renamed the town that surrounded
the Tsarskoye Selo preserve to Pushkin.

With the invasion by three million German troops
in the summer of 1941, Soviet officials began evacuating palace treasures east toward Siberia. As the Germans advanced toward St. Petersburg, the curators of
the Amber Room attempted to dissemble and evacuate the panels for safekeeping. But the years had madethe amber very brittle, and the pieces crumbled easily,
forcing the curators to abandon the effort. Instead,they covered the room with wallpaper veneer in an attempt to disguise the amber (Krylov, 1999).
By September 1941, the German army had advanced to the outskirts of Leningrad and occupied
Pushkin and the Catherine Palace. The Amber Roomwas a priority for removal because it had been included in the Kummel Report, a list of German-madeartworks to be “repatriated” to German soil (Owen,2009). The German army dismantled the room panels and decorations within 36 hours, packing it in 27
crates, and shipped it by rail to Königsberg, where it
was reassembled and displayed in the city’s castle(Krylov, 1999). Two years later, museum director Dr.
Alfred Rohde was ordered to dismantle the room
again and crate it in the event that British or U.S.

HISTORY OF THE AMBER ROOMGEMS & GEMOLOGY

The extreme changes of temperature and humidity
created problems. The temperature-sensitive glue
and the wood base expanded or contracted with thechanges, causing some of the amber pieces to crack
or fall off (Gierlowski, 2006a; Owen, 2009; figure 5).
Besides making continual repairs, the staff constructed a number of amber furniture pieces andsmall objets to furnish the room. While there was noformal opening ceremony, researchers and historians
agree that the main design and construction, otherthan conservation and repair, was completed in 1780,
some 73 years after the project was begun (Gierlowski, 2006a).

THE LOOTING OF THE ROOM

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bombers attacked the city. The room panels were last
seen January 12, 1945, when Dr. Rohde wrote thatthe amber panels were being crated. “As soon as it isdone, I shall evacuate the panels to Wechselberg near
Rochlitz in Saxon” (Owen, 2009). By then the Allied
air raids on Königsberg had already begun, though thecastle had remained intact. The air raids eventuallydestroyed most of Königsberg Castle, leaving theouter walls and some battlements. In the spring of1945, Soviet troops advanced into the city and leveled the remainder of the castle.
Immediately following the war, the Soviet government made finding the Amber Room a priority. It
seized the territory of East Prussia as a Russian
province (including Königsberg, renamed Kaliningrad
in 1946), and soon afterward dispatched a group of investigators to search the ruins of the castle. They located several items of furniture from the Catherine
Palace in an intact tower and, the following year, discovered the ruins of three of Giuseppe Zocchi’s Florentine mosaics from the room (Owen, 2009; figure 6).
While there have been numerous theories about
the fate of the Amber Room, the only certainty isthat it disappeared between the time of the German

Figure 6. This photo, purportedly taken by a Germansoldier, shows the destruction of the Catherine Palace
during the German siege of St. Petersburg in WorldWar II. The panels from the Amber Room were seizedby the German army at the beginning of the siege andtransported to a castle in Königsberg for display. They
were never recovered after the war. Photo courtesy of
REX/Shutterstock.com.

invasion in 1941 and the arrival of the Soviet troops
in Königsberg in 1945. Erich Koch, the SS commander who had ordered the removal of the amber
panels from the city, reportedly led a group of Russian officials on a search during the 1950s but failed
to find them. He died in 1986 without ever providing
additional information (Grimaldi, 1996; Blumberg,2007). In 1967, the Soviet government formed a commission to systematically search known art repositories in the USSR and Germany for the Amber
Room panels. The commission continued the search
until 1984, five years after the decision was made torecreate the room (Owen, 2009).
Most historians believe that the Amber Room wasdestroyed by Allied bombing raids on the castle afterJanuary 1945 or the subsequent Russian invasion andshelling of the city. One museum conservator, anamber expert, noted that the panels, if ever discovered, would be too deteriorated to be of any use today(Varoli, 2000). Since the war’s end, numerous parties
have appeared from time to time claiming, without
substantiation, to have found the missing amber panels. Most recently, in October 2017, a group of treasure hunters claimed to have located them behind thedoors of a Polish bunker (Wight, 2016; “Amber Room:
Priceless Russian treasure…”, 2017).
While the room panels have never been found,some pieces of the original have surfaced over theyears, most importantly one of the Zocchi mosaics,“Touch and Smell.” The ruins of the other three mosaics were found in the destroyed Königsberg Castle
in 1945, and this piece had been considered lost until
then. It was offered for sale by Meinhardt Kaiser toan antiques dealer in Bremen, Germany, in 1997.
The dealer alerted police, and Kaiser led them to a
man named Rudi Wurst, whose father had been partof the SS unit that escorted the train carrying theAmber Room components from the Catherine
Palace to Königsberg in 1941. Police believe that thispiece had been long separated from the rest of theroom’s treasures. Locating it helped the restorers
achieve much greater historical accuracy in theirrecreation (National Geographic, 2004; Owen, 2009;
A. Krylov, pers. comm., 2017).

THE RECONSTRUCTION
The end of World War II left the entire Catherine
Palace in ruins. An exhibit of wartime photographs(Tsarskoye Selo State Museum, 2013) shows part ofthe palace ablaze and some interior images of the ruined structure. A photograph purported to be of the386

HISTORY OF THE AMBER ROOMGEMS & GEMOLOGYWINTER 2018

Amber Room shows the walls completely stripped
to bare brick, except for fragments of the paintings
above the cornice. The roof is collapsed, leaving theroom exposed to the elements.
In the 1950s, the Soviet government embarked ona project to restore this and other historical sites destroyed and damaged during the war. Reconstruction
took 25 years, and the Catherine Palace was reopened to the public in the summer of 1980. The
Amber Room, however, had only been minimallyrenovated. The imitation amber mosaic painting
over the cornices had been redone, and the parquet
floors, decorated ceilings, and mirrored pilasters were
all restored as closely as possible to the original designs. The walls, however, remained unadorned(Zhuravlov, 2006). The empty walls were temporary;in April of the previous year, the Federal Council of
Ministers had issued an order to begin reconstructionof the panels for the Amber Room (Gierlowski,
2006a). The mandate was to recreate the room as
closely as possible to the design completed in theeighteenth century. The challenge was formidable
since very little documentation of the original room
existed. Available resources included:• Eighty-six black-and-white photographs of theroom, taken in the late 1930s for a planned
restoration.
• A single color slide of one section of the room,from 1937. The slide showed the southwest
corner and included two of the mosaics, theirframes, six mirrored pilasters, the statues, candelabras, and the gilding around the cornice.
The slide provided some information on how
various colored pieces of amber were assembled
on the walls in irregular but aesthetically pleasing patterns.
• Seventy-six amber fragments found in the destroyed room. Some were pieces of wall decorations and chips from amber carvings. Thesegave researchers information on the thickness
and hues of the amber pieces used on the walls.
• A miniature chest assembled with amber, dating from the time of the Amber Room construction, which survived in the Catherine
Palace collection but was in very poor condition (Krylov, 2006). While working on its
restoration, the team found the signature of
Gottfried Turau. Thus, the team had an opportunity to study firsthand the techniques of oneof the room’s creators (Gierlowski, 2006b).

HISTORY OF THE AMBER ROOM

• The curator of the Amber Room from 1916 to
1941, Anatoly Kuchumov, who was still alive
and able to help plan the reconstruction.
Other than the amber itself and the oak frames
and base, no one knew the composition of the othermaterials employed in the frames and adhesives (M.
Trutanova, pers. comm., 2017).
With so little to guide them, several years of research were necessary before the reconstruction could
begin (M. Trutanova, pers. comm., 2017). The researchteam, assembled two years before the decision to
begin the reconstruction, was composed of Alexander
Krylov, Alexander Zhuravlov, and three other graduates of the Mukhina Academy of Arts and Design at
Leningrad State University (now St. Petersburg State
University). They began by studying other amber objects that had been removed from the Catherine
Palace well before the German invasion, examining
the few amber objects that had been removed from thepalace and hidden in a Siberian bunker just prior to
the invasion. In addition, the research team assembled
all the documents on seventeenth- and eighteenthcentury amber craft they could locate, including an
original drawing by Andreas Schlüter from 1701
(Krylov, 1999). They enlarged and enhanced the grainy
1930s photographs to reveal shadings and grayscales
that would offer clues to color patterns of the amber
mosaics and details in the carvings (Owen, 2009).
Each piece was cleaned thoroughly and photographed on a white background. They were matchedagainst similar pieces located in the photographs,
which allowed the team to match the actual color in
the reconstructed elements (Krylov, 2006).
The researchers tested what they had learned fromrestoring and reconstructing other amber objects suchas furniture and sculptures that resided in the Hermitage Museum and Pavlovsk Palace, both in St. Petersburg, and the Oruzheynaya Palace in Moscow.
Between 1979 and 1984, the team, which included
Zhuravlov and Krylov, recreated a number of historical pieces. Among these were a chessboard with 32
carved figures, the original of which was made in Germany in the eighteenth century and housed at theHermitage; a casket bearing a figure of the Greek goddess Dione, also from the Hermitage, that was madein Danzig in the seventeenth century; a large cameowith a likeness of Empress Elizabeth from the Amber
Room; and six amber obelisks from Pavlovsk (Zhuravlov, 2006). To test their techniques, they created amodel panel of the Amber Room from simulated
amber (Owen, 2009).

GEMS & GEMOLOGYWINTER 2018387

It took three years from the official approval before the room reconstruction could begin in earnest.
The Restavrator, the team that would perform all of
the reconstruction work, was formed in 1982.
Headed by Boris Igdalov and including Marina Trutanova, they commenced work in a studio in St. Petersburg (Zhuravlov, 2006). The distance between St.
Petersburg and Pushkin would allow the work to be
kept secret (Owen, 2009).
Much research remained, however. First, theteams investigated the wood to use for the baseboards and the adhesives to hold the amber pieces
in place. For the baseboards, the restoration team decided to use pressure-treated pine rather than theoak used in the original, because it would be lesslikely to absorb moisture or expand and contract
with changes in temperature and humidity. The foilbacking chosen for the amber was brass instead ofbronze (M. Trutanova, pers. comm., 2017).
To determine the makeup of the adhesive, the research team submitted several of the surviving
pieces of amber to the Leningrad Institute of Criminal Investigation. Through spectroscopic analysis,
the Institute found that the adhesive consisted of
40% beeswax and 60% dammar resin, a gum fromthe Dipterocarpaceae family of trees in India andEast Asia that was used for ship caulking at the time
the original room was constructed (Zhuravlov,
2006). Determining the correct adhesive was morethan a matter of historical accuracy. Permanent adhesives were not suitable because they would have
prevented the replacement of amber pieces broken
during the reconstruction process or in future repairs
or restorations. In addition, permanent adhesives
would likely crack over time (M. Trutanova, pers.
comm., 2017).
Using the crime lab’s findings as a guide, the reconstruction team developed an adhesive frombeeswax and a type of pine resin that melted at about
140°F (60°C). This combination allowed workers to
use a commercial hair dryer to apply or remove
amber pieces. The research team tested this andother adhesives, subjecting them to heat (three hours
at 40ºC), cold (2.5 hours at –15ºC), ultraviolet light(2.5 hours), and a high-moisture environment (14hours) (M. Trutanova, pers. comm., 2017; A. Zhuravlov-Nikiforova, pers. comm., 2017). Next was acquiring the amber. The research team estimated thatthe reconstruction would require 6,000 kg of “bestquality” amber. The wall areas measured 86.12
square meters. The decorative objects and motifs
would require an additional 122 square meters of ma-

terial. The average thickness of each piece of amber
was planned at 5 mm, similar to the original (Zhuravlov, 2006).
With the approval of the Soviet government, thereconstruction team was given access to the amber
deposits in the Sambia Peninsula, which were thenunder state control. While the amount of amber required for the reconstruction was substantial (6,000
kg or 3 metric tons), production in the Samland region was much higher, ranging between 595 and 744
metric tons yearly from 1979 to 1988 (KosmowskaCeranowicz, 2006).
With supplies assured by the Soviet government,
the workshop team began researching dyes and treatments that would have been used in the eighteenth
century to recreate the yellow to reddish orange patterns on the original walls. No one knew what materials were used for the original dyes, so a team fromthe Leningrad Institute of Technology developed dyesthat would not fade, change color, or fully absorb into
the amber (Gierlowski, 2006b). While the ingredientsused in the dyes are proprietary, the process involves
immersing the amber into boiling water for 10 minutes, with the appropriate dyes added afterward (M.
Trutanova, pers. comm., 2017). However, a divisiondeveloped among researchers between those whowanted to employ natural-color amber and those
who wanted to dye the material to the darker shades
it had assumed by the time the 1937 color slide wastaken. Ultimately, the latter group prevailed (Gierlowski, 2006a).
Before dyeing, the amber to be mounted on thewall in mosaic patterns was sliced to 3 mm thick instead of the planned 5 mm—presumably a cost reduction—and then fitted onto the wood panel withoutadhesive. The reconstruction team then numberedeach piece and dyed them the appropriate colors (M.
Trutanova, pers. comm., 2017). Not all of the reconstruction followed eighteenth-century techniques.
Some of the amber was treated at high pressure andtemperature to improve its translucency and matchthe colors from the original room. The material wasplaced in pressure chambers filled with nitrogen or
argon, and then heated to 300°C. In other cases,
pressed amber—material left over from carvings or
cuttings, ground into powder, and pressed into the appropriate shapes before dyeing—was used in the reconstruction (Gierlowski, 2006b). In all, 4.2 square
meters of pressed amber was used in the wall panels.
The amber mosaics lining the wall panels were
only the beginning of the reconstruction. The ornate
decorative motifs such as scrolls, wreaths, laurels

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GEMS & GEMOLOGYHISTORY OF THE AMBER ROOM

WINTER 2018

The only exception was in the materials—the original contained various colored marble slices insteadof the decorative stones used by the studio (Krylov,
2006). The original mosaic is kept in storage at thepalace but put on display for significant occasions (M.
Trutanova, pers. comm., 2017; see figures 8–10).
After the collapse of the Soviet Union in 1991, theRussian government could no longer fund the project,
and work was nearly suspended with fewer than 40%of the panels completed (Varoni, 2000). The Restavrator studio, which numbered about 50 artisans, wasliquidated, though some work continued. Up to thatpoint, the government had spent the equivalent of
US$7.85 million on the reconstruction—largely onsalaries since the amber had been provided as a state

Figure 8. A craftsman in the Tsarskoye Selo Amber
Workshop completing a carving for the mosaic“Touch and Smell” from slices of jasper, malachite,quartz, chalcedony, and nephrite. Photo courtesy ofTsarskoye Selo Amber Workshop.

Figure 7. A corner section and end table showing thedetail of the multi-hued recreated amber mosaics, thebas-relief employing darker shades of amber, and thetable itself, which is also coated with amber. Photo
courtesy of Amberif.

(which used the darkest-colored pieces), floral bas-reliefs, and objects such as grotesques and other sculptures were all made from carved amber. While thecarving and assembly skills required were transferablefrom jewelry and sculpting crafts, they proved extremely time-consuming (Krylov, 2006; figure 7).
Working from the black-and-white photos, the workshop recreated the destroyed Zocchi mosaics of thesenses using jasper, malachite, quartz, chalcedony,and nephrite.
The comparison with the recently discovered
Zocchi mosaic in Bremen validated their reconstructive work, which was nearly identical to the original.

HISTORY OF THE AMBER ROOMGEMS & GEMOLOGYWINTER 2018389

Figure 9. Detail of theoriginal “Touch andSmell” mosaic panel
made from colored marble pieces. The panel
was apparently stolen by
a German officer as thecontents of the Amber
Room were being evacuated from Königsberg
Castle in 1941. It was
discovered in Bremen,
Germany, in 1997. Photo
courtesy of Tsarskoye
Selo Amber Workshop.

resource (A. Zhuravlov-Nikiforova, pers. comm.,2017). The new market economy meant that instead
Figure 10. Detail showing the Florentine mosaic“Sight,” one of four such recreated mosaics in theroom. The frames are fashioned from carved andsliced pieces of amber of various hues. Photo courtesyof Amberif.

390

HISTORY OF THE AMBER ROOMof relying upon the Russian government for funding,the company had to raise funds from private sources(Gierlowski, 2006b).
Through the intercession of Dr. Burkhart Gores,
the director of the Prussian Palaces and Gardens
Foundation, funding was obtained in 1999 from theGerman energy company Ruhrgas, which had extensive dealings in Russia (Owen, 2009). Ruhrgas agreed
to provide an additional US$3.5 million to complete
the reconstruction and ordered its completion by April
2003. Ruhrgas chairman Friedrich Spath told the New
York Times, “The Amber Room has enormous emotional significance for both Germany and Russia. And
it is a leading symbol of a time when close German
and Russian relations were a model for the world.” At
that time, Ruhrgas was receiving one-third of its natural gas supplies from Russia (Varoli, 2000).
With new funding, the Restavrator reorganized
into a corporation named the Tsarskoye Selo Amber
Workshop to resume its work full time and complete
it by the contracted deadline. The new company alsobegan earning income by manufacturing and sellingamber carvings, miniature chests, and chess sets that
resembled historical pieces, and taking commissions
to restore or reconstruct other amber pieces in museums. This, along with the use of synthetics, raised
objections from some members of the research team
who felt they were acting against the Venice Charterof 1964, which forbids the use of contemporary techniques and materials and “conjecture” in reconstructing historical monuments (Gierlowski, 2006b;
Owen, 2009).

GEMS & GEMOLOGYWINTER 2018

Figure 11. Two sections of the reconstructed Amber Room wall showing the mirrored pilasters that separate the panels, the Florentine mosaics, and the intricate amber wreaths and clusters on and atop the cornice. Photo by Sergey
Bogomyako/Shutterstock.com.

The completed room used some 100,000 pieces ofamber encompassing more than 150 square metersof wall space. While the design was as faithful as possible, some who remembered the original Amber
Room believed the reconstructed room was brighter,though others countered that the varnishes used on
the amber surfaces in previous repair and restoration
efforts had darkened over the years (Owen, 2009; seefigures 11 and 12).
In May 2003, as the city of St. Petersburg celebrated its 300th anniversary, a summit of world leaders—including Russian President Vladimir Putin,
German Chancellor Gerhard Schroeder, U.S. President George W. Bush, French President Jacques
Chirac, British Prime Minister Tony Blair, ItalianPrime Minister Silvio Berlusconi, and Japanese Prime

Minister Junichiro Koizumi—formally opened the reconstructed Amber Room to the public. According tosaint-petersburg.com, the tourist attraction receives
about 7,000 daily visitors during the peak summer
months.
The Tsarskoye Selo Amber Workshop remains onsite for ongoing maintenance because the temperature-sensitive adhesives require constant attention.
Amber itself is called a “living stone” that can react
to relatively small changes in temperature and humidity. Inspectors check the room weekly (After the
Amber Room, 2013). Other rooms in the Tsarskoye
Selo complex are also undergoing reconstruction, including the church, the Agate Room, and the Catherine Palace Museum, as well as restoring amber
artifacts in other Russian museums. In addition, theHISTORY OF THE AMBER ROOMGEMS & GEMOLOGYWINTER 2018

391

Figure 12. A section of the wall of the reconstructed Amber Room. Photo courtesy of Amberif.

studio continues to produce amber objects for sale tohelp offset the high costs of maintaining the Amber
Room.

CONCLUSIONS
Although many articles have been written about theoriginal Amber Room, few have documented its reconstruction, and fewer still have offered detailed accounts of both the original and reconstructed rooms.
Its reconstruction was fraught with a number of chal-

ABOUT THE AUTHOR
Mr. Shor is a senior industry analyst at GIA in Carlsbad, California.
ACKNOWLEDGMENTS
The author would like to thank Ewa Rachon, project director at
Amberif and Amber Mart (Gdansk, Poland), who provided introductions and offered valuable insights for the manuscript; Alexan-

392

HISTORY OF THE AMBER ROOM

lenges, but the result is regarded as being faithful tothe version of the Amber Room that was housed in
the Catherine Palace from 1780 to 1941. Firsthandaccounts from the principal researchers, designers,
and builders of the reconstructed room describe a
combination of eighteenth-century techniques,
many of which had to be relearned or adapted tomodern materials, offering insight into the significant challenges encountered to reconstruct this cultural landmark.

der Krylov, an amber craftsman who helped design the reconstruction; and Anastasia Zhuravlev-Nikiforova, who provided
some of her father’s, Alexander Zhuravlov’s, papers on the reconstruction of the room. Boris Igdalov and Marina Trutanova of theAmber Workshop (Tsarskoye Selo) are thanked for sharing theirresearch and invaluable expertise.

GEMS & GEMOLOGYWINTER 2018

REFERENCES
After the Amber Room: History of the Tsarskoselskaya Workshop(2013) Avrora-Design, St. Petersburg.
Amber Room: Priceless Russian treasure stolen by Nazis “discovered” by German researchers (2017) www.independent.co.uk/
news/world/europe/amber-room-nazis-russian-catherinepalace-st-petersburg-tsar-second-world-war-stolen-treasurea8008526.html
Blumberg J. (2007) A brief history of the Amber Room. Smithsonian.com, https://www.smithsonianmag.com/history/a-briefhistory-of-the-amber-room-160940121/
Butrimas A., Jovaiša E. (2013) The Balt’s amber route to classicalcivilization. Paper presented at International Amber Researcher
Symposium, March 20–23.
City of Gdansk (2017) Gdansk treasures – amber. www.gdansk.pl/en/about-gdansk/Gdansk-treasures-Amber,a,3019
Clark N.L.D (2010) Amber: Tears of the Gods. Dunedin Academic
Press, Edinburgh, pp. 23–28.
Czebreszuk J., Szmyt M. (2013) Amber in Europe 3000 Years BCE.
Paper presented at International Amber Researcher Symposium, March 20–23.
Gaigalas A., Halas S. (2009) Stable isotopes (H,C,S) and the origin
of Baltic amber. Geochronometria, Vol. 33, No. 1, pp. 33–36,
http://dx.doi.org/10.2478/v10003-009-0001-9
Gierlowski W. (2006a) Amber Room – the founders and creators.
In B. Kosmowska-Ceranowicz and W. Gierlowski, Eds., Amber:
Views, Opinions. Scientific Seminars: AMBERIF—1994–2005.
International Amber Association, Gdansk, Poland, pp. 147–
155.
——— (2006b) Reconstruction of the Amber Room as an impulse
for the creation of copies and reconstructions of lost historicalartifacts. In B. Kosmowska-Ceranowicz and W. Gierlowski,
Eds., Amber: Views, Opinions. Scientific Seminars: AMBERIF—1994–2005. International Amber Association, Gdansk,
Poland, pp. 165–172.
Grimaldi D.A. (1996) Amber: Window to the Past. Harry N.
Abrams Inc. in association with the American Museum of Natural History, New York, pp. 147–191.
Hein J. (1991) Ivories by Gottfried Wolfram. Scandinavian Journalof Design History, Vol. 1. pp. 7–34.
Kosmowska-Ceranowicz B. (2006) Finds, deposits and mines ofamber and other fossil resins. In B. Kosmowska-Ceranowicz
and W. Gierlowski, Eds., Amber: Views, Opinions. Scientific
Seminars: AMBERIF—1994–2005. International Amber Association, Gdansk, Poland, pp. 9–13.

——— (2009) Baltic amber deposits. InColor. Fall/Winter, pp. 22–
24.
Krylov A. (1999) Reconstructing the amber masterpiece. Paper presented at International Amber Research Symposium, March
23–24.
——— (2006) Reconstructing the Amber Room. Selected problems. In B. Kosmowska-Ceranowicz and W. Gierlowski, Eds.,
Amber: Views, Opinions. Scientific Seminars: AMBERIF—
1994–2005. International Amber Association, Gdansk, Poland,
pp. 160–162.
Langenheim J.H. (1990) Plant resins. American Scientist, Vol. 78,
No. 1., pp. 16–24.
Mazurowski R. (2011) From the research on the Late Neolithic amber
art in the Neidzwiedziowka microregion near Nowy Dwor Gdanski (3100–2400 BCE) Session of the World Amber Council, May
27–28. http://prusaspira.org/pogezana/Bursztyn.pdf
National Geographic (2004) The mystery of the Amber Room.
https://video.nationalgeographic.com/video/treasurewars/amber-room-tw
Netzer S. (1993) Bernsteingeschenke in der Preussischen Diplomatie des 17 Jahrhunderts. Yearbook of the Berlin State Museum, Berlin, pp. 227–246.
Owen J. (2009) Forever amber: The impact of the Amber Room on
Russia’s cultural stature then, now and in the future. Master’s
thesis, Georgetown University, Apr. 27, https://repository.
library.georgetown.edu/bitstream/handle/10822/552838/
owenJennifer.pdf
Tsarskoye Selo State Museum (2013) The loss of the palaces:
Tsarskoye Selo in 1941–1944. http://eng.tzar.ru/shows/show/archive/?id=3142
Varoli J. (2000) Amber Room, lost to war, is recreated. New YorkTimes, Jan. 23, https://www.nytimes.com/2000/01/23/arts/artarchitecture-amber-room-lost-to-war-is-recreated.html
Wight E. (2016) Is 60-year hunt for the missing $400million Amber
Room finally over? Daily Mail, Apr. 22, http://www.dailymail.
co.uk/news/article-3552241/Is-60-year-hunt-missing-250million-Amber-Room-FINALLY-New-images-Nazi-looted-treasure-hidden-sealed-wall-secret-room-underground-bunker-Pola
nd.html
Zhuravlov A. (2006) Amber Room - Beginning the reconstruction.
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Views, Opinions. Scientific Seminars: AMBERIF—1994–2005.
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162.

For online access to all issues of GEMS & GEMOLOGY from 1934 to the present, visit:

gia.edu/gems-gemology

HISTORY OF THE AMBER ROOMGEMS & GEMOLOGYWINTER 2018393

FEATURE ARTICLESTHE COLOR ORIGIN OF GEM DIASPORE:
CORRELATION TO CORUNDUM
Che Shen and Ren Lu

Color-change diaspore, known commercially as Zultanite, is sought by designers and consumers for its special
optical characteristics, namely its color and color change. Understanding the color origin of gem-grade diaspore
could provide a scientific basis to guide its gemological testing, cutting, and valuation. This study uses ultraviolet-visible (UV-Vis) spectra and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) to
examine the color origin of color-change diaspore and to compare it with corundum. As Raman spectra vibration
intensities are closely related to crystal direction for diaspore, crystal orientation was determined through Raman
spectroscopy. The color correlation between color-change diaspore and corundum confirmed the identity ofeach chromophore. In addition, the effectiveness of different chromophores such as Cr3+, Fe3+, Fe2+-Ti4+ pairs,
and V3+ between gem-quality diaspore and corundum is compared quantitatively.

Gem-quality diaspore occupies an important
position in the gem market due to its rarity,
striking pleochroism, and color-change phenomenon (figure 1). The material’s value depends onthese factors. A clear understanding of color origin
offers considerable benefits for gemological testing,cutting, and even valuation of gem diaspore.
By replacing the major elements in definite structural units through isomorphous substitution, traceelements play an important role in the color of gemstones. The AlO6 octahedra is a significant structuralunit that produces color when different trace elements substitute for Al. For example, Cr 3+ substitutes for Al3+ in the AlO6 octahedra in jadeite andspinel, causing green and red color (Lu, 2012; Malsy,2012), while the substitution of Fe3+ for Al3+ in sapphire produces yellow color (Emmett et al., 2003).
Diaspore and corundum have a similar chemicalcomposition and crystal structure (see figure 2). Diaspore, with the chemical formula AlO(OH), belongs tothe orthorhombic space group 2/m 2/m 2/m (Hill,1979); corundum, with the chemical formula Al2O3,
belongs to the trigonal space group 3̅ 2/m (Lewis et al.,1982). The crystal structure of diaspore consists of
AlO4(OH)2 octahedra, whereas the corundum crystal

See end of article for About the Authors and Acknowledgments.
GEMS & GEMOLOGY, Vol. 54, No. 4, pp. 394–403,
http://dx.doi.org/10.5741/GEMS.54.2.394© 2018 Gemological Institute of America

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COLOR-CHANGE DIASPORE

structure consists of AlO6 octahedra (Hill, 1979; Lewis
et al., 1982). Both types of crystals are composed solelyof octahedral units. In addition, the diaspore structureis able to convert to corundum structure through dehydration (Iwai et al., 1973). Due to their closely related
crystallographic structure and chemical composition,

In Brief• Gem-quality diaspore with an attractive color and remarkable color-change phenomenon is rare and often
highly valued.
• The AlO6 octahedral structural unit, a very important
structural unit related to gemstone color, is very similar
between diaspore and corundum.
• The structural similarity between diaspore and corundum helps us confirm the color origin of diaspore
quantitatively.

we may speculate that there is also a close color correlation. There are two other reasons for this hypothesis:
1. Compared to other gemstones containing the
AlO6 octahedral structural unit, diaspore andcorundum share the closest similarity in average Al-O bond length, octahedral volume, anddegree of distortion of octahedral sites (quantified by determining the octahedral quadratic
elongation). For specific data, refer to table 1.

GEMS & GEMOLOGYWINTER 2018

Figure 1. This 24.60 ct color-change diaspore is shown under D65 illumination (left) and A illumination (right).
Photos by Robert Weldon, courtesy of Zultanite Gems LLC.

2. The structural similarity between corundumand diaspore was first referred to by Deflandre(1932). Both diaspore and corundum are connected by octahedral units, and both containedge-shared octahedra. However, there are faceshared octahedra along the c-axis that only exist
in corundum, and this is the main difference between the two. Other related studies involving
X-ray powder photography (Francombe andRooksby, 1959), single-crystal X-ray techniques,scanning electron microscopy (SEM), and hightemperature optical microscopy (Iwai et al.,1973) have confirmed a structural similarity between the two gem materials.
This intensely close relationship between corundum and diaspore with respect to the octahedral Al
site and their overall structural similarity indicatesthat chromophores substituted into the Al site of bothmaterials are expected to present similar UV-visible
absorption features. Consequently, this study adopts
an analogy to address the color origin of diaspore byquantitatively analyzing the trace-element chemistryin diaspore from two geographic origins—Myanmar(formerly Burma) and Turkey—and comparing themwith high-quality natural and synthetic corundum.
The research aims to use the color correlation between diaspore and corundum to confirm the color
origin of gem diaspore.

MATERIALS AND METHODS
Samples. Nine diaspore samples from Turkey werepurchased from a gem dealer at the Beijing International Jewelry Show in November 2016. Forty slices
of diaspore were collected in the field from Mogok,
Myanmar, by author RL. All samples were prepared
as wafers. These wafers are perpendicular to the aaxis, b-axis, and c-axis, respectively. Photos of samples are shown in table 2.
Raman and Photoluminescence (PL) Spectroscopy.
Raman and PL spectra were collected from the samples with a Renishaw inVia Raman microscope system at the Gemstone Center of Hebei GEO
University in China. Raman spectra were collectedfrom 100 to 1400 cm–1 using Nd-YAG laser excitation, producing highly polarized light at 532 nm

TABLE 1. Crystallographic parameters of corundum, diaspore, and spinel.
Gemstone

Averagedistance of
Al-O (Å)

Octahedral
volume (Å3)

Octahedral
quadratic
elongation

Deviation of average AlO distance (% difference
from corundum)

Deviation of octahedral
volume (% difference
from corundum)

Deviation of quadratic
elongation (% difference
from corundum)

Corundum

1.91339.07541.0202000Diaspore

1.91549.1042

1.02030.109760.317349.8020 × 10–3

Spinel

1.93279.49551.0092

1.01404.62901.0782

Note: The crystallographic parameters are from Lewis et al. (1982), Hill (1979), and Peterson et al. (1991).

COLOR-CHANGE DIASPOREGEMS & GEMOLOGYWINTER 2018

395

a

b

c

t

b

c
t
b

t
t

c

a

(1800 lines/mm grating, 10 s). The orientation of all
samples was carefully controlled. The polarization
direction of the injected laser was parallel to the aaxis, b-axis, and c-axis. The 600–800 nm spectral
ranges for Raman photoluminescence analysis (underliquid nitrogen conditions) were excited by an NdYAG laser at 532 nm (1800 lines/mm grating, 10 s).

Figure 2. These views of thecrystal structure of diaspore(top) and corundum (bottom)
illustrate the basic building
blocks, AlO4(OH)2 and AlO6
octahedra, and their geometric relationships. The crystallographic orientation isshown in the upper left cornerprojected down the c-axis.
The blue spheres in the diaspore’s crystal structure represent the hydrogen atoms. The
structure is characterized byedge-shared octahedral double-chains, which are extended along the a-axis. The
corner-linked octahedral layers are connected along the aaxis. In addition, theOH-vector is approximately
parallel to the a-axis. In the
crystal structure of corundum, each octahedron isedge-shared, with three octahedra in the a-b plane. All octahedra are face-shared, with
one octahedron along the caxis. The letters b, c, and t
represent the different layers
in corundum (bottom, center,and top). Based on Hill (1979)
for diaspore and Lewis et al.
(1982) for corundum.

with 27Al using a fixed internal standard method. We
selected three spots on each sample for general chemical composition.

LA-ICP-MS Analysis. For trace-element analysis, weused an Agilent 7900a ICP-MS coupled with a deepUV laser at 193 nm excitation at the State Key Laboratory of Geological Processes and Mineral
Resources, China University of Geosciences in
Wuhan. NIST glass standard SRM 610 and USGS
glass standards BHVO-2G, BIR-1G, and BCR-2G
were used for external calibration. Ablation wasachieved using a 44 μm diameter laser spot size, afluence of around 5 J/cm2, and a 6 Hz repetition rate.
The diaspore was initially standardized internally

UV-Vis Spectroscopy. Five diaspore samples (Dia-006a, Dia-006-b, Dia-006-c, Dia-Bur-001, and Dia-Bur-002)
were prepared as well-polished, oriented wafers withvarious thicknesses. UV-Vis spectra were collectedwith a Perkin-Elmer Lambda 650 UV-Vis spectrophotometer equipped with mercury and tungsten lightsources and photomultiplier tube (PMT) detectors installed in an integrating sphere. The spectra were collected at the Gemological Institute, China Universityof Geosciences in Wuhan. Polarized spectra were collected in the 300–800 nm range with 1 nm spectral
resolution at a scan speed of 267 nm/min. The spectral
baseline was corrected by subtracting spectral offsets
at or beyond 800 nm, where the chromophores’ features were insignificant or nonexistent.

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TABLE 2. Trace-element composition of diaspore by LA-ICP-MS (in ppma), withstandard deviation in parentheses.
Dia-006

Dia-008

Dia-Bur-001

Dia-Bur-002

110 (3)185 (0.9)220 (13)418 (5)Traceelement,
with
detection
limit
Ti—9
V—0.1

6 (0.2)4 (1)44 (2)

359 (2)

Cr—1

36 (0.7)

32 (2)

2166 (58)2081 (29)Fe—201169 (12)548 (53)

4 (bdl)1 (bdl)bdl = below detection limit

RESULTS AND DISCUSSION
Chemical Analysis. Table 2 shows the chemicalcomposition (expressed in ppma) of two diaspore
samples from Turkey (Dia-006, Dia-008) and two
from Myanmar (Dia-Bur-001, Dia-Bur-002). We concluded that the Burmese samples contained more Cr,
while the Turkish diaspore had a higher Fe content.
However, the V content of the Burmese samples washigher than that of the Turkish samples, especiallyin Dia-Bur-002 (358 ppma).
Raman Spectroscopy. Unlike Turkish diaspore,
Burmese material often occurs as thin crystals thatare difficult to orient by crystal growth characteristics. However, Raman vibration is closely related to
crystal direction (see http://rruff.info/diaspore/display=default/R060287). By comparing the Raman
spectra of the diaspore from Myanmar with the ori-

ented sample from Turkey, the Burmese diaspore
could be oriented properly. Raman spectra of both the
Burmese and Turkish diaspore were collected in the
100–1400 cm–1 range.
According to previous research by Ruan et al.
(2001) and San Juan-Farfán et al. (2011), the band at
154 cm–1 is assigned by the rotation of two edgeshared AlO6 octahedra around the c-axis. The mostintense peak, at 447 cm–1, is related to Al-O symmetric stretching modes, which means the different polarization direction of the laser has little impact on
this peak. Therefore, we normalized the peak intensity at 447 cm–1 and compared the intensity at 154
cm–1. When the polarization direction of the injected
laser is parallel to the c-axis, the intensity of the 154
cm–1 peak is much stronger than those that run parallel to the b-axis and a-axis (see note on figure 3).
Based on figure 4, we can accurately diagnose the

INTENSITY (COUNTS)

20000015000010000050000

154 cm–1 rotation of two edge-shared
AlO6 octahedra around the c-axis

R AMAN SPECTRA
447 cm–1 Al-O

E || a
E || b
E || cFigure 3. The Raman
spectra of the Turkish
diaspore, with the polarization direction of
the injected laser parallel to the c-axis (bluetrace), the b-axis (orange trace), and the aaxis (green trace).

0
200

400

600

800

1000

1200

1400

RAMAN SHIFT (cm–1)

COLOR-CHANGE DIASPOREGEMS & GEMOLOGYWINTER 2018

397

R AMAN SPECTRA

100000

80000

60000

40000

447 cm–1 Al-O

154 cm–1 rotation of two edge-shared
AlO6 octahedra around the c-axis

INTENSITY (COUNTS)

120000

E || a
E || cFigure 4. The Raman
spectra of Burmese diaspore with the polarization direction of theinjected laser parallelto the short side, or aaxis (orange trace), andthe c-axis (blue trace).

c
5 mm

a

20000

0
200

400

600

800

1000

1400

1200

–1

RAMAN SHIFT (cm )crystal orientation by Raman vibration (154 cm–1).
The Burmese diaspore wafers were manufactured
perpendicular to the b-axis based on perfect cleavage
along the {010} direction. Hence, we can consider thelong side of the wafer parallel to the c-axis, and theshort side parallel to the a-axis.

(E vector) is parallel to the a-axis, diaspore shows UVvisible absorption features similar to those of corundum (see figure 5). Our corundum samples included
three synthetic sapphires—a Cr-bearing synthetic
ruby, a Fe-Ti bearing synthetic blue sapphire, a Vbearing color-change sapphire—and one natural yellow Fe-bearing sapphire from Garba Tula, Kenya.
In order to make our initial comparisons between
chromophores in corundum and diaspore, we havechosen to compare the spectra of corundum collected from the o-ray (R. Lu, previously unpublisheddata) with those of diaspore collected from the orientation of polarized light parallel to the a-axis.
From LA-ICP-MS data, we know that the Cr content
is significantly higher in Burmese samples than in
Turkish samples. However, as the Fe content is near

UV-Vis and PL Spectroscopy of Cr3+. Corundum, auniaxial crystal, shows dichroism. Its UV-Vis spectra
are often collected from two orthogonal orientations
with polarized light (o-ray and e-ray). As a biaxial
crystal, diaspore shows trichroism; its UV-Vis spectra
are collected from three orthogonal orientations withpolarized light (E ǁ a, E ǁ b, and E ǁ c). In gem cutting,the table of a ruby or sapphire is generally perpendicular to the c-axis. When the polarization direction

ABSORPTION COEFFICIENT (cm–1)

UV-VIS SPECTRA
6

Sapphire: O-ray—1000 ppma Fe

377
5

Dia-006: E || b—1000 ppma Fe
Dia-006: E || c—1000 ppma Fe

388

Dia-006: E || a—1000 ppma Fe
4

398
384

3

450
2

448

1

0
350

400

450

500

550

600

650

700

750

WAVELENGTH (nm)398

COLOR-CHANGE DIASPOREGEMS & GEMOLOGY

Figure 5. The three polarizations of diaspore (E ǁ a,
E ǁ b, E ǁ c) were collected
to compare with the spectra of sapphire (o-ray).
Peaks at 377 and 388 nm
in sapphire and at 384 and398 nm in diaspore are attributed to Fe3+. The heightof sapphire’s 377 and 388
nm peaks (384 and 398 nm
in diaspore) is closely related to directionality. In
diaspore, the best matchwith the spectrum of
corundum (o-ray) is shown
when the polarization direction is parallel to the aaxis (E ǁ a).

WINTER 2018

BOX A: SPECTRAL FITTING BASED ON THE BEER-LAMBERT LAW
There are additive properties that exist in a UV-Vis spectrum. A simple mathematical step will lead to the following equation:
A = A1 + A2 + … + An
where:• A is total absorbance of all absorbers• A1, A2, … , and An are the absorbance of each absorber nFigure A-1 illustrates how this is accomplished.
According to the Beer-Lambert law, the absorption is
proportional to the concentration of absorbers (chromophores) through which light passes. It can be expressedsimply by the following mathematical expression:
n
A=1

∑

εi ci

i=1

where:• A is absorbance• l is the path length of the light beam through thematerial sample• εi is the molar attenuation coefficient or absorptivity of the attenuating species i in the material
sample• ci is the concentration (in ppma) of the attenuating species i in the material sample
Based on this law, if we have collected the absorption
spectrum of a chromophore at a certain thickness, we
can simulate absorption spectra of different concentrations and thicknesses within a certain range. Figure 6
shows two spectra of Burmese diaspore. By subtracting
the two spectra, we will essentially obtain only the V absorption since the Cr concentrations are almost thesame. Since we have the pure V3+ spectrum, it is easy toobtain the pure Cr3+ spectrum by subtracting the pureV3+ spectrum from the spectrum of Burmese diaspore.

UV-VIS SPECTRA
2+4+Violet sapphire (Cr: 1000 ppma; Fe -Ti :60 ppma) O-ray; 1 mm thick
3.0

Violet sapphire
L*: 36 a*: 33 b*: –52

Blue sapphire
L*: 58 a*: 10 b*: –47

ABSORBANCE

2.5

Ruby (Cr: 1000 ppma; Fe2+-Ti4+: 0 ppma)
O-ray; 1 mm thickBlue sapphire (Cr: 0 ppma; Fe2+-Ti4+:
60 ppma) O-ray; 1 mm thick

2.0

Ruby
L*: 62 a*: 49 b*: –29
1.5

1.0

0.5

0.0
300

400

500

600

700

800

900

Figure A-1. The absorption of violet
sapphire (violet dotted line) shown here
represents the sum of the other two
spectra: ruby (red line) and blue sapphire (blue line). The color circles calculated under D55 illumination aredemonstrated for all of the spectra. We
may conclude that violet is a combination of Cr3+ red with Fe2+-Ti4+ blue. As
described above for the additive properties, the absorption of violet sapphire(A) is calculated from two known sets:
A1 (the absorption of ruby) and A2 (theabsorption of blue sapphire). However,
we could also use the difference (A–A1)of any two spectra to show the remaining absorption (A2).

WAVELENGTH (nm)zero in the Burmese samples, we disregarded the absorption of Fe in the UV-Vis spectra of that material.
The spectra of Dia-Bur-001 and Dia-Bur-002 areshown in figure 6. Although the Cr content of thetwo samples is almost the same (2166 and 2081
ppma, respectively), there is a large difference in theabsorption intensity. This difference is related to theabsorption of vanadium. By subtracting the two
spectra, we essentially obtain only V absorption,
which can be subtracted from the other spectra toobtain the pure Cr spectrum (see box A). Based on

the author’s color analysis, chromium will cause aslight color-change phenomenon in diaspore (figure7). Additionally, we used the PL spectra (figure 8) toconfirm that gem diaspore and ruby show comparable fluorescence spectra (694/693 nm for ruby and690/693 nm for diaspore).

COLOR-CHANGE DIASPOREGEMS & GEMOLOGYUV-Visible Spectroscopy of Fe3+ in Diaspore and Sapphire. The UV-Vis spectrum of Turkish diaspore (figure 9) shows features corresponding with those of
Fe3+-bearing yellowish sapphire from Garba Tula,

WINTER 2018399

INTENSITY (COUNTS)

ABSORPTION COEFFICIENT (cm–1)

PL SPECTRAUV-VIS SPECTRA
Dia-Bur-002: E || a—2081 ppma Cr, 359 ppma V

30

Dia-Bur-001: E || a—2166 ppma Cr, 44 ppma V
20

10

0
350

400

450

500

550

600

650

700

750

150000spinel100000

ruby

50000

diaspore

0

800

680

685

WAVELENGTH (nm)Figure 6. The UV-visible spectra of the Burmese diaspore samples show a large difference in absorption
intensity.

UV-VIS SPECTRA
50

Diaspore: E-ray || a—1000 ppma Cr
Ruby: O-ray—1000 ppma Cr

ABSORPTION COEFFICIENT (cm–1)

45

Ruby (D65)
L*: 35 a*: 68 b*: –22

Ruby (A)L*: 42 a*: 72 b*: –14

40

35

30

1.2

25

1.0
0.8

20

0.6
15
690

692

694

696

698

700

10

5

0
350

400

450

500

550

600

650

700

750

WAVELENGTH (nm)400

COLOR-CHANGE DIASPORE

700

diaspore show an obvious absorption band at around
570 nm. Based on the LA-ICP-MS data, chromium andvanadium are very low in Turkish diaspore. In blue
sapphire, the absorption at around 580 nm is attributed

UV-Visible Spectroscopy of Fe2+-Ti4+ Pairing in Diaspore and Sapphire. The UV-Vis spectra of the Turkish

Diaspore (A)L*: 67 a*: 15 b*: 4695

Figure 8. The PL spectra of natural ruby and one of
the Burmese diaspore samples show very similar
characteristics based on table 1. The crystallographic
parameters of diaspore are very close to those of ruby,but quite different from those of spinel. The PL spectra of spinel (data provided by Dr. Chengsi Wang) areconsiderably different from those of ruby and diaspore. Therefore, we can also use PL spectra to demonstrate that the structural units of diaspore and rubyare very closely related.

Kenya. In those sapphires, the peak at 388 nm is attributed to Fe3+, while the peaks at 377 and 450 nm
are attributed to Fe3+-Fe3+ pairs (Ferguson and Fielding, 1971, 1972; Krebs and Maisch, 1971). The spectraof diaspore show features very similar to those of
Fe3+-bearing sapphire. Hence, the peaks at 384 and448 nm are attributed to Fe3+-Fe3+ pairs, and the peakat 398 nm is attributed to Fe3+.

Diaspore (D65)
L*: 67 a*: 4 b*: 6690

WAVELENGTH (nm)GEMS & GEMOLOGY

800

Figure 7. The calculated UVvisible spectra of diasporeand synthetic ruby—both
only containing Cr—have
similar absorption regions
but show much different intensities. The color circles
above the spectra, calculated
under D65 and A illumination, demonstrate coloration
for diaspore and ruby with
1000 ppma Cr concentrations for a 5 mm path length.
(The spectra of 1000 ppma
and 5 mm path length arecalculated rather than taken
directly from the sample. A
similar method is used in
the analysis of the otherchromophores.) According to
the author’s calculation, thechromophore effectiveness of
Cr 3+ in ruby is about 5–10
times higher (peak intensity)
than in diaspore.

WINTER 2018

UV-VIS SPECTRA

ABSORPTION COEFFICIENT (cm–1)

Dia-006: E-ray || a—1000 ppma Fe
6

Sapphire: O-ray—1000 ppma Fe

377
5

388

4

Diaspore (L*: 90 a*: –4 b*: 16)
384

3

398

450

2

448

Sapphire (L*: 98 a*: –7 b*: 29)

1

0
400

450

500

550

600

650

700

750

800

WAVELENGTH (nm)to an Fe2+-Ti4+ pairing (Emmett et al., 2003). It is possible that the absorption at around 570 nm in diaspore
is related to Fe2+-Ti4+ (see figure 10). In blue sapphire,
the absorption of the Fe2+-Ti4+ pair does not cause thecolor-change effect because the absorption band ex-

tends to the near-infrared region, so the transmission
rate of red areas and green areas is not relatively equal.
But in diaspore, these transmission areas are fairly
equal. The value of a* has changed from –3 to 1, whichmeans the color will change from green to red.

UV-VIS SPECTRA
Dia-006: E-ray || a—50 ppma Fe2+-Ti4+

30
28

ABSORPTION COEFFICIENT (cm–1)

26

Sapphire: O-ray—50 ppma Fe2+-Ti4+
Sapphire (D65)
L*: 10 a*: 26 b*: –71

Sapphire (A)L*: 5 a*: 22 b*: –75

Diaspore (D65)
L*: 95 a*: –3 b*: 8

Diaspore (A)L*: 96 a*: 1 b*: 7

24
22
20

Calculated for 50 ppma
Fe2+-Ti4+ pair with 5 mm path

18
16
14

Diaspore (D65)
L*: 77 a*: –7 b*: 31

12

Diaspore (A)L*: 78 a*: 6 b*: 27
Calculated for 250 ppma
Fe2+-Ti4+ pair with 5 mm path

10
8

0.25

6

0.20
0.15

4

500

2

540

580

620

0
350

400

450

500

550

600

650

700

750

WAVELENGTH (nm)COLOR-CHANGE DIASPORE

Figure 9. The UV-visible
spectra of Turkish diaspore
and yellowish sapphirefrom Garba Tula, Kenya,
exhibit closely matched absorption features, especiallywhen polarized light is parallel to the a-axis. The color
circles are calculated under
D55 illumination, demonstrating the coloration fordiaspore and sapphire with
1000 ppma Fe concentrations for a 5 mm path
length. According to the author’s calculation, the chromophore effectiveness of
Fe 3+ in sapphire is about 1.6
times higher (peak intensity) than in diaspore.

GEMS & GEMOLOGY

800

Figure 10. The UV-visible
spectra of Turkish diaspore
and blue synthetic sapphire(containing Fe2+-Ti4+ only).
The two spectra have similar
absorption regions but showmuch different absorption intensities. The color circles,
calculated under D65 and A
illumination, demonstrate
the coloration for sapphireand diaspore with 50 ppma
Fe2+-Ti4+ pair concentrations
for a 5 mm path length. Since
the color swatches of diaspore calculated using 50
ppma concentration of Fe2+Ti4+ pairs do not show a clear
color change, we must calculate the colors, which are
shown in the spectra, at ahigher concentration of Fe2+Ti4+ pairs (250 ppma) for a 5mm path length. The chromophore effectiveness of the
Fe2+-Ti4+ pair is about 50
times higher (peak intensity)
in sapphire.

WINTER 2018

401

UV-VIS SPECTRA
40

ABSORPTION COEFFICIENT (cm–1)

Diaspore: E-ray || a—500 ppma V
Sapphire: O-ray—500 ppma V

3530

Diaspore (D65)
L*: 44 a*: 57 b*: –34

Diaspore (A)L*: 41 a*: 48 b*: –35

Sapphire (D65)
L*: 82 a*: –10 b*: 22

Sapphire (A)L*: 82 a*: 5 b*: 14

25

20

15

1.4
1.2
1.0
0.8
0.6
0.4

10
500

540

580

600

5

0
350

400

450

500

550

600

650

700

750

800

WAVELENGTH (nm)

Emmett et al. (2017) proposed that Si plays a rolein the color chemistry of corundum. If corundum contains Ti, Si, Mg, and Fe, the Fe will pair with Si before
Ti. If diaspore is similar to corundum, Fe will chargecompensate Si before Ti. However, the instruments
used for LA-ICP-MS show significant interferences forthe three silicon isotopes (Shen, 2010), and as a result
the Si content is higher than the value shown. The author does not take Si into consideration because of this
instrumental error, and assumes that all of the Ti pairs
with Fe. Therefore, the actual content of the Fe2+-Ti4+
pair may be lower than the content determinedthrough analysis.
UV-Visible Spectroscopy of V in Diaspore and Sapphire. In natural corundum, vanadium content is generally very low. Synthetic sapphire, which has been
manufactured with V, will show an obvious colorchange effect. This type of synthetic sapphire is similar to natural alexandrite. However, there is some V
in natural diaspore from Myanmar, which plays animportant role in color origin and color change.
We compared the spectra of diaspore (containing
V only; see box A) to pure vanadium-bearing syn-ABOUT THE AUTHORS
Mr. Shen is a graduate student at the Gemmological Institute,
China University of Geosciences in Wuhan. In 2018, he was a
research intern at the Gemological Institute of America in Carlsbad, California. Dr. Lu is a professor at the Gemmological Institute, China University of Geosciences in Wuhan.

402

COLOR-CHANGE DIASPORE

Figure 11. The UV-visible
spectra of diaspore (after
calculation) and synthetic
sapphire (containing V
only). The two spectra
show similar absorption
regions but different absorption intensities. The
color circles are calculated
under D65 and A illumination and demonstrate coloration for sapphire anddiaspore with 500 ppma V
concentrations for a 5 mmpath length. According to
the author’s calculation,
the chromophore effectiveness of V 3+ in diaspore isabout 2–7 times higher(peak intensity) than insapphire.

thetic sapphire. They also show similar absorption
characteristics in their UV-Vis spectra, as both peaks
are at around 400 nm and 560 nm in diaspore andsapphire (see also figure 11).

CONCLUSIONSIn color-change diaspore, Cr3+, V3+, and Fe2+-Ti4+ pairs
are the chromophores, and all of these contain an absorption area at around 560–580 nm. These chromophores may all play a role in causing thecolor-change effect. Raman spectroscopy proved to
be a powerful tool for determining the crystal orientation of the Burmese diaspore wafer; it is also useful
to measure and compare the directional UV-Vis spectra of diaspore and corundum. Because of their structural similarity, we can confirm the color correlation
between corundum and diaspore and compare the effectiveness of the chromophores. According to thecalculation, the chromophore effectiveness of Cr3+,
Fe3+, and Fe2+-Ti4+ in corundum is about 5–10, 1.6, and50 times higher, respectively, than in diaspore. However, the chromophore effectiveness of V3+ in diaspore is approximately 2–7 times higher than incorundum.

ACKNOWLEDGMENTS
The authors would like to thank Mr. Yungui Liu at HGTC (Gemstone Center of Hebei GEO University) provided Raman and PL
testing. Dr. Aaron Palke (GIA, Carlsbad) and anonymous peer
reviewers provided many helpful comments and suggestions.

GEMS & GEMOLOGYWINTER 2018

REFERENCES
Deflandre M. (1932) La structure cristalline du diaspore. Bulletinde la Société Française de Minéraologie et de Cristallographie,Vol. 55, pp. 140–165.
Emmett J.L., Scarratt K., McClure S.F., Moses T., Douthit T.R.,
Hughes R., Novak S., Shigley J.E., Wang W., Bordelon O., Kane
R.E. (2003) Beryllium diffusion of ruby and sapphire. G&G,
Vol. 39, No. 2, pp. 84–135, http://dx.doi.org/10.5741/GEMS.
39.2.84
Emmett J.L., Stone-Sundberg J., Guan Y., Sun Z. (2017) The roleof silicon in the color of gem corundum. G&G, Vol. 53, No. 1,
pp. 42–47, http://dx.doi.org/10.5741/GEMS.53.1.42
Ferguson J., Fielding P.E. (1971) The origins of the colours of yellow, green and blue sapphires. Chemical Physics Letters, Vol.
10, No. 3, pp. 262–265.
Ferguson J., Fielding P.E. (1972) The origins of the colours of natural yellow, blue, and green sapphires. Australian Journal ofChemistry, Vol. 25, No. 7, pp. 1371–1385.
Francombe M.H., Rooksby H.P. (1959) Structure transformations
effected by the dehydration of diaspore, goethite and delta ferricoxide. Clay Minerals, Vol. 4, pp. 1–14, http://dx.doi.org/
10.1180/claymin.1959.004.21.01
Hill R.J. (1979) Crystal structure refinement and electron density distribution in diaspore. Physics and Chemistry of Minerals, Vol. 5, No. 2, pp. 179–200, http://dx.doi.org/10.1007/
BF00307552
Iwai S.I., Yamamoto H., Morikawa H., Isobe M. (1973) Topotactic
thermal-transformation of diaspore to corundum. Mineralogical Journal, Vol. 7, No. 2, pp. 137–158, http://dx.doi.org/
10.2465/minerj1953.7.137
Krebs J.J., Maisch W.G. (1971) Exchange effects in the optical-ab-

sorption spectrum of Fe3+ in Al2O3. Physical Review B, Vol. 4,
No. 3, p. 757.
Lewis J., Schwarzenbach D., Flack H.D. (1982) Electric field gradient and charge density in corundum, α-Al2O3. Acta Crystallographica, Vol. 38, No. 5, pp.733–739, http://dx.doi.org/10.1107/
S0567739482001478
Lu R. (2012) Color origin of lavender jadeite: An alternative approach. G&G, Vol. 48, No. 4, pp. 273–283, http://dx.doi.org/
10.5741/GEMS.48.4.273
Malsy A.K. (2012) Orangey-red to orangey-pink gem spinels froma new deposit at Lang Chap (Tan Huong-Truc Lau), Vietnam.
Journal of Gemmology, Vol. 3, No. 1, pp. 19–27,
http://dx.doi.org/10.15506/JoG.2012.33.1.19
Peterson R.C., Lager G.A., Hitterman R.L. (1991) A time-of-flightneutron powder diffraction study of MgAl2O4 at temperatures
up to 1273 K. American Mineralogist, Vol. 76, No. 9-10, pp.
1455–1458.
Ruan H.D., Frost R.L., Kloprogge J.T. (2001) Comparison of Raman
spectra in characterizing gibbsite, bayerite, diaspore andboehmite. Journal of Raman Spectroscopy, Vol. 32, No. 9, pp.
745–750, http://dx.doi.org/10.1002/jrs.736
San Juan-Farfán R.E., Bayarjargal L., Winkler B., Haussühl E., Avalos-Borja M., Refson K., Milman V. (2011) Pressure dependenceof the lattice dynamics of diaspore, α-AlO (OH), from Raman
spectroscopy and density functional perturbation theory.
Physics and Chemistry of Minerals, Vol. 38, No. 9, pp. 693–
700, http://dx.doi.org/10.1007/s00269-011-0442-3
Shen A.H. (2010) Silicon in sapphires—its role and detectability
by LA-ICP-QMS. Goldschmidt Conference Abstracts 2010, p.
A945.

GEMS & GEMOLOGY requires each manuscript
submitted for publication to undergo a rigorous
peer review process, in which each paper is evaluated by at least three experts in the field prior toacceptance. This is essential to the accuracy, integrity, and readability of G&G content. In addition to our dedicated Editorial Review Board, we
extend many thanks to the following individuals
who devoted their valuable time to reviewing
manuscripts in 2018.

COLOR-CHANGE DIASPOREGEMS & GEMOLOGY

Non-Editorial Board Reviewers
Laurent Cartier • John Chapman • Sally EatonMagaña • Ronnie Geurts • Al Gilbertson• George Harlow • Peter Heaney • Darrell
Henry • Artitaya Homkrajae • Richard Hughes• John King • Rachel King • Yan Liu • Cigdem
Lule • Laura Otter • Dieter Quast • Ewa
Rachón • Ilene Reinitz • Sudarat Saeseaw• Russell Shor • Jana Smith • Monica SolorzanoKraemer • Jeffrey Spier • Ziyin Sun • John
Valley • Alexander Zaitsev • Chunhui Zhou

WINTER 2018403

FEATURE ARTICLESCORUNDUM WITH SPINEL CORONA FROM
THE TAN HUONG–TRUC LAU AREA INNORTHERN VIETNAM
Nguyen Ngoc Khoi, Christoph A. Hauzenberger, Chakkaphan Sutthirat, Duong Anh Tuan,
Tobias Häger, and Nguyen Van Nam

Corundum deposits in the Tan Huong–Truc Lau area of Vietnam are hosted mainly in gneiss and partly in feldspathic
pegmatoid and marble. Encountered here in both primary and secondary placer deposits is a considerable quantity ofstones with a well-developed spinel corona following the morphology of the corundum core. The genesis of the observed
spinel corona can be explained by their reaction textures, chemical composition, and mineral inclusions as well as byapplying thermodynamic phase equilibria calculations. The following reactions were found to be responsible for theformation of the spinel corona around corundum in gneiss:biotite + corundum → spinel + K-feldspar + fluid, orgarnet+ corundum → spinel + sillimanite
For corundum-spinel associations in metacarbonate rocks, the relevant reaction is:
dolomite + corundum → spinel + calcite + carbon dioxide
Mineralogical and chemical studies have shown that the gem quality of ruby and sapphire grains from Tan Huong–
Truc Lau deteriorated substantially after their formation due to this corona texture.

C

See end of article for About the Authors and Acknowledgments.
GEMS & GEMOLOGY, Vol. 54, No. 4, pp. 404–417,
http://dx.doi.org/10.5741/GEMS.54.4.404© 2018 Gemological Institute of America

One of the remarkable phenomena of these deposits
is that in some secondary (alluvial and diluvial) and primary deposits, the corundum is frequently surrounded
by a well-developed spinel corona. This corona mainly
follows the morphology of the corundum crystal.
These encrusted stones have an unattractive yellowish
gray or brownish gray to almost black appearance until
the spinel corona is removed to occasionally uncovera gem-quality corundum core (figure 2).
Several questions related to this mineral assemblage arise. Why did the spinel corona form aroundthe corundum core, and what reaction(s) occurred
during the corundum → spinel transformation? What
were the characteristics of the corundum before thistransformation, and how was its quality affected
afterward? What was the original host rock? These
questions are of scientific and also economic importance. According to the information from DOJI’s
Truc Lau mine (Khoi et al., 2011), approximately
30% of the corundum recovered from this type of deposit has a spinel corona, which sometimes hides thegem-quality corundum core almost entirely. To an-

404

GEMS & GEMOLOGY

orundum occurrences in northern Vietnam
are hosted not only in marble but also in partly
migmatized gneiss. Gneiss-hosted corundum
deposits are located mainly in the Tan Huong–TrucLau area of the Day Nui Con Voi range in the Red
River shear zone (RRSZ, figure 1). Here the partly
migmatized gneiss contains gray, grayish white tobluish, and yellowish gray sapphires, while dark red
to pinkish ruby occurs in the marble lenses intercalated with gneiss and in the weathered feldspathic
pegmatoid rocks (Khoi et al., 2011, 2016). The gemological properties of corundum from the Tan Huong–
Truc Lau area and the mineralogy, petrology,pressure-temperature (P-T) formation conditions,and genetic model of these gneiss-hosted deposits
were reported by Khoi et al. (2011, 2016).

VIETNAMESE CORUNDUM WITH SPINEL CORONAWINTER 2018

To

QUATERNARY
Sediments

La
o

Ca

Ch

i

ay

NEOGENE

Khoan Thong

Ri

ve

r

Lo

Lang Chap

Sediments
PALEOGENE
Tan Huong Complex: biotite granite,
granosyenite, pegmatite

ga Luc Yenmzone

Truc LauTRIASSIC
Nui Chua Complex: pyroxene gabbro,
gabbrodiorite, hornblende diorite

Minh Tien

Re

Phia Bioc Complex: biotite granite,
pegmatite, aplitedAn Phuriv

NEOPROTEROZOIC-CAMBRIAN
An Phu Formation: graphite-bearing marble,
two-mica schist

e
sh
er
ar

Thac Ba
Lake

zo
ne

Thac Ba Formation: quartz-mica schist,
epidote-biotite-hornblende schist, marble

Mong Son

PALEO-MESOPROTEROZOIC
Ngoi Chi Formation: quartz-biotitesillimanite-garnet schist, amphibolite, marble

Bao AiRedR

ive

Nui Voi Formation: biotite-sillimanitegarnet plagiogneiss, amphibole gneiss,amphibolite, diopside marble

Kinh Lar

Figure 1. Simplified geologic map showing thelocations and rock formations of the gneisshosted corundum
occurrences in the Day
Nui Con Voi range andmarble-hosted occurrences in the adjacent
Lo Gam structural zone
(modified after Xuyen,
2000 and Vinh, 2005).

Tan Huong
CORUNDUM DEPOSITS
Khoan Thong–An Phu area (“old mines”)

To

N

i

Tan Huong–Truc Lau area (“new mines”)

R70

0

10 km

SecondaryPrimarynoHaTran Yen

Yen Bai Cityswer these questions, we have conducted a petrographic (macro- and microscopic) and chemical studyof corundum with an associated spinel corona. Thisdata set, together with available published P-T conditions of the host rocks (Khoi et al., 2016) and thermodynamic phase equilibria calculations as well as
inclusions in mineral phases, was used to explain thegenesis of the spinel corona.

Primary

Secondary

Fault

Road

GEOLOGICAL SETTINGSCorundum occurrences and deposits in northern Vietnam’s Yen Bai Province are located in marble and in
partly migmatized gneiss of the Red River shear zone.
The more than 1,000 km NW-SE trending RRSZ fault
zone is one of Southeast Asia’s most distinct geologicaldiscontinuities with a left-lateral shear sense. Alongthe shear zone, several suites of high-grade metamor-

Figure 2. Some encrusted stones have an
unsightly yellowish
gray or brownish grayappearance until the
spinel corona is cut
away to reveal a gemquality corundum corewith an appealing color
and possibly a star effect (right). Photos by
N.N. Binh, DOJI Gold& Gems Group.

SpinelRuby
Ruby

Star effect

1 cm

VIETNAMESE CORUNDUM WITH SPINEL CORONA

1 cm

SpinelGEMS & GEMOLOGYWINTER 2018405

phic rocks were exhumed (see figure 1) between 35 and17 million years ago (Leloup et al., 1995, 2001).
The gneiss-hosted corundum deposits in Tan
Huong–Truc Lau are located entirely within the Day
Nui Con Voi range, which is composed of high-grade
metamorphic rocks with sillimanite-biotite-garnet
gneiss, mica schist, and amphibolite, all locally intercalated with marble lenses. These rocks appear tohave been intruded by granite, syenite, and pegmatiteof the Tan Huong magmatic complex (again, see figure 1). In contrast, the marble-hosted corundum deposits in the nearby Lo Gam zone occur in a thickmetasedimentary sequence, composed of marble andoverlying sillimanite-biotite-garnet schist (Long et al.,2004). These units, bounded by left-lateral faults, areintruded by granitic rocks and related pegmatite ofTriassic age (Trinh and Vinh, 1997).
40
Ar/39Ar dating of biotite and phlogopite syngenetic with corundum has yielded an Oligocene
minimum age for the deposits in the Lo Gam tectonic zone and a Miocene minimum age for those in
the Day Nui Con Voi range (Leloup et al., 2001; Garnier et al., 2002, 2008; Khoi et al., 2016). In the Tan
Huong–Truc Lau area, corundum-hosting lithologies
can have one of four variations:• Gneiss to partly migmatized gneiss containing
gray, grayish white to bluish, and yellowish
gray sapphire (figure 3, left). Examples include
the Co Man outcrop at the Truc Lau valley and
the Kinh La occurrence (Long et al., 2004;
Thuyet, 2008; Nam, 2012; Khoi et al., 2016).
• Weathered feldspathic (pegmatoid) rocks usually found within gneiss, hosting dark red topinkish ruby crystals. Occurrences include
Slope 700 (figure 3, right) and kilometer markers
13, 15, and 23 along National Road 70 (Nam,2012; Khoi et al., 2016).

• Marble in lenses and boudins intercalated
within gneiss, mica schist, and amphibolite,
containing ruby and sapphire—for example, theSlope 700 outcrop (Bao Ai occurrence), the Tan
Huong drill core (Long et al., 2004), and theTruc Lau mine.
• Amphibolite transformed by metasomatism
into biotite schist, bearing gray to dark graysapphire—for example, the Km 15 occurrence(Long et al., 2004).
The corundum-bearing host rocks in the Tan
Huong–Truc Lau area appear to have originated fromthe metamorphism of fine-grained sediments of variable composition (Katz, 1972, 1986; Simandl and Paradis, 1999; Khoi et al., 2010, 2011, 2016). For example,
gneiss from the Co Man outcrop and the Kinh La occurrence has a wide compositional range: 50–90%
feldspar, up to 40% biotite, and up to 20% sillimanite.
In addition, ruby-bearing feldspathic rocks (e.g., theSlope 700 outcrop) typically consist of K-feldspar andbiotite (or vermiculite; again, see figure 3, right). Temperatures of 650–760°C and pressures of 5–7.6 kbar
have been calculated for the metamorphism andcorundum formation, which corresponds to upper amphibolite to lower granulite facies (Khoi et al., 2016).
The primary deposits and host rocks are usually
deeply weathered, forming numerous secondary deposits. The secondary (eluvial, diluvial, and alluvial)
corundum deposits generally contain dark red ruby,pink sapphire, and red and brown spinel, as well assome garnet, trapiche-like bluish gray sapphire, sillimanite, and quartz. Corundum samples with spinelcorona have been found in different primary and secondary deposits and occurrences in the Tan Huong–
Truc Lau area. For this study, specimens were takenfrom the Kinh La primary occurrence and the Truc
Lau secondary (alluvial) deposit.

Crn

Kln
Vrm

Crn
Crn

1 cm

406

VIETNAMESE CORUNDUM WITH SPINEL CORONA

1 cm

GEMS & GEMOLOGY

Figure 3. Left: This sample
of corundum-bearing gneissfrom the Co Man outcrop
contains mainly feldspar,
biotite, sillimanite, and sapphire crystals up to 3 cm
long. Right: Weathered
feldspathic rock from the
Slope 700 outcrop typicallyconsists of kaolinite (Kln),vermiculite (Vrm), and ruby(Crn). Photos by N.V. Nam.

WINTER 2018

Spl
Crn

Figure 4. In this outcrop
at the Kinh La occurrence, several samples
of primary corundumwith spinel corona werecollected for this study.
Bt = biotite, Kfs = Kfeldspar, Crn = corundum, Spl = spinel.
Photos by N.N. Khoi.

Kfs

Bt

1 cm

The Kinh La (Km 13) occurrence is located 2 km
southwest of the Tan Huong mine, at 21°48′55″N,
104°52′12″E (again, see figure 1). The gem-bearing
body is 0.1 to 1 m thick and 100 m long. The corundum ranges in color from black to bluish gray andfrom 0.1 to 5 cm in size (figure 4).
The Truc Lau deposit, located at 22°02′05″N,
104°40′46″E, occupies a large valley, about 5 km long,that contains eluvial and alluvial sediments (Khoi etal., 2011). The eluvium consists of three layers: topsoil (averaging 1 m thick); a gem-bearing layer (0.8–1
m thick) containing corundum and spinel that iscomposed of pebble, gravel, and sand; and a deeply
weathered gneiss layer (3 m thick) that typically contains ruby and sapphire. Compared to the eluvium,
the alluvial deposits at Truc Lau are thicker (approximately 10 m thick). Ruby, sapphire, and spinel arefound within a gravel paleoplacer (1.2–5.0 m thick)that lies on bedrock and is buried below 0.5–3.5 m of
Quaternary sediments and 0.5–1.5 m of topsoil (Khoiet al., 2011).
Gem corundum here usually shows a tabular
crystal form with deformed polysynthetic twinningalong rhombohedral faces, and growth zones are typically sharp. Colors range from pink to pinkish red,and color irregularities such as zoning and spots orpatches are rare. Many stones, particularly the sapphire, have low transparency due to abundant fracturing and inclusions. Mineral inclusions such as
ilmenite, magnetite, plagioclase, muscovite, biotite,
apatite, zircon, and chlorite are found in corundumfrom the primary deposits. Among these, dark inclusions (e.g., biotite, ilmenite, and magnetite) are mostcommon. Primary and secondary gas-liquid inclusions also occur frequently in this corundum. Common mineral inclusions in corundum from thesecondary deposits are rutile, ilmenite, zircon, apatite, plagioclase, calcite, boehmite, and mica (margarite and muscovite), nearly identical to those incorundum from the primary deposits (Khoi et al.,2011, 2013, 2016).

VIETNAMESE CORUNDUM WITH SPINEL CORONAGEMS & GEMOLOGY

MATERIALS AND METHODSFor this study, we analyzed 53 samples of corundumwith spinel corona: 18 from the Kinh La primary occurrence and 35 from the Truc Lau placer deposits(figures 5–7). These samples were initially investigated using optical microscopy (gemological andpetrological) and scanning electron microscopy(SEM). Mineral inclusions were identified with thehelp of Raman spectroscopy, SEM, and optical microscopy. A quantitatively equipped SEM microscope
was subsequently used to analyze mineral chemistryof both the corundum host and the spinel corona inseveral specimens. Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) wasapplied for trace-element analysis of these samples
as well as other alluvial gem corundum from TrucFigure 5. Gray corundum coated by a black spinel(hercynite) layer, from the Kinh La primary occurrence. Photo by N.V. Nam.
Spl
Crn

1 cm

WINTER 2018407

Figure 6. Left: Roughstones from the Truc
Lau secondary deposit,
some of which containa spinel corona. Right:
Twelve pieces of corundum with spinel corona
were selected from the
lot and used for thisstudy. Photos by N.N.
Khoi.

Lau for comparison and further discussion. Some of
the chemistry data used in this study—such as traceelement composition of the corundum core and microprobe analyses of the spinel corona and othercoexisting minerals from the Kinh La primary occurrence—were published previously (Khoi et al., 2013,2016).
Major elements were determined by SEM analysis, using a JEOL 6310 unit equipped with a Link ISIS
energy-dispersive X-ray (EDX) spectrometer and a
Microspec wavelength-dispersive X-ray (WDX) spectrometer at the NAWI Graz Geocenter, Departmentof Petrology and Geochemistry, Karl Franzens University in Graz, Austria. Accelerating voltage was set
to 15 kV and sample current to 6 nA on a probe current detector (PCD). The elements Al, Mg, and Zn
were determined by EDX; Ti, Cr, and Fe were quantified by WDX. Detection limits were around 0.1
wt.% for EDX and about 0.03 wt.% for WDX. For additional analyses we used a JEOL JXA-8100 electronprobe microanalyzer (EPMA) at the Department of
Geology, Chulalongkorn University in Bangkok.
Trace elements were determined by LA-ICP-MS
using an ESI NWR193 laser ablation unit coupled toan Agilent 7500 ICP-quadrupole MS at the NAWI
Graz Central Lab for Water, Minerals and Rocks, University of Graz and Graz University of Technology.

Material was ablated using a 193 nm laser pulsed at 9
Hz and a 75 µm spot size corresponding to an energyof ~7 J/cm². Helium was used as a carrier gas at ~0.8
L/min flow, and data was acquired in time-resolved
mode. NIST 610 and 612 glasses were routinely analyzed for standardization and drift correction. The
glass standard BCR-2 was analyzed as an unknown
and could be reproduced to within a 10% relative
error. Aluminum was used as an internal standard.
Mineral abbreviations presented here follow Whitney
and Evans (2010).

MACROSCOPIC AND MICROSCOPIC STUDY
Corundum with Spinel Corona from Primary Deposits. At Kinh La, corundum occurs in a sillimanite+ biotite + plagioclase + K-feldspar + ilmenite ± garnet ± hercynite ± magnetite migmatitic gneiss. The
corundum crystals are often coated by hercynite-richspinel (figures 5 and 8), with or without signs of corrosion. The corundum core in the samples is gray todark gray, while the spinel rim is dark gray to black.
The size of the corundum core frequently ranges
from 10 to 30 mm, while the spinel corona has athickness of a few millimeters to several centimeters. As can be seen in figure 8, the thickness of thespinel corona increases at the expense of the corundum core.

Crn

Spl
Crn

Figure 7. Spinel-coatedruby (left) and sapphire(right) crystals from theTruc Lau deposit. Photos by N.N. Khoi.

Spl

1 cm

408

VIETNAMESE CORUNDUM WITH SPINEL CORONA

1 cm

GEMS & GEMOLOGYWINTER 2018

ter-sized flakes or alternating with K-feldspar, plagioclase, spinel, and corundum.
Petrographic study of the samples also revealed
other minerals, such as sillimanite, garnet, and quartz.
The sillimanite usually has a long prismatic, needlelike shape. The garnet is subhedral to anhedral,strongly fractured, and millimeter- to centimeter-sized(figure 11).

Kfs+PlCrn
Spl
Bt
Kfs+PlBt
Bt

1 cm

Figure 8. Gray corundum coated by a dark spinel corona in sillimanite + biotite + plagioclase + K-feldspar+ ilmenite ± garnet ± hercynite ± magnetite
migmatitic gneiss. Sample H7005 from the Kinh La
occurrence. Photo by N.N. Khoi.

Under transmitted light, coarse twin lamellae andfractures are prominent in the corundum core. Frequently encountered in the corundum are ilmenite
and magnetite inclusions (figure 9), as well as somezircon and apatite.
Under transmitted light, the spinel corona is green
to deep green in color (figure 10) and translucent. It occurs as coarse xenoblastic crystals that formed duringmetamorphic overprint and took their outlines fromneighboring crystals. Common inclusions in thespinel are biotite and K-feldspar. K-feldspar and plagioclase (figure 10) usually account for 20–70% of theground mass, occurring as aggregates of tabular subhedral to anhedral crystals together with corundum,
biotite, and hercynite. Biotite, accounting for 10–90%
of the samples, occurs as aggregates of brown millime-

Corundum with Spinel Corona from Secondary Deposits. Figure 12 shows hand specimens of corundumwith spinel corona collected from the Truc Lau secondary deposit. The color of the corundum core showsmuch more variety than samples from primary deposits, ranging from white to gray to pink, pinkish red,and dark red. The shape of the internal corundum ismostly irregular to subrounded, and the boundary of
the surrounding spinel corona is marked by a sharpchange in color. Signs of corrosion are apparent insome samples. Almost all of the internal corundum

In Brief• Corundum deposits in northern Vietnam are hosted
mainly in marble and gneiss.
• An interesting phenomenon that occurs in somecorundum found in the gneiss-hosted deposits is a rim
or “corona” of spinel.
• This spinel corona, which formed through metamorphic reactions, causes a substantial deterioration of thegem quality of the ruby and sapphire.

grains are fractured to some extent and range in size
up to tens of millimeters, and in rarer cases up to hun-

Ilm
Crn
Ilm
Ilm
Ilm

Ilm

Corundum

Ilm
Ilm
1 mm

VIETNAMESE CORUNDUM WITH SPINEL CORONA

Figure 9. Ilmenite inclusions in corundum corefrom the Kinh La occurrence, shown in crosspolarized light on theleft and as a backscattered electron (BSE)
image on the right.
Photomicrographs by
C.A. Hauzenberger.

Ilm

0.5 mmGEMS & GEMOLOGYWINTER 2018

409

Kfs

Grt

Spl

Bt

Bt

Figure 10. Spinel (hercynite), biotite, and K-feldspar insample H7005, migmatized corundum-bearing gneissfrom the Kinh La occurrence, shown in parallel-polarized light. Photomicrograph by N.V. Nam; field ofview 1.2 mm.

dreds of millimeters. Some corundum grains show a
distinct corona texture due to the presence of a spinelrim. The spinel corona has gray, dark gray to yellow,
brown, and sometimes pink to grayish red color witha thickness ranging up to tens of millimeters. Grains
have either comb-like (palisade) or xenoblastic texture.
In general, four different types of corundum samples with spinel corona from secondary deposits canbe recognized (again, see figure 12):Type I: A nearly inclusion-free ruby crystal surrounded by a dense, nearly inclusion-free Mgspinel (figure 12A)
Type II: A sapphire crystal surrounded by a thin,palisade-type Mg-spinel rim (figure 12B)

Figure 11. Biotite and garnet in sample H7005 fromthe Kinh La occurrence, shown in cross-polarized
light. Photomicrograph by N.V. Nam; field of view
1.2 mm.

Type III: A pink sapphire/ruby surrounded by adark Mg-Fe-Al spinel phase (figure 12C)Type IV: A sapphire surrounded by a hercyniterich spinel (figure 12D)
Inclusions were generally rare in all four types. In
each type, corundum typically contains Al-hydroxideand subordinate rutile inclusions (figure 13A). In thetype I sample, calcite and dolomite were found in thespinel rim (figure 13B) while a Ba-rich feldspar and plagioclase were found in the corundum. The spinel rim
in type II samples was partially developed as a seriesof elongated grains growing perpendicular to the sapphire surface and was either completely free of inclusions or showed only a few small calcite and dolomite

Figure 12. Samples of corundum with spinel corona from the Truc Lau secondary deposit. Photos by C.A.
Hauzenberger.

A

B

C
SpinelSpinelSpinel

410

Hercynite

Sapphire
Ruby

Ruby

D

VIETNAMESE CORUNDUM WITH SPINEL CORONAGEMS & GEMOLOGY

Sapphire

WINTER 2018

A

2 mm

B

20 µm

SpinelAl-Hydroxide

SpinelDolomite

Calcite
Ruby

C

1 mm

D

200 µmSpinelApatiteF-pargasite

Sapphire
Sapphirine

SpinelF-phlogopite
F-phlogopite

E

1mm

F

2mm

Phlogopite

SpinelIlmenite
Chlorite

Sapphire
SpinelFigure 13. BSE images ofinclusions in corundum
cores and spinel corona.
A: Al-hydroxide incorundum. The spinel isan inclusion-free type I.
B: Dolomite and calcite
inclusions in type I
spinel. C: Apatite, sapphirine, F-phlogopite,
and F-pargasite in thespinel corona of the typeII sample. D: Palisadespinel rim around a sapphire (type II sample). E:
Phlogopite, chlorite, andsapphire within thespinel corona (type III
sample). F: Sapphire surrounded by a hercyniterich spinel containing
inclusions of ilmenite
and monazite (type IV
sample). Images by C.A.
Hauzenberger.

Monazite
Sapphire

SpinelPhlogopite

inclusions (figure 13C). In one type II sample, sapphirine, fluorian pargasite, and fluorian phlogopite
were identified in the spinel corona (figure 13D). TypeIII samples contain phlogopite and chlorite within thespinel corona (figure 13E). Type IV contains numerous
ilmenite inclusions and a smaller number of apatite,monazite, and zircon inclusions (figure 13F).

CHEMICAL COMPOSITION
Corundum with Spinel Corona from Primary Deposits. The major element compositions of the corundum cores in samples from the Kinh La primaryoccurrence are shown in table 1, while trace-element
contents by LA-ICP-MS analysis are from table 2.a in
Khoi et al. (2016). In general, the corundum core
showed high Fe content (5119 to 5717 ppm) and low

VIETNAMESE CORUNDUM WITH SPINEL CORONA

Ti and Cr content (16 to 81 and 55 to 62 ppm, respectively). Other elements such as Ga, Mg, and V were
found in all samples, but with low content.

TABLE 1. Major element compositiona (wt.%) of 12 samples of corundum core from the Kinh La primary deposit.
Oxide

Content

Al2O3

99.15–99.36 (99.25)

TiO2

0.12–0.21 (0.22)

Cr2O3

0.00–0.09 (0.05)

FeO

0.45–0.97 (0.25)

Total

99.80–100.54 (100.10)aAnalyzed by EPMA. Values are averaged from three to five analyses. Averageoxide contents are shown in parentheses.

GEMS & GEMOLOGYWINTER 2018

411

TABLE 2. Major element compositiona (wt.%) of corundum cores from the Truc Lau secondary deposit.
Sample

TLM2

TLM3

TLM5

TLM6

TLM7

TLL5

Al2O3

99.88

99.86

99.15

99.97

99.43

99.60

TiO2

0.035

0.040

<0.03

<0.03

0.067

0.033

Cr2O3

0.238

0.162

0.233

0.160

<0.03

0.090

FeO

<0.03

0.053

0.054

0.075

0.501

<0.03

Total

100.15100.11

99.44

100.21100.0099.73

aValues are averaged from three to five analyses.

Representative analyses of the spinel rim andother minerals encountered with corundum fromthe Kinh La primary occurrence were also presented
in tables 3.a through 3.d of Khoi et al. (2016). Generally, minerals of the samples from Kinh La are extremely iron-rich. The spinel is nearly pure
hercynite with very low V and no Cr and Zn content. Garnet was observed in only one sample, with~80 mol.% almandine content, grossular and pyrope
contents of ~10 mol.% each, and spessartine below
5 mol.%. The biotite is nearly pure annite withsome Tschermak substitution and up to 5 wt.%
TiO2. The feldspathic matrix usually consists of plagioclase with XAb of ~0.75 and K-feldspar with albite
content of about 25 to 30 mol.%. Magnetite and ilmenite are frequently encountered, either as inclusions in corundum, spinel, and garnet or as single
phases in the matrix.
Corundum with Spinel Corona from Secondary Deposits. Tables 2 and 3 present the analyses of thecorundum core. Ruby has relatively low Cr2O3 values. The TiO2 concentrations are below the detection
limit and the FeO values slightly above. The sapphire
sample contained about 0.5 wt.% Fe2O3 and very low
Cr2O3 and TiO2 values.
Spinel corona compositions are shown in table 4.
The composition is of a nearly pure Al-Mg spinel(sensu stricto), with only minor amounts of FeO(<0.7 wt.%, except the spinel corona around sapphirein one sample, with FeO = 1.27 wt.%), Cr2O3, and
ZnO.

GENESIS OF SPINEL CORONA AROUNDCORUNDUM
Corundum with Spinel Corona from Primary Deposits. In many unaltered corundum-bearing rocks
from primary deposits, the corundum crystals wereenclosed by a spinel corona (figures 5 and 8). Petrographic investigation and, to some extent, the chemical composition of corundum grains with spinelcorona from primary occurrences can be used to explain the genesis of the spinel corona. The Mg-Fe-Alrich spinel and the hercynite-rich spinel corona
samples were formed in migmatitic SiO2-undersaturated and Fe-rich gneiss. The mineral assemblage istypically corundum surrounded by a hercynitic
spinel–magnetite phase, Fe-rich biotite, plagioclase, K-

Figure 14. Corundum + spinel + biotite + garnet mineral assemblage from the Kinh La occurrence, shownin parallel-polarized light. Photomicrograph by N.V.
Nam; field of view 1.2 mm.
Bt

Grt

Crn

TABLE 3. Trace-element compositiona of corundum
cores from the Truc Lau secondary deposit (ppma).
Sample

9

Be

24

Mg

49

Ti

51

53

V

Cr

56

Fe

71

Ga

118

Sn

TLM2

<0.05

68.1

142

196

940

15.4

61.0

6.20

TLM3

<0.05

67.6

108

23.1

926

30.2

31.1

0.21

TLM5

<0.05

39.4

46.6

288

1304

11.1

53.3

0.18

TLM6

<0.05

57.6

82.3

349

1338

60.4

107

0.54

TLM7

<0.05

131

363

6.59

<1

2572.1 74.5

1.12

TLL5

<0.05

82.6

126

248

674

8.37

44.2

0.20

Spl

a

Values are averaged from three to five analyses.

412

VIETNAMESE CORUNDUM WITH SPINEL CORONAGEMS & GEMOLOGYWINTER 2018

TABLE 4. Major element compositiona (wt.%) of spinel rims on corundum from the Truc Lau secondary deposit.
Sample

TLM2

TLM3

TLM5

TLM6

TLM7

TLL5

Al2O3

69.47

70.59

70.09

70.46

69.58

70.00

TiO2

<0.03

<0.03

<0.03

<0.03

<0.03

<0.03

Cr2O3

0.208

0.114

0.266

0.130

<0.03

0.326

FeO

0.353

0.654

0.050

0.667

1.272

0.255

MgO

28.52

28.90

28.86

28.89

28.51

28.97

ZnO

0.74

0.11

<0.1

<0.1

0.16

<0.1

Total

99.29

100.3799.26

100.14

99.52

99.55

a

Values are averaged from three to five analyses.

feldspar (figures 10, 15, and 17). In some samples thecorundum and spinel are surrounded by garnet (almandine + pyrope + grossular or almandine-rich garnet; figures 14 and 16) and sillimanite (figure 16).
The significant amounts of Fe and Mg containedin the spinel grains, along with textural observations,suggest that the spinel might have been formed by
the reaction of corundum and Mg-Fe containing silicate mineral, biotite, and/or garnet.
In the same calc-silicate rock were some portions
with abundant biotite mica and some where it had
been exhausted. Generally, corundum-bearing rocks
were subjected to regional upper amphibolite to lower
granulite facies metamorphism (about 650–760°C and
5.0–7.6 kbar; Khoi et al., 2016). In spite of these conditions, the corundum could have been stable duringmetamorphism. During prograde metamorphism,

however, the corundum-bearing assemblages reactedwith biotite to form spinel. This reaction is dependent not only on pressure and temperature, but also on
the composition of the fluid phase (ratio of H2O toCO2), and thus it may occur in one locality but not in
another due to different fluid compositions. Observations revealed that the outer edge of the corundum
was eroded to varying degrees and became less hexagonal, and the corundum core became thinner andthinner, while the spinel corona around the corundum crystal became thicker depending on the different stages of reaction (see figure 17, stages 1 to 4).
Therefore, it is assumed that a reaction between
corundum and biotite mica formed spinel as the
major product along with K-feldspar:

Figure 15. Corundum with hercynite-rich spinel corona in a sample from the Kinh La primary occurrence, shown in cross-polarized light. Photomicrograph by N.V. Nam; field of view 1.2 mm.

Figure 16. Corundum + spinel + garnet + sillimanite
assemblage in a sample from the Kinh La primary occurrence (parallel-polarized light). Photomicrographby N.V. Nam; field of view 1.2 mm.

BiotiteCorundum(1)
K(Mg, Fe)3[AlSi3O10](OH)2 + 3Al2O3

Grt

SpinelK-feldspar Fluid3(Mg, Fe)Al2O4 + KAlSi3O8 + H2O

Spl

Bt
Crn

Crn

Spl
Kfs

Sil

VIETNAMESE CORUNDUM WITH SPINEL CORONAGEMS & GEMOLOGYWINTER 2018413

If garnet and sillimanite are present in the samples, the following reaction can be proposed:
Spl

4

Crn

2

Bt

1

(2) Garnet(Fe, Mg)3Al2[SiO4]3

Kfs+

Corundum
5Al2O3Spinel3(Mg, Fe)Al2O4+

Sillimanite
3AlO[AlSiO4]

The above reactions, alone or in combination, areresponsible for the observed corundum-spinel textural features.
3

Figure 17. Observed stages of spinel corona formation around corundum grains. As can be seen, fromstage 1 to stage 4 the spinel rim around the corundum crystal became progressively thicker, while thecorundum core became thinner (until exhausted) andless perfectly hexagonal. Photo by N.N. Khoi.

This reaction could have been continuous until
all the mica was exhausted or the corundum grains
were completely transformed into spinel (see figure
17, stage 4). The reaction suggested on the basis ofinvestigations of a hand specimen (figure 17) and athin section (see figure 15) is illustrated in figure 18.
The corundum-spinel reaction would have continued until all the adjoining biotite was exhausted.
This type of reaction is fluid dependent, and thechemical potential gradient in Al2O3 is the main driving force. As a result of this type of reaction, the quality of corundum was significantly reduced for almost
all of the samples in the study.

Spl

Corundum with Spinel Corona from Secondary Deposits. Since samples recovered from secondary deposits are not enclosed in their original host rock,mineral compositions and inclusions must be used
to determine the source and possible mineral reaction that led to the observed spinel-corundum texture. The spinels in types I and II are pure Al-Mg
spinels (see table 4) with calcite and dolomite inclusions (see figure 13B). The chemical composition
points toward an Fe-poor host rock, either (a) ultramafic rock (containing some Fe) or (b) metacarbonate(marble). Based on the scarcity of ultrabasic rocks andthe nearly Fe-free spinel composition, we conclude
that this type of corundum with spinel corona most
likely developed in a metacarbonate rock. Additionally, the calcite and dolomite inclusions in the spinelcorona clearly point toward this host rock source.
Corundum typically forms in metacarbonate rocks
during prograde metamorphism from an originallysedimentary deposited Al-hydroxide phase such as
diaspore and/or boehmite. With increasing temperature, corundum could transform to spinel if dolomite
is present by the following reaction (Hauzenberger etal., 2010, 2012; Häger et al., 2010):(3)

Corundum
Dolomite
3MgCa(CO3)2 + 3Al2O3

Kfs

CarbonSpinelCalcite dioxide
3MgAl2O4 + 3CaCO3 + 3CO2

Spl

Bt

Crn

414

VIETNAMESE CORUNDUM WITH SPINEL CORONA

Crn

GEMS & GEMOLOGY

Figure 18. Schematic
illustration of the nonuniform enlargement ofspinel corona due tothe reaction of corundum and biotite.

WINTER 2018

T VS. XCO2
800

800

Spl + Cal + CO2
700

700

Spl + Sil
Alm + Crn

Kinh La

600

T (°C)

T (°C)

Crn + DolSpl + Kfs +H2O

600

Truc Lau

Bt + Crn

500

500

Crn + H2O

Crn + H2O
P = 0.7 GPa

Dsp

P = 0.7 GPa

Dsp
400

400
0.2

0.4

0.6

0.8

0.2

XCO

0.4

0.6

0.8

XCO

2

2

Figure 19. T vs. XCO2 diagram showing the phase relations and mineral reactions that formed the spinel corona.
The arrows indicate the possible direction to overstep the reactions (T increase or change in fluid composition).
Spl = spinel, Kfs = K-feldspar, Sil = sillimanite, Bt = biotite, Crn = corundum, Dsp = diaspore, Cal = calcite, andDol = dolomite.

Similar to the samples from primary sources, theouter edges of the corundum core were also eroded todifferent extents, suggesting a disequilibrium between
the two phases. As a result, the spinel rim around thecorundum crystal became thicker and the corundumcore became less perfectly hexagonal, depending on
the stage of this corundum-consuming reaction (seefigure 12). The difference between the spinels of different stages clearly indicates the role of the above hypothesized reaction, which led to the increase in theamount of spinel and thickening of the corona, with asimultaneous reduction in the amount of corundum.
The spinel composition in types III and IV is a hercynite-rich spinel to hercynite with phlogopite inclusions (see again, figure 13E). In this case theabove-mentioned reaction (1) could also be hypothesized for corundum → spinel transformation.
The three equations above describing reactions ofcorundum → spinel transformation were calculated
in a T vs. XCO2 diagram (figure 19). A T vs. XCO2 diagram
is used instead of a P-T diagram to demonstrate theimportance of fluid composition for the stability ofmineral assemblages and hence possible mineral reactions, especially in metacarbonate. The observed
spinel corona textures are evidence that a reaction
must have proceeded quickly. While changes in P andespecially T are usually relatively slow, a change influid composition can be accomplished very quickly
and thus is the likely mechanism to produce the observed spinel corona. The spinel-forming reactions arestrongly dependent on the mole fraction of CO2 in thefluid phase (XCO2). A drop in XCO2 below ~0.2 destabilizes corundum and dolomite, and spinel and calcite
form at a temperature of about 600–700°C. A final
late-stage H2O-rich fluid infiltration is recorded in diaspore veins (confirmed by Raman spectroscopy) crosscutting the corundum core as well as the spinelcorona, as shown in figure 13A. As seen in figure 19,
this event must have occurred below 450°C.
Reaction textures in corundum and spinel havebeen studied to some extent elsewhere: by Schmetzer et al. (1996) and Sunagawa et al. (1999) in
trapiche ruby, by Das et al. (2014) in Indian rubyfrom alluvial deposits, and by Francis et al. (2002,
2004) in Sri Lankan ruby and sapphire from marble.
Samples of sapphire with spinel corona were also
found rarely in pegmatite and nepheline syenite
rocks at Mogok, Myanmar (Themelis, 2008). The hypothesized reaction (1) is essentially similar to theone proposed by Francis et al. (2002, 2004) for the
corundum-spinel texture found in marble from Sri
Lanka (Katz, 1986):

VIETNAMESE CORUNDUM WITH SPINEL CORONAGEMS & GEMOLOGY(4) Phlogopite
Corundum
KMg3[AlSi3O10](OH)2 + 3Al2O3

SpinelK-feldspar Water
3MgAl2O4 + KAlSi3O8 + H2O

WINTER 2018415

the spinel crust sometimes reveals gem-quality rubyinside (figure 20).
Ruby

Spinel coating

Figure 20. Cutting away the spinel coating revealed ahigh-quality internal ruby core. Photo by N.N. Khoi.

Here, the Mg biotite end member phlogopite reacted with corundum to form pure Mg spinel.
As shown above, corundum occurrences and deposits in northern Vietnam are hosted not only inmarble of the Lo Gam structural zone, but also inpartly migmatized gneiss of the Day Nui Con Voi
range in the Red River shear zone (see again, figure1). It is interesting to note that until now corundumcrystals with spinel corona were found only in theso-called gneiss-hosted deposits, both primary andsecondary, in the Tan Huong–Truc Lau area (Khoi etal., 2011, 2016).
Local gem dealers call the spinel-encrusted corundum “gamble merchandise” (hàng mở bát) or“coated merchandise” (hàng bọc), indicating the uncertainty of dealing with these goods. Cutting away

ABOUT THE AUTHORS
Dr. Khoi (khoinn@vnu.edu.vn) is an associate professor of geology
at the Hanoi University of Science and director of the DOJI Institute and Laboratory for Gemology and Jewelry. Dr. Hauzenberger
is a professor of petrology and geochemistry at the University ofGraz, Austria. Dr. Sutthirat is an associate professor of geology in
the Faculty of Science and director of Environmental ResearchInstitute at Chulalongkorn University in Bangkok. Mr. Tuan is vicegeneral director of DOJI Gold & Gems Group in Hanoi. Dr. Häger
is senior scientist at the Centre for Gemstone Research atJohannes Gutenberg University and lecturer in gemstone and jewelry design at the University for Applied Sciences in Idar-Oberstein,
Germany. Dr. Nam is senior researcher of the Vietnam Institute of
Geosciences and Mineral Resources in Hanoi.

416

VIETNAMESE CORUNDUM WITH SPINEL CORONACONCLUSIONSCorundum with a spinel corona is a noteworthy
characteristic of both primary and secondary depositsof the Tan Huong–Truc Lau area in the Red River
shear zone of northern Vietnam. Typically, corundum formed during regional prograde, upper amphibolite to lower granulite facies metamorphism(650–760°C and 5.0–7.6 kbar) from an originally sedimentary deposited Al-hydroxide phase such as diaspore and/or boehmite (bauxitic layers).
During high-grade metamorphism, corundum reacts with biotite, garnet, or dolomite at a certain stage
to form spinel, producing the typical spinel corona.
This transformation process can be explained by thefollowing reactions:(a) biotite + corundum → spinel + K-feldspar +fluid (H2O)(b) corundum + garnet → spinel + sillimanite forcalc-silicate gneissic rocks(c) corundum + dolomite → spinel + calcite + carbon dioxide for metacarbonate rocks
These reactions, either singularly or in combination, might have given rise to the observed corundumspinel textural features. The macroscopic reaction
textures associated with corundum are important in
the sense that they reveal how it was affected after formation. Because of volume change during the transformation of corundum to spinel, fracturing occurredin the involved phases, and these fractures were often
filled with retrograde reaction products such as diaspore. Hence, the gem quality deteriorated substantially after the formation of the corona.

ACKNOWLEDGMENTS
This research is funded by the Vietnam National Foundation for
Science and Technology Development (NAFOSTED) under grant
number 105.02-2012.08. We would like to thank ASEA-UNINET
for financial support. We also thank DOJI Gold & Gems Groupand its technical staff for their assistance with this work. Researchfacilities were provided by the Institute of Earth Sciences (Mineralogy and Petrology) at Karl-Franzens-University of Graz (Austria),
the Institute of Geosciences (Gemstone Research Center) at Johannes Gutenberg University (Mainz, Germany), the Hanoi University of Science (Vietnam National University), Chulalongkorn
University (Bangkok), and the Vietnam Institute of Geosciences
and Mineral Resources.

GEMS & GEMOLOGYWINTER 2018

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Nhung N.T. (2011) Ruby and sapphire from the Tan Huong–Truc
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teristics of gneiss-hosted corundum deposits of Tan HuongTruc Lau area, northern Vietnam. Proceedings of the 33rd International Gemmological Conference (IGC33), Hanoi,
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NOTES & NEW TECHNIQUESTHE GEMOLOGICAL CHARACTERISTICS OF PIPIPEARLS REPORTEDLY FROM PINCTADA MACULATA
Nanthaporn Nilpetploy, Kwanreun Lawanwong, and Promlikit Kessrapong

Pipi pearls originating from the bivalve mollusk Pinctada maculata are usually small natural pearls with adesirable and variable range of moderate to strong colors. This study details their characteristic features, including their internal structures and the spectroscopic
data that may aid in their identification. The samples
were examined by microradiography to reveal therange of internal structures found within these natural
pearls. Spectroscopic studies were also employed using
conventional gemological methods such as ultravioletvisible (UV-Vis) reflectance, Raman, and photoluminescence (PL) spectroscopy. The spectroscopic results
showed some characteristic patterns such as a distinct
absorption feature around 495 nm in the UV-Vis spectra and peaks at 1380 and 1540 cm–1 in the Raman
spectra. The spectral features show some similarities toother mollusk species within the same family but may
still assist gemologists in separating, to some degree,
Pinctada maculata species from their relatives.

exceed 8 mm in diameter (Krzemnicki, 2014). Basedon GIA’s experience, 6 mm or under is more typicalof the species.
Pipi pearls are known to occur as natural pearls
rather than cultured and, compared with other Pinctada species, are deemed rare. One report recorded
only one gem-quality pearl found from a total of 355
mollusks (Passfield, 1997). In 1950, several cultured
pearl experiments using Pinctada maculata reportedly took place but were unsuccessful (Segura et al.,2014). In the late 1990s, a few Pinctada maculata
cultured blister pearls resulted from experiments inthe waters off Penrhyn, an island in the northernatoll of the Cook Islands (Kessrapong et al., 2017).
The nacre covering the bead nuclei did not fully overgrow the nuclei, however, and this attempt was notvery successful. Some reports suggest that the Pinctada maculata mollusk is not abundant enough for

In Brief• Pearls originating from the Pinctada maculata mollusk
are rare and no known commercial cultured pearl production has been reported.

In the Polynesian language, pipi means “small” or“tiny” and is used to refer to the small, predominantly yellow or “golden” pearls that originate fromthe bivalve mollusk Pinctada maculata (Gould,1846). As the smallest mollusk species in the Pinctada genus, Pinctada maculata rarely exceeds 5 cm
when measured in the anterioposterior or dorsoventral positions. The mollusk lives in the Indo-Pacific
Ocean, mostly around French Polynesia and the
Cook Islands, where they are often found in association with the Pinctada margaritifera mollusk species(Strack, 2006). Pearls from Pinctada maculata often
form in round to near-round shapes. As the name implies, the small shells produce small pearls that rarely• Previous studies on pipi pearls were less comprehensive than this work and the results provide some information on the characteristics that may assist in theidentification of pearls produced by the Pinctada maculata mollusk.
• The combination of the nature of a pearl's internal
structure via microradiography and its spectroscopic
results (ultraviolet visible (UV-Vis) reflectance, Raman,
and photoluminescence (PL) spectroscopy) help indicate whether a pearl formed in a Pinctada maculata
mollusk or another species.

See end of article for About the Authors and Acknowledgments.
GEMS & GEMOLOGY, Vol. 54, No. 4, pp. 418–427,
http://dx.doi.org/10.5741/GEMS.54.4.418© 2018 Gemological Institute of America

commercial exploitation. Local regulations also protect them from being harvested by foreigners, further
limiting the chances of cultured pearl production(Buscher, 1999). Given the limited documentation of
Pinctada maculata cultured pearls, it is almost certain that all pearls currently fished from the species
are natural pearls.

418

GEMS & GEMOLOGYNOTES & NEW TECHNIQUESWINTER 2018

Figure 1. Pinctada maculata pearls alongside a Pinctada maculata mollusk valve with an attached blister pearl. The
pearls range from 2.20 mm to 6.49 × 4.83 × 4.49 mm, and the shell measures approximately 28.54 × 26.50 mm.
Photo by Nuttapol Kitdee.

The spectroscopic data of Pinctada maculata
shells and pearls appear to show some characteristicfeatures that would help with their identification.
While some previous work on the spectra of Pinctada
maculata pearls has been undertaken (Segura et al.,2014), the results were inconclusive and could not
specify the mollusk. The authors decided to pursue
this study to record the characteristic features of reported Pinctada maculata pearls in order to share thedata with the wider gemological community.

GIA’s Bangkok laboratory received 31 pearl samples
that were claimed to be natural Pipi pearls originating from Pinctada maculata mollusks. One shellsample included an attached blister or blister pearl(figure 1). The pearls varied widely in color and exhibited a range of different tones. Colors within thegroup included white, cream, yellow—some ofstrong saturation, referred to as “golden” in the trade(GIA Pearl Grading Color Reference Charts, 2000)—
and yellow-orange to dark brown. Their sizes ranged
from 2.22 × 2.20 mm to 6.49 × 4.83 × 4.49 mm, andtheir weights ranged from 0.06 to 1.00 ct. The shellmeasured approximately 28.54 × 26.50 mm andweighed 5.04 grams. As indicated by the measurements, some of the samples fell within the size range
known in the trade as “seed pearls.” This term isusually applied to very small natural pearls between
two and three millimeters when sieved (CIBJO,
2016).
Real-time microradiography (RTX) analysis was
performed on the samples in three orientations usinga Pacific Industries (PXI) GenX 90 X-ray system with
4 micron microfocus, 90 kV voltage, and 0.18 mA
current X-ray source with an exposure time of 200–

NOTES & NEW TECHNIQUESGEMS & GEMOLOGY

MATERIALS AND METHODSWINTER 2018

419

A
350 milliseconds per frame, and a PerkinElmer 1512
4"/2" dual-view flat panel detector with maximum
128 frames average and 74.8 micropixel pitch with
1944 × 1536 pixel resolution. Ultraviolet-visible (UVVis) spectra were obtained using an Agilent Cary 60
spectrophotometer with a custom-made GIA integrated sphere diffuse reflectance accessory (DRA) incorporating an 80 Hz xenon flash lamp source.
Spectra were recorded in the 200–800 nm range witha data interval set at 1.0 nm and a 1.5 nm fixed spectral bandwidth and scan rate of 184.62 nm/min overa 3.5 mm2 area. Raman and photoluminescence (PL)spectra were collected using a Renishaw inVia Reflex
micro-Raman spectrometer system with a 50× magnification Leica objective lens and a 514 nm argonion laser. A laser power of 50 mW was used directlyon the samples, and the system was calibrated using
the standard internal silicon 520 cm–1 method. The
Rayleigh radiation was blocked using edge filters. The
laser was set at 100% power with three accumulations and an exposure time of 10 seconds with a grating of 1800 grooves/mm. PL spectra were collectedwith the laser power set at 50% with one accumulation and an exposure time of 15 seconds with a grating of 1200 grooves/mm. The fluorescence reactionsof the pearls were observed under UV radiation usinga GIA-designed long-wave UV unit with a 4-watt UVlamp emitting 365 nm radiation. A GIA binoculargemological microscope was used to observe surface
structures, determine the nature of the color (namely
natural or artificial deposition), and assist with thedetection of any other potential treatments.

1 cm

B

1 cm

C

1 cm

D

1 cm

E

1 cm

F

1 cm

RESULTSInternal Structures. Pearls are composed of CaCO3 in
the form of aragonite or calcite, conchiolin (an organic component), and water, as well as other residual substances (Southgate and Lucas, 2008). The
radiopacity of the main CaCO3 component and the
Figure 2. Macro images of nine pearls (A–I, left column)
weighing 0.11–0.97 ct. Photos by Sasithorn Engniwat.
The RTX results for six pearls (A–F, right column) revealed natural internal structures, typical of manynacreous pearls, while the structures of the other three
pearls (G–I, right column) showed some features thatmight raise suspicion, such as seed-like features (G–H,
green arrows) and off-round cores. Radial structure isevident in the organic-rich area of pearl I, and the blue
arrows indicate the twin cores, one of which is ovoid.
Spectroscopic analysis was also carried out on pearls B,
D, and G (labeled P593, P587, and P588, respectively).

420

NOTES & NEW TECHNIQUES

G

1 cm

H

1 cm

I

1 cm

GEMS & GEMOLOGYWINTER 2018

other components differ—the former is denser, while
the latter are more transparent—allowing the internal structures to be viewed on the resulting images(Farn, 1986; Webster, 1994).
Microradiography was carried out on all the Pinctada maculata pearl samples and revealed clear natural pearl structures (Alexander, 1941; Farn, 1986;
Taburiaux, 1986) in the majority. Growth arcs fromthe center toward the surface of the pearl, akin to thering structure seen in onions or cross-sections of trees,
together with faint organic-rich shadows positionedon the curves of some arcs, all typical of many natural
pearls (figure 2, A–C), were present in most of the samples, although it is the authors’ experience that some,such as pearl B, show a very faint structure (figure 2B,
red arrow), which is also typical of natural pearls. Another commonly encountered structural feature ofmany natural pearls—a small dark radio-translucent,rounded organic-rich core—was also evident in the
RTX results of many samples (figure 2, D–F). Anothercommon feature in the way of a growth boundary was
visible in the RTX results of pearl D (figure 2D, redarrow). Two organic-rich cores, one on each side of theboundary, were also visible. “Twins,” or pearls formedof aggregates of pearls, are not uncommon in natural
pearls from a number of species (Krzemnicki et al.,2010).
The last three pearls (figure 2, G–I) revealed internal structures with similarities to those that havebeen noted in pearls from Pinctada maxima andPinctada radiata (Krzemnicki et al., 2010; Sturman
et al., 2015) but differed from most of the other natural samples in the group we examined. Only thesethree pearls from the group exhibited such organicrich core structures. While the structures are likely
natural, the minute whitish core in the center withsome associated gaps between the concentric rings
and the additional odd irregular white feature at theouter concentric rings or near the core of two of thepearls (figure 2, G–H, green arrows) raised someminor concerns about their identity (Sturman et al.,2016). The remaining pearl showed a twin structure(figure 2I, blue arrows) consisting of concentric organic-rich features with radial structures and a nearoval core in one part. While it is entirely possible fornatural pearls such as this one to possess an unusually shaped core, it is the authors’ experience that elliptical, drop, or other elongated core features are
more often associated with non-bead-cultured pearls.
Among the group selected for examination was
one blister/blister pearl1 attached to the valve of a
Pinctada maculata shell (figure 3A). In keeping withNOTES & NEW TECHNIQUES

many blisters/blister pearls, the preliminary observations of the RTX results showed the internal structureof the pearl “superimposed” with the growth featuresand imperfections of its host shell (figure 3B). The imperfections, found in the shells of most mollusk
species, were present as veins or channels created bya living organism boring its way through the shellthroughout its life. While it was unclear from initialobservation whether this would be classified as a blister or a blister pearl, more detailed RTX analysis soonrevealed that it was solid and possessed clear concentric rings more characteristic of a blister pearl than ablister (figure 3C).
Fluorescence Reactions. All the samples were examined under long-wave ultraviolet (LWUV) radiation.
Their reactions varied in relation to their color saturation. Most of the darker samples were inert, while
the lighter-color pearls and lighter-color areas onsome of the more saturated pearls showed a moderate to strong chalky bluish green reaction. These fluorescence reactions are not diagnostic in any way andmay be observed in pearls of similar saturations fromother Pinctada species (Elen, 2001; Nilpetploy et al.,2018). Their reactions are also in keeping with naturally colored pearls and do not indicate the presenceof any color treatment (Elen, 2001; Zhou et al., 2012).
Spectroscopic Results. Some of the Pinctada maculata
pearl samples showing the most homogenous coloration were also selected for UV-Vis, Raman, and PL
spectroscopic examination. Many were too small (approximately 3 mm or less) to examine with the external DRA of the UV-Vis and would have produced noisy
spectra while potentially damaging the DRA’s integrated sphere. Owing to the instrument’s limitations
and the generally smaller size of Pinctada maculata
pearls, it was only possible to examine six samples
with enough variation in their coloration with the UVVis spectrophotometer to show the results of theRaman and PL analyses. The spectral results directly
corresponded with the color saturation and tone of thesamples. The lighter samples showed higher reflectance values while the darker and more saturated
ones exhibited less reflectance in the UV-Vis spectra.

1
A blister is a structure that forms on the inside surface of a mollusk’sshell and has the appearance of a pearl but is not a pearl by definition. A blister pearl forms in the body of a mollusk but for some reason moves to a position near the inside surface of a mollusk’s shell.
Layers of nacre are subsequently secreted over the pearl so that it becomes attached to the shell.

GEMS & GEMOLOGYWINTER 2018

421

A

B

1 cm

C

Figure 3. A blister pearl attached to its shell (A), measuring approximately 28.54 × 26.50 mm. Photo by Sasithorn
Engniwat. RTX analysis revealed the shell with its blister/blister pearl (B), and when examined in more detail theblister pearl’s internal structure (C).

The UV-Vis spectra of the six pearls displayed adiffuse reflectance decrease between 330 and 460 nm(figure 4, blue shaded area), and four showed a clear
feature at 495 nm (figure 4, indicated by a red dottedline) and a reflectance maximum between 550 and
720 nm (figure 4, green shaded area). Samples P590
and P593 did not show the 495 nm feature but did reveal a spectrum that differed from those of the othersamples. In addition, a weaker feature around 445–
455 nm was observed in P586 and P589. Other lightly
colored pearl samples (white and light gray) were also
examined. As expected, they did not exhibit any helpful features, so their spectra are excluded.
Raman spectra were collected for the same pearls(figure 5) in the same area tested when recording the

UV-Vis spectra, and as expected all showed the doublet peaks at 701, 704 cm–1 attributed to the ν4 (inplane bending), a prominent peak at 1086 cm–1
attributed to the v1 (symmetric stretching), and weakfeatures at 1464 and 1574 cm–1 attributed to the v3(in-plane asymmetric stretching) of aragonite; the latter peak was recorded by previous authors (Urmos etal., 1991; Buzgar and Apopei, 2009). Furthermore, thespectra exhibited two small features at 1380 and
1540 cm–1 (figure 5, indicated by red dotted lines)
most likely associated with pigments responsible forcoloring the pearls. Samples P590 and P593 did notshow any helpful features in their UV-Vis spectra (figure 4); however, two weak features were observed in
the Raman spectra (figure 5). Other lightly colored

UV-VIS SPECTRA
100

495 nmFigure 4. UV-Vis spectra of six Pinctada maculata samples. Four ofthe samples display aclear 495 nm feature(red dotted line). A diffuse reflectance decrease is also visible
between 330 and 460
nm (blue shaded area),
as well as a broad reflectance band around
550–720 nm (green
shaded area).

90

P587
80

REFLECTANCE (%)

P590
70
60

P586
P589

50

P593
P588

40
30
20
10
250

300

350

400

450

500

550

600

650

700

750

WAVELENGTH (nm)422

NOTES & NEW TECHNIQUESGEMS & GEMOLOGYWINTER 2018

R AMAN SPECTRA
1086 cm–1
1380 cm–1

1540 cm–1

1464 cm–1

701, 704 cm–1

1574 cm–1

P587

P586

INTENSITY

P588

P590

P589

P593

200

400

600

800

1000

1200

1400

1600

RAMAN SHIFT (cm–1)

Figure 5. Raman spectra of six Pinctada maculata samples showing the aragonite-related peaks at 701, 704, 1086,
1464, and 1574 cm–1, with two additional features at 1380 and 1540 cm–1 (red dotted lines). The spectra were normalized and offset for clarity, each shifted upward by 30%.

samples (white and light gray) were also tested, but
as with the UV-Vis work, they did not show any
helpful features either and therefore their spectra are
excluded.

The PL spectra of four samples exhibited threebroad peaks at approximately 620, 650, and 680 nm(figure 6, indicated by red dotted lines). Additional
peaks of varying intensity, most likely corresponding

PL SPECTRA~620 nm~650 nm~680 nm

Figure 6. PL spectra of
six Pinctada maculata
samples showing thethree broad peaks at
approximately 620, 650,
and 680 nm (red dottedlines), as well as a seriesof peaks between 545
and 565 nm (blueshaded area). The lattercorrespond to Ramanpeaks observed between
1106 and 1756 cm–1.

INTENSITY

P586

P587
P590

P589
P588
P593

520

570

620

670

720

770

WAVELENGTH (nm)NOTES & NEW TECHNIQUESGEMS & GEMOLOGYWINTER 2018

423

TABLE 1. Comparison of features used in the separation of Pinctada maculata pearls from other mollusks.
Mollusk

UV-Vis spectra (nm)Characteristic features
Raman spectra (cm–1)

PL spectra (nm)330–460, 495

1380, 1540

~620, 650, 680

Pinctada maculata

References
This study
Miyoshi et al. (1987);
Iwahashi and Akamatsu(1994); Elen (2002);
Karampelas et al. (2011);
Homkrajae (2016);
Nilpetploy et al. (2018)

Pinctada margaritifera

330–460 (only in yellow),
405, 495, 700

Bands between 1100 and
1800~620, 650, 680

Pinctada mazatlanica

330–460 (only in yellow), 1380, 1540 (only in yellow)
405, 700~620, 650, 680

Homkrajae (2016)
Miyoshi et al. (1987);
Iwahashi and Akamatsu(1994); Kiefert et al. (2004)

Pteria penguin andPteria sterna
Pinctada maxima(moderate to dark colors)
Pinctada maxima(yellow color range)

405, 495

Bands between 1100 and
1800~620, 650, 680

495—~620, 650, weak 680

330–460

1380, 1540—

to Raman peaks between 1106 and 1756 cm–1, werealso observed between 545 and 565 nm (figure 6, blue
shaded area) in all the spectra. Even though the bodycolor of sample P590 was lighter than the others, it
still exhibited three obvious features in the PL spectra, but the UV-Vis spectra obtained from it were not
helpful. The three bands in samples P586 and P593
were less prominent than noted in the other four
pearls. As with the UV-Vis and Raman spectra collected from the white and light gray pearls, their lackof diagnostic features precluded their spectra frombeing included in this report.
The representative spectra from all the spectral
methods, together with observation through a gemological microscope, did not reveal anything to indicatethat the pearls were treated (i.e., color concentrations,veining, and patchiness via transmitted lighting), thus
proving the natural color origin of the samples examined (Elen, 2001; Zhou et al., 2012).

Karampelas (2012)
Elen (2001); Cartier andKrzemnicki (2016); GIA
reference pearls collectedfrom Jewelmer farms

The majority of pearl samples revealed natural structures, including three (figure 2, G–I) that exhibited
more pronounced structures than the others. The
concentric rings within the organic-rich core structures were very distinct and are similar to those ofother natural pearls from Pinctada species examinedin the laboratory. Such structures have, for example,
been observed in both natural and non-bead-cultured
Pinctada maxima pearls, with sufficient differences

between the two to separate them in most cases(Sturman et al., 2015). However, since the samples
in this study reportedly formed in a different mollusk
species and their other gemological features (appearance and spectra) differ, it is more likely that thesepearls too are natural and are not the challenging
non-bead-cultured pearls that have been misrepresented as natural. Nevertheless, since the samples
were not found by the authors in situ within a specific mollusk, other gemologists could disagree withthe result based on their interpretation of the structures. On the other hand, the natural blister pearl attached to the valve of a Pinctada maculata specimen
was from the same source as the other samples, providing a degree of assurance that their claimed origin
is the same. The authors failed to find any publishedrecord of non-bead-cultured pearls from Pinctada
maculata mollusks. Therefore, the data we obtained
indicates that the samples in this study likely formed
within Pinctada maculata mollusks.
The spectroscopic work revealed features consistent with those observed for naturally colored pearls
from various Pinctada species mollusks, including
Pinctada maculata (table 1). The UV-Vis reflectancespectra results provide the most helpful features toindicate that the pearls possibly originated from
Pinctada maculata, including a clear 495 nm feature
in most of the samples. However, this feature has
also been recorded in some naturally colored pearls
from other mollusks such as Pinctada margaritifera

424

GEMS & GEMOLOGYDISCUSSIONNOTES & NEW TECHNIQUESWINTER 2018

(Elen, 2002; Karampelas et al., 2011), Pteria penguin(Miyoshi et al., 1987; Iwahashi and Akamatsu,
1994), and Pteria sterna (Kiefert et al., 2004), often
in association with a feature at 405 nm that is reportedly related to uroporphyrin protein (Iwahashi
and Akamatsu, 1994). Moreover, previous researchalso reports that the 495 nm feature is present inmoderate to dark Pinctada maxima cultured pearls
covering a range of colors (Karampelas, 2012).
While most Pinctada maculata samples display
the 495 nm feature, they do not show other features
at 405 and 700 nm. This could provide a way to separate them from pearls that form in Pinctada margaritifera, Pinctada mazatlanica, Pteria penguin, andPteria sterna mollusks.
Furthermore, the diffuse reflectance decreasearound 330–460 nm in most samples is similar tothat seen in naturally colored yellow pearls from
Pinctada maxima (Elen, 2001), Pinctada margaritifera (Elen, 2002), and Pinctada mazatlanica (Homkrajae, 2016). When comparing the UV-Vis spectra ofyellow Pinctada maculata with Pinctada maxima,
Pinctada margaritifera, and Pinctada mazatlanica
pearls (figure 7), some similarities are evident between some samples, yet differences that may allow
separation also exist. The 495 nm feature (figure 7,
indicated by a red dotted line) usually appears to be
fairly pronounced in Pinctada maculata pearl. It is
not present in Pinctada maxima or Pinctada mazatlanica samples, while Pinctada margaritifera pearl

shows the feature to varying degrees depending on
its color, tone, and saturation. Unlike the other mollusks, nearly all Pinctada margaritifera and Pinctada
mazatlanica pearls show the 700 nm feature, whichhelps differentiate them from the other Pinctada
species.
The majority of Pinctada maculata samples show
two features at 1380 and 1540 cm–1 in their Raman
spectra. Similar features have also have beenrecorded in naturally colored yellow Pinctada maxima pearls (Cartier and Krzemnicki, 2016). Moreover,based on prior experience when compared withknown naturally colored “golden” Pinctada maxima
pearls sourced directly from Jewelmer’s pearl farms(internal GIA research, unpublished results), thesefeatures are typically present in pearls of both
species, and in those of Pinctada mazatlanica witha yellow component, but they are not recorded inpearls of a yellow hue range from other mollusk
species. The specific cause of these features is unknown, and their positions do not exactly matchwith other known color pigments recorded (Karampelas et al., 2009; Bergamonti et al., 2011; Zhou andDzikowski, 2015; Cartier and Krzemnicki, 2016).
While the features around 1540 cm–1 show some similarity to the Raman peak recorded in freshwater
pearls attributed to polyenic proteins (Soldati et al.,2008), the pearls from this study are saltwater, andtherefore the features’ relevance is questionable since
the positions do not match exactly.

UV-VIS SPECTRA
100

495 nmPinctada maxima

90

Pinctada maculata

Figure 7. Comparative
UV-Vis spectra of four
yellow Pinctada maxima, Pinctada maculata,
Pinctada mazatlanica,
and Pinctada margaritifera pearls showing
some spectral featuresthat help distinguishthem from one another.

REFLECTANCE (%)

80

Pinctadamazatlanica

70
60

Pinctadamargaritifera

50
40
30
20
10
250

300

350

400

450

500

550

600

650

700

750

WAVELENGTH (nm)NOTES & NEW TECHNIQUESGEMS & GEMOLOGYWINTER 2018

425

The three PL spectral features at approximately
620, 650, and 680 nm have been recorded in naturallycolored pearls, usually with moderate to darker tones
and saturations, from Pinctada maxima (Karampelas, 2012), Pinctada margaritifera (Nilpetploy etal., 2018), Pinctada mazatlanica (Homkrajae, 2016),
Pteria penguin (Miyoshi et al., 1987; Iwahashi and
Akamatsu, 1994), and Pteria sterna (Kiefert et al.,2004). The peak around 620 nm is reportedly associated with the uroporphyrin protein (Iwahashi and
Akamatsu, 1994). A Pinctada maculata blister pearl
sample (again, see figure 3) was also subjected tospectroscopic analysis. The PL spectrum of the blister pearl showed the same three features referred toabove, indicating a natural coloration. The Raman
results were not so helpful, probably because of thesample’s light color, while a useful UV-Vis spectrum
could not be obtained owing to the limitation of thespecimen’s shape.

Pipi pearls found in Pinctada maculata mollusks
are almost always natural since successful cultivation using this mollusk has never been documented, and the authors are aware of no suchcommercial products in the market. Even though
Pinctada maculata pearls are small, owing to themollusk being the smallest member of the Pinctada
genus, their color range is desirable enough to warrant interest, and it is not inconceivable that futuretechnology might permit commercial quantities ofcultured pearls to be produced one day. Unfortunately, the mollusk’s population is limited in comparison to economic species such as Pinctada
maxima or Pinctada margaritifera mollusks. Pinctada maculata’s small size and limited geographicalhabitat may make investment in any culturing venture unlikely.
The internal structures found in this study did
not reveal evidence of any culturing, and virtually
every sample showed structures routinely observed
within natural pearls from a wide variety of mollusks. It would not be possible to conclude that apearl formed within a Pinctada maculata mollusk
based only on its structure, but there could bestrong indications that a pearl originated from themollusk if its internal structure, external appearance, and spectral characteristics were all taken
into account and met the relevant criteria. For example, pearl P587 (figure 2D) shows a distinct uneven yellow color that may be observed for either

Pinctada maculata or Pinctada maxima pearls;
however, there are some brownish yellow areas andits size is also small, under 6 mm, which is more
toward Pinctada maculata pearls. Moreover, its
UV-Vis spectra (the presence of the 495 nm featurein particular), PL spectrum (a weak three-peak pattern), and small dark organic core (albeit a twincore pearl with a boundary) all strongly suggest that
it was recovered from a Pinctada maculata mollusk. Samples P606 and P609 (figure 2, E–F) also
show small organic cores more typical of yellow toorange pearls that form in Pinctada maculata mollusks, but they were too small to obtain UV-Vis
spectra. However, their PL spectra did show thethree bands seen in other Pinctada maculata pearlsof similar colors and not the pattern seen in comparable Pinctada maxima pearls. Most natural
Pinctada maculata pearls are colored and smaller
than natural or non-bead-cultured Pinctada maxima pearls, and this may assist to some extent inseparating them.
Although the spectroscopic results of some of
the Pinctada maculata samples revealed characteristic features that help in some respects with theirmollusk identification (e.g., sample P587), they also
shared other features in common with other mollusk species such as Pinctada maxima, Pinctada
margaritifera, Pteria penguin, and Pteria sterna.
Therefore, no definitive information can be gleaned
from the spectra of Pinctada maculata pearls thatwill guarantee their separation from other mollusk
species, so other factors such as external appearance
and internal structures must also be considered.
Since mollusks of the Pinctada genus and Pteria
genus are members of the Pteriidae family, it is not
surprising that they share some common traits withrespect to composition, appearance, and spectral
characteristics. While some of these traits may not
be precise matches, they still provide useful criteriawith which to make a well-reasoned conclusion on
the identity of the mollusk that produced a specificpearl.
Further study of known Pinctada maculata pearls
and their mollusks, ideally sourced directly from theocean, would be the best option to enforce the findings provided by samples we believed to be from thesame mollusk. In order to make the findings evenmore comprehensive, the full structural and spectroscopic details of natural pearls from other known
mollusks (e.g., Pinctada and Pteria species) ideallyshould be studied and compared.

426

GEMS & GEMOLOGYCONCLUSIONSNOTES & NEW TECHNIQUESWINTER 2018

ABOUT THE AUTHORSACKNOWLEDGMENTS

Ms. Nilpetploy (née Somsa-ard) is a staff gemologist, and Ms.
Lawanwong and Mr. Kessrapong are analytics technicians, inpearl services at GIA in Bangkok.

The authors would like to thank GIA colleagues in Bangkok, New
York, and Carlsbad for their valuable assistance. Suggestions from
two anonymous peer reviewers and Elisabeth Strack, the third peer
reviewer, to improve the content are also greatly appreciated.

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T. (2009) Role of polyenes in the coloration of cultured freshwater pearls. European Journal of Mineralogy, Vol. 21, No. 1, pp.
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Karampelas S., Fritsch E., Gauthier J.-P., Hainschwang T. (2011)
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NOTES & NEW TECHNIQUESGEMS & GEMOLOGYWINTER 2018427

CHARTSINCLUSIONS IN NATURAL, SYNTHETIC, AND
TREATED DIAMOND
Nathan D. Renfro, John I. Koivula, Jonathan Muyal, Shane F. McClure, Kevin Schumacher, and James E. Shigley

Figure 1. Diamonds such as this 1.15 ct round brilliant are some of the most highly sought-after gem materials
and may contain inclusions that give the gemologist clues about their origin or treatment status. Photo by
Robert Weldon.

Diamonds (figure 1) are the subject of the latest
chart in our series on the micro-features of
gemstones. One of the most highly-sought
gem materials, diamond—like emerald, sapphire, andruby—may be treated or grown in laboratory conditions. While many diamonds contain inclusions thatare indicative of their origin or treatment status,

See end of article for About the Authors.
GEMS & GEMOLOGY, Vol. 54, No. 4, pp. 428–429,
http://dx.doi.org/10.5741/GEMS.54.4.428© 2018 Gemological Institute of America

many gem-quality diamonds are free of such diagnostic characteristics and will require advanced
gemological testing to determine whether they aremined, laboratory grown, or treated. For example,
chromian garnet inclusions can indicate the diamond
formed in a peridotitic environment, while omphacite and kyanite would suggest an eclogitic environment. Other features that are notably diagnostic
to the gemologist are so-called “flash-effect” colors
that decorate lead glass–filled fractures and taperingtubes that indicate laser drilling.
Gem-quality synthetic diamonds have been commercially available since 1986; however, recent im-

428

GEMS & GEMOLOGYDIAMOND INCLUSIONS CHART

WINTER 2018

provements in growth methods are responsible forincreases in both the size of finished stones and thequantity produced. Chemical vapor deposition(CVD) and high-pressure, high-temperature (HPHT)
processes have had increasing impact in the diamond trade, with CVD stones reaching finishedsizes of more than five carats (Eaton-Magaña andShigley, 2016) and a 15 ct HPHT-grown specimen recently reported (Ardon and Eaton-Magaña, 2018).
Melee-size material is also becoming widely available. As a result, GIA offers a melee screening service and has developed a consumer diamondscreening device, the iD100, to separate natural andsynthetic specimens.

Treatments intended to improve a diamond’s clarity have been around since the late 1970s and include
laser drilling and the filling of cracks with a lead
glass; this glass reduces the impact of a crack’s appearance on the stone (Koivula et al., 1989). Other
treatments may improve or modify the bodycolor ofa diamond. Irradiation and HPHT treatment can accomplish this but often leave no microscopic evidence of the process.
While the accompanying chart is not meant to becomprehensive, it aims to remind the gemologist of
the microscopic evidence that one may encounter andwhat that evidence indicates regarding a diamond’snatural, treated, or synthetic origin.

ABOUT THE AUTHORS
Mr. Renfro is manager of colored stones identification, and John
Koivula is analytical microscopist at GIA in Carlsbad, California.
Mr. Muyal is a staff gemologist, Mr. McClure is global director ofcolored stone services, Mr. Schumacher is a photo and video
producer for Gems & Gemology, and Dr. Shigley is distinguishedresearch fellow at GIA in Carlsbad.

REFERENCES
Ardon T., Eaton-Magaña S. (2018) Lab Notes: 15 carat HPHT synthetic diamond. G&G, Vol. 54, No. 2, pp. 217–218.
Eaton-Magaña S., Shigley J.E. (2016) Observations on CVD-grownsynthetic diamonds: A review. G&G, Vol. 52, No. 3, pp. 222–
245, http://dx.doi.org/10.5741/GEMS.52.3.222

Koivula J.I., Kammerling R.C., Fritsch E., Fryer C.W., Hargett D.,
Kane R.E. (1989) The characteristics and identification of filled
diamonds. G&G, Vol. 25, No. 2, pp. 68–83, http://dx.doi.org/
10.5741/GEMS.25.2.68

Additional Reading
For a list of references pertaining to inclusions innatural, synthetic, and treated diamond, go to
www.gia.edu/gems-gemology/winter-2018-suggestedreading-diamond-chart or scan the QR code on the right.

DIAMOND INCLUSIONS CHARTGEMS & GEMOLOGYWINTER 2018429

Editors
Thomas M. Moses | Shane F. McClure

Natural DIAMOND Mistaken as
HPHT Synthetic
When a declared synthetic diamond is
submitted to a GIA laboratory, it is notoften that the diamond turns out to benatural. But this was the case recently
when a D-color 2.23 ct round brilliant
was submitted to the Carlsbad laboratory for a synthetic diamond grading
report (figure 1). Its infrared absorption
spectrum established it as type IaA>B,
with nitrogen aggregates around 80
ppm, confirming a natural color origin.
Since it was stated as synthetic, further
analysis was performed.
There are very few gemological indicators of lab-grown diamonds (S.
Eaton-Magaña and C.M. Breeding,“Features of synthetic diamonds,”
Summer 2018 G&G, pp. 202–204).
Yet one of the most reliable and easily
seen observations is the lack of birefringence (or strain) patterns in HPHT
synthetics when viewed between
crossed polarizers. To our knowledge,
visible strain in HPHT-grown synthetic diamonds has only been documented in one rare case (Winter 2016
Lab Notes, pp. 417–418).
Although strain observations are
rarely used by many in the trade, thisnatural diamond was perhaps presumed to be synthetic due to its apparent lack of observable strain. Whenviewed under crossed polarizers, theFigure 1. This D-color 2.23 ct
natural diamond was originallysubmitted as a synthetic.

strain was very difficult to discern(figure 2, left), and this apparent absence was consistent with our observations of HPHT synthetics. Withextensive searching and careful positioning, the strain was visible in a few
scattered areas of the diamond. The
observed strain was linear in appearance, consistent with type Ia natural
diamonds (figure 2, right).
With further investigation using
a variety of techniques such as photoluminescence spectroscopy andDiamondView imaging, all tests confirmed a natural origin. Additionally,
microscopic observation revealed
unidentified dark natural crystal inclusions (figure 3), which might havebeen mistaken for metallic flux.
Subsequently the client indicatedthat this stone was believed to be synthetic after examination by anotherparty in the trade. However, several
gemological and spectroscopic tests
confirmed its natural origin.
This diamond demonstrates whystones of uncertain origin should besubmitted to a gemological laboratory
for further testing. It also provides
confirmation that occasional excep-

Figure 2. An apparent lack of strain was observed throughout most of thestone, with strain visible only around inclusions (left). Such observations
are common in HPHT synthetics and not generally seen in natural or
CVD synthetic diamonds. With extensive searching and careful positioning, linear strain was visible within small areas of the stone (right). Fieldof view 7.19 mm.

Editors’ note: All items were written by staff
members of GIA laboratories.
GEMS & GEMOLOGY, Vol. 54, No. 4, pp. 430–439.
© 2018 Gemological Institute of America

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LAB NOTESGEMS & GEMOLOGYWINTER 2018

Figure 3. Microscopic examination shows discernible dark mineral inclusions that occur naturally in diamonds and could have been mistaken for
metallic flux inclusions. Field of view 3.57 mm.

tions exist for the general guidelinesthat help distinguish natural from labgrown diamonds. In this case, the correction worked to the client’s
advantage.
Garrett McElhenny and
Sally Eaton-Magaña

Manufactured GOLD-IN-QUARTZ
Jewelry
Due to its desirability, gold is often
imitated with minerals such as pyrite
or with gold plating. Gold occurs insmall quantities in many kinds ofrocks throughout the world. It is typically found in epithermal deposits
where hydrothermal fluids deposit
gold, along with pyrite and other sulfides, into cracks and faults of rocks—
commonly quartz-bearing rocks (J.W.
Anthony et al., Handbook of Mineralogy, Vol. 1: Elements, Sulfides, Sulfosalts, Mineral Data Publishing, Tucson,
Arizona, 1990). Due to the aggregate
structure of this material, the gold
contained in natural gold-in-quartz isdeposited irregularly, showing a morenatural-looking sporadic veining system in the host quartz (figure 4).
The Carlsbad lab was recently
sent three jewelry pieces—twobracelets and a ring—for identification reports (figure 5). The ring and

LAB NOTES

one of the bracelets were set with numerous white stones cross-cut withyellow metallic veins. One bracelet
had black stones cross-cut with similar yellow metallic veining. Standard
gemological testing of both the whiteand black stones revealed properties
consistent with quartz; these results
were confirmed with Raman spectroscopy. The Raman analysis of theblack stones indicated the presence ofamorphous carbon, which drew some
suspicion.
These jewelry pieces initiallyseemed to contain natural gold-inquartz. Upon further inspection, theyellow metallic veining system appeared inorganic in the host quartz due
to its very consistent appearance in all
the stones. In the three pieces, themetallic veins had a spiderweb-likestructure, and a colorless polymer was
also present alongside the metallic
veins (figure 6, left). The colorless polymer areas also showed undercutting,and the metallic veining had areas ofincomplete filling (figure 6, center andright). These features were consistent
with the manufactured gold-in-quartz
products that were first introduced tothe market at the 2005 Tucson shows(B. Laurs, “Manufactured gold/silverin-quartz,” Spring 2005 G&G, pp. 63–
64). This material was composed ofpolymer, quartz, and metallic veining
similar to what was observed in thestones we examined. Even with theslight difference in the face-up appearance of the natural and manufactured
gold-in-quartz, the manufacturer
claims that the only way to clearly distinguish this imitation material iswith chemical analysis of the metalalloy.

Figure 4. The gold veins in natural gold-in-quartz are irregular and show anatural nugget structure below the surface. Field of view 4.79 mm.

GEMS & GEMOLOGYWINTER 2018

431

Figure 5. Manufactured gold-in-quartz, set in two bracelets and a ring thatwere submitted for identification reports.

Laser ablation–inductively coupled plasma–mass spectrometry (LAICP-MS) analyses were performed on
the yellow metallic veins in the whiteand black stones of each bracelet tofurther separate them from natural
gold-in-quartz. Each ablation spot was
drilled twice into the veins. The
chemistry of the first spot was very
similar for the stones in bothbracelets. The vein was mainly composed of gold (Au) and silver (Ag) withtraces of nickel (0.90–2.67 parts per
million weight, ppmw) and copper(23.58–30.02 ppmw). The gold to silver weight ratio (Auppmw/Agppmw) was
between 2.71 and 3.33. The chemistryof the second spot on the same position showed little gold or silver and asignificant amount of silica, which in-dicated that the laser had passed
through the yellow metallic layer andinto the host quartz below.
One natural gold-in-quartz cabochon obtained from the GIA Museum
was analyzed for comparison. The
veins found in the natural sample(again, see figure 4) were composed
mainly of yellow metallic materials,
with additional gray metallic minerals. The same experimental procedures were applied to both the yellow
and gray areas. The chemistry of thegray metallic areas identified them as
an iron sulfide mineral. The chemistry of the first spot on a yellow
metallic area showed a large amountof gold and silver with traces of copper(215–257 ppmw). The gold and silver
weight ratio (Auppmw/Agppmw) was be-

tween 7.84 and 8.04. It was evident
that the concentration of gold in theyellow metallic veins in the natural
gold-in-quartz was much higher thanthat of the yellow metallic veins in
the white and black panels of the twobracelets. In addition, the naturalveins had a higher copper concentration than the two bracelets.
The manufactured gold-in-quartz
materials first reported in 2005 arestill circulating in the market today.
Consumers should be aware of thiswhen purchasing pieces reported tocontain gold-in-quartz. The telling indicator of manufactured gold-inquartz is the consistent texture of its
yellow metallic veins. The gold in thenatural version is much more sporadic and appears as chunky conglomerated nuggets.
Nicole Ahline and Ziyin Sun

Freshwater PEARLS, Blister andLoose, with Their Host Shells
GIA occasionally receives blister
pearls attached to their host shells for
identification (Winter 2015 Lab Notes,
pp. 432–434; Summer 2017 Lab Notes,
pp. 231–232), which can provide helpful information on the overall growth
conditions and the mollusk species.
Recently the New York laboratory had
an opportunity to study three freshwater specimens: two blister pearls still
attached to their shells, and one loose“wing” pearl that was reportedly

Figure 6. Unnatural veins in manufactured gold-in-quartz. Left: This vein is filled with both polymer, which is notflush with the host quartz, and gold (field of view 4.79 mm). Center: A vein of polymer running alongside a vein ofgold with undercutting visible at the boundary of the polymer vein and the host quartz (field of view 3.57 mm).
Right: Polymer fills an incomplete gold vein; the rest of the vein is recessed below the host quartz (field of view
7.19 mm).

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LAB NOTESGEMS & GEMOLOGYWINTER 2018

Figure 7. Three freshwater pearls attached to their host shells. Left toright: A blister pearl measuring approximately 37.45 × 27.48 mm, a loose
wing pearl measuring 35.82 × 9.37 × 5.94 mm and weighing 10.60 ct, anda blister pearl measuring approximately 23.60 × 19.49 mm. Specimens
courtesy of Mississippi River Pearl Jewelry Co. LLC.

found in the shell with which it was
submitted (figure 7).
While approximately 1,000 speciesof freshwater mussels have been identified worldwide, the United Statesalone is said to host about 300 species,
compared to 96 species in Africa, 60 in
China, and 12 in Europe (Virginia Department of Game and Inland Fisheries, 2018, https://www.dgif.virginia.
gov/wildlife/freshwater-mussels/).
The number of U.S. species shows
the spectacular diversity of its freshwater resources. Hence, it proves
how difficult it can be to apply correct zoological names to specificshells. However, experienced local
fishermen who harvest the mussels
are often the source of helpful
information (T. Hsu et al., “Freshwater pearling in Tennessee,” 2016,
https://www.gia.edu/gia-newsresearch/freshwater-pearling-tennessee). The owner claimed that theloose wing-shaped pearl (figure 7, center) was found in a Potamilus purpuratus “Bluefer” mussel in a U.S. river.
Bluefer mussels exhibit a pinkish purple to deep purple nacre lining andcan produce pearls of a similar color
range. Energy-dispersive X-ray fluorescence (EDXRF) spectrometry confirmed that it originated from a
freshwater environment, based on its

LAB NOTES

chemistry result of more than 1000
ppmw manganese. Freshwater pearls
usually show higher than 100 ppmw
manganese content. Real-time X-ray
microradiography (RTX) revealed anatural growth structure, while
Raman spectroscopy detected aragonite and polyenic peaks, the latter indicating the presence of natural
coloring pigments (S. Karampelas etal., “Role of polyenes in the coloration of cultured freshwater
pearls,” European Journal of Mineralogy, Vol. 21, 2009, pp. 85–97). This
specimen also displayed the characteristic elongated, flat, and slightly
curved shape characteristic of wing
pearls that, as the name implies, resembles the shape of a bird’s wing.

Wing pearls commonly form in thehinge area within shells, and it wasinteresting to see a similar-sized cavity in the shell submitted with thispearl.
The other two blister pearls werealso claimed to have originated froma freshwater environment, and thiswas confirmed by their optical X-ray
fluorescence reactions. Both specimens showed a strong yellowish
green luminescence under X-ray excitation, a result that agrees with pearls
from a freshwater environment due totheir higher manganese content (H.A.
Hänni et al., “X-ray luminescence, avaluable test in pearl identification,”
The Journal of Gemmology, Vol 29,
No. 5/6, 2005, pp. 325–329). According to the owner, the smaller shell(figure 7, right), possibly a washboard
mussel (Megalonaias nervosa), wasfound in a U.S. river, while the larger
shell (figure 7, left) is likely a hybrid
Hyriopsis mussel commonly used bycultured pearl farmers in China. Blister pearls form when a whole pearl
within the connective tissue breaks
through the mantle due to its size
and/or weight, or for some other reason, and presses against the nacreous
inner surface of the shell, where subsequent nacre deposition fuses thepearl to the shell (E. Strack, Pearls,
Ruhle-Diebener-Verlag, Stuttgart, Germany, 2006, p. 124).
The size of these two blister pearls
is impressive, and both protrude conspicuously from the shell while still
attached to their hosts (figure 8). The
RTX results of the smaller blister

Figure 8. Close-up images of the freshwater blister pearls from China (left)
and the United States (right) attached to their hosts.

GEMS & GEMOLOGYWINTER 2018

433

Figure 9. The RTX structure of
the large blister pearl (shown on
the left in figures 7 and 8) revealed a void-like structure inwhich a near-oval feature is visible (indicated by the arrow).

Figure 10. Inclusions in the 1.70 ct ruby from Montana. Left: Close-up of a
glassy melt inclusion with an associated thin film showing geometric patterns; field of view 1.76 mm. Right: A melt inclusion with an iridescentthin film, partial hexagonal zone of particles, and short needles; field ofview 3.81 mm.

pearl revealed concentric growth arcs
proving its natural origin. However,the RTX results of the larger blister
pearl revealed a void-like structurethat may be found within natural andnon-bead-cultured pearls, but a nearoval feature inside the void is uncommon in natural pearls (figure 9). GIA
gemologists believe this oval feature
was the triggering mechanism thatlikely resulted in the formation of theblister pearl. Whether this oval feature is a by-product of pearl culturing
or a natural formation is hard to prove
without examining the blister pearl
thoroughly in other orientations,which was precluded by its size andposition. While the identification ofsome freshwater pearls remains challenging, these known freshwater samples together with their host shells
serve as useful references for laboratory gemologists.

sions (figure 10). There were several
glassy melt inclusions and small crystals with associated reflective thinfilms. The thin films often displayed
hexagonal geometric patterns conforming to the crystallographic orientation of the host ruby. These
resembled the patterns commonly
seen in rubies from Thailand andCambodia and have also been documented in Montana corundum (Fall2015 G&G Micro-World, pp. 329–
330). A partial hexagonal zone of par-ticles and more loosely spaced unaltered exsolved rutile needles was alsopresent, a feature that would be very
unusual in Thai/Cambodian rubies. A
large intact colorless crystal as well as
smaller white crystals were locateddeep within the stone, so we were unable to conclusively identify themwith Raman spectroscopy. This inclusion scene is consistent with unheated corundum from Montana.
LA-ICP-MS was used to determine
the stone’s trace-element chemistry,

Figure 11. The 1.70 ct Montana ruby alongside rough pink to purple corundum samples from the GIA reference collection. These reference samples,collected from Montana’s Eldorado Bar along the Missouri River andWildcat Gulch, part of the Rock Creek deposit, were used to help determine the country of origin.

Joyce Wing Yan Ho

A Rare RUBY from Montana
The Carlsbad laboratory recently received a 1.70 ct purplish red octagonal
modified brilliant-cut ruby measuring
6.28 × 6.25 × 4.56 mm for an identification and origin report. Standard
gemological testing gave a chromium
spectrum indicating ruby and a hydrostatic SG of 4.00. The stone displayeda weak red fluorescence in long-wave
UV and no fluorescence under shortwave UV.
Microscopic examination showed
an interesting combination of inclu-

434

LAB NOTESGEMS & GEMOLOGYWINTER 2018and the results were compared tocorundum samples from GIA’s coloredstone reference collection. Trace element measurements indicated rangesof 15.1–17.2 ppma Mg, 14.7–16.9
ppma Ti, 3.67–3.87 ppma V, 359–406
ppma Cr, 1500–1580 ppma Fe, and
14.6–14.7 ppma Ga. The chemistry
matched well with reference stones
GIA has collected from Montana’s
secondary deposits (figure 11) but not
our Thai/Cambodian ruby reference
samples. In particular, Thai/Cambodian rubies tend to have higher Mg(often above 100 ppma), while thisstone had much lower Mg levels.
Montana’s secondary deposits produce sapphires in a wide range of
mostly pastel colors. Pink corundum
tends to be rarer than blue or green,
and those that possess the depth ofcolor to be called ruby are quite rare,
particularly without any treatments.
The color, combined with the large
size, makes the 1.70 ct ruby fromMontana an exceptional specimen—
this is only the second such report issued by the lab to date. With a
combination of microscopic observation, advanced testing methods, andGIA’s reference collection, we wereable to confirm the country of origin.
Claire Malaquias

Large Pargasite Inclusion in
Kashmir SAPPHIRE

ment of Kashmir sapphires,” Winter1990 G&G, pp. 267–280).
Recently, a 14.06 ct octagonal-cut
blue sapphire (figure 12) submitted to
GIA’s Carlsbad laboratory for origin
determination was of particular interest for its several unusually large,
eye-visible pargasite crystal inclusions. Standard gemological properties confirmed the host sapphire’s
identity, and advanced analytical
testing specified its metamorphic geological origin.
Microscopic examination revealed
an inclusion scene reminiscent of“new Kashmir,” a term referring toKashmir sapphires that have comeinto the market since the 2000s. The
blue sapphire featured several negative
crystals, black graphite inclusions,
unidentified rounded and needleshaped colorless crystal inclusions(probably slender zircon rods or pargasite), reflective thin films, and fluid
fingerprints.
Classic Kashmir sapphire features were also observed, such as“milky” turbid whitish broad bands,
clouds, a parallel chromium-enrichedzone (which glows red under longwave UV illumination), ladder-like/antenna-like stringers, and snowflakelike inclusions.

Figure 12. This 14.06 ct octagonal
blue Kashmir sapphire exhibits
large, eye-visible inclusions ofprismatic pargasite.

The main inclusion features, thepargasite crystals (figure 13), weretransparent with a brownish green
bodycolor. Many of them were doubly terminated with a flat, columnar
prismatic morphology with striations
along their length, surrounded byhalo- or rosette-like thin reflective

Figure 13. A large prismatic pargasite mineral inclusion. Field of view
7.19 mm.

Kashmir sapphires are known to haveoccurred in kaolinized plagioclase
feldspar pegmatites, found as pockets
between metamorphic stratified
beds/cliffs of the Himalayan Zanskar
Range. These sapphires captured
many cognate mineral inclusions—such as pargasite, plagioclase feldspar,
tourmaline, and zircon—which demarcate the pockets against the country rock (E.J. Gübelin and J.I. Koivula,
Photoatlas of Inclusions in Gemstones, Vol. 3, Opinio Publishers,
Basel, Switzerland, 2008, p. 194).
Pargasite mineral inclusions (prismatic or as long, fine needles) in blue
sapphire are regarded as a strong indicator of Kashmir origin. (R. Schwieger,“Diagnostic features and heat treat-

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435

R AMAN SPECTRA
12000

Pargasite inclusion from sample
Pargasite RRUFFID = R050321
10000

INTENSITY

8000

6000

4000

2000

in sapphires from other countries.
Nonetheless, pargasite inclusions area strong indicator of Kashmir origin.
With the support of advanced analytical instrumentation (UV-Vis and LAICP-MS) in addition to careful
examination of the overall internalfeatures (milky bands, ladder-likestringers, and snowflakes), the presence of pargasite inclusions can conclusively determine a Kashmir origin.
Jonathan Muyal

0
130

330

530

730

930

1130

RAMAN SHIFT (cm–1)

Figure 14. Unoriented Raman spectra with 514 nm excitation confirmed
the pargasite mineral inclusion identity (blue spectrum), using the RRUFF
database as a reference (red spectrum).

films. The pargasite crystal’s surface
pits and altered appearance suggested
that these pargasite crystals were protogenetic inclusions present in thepegmatitic growth environment before the sapphire began to form.
Raman microspectrometry analysis(figure 14) confirmed the identity ofseveral crystal inclusions as pargasite.
The absence of 3309 peak series inIR spectroscopy and the microscopic
observation of unaltered internal fea-tures supported an unheated call. The
classic metamorphic UV-Vis absorption spectra, the metamorphic-type
low-Fe chemistry data collected with
LA-ICP-MS, and the observed inclusion scene supported a Kashmir origin conclusion. The issued GIA
report identified the stone as a natural sapphire from Kashmir with no indications of heating.
Pargasite was once thought to be
unique to Kashmir until it was found

SYNTHETIC DIAMONDS
An Irradiated CVD Synthetic
Melee Diamond Found in Irradiated Natural Melee Diamonds
Mixing of synthetic melee diamondswith natural melee diamonds has beenreported several times. Those examples were colorless (Winter 2016 Lab
Notes, pp. 416–417; Summer 2017 Lab
Notes, pp. 236–237) and yellow (Winter 2014 Lab Notes, pp. 293–294). Recently, GIA’s Tokyo lab found a single
irradiated green-blue CVD synthetic
melee diamond in a parcel of similarlycolored irradiated natural melee.
The parcel of 300 uniformly greenblue round melee was submitted for
identification (figure 15). Each diamond’s color was attributed to strong

Figure 15. This group of 300 green-blue diamonds (1.97 carats total) was screened by GIA’s Tokyo laboratory.
Among these, 299 were irradiated natural melee diamonds and the one on the right was an irradiated CVD synthetic melee diamond.

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LAB NOTESGEMS & GEMOLOGYWINTER 2018

PL SPECTRUM

INTENSITY

GR1

SiV
596/597

550

600

650

700

750

800

WAVELENGTH (nm)Figure 16. DiamondView imaging
revealing weak linear striationsin the pavilion of the irradiated
CVD synthetic melee diamond.

Figure 17. The photoluminescence spectrum of the green-blue CVD synthetic melee diamond at liquid nitrogen temperature shows a strong GR1
peak. The SiV – center defect can be observed at around 736 nm. The doublet at 596/597 nm indicates that this diamond did not undergo annealing after synthesis.

GR1 by irradiation treatment. Infraredabsorption spectroscopy, photoluminescence spectroscopy, and DiamondView analysis confirmed that 299 ofthem were irradiated natural diamonds and one of them was an irradiated CVD synthetic diamond. The
CVD synthetic diamond weighed
0.007 ct, with a diameter of 1.14 mm.
DiamondView images of the synthetic showed very weak linear striations in the pavilion (figure 16). Dark
inclusions were observed under the
microscope. The infrared spectrum
showed a peak at 3123 cm–1, and thephotoluminescence spectrum showeddoublet peaks at 596/597 nm (figure17). These peaks are seen in CVD
synthetic diamonds without post-annealing. The photoluminescence
spectrum also showed a small, broad
SiV– center defect at 737 nm next to avery strong GR1 center at 741 nm (figure 17). From the peak at 3123 cm–1
and the 596/597 nm doublet peak,this diamond was concluded to be irradiated without pre-annealing.
Irradiated CVD synthetic diamonds are rarely seen at GIA, which
had examined only six of them before
this report (Fall 2014 Lab Notes, pp.

240–241; Fall 2015 Lab Notes, pp. 320–
321; Summer 2018 Lab Notes, pp. 215–
216). Previously reported irradiated
CVD synthetic diamonds were relatively large, from 0.43 to 1.34 ct. Thisis the first melee-sized irradiated CVD
synthetic diamond examined by GIA.

LAB NOTES

Shoko Odake

Gemological Analysis of Lightbox
CVD-Grown “White” Diamonds
Lightbox, a De Beers company, hasbegun selling “white,” pink, and blue
CVD laboratory-grown diamonds at aflat rate of $800 per carat. Through athird-party vendor, we recently had
the opportunity to examine two such
samples (0.24 and 0.26 ct) intended forsetting in a pair of earrings. Both werenear-colorless with color grades equivalent to G color and cut grades of Excellent and Very Good, respectively.
Both lab-grown diamonds had very
few clarity characteristics. The 0.24 ct
sample had a pinpoint in a bezel facet,
and the 0.26 ct round (figure 18, left)
had a feather in a star facet, both withVVS clarity. However, the grade-setting feature for both was the Lightbox
logo, internally inscribed underneath

GEMS & GEMOLOGY

the table facet (figure 18, center). As aresult of the Lightbox mark, the clarity grade for both was reduced to VS.
The laser-inscribed internal feature isreportedly made using technology developed by Opsydia (Gem and Jewellery Export Promotion Council, “DeBeers to use Opsydia’s laser tech to inscribe lab-grown diamonds in Lightbox Jewelry,” https://www.gjepc.org/
news_detail.php?id=4075). It is composed of dual narrow lines ~2.5 microns wide with a total area of 300 ×
300 microns, positioned about 200 microns below the table surface.
Spectroscopic analysis showedboth samples had very similar features that were consistent withpreviously analyzed CVD products
from other manufacturers. IR absorption spectroscopy confirmed thesesamples as type IIa with no detectible
single nitrogen at 1344 cm–1. Photoluminescence (PL) spectra showedthat both had the 596/597 nm doublet,indicating that they were as-grown
and not subjected to post-growth
HPHT processing (S. Eaton-Magaña
and J.E. Shigley, “Observations on
CVD-grown synthetic diamonds: A
review,” Fall 2016 G&G, pp. 222–

WINTER 2018

437

Figure 18. The 0.26 ct near-colorless CVD-grown diamond (left) has an internal inscription showing the Lightbox
logo, composed of dual narrow lines. The logo is easily detected with a microscope (center) and clearly visible in
the DiamondView image (right), in which the red fluorescence is due to nitrogen-vacancy centers. Also seen in
the DiamondView image are subtle striations, additional evidence of the CVD origin. The outer square of theLightbox logo measures 300 microns on each side.

245). Faceted, as-grown near-colorless
CVD samples are less common sincemost manufacturers grow CVD layers quickly, but with a brown color,knowing that they can be HPHT
treated to improve color appearance
after growth. Approximately 75% of
the CVD material in this color range
examined by GIA has been HPHT

treated after growth (S. Eaton-Magaña, “Summary of CVD lab-grown diamonds seen at the GIA laboratory,”
Fall 2018 G&G, pp. 269–270).
Through crossed polarizers, we observed very low birefringence compared with the majority of CVD-growndiamonds examined. Additionally,both samples showed very strong

Figure 19. This 514 nm PL spectrum collected on the 0.26 ct sample atliquid nitrogen temperature shows strong nitrogen vacancy centers at 575
and 637 nm and the 596/597 nm doublet, evidence of an as-grown CVD
sample.

PL SPECTRUM
NV0, 575

NV–, 637

100000INTENSITY (COUNTS)

596/597 nm doublet
80000

60000

592

40000

594

596

598

600

602

604

Raman

emission from nitrogen-vacancy centers by PL spectroscopy (figure 19), as
well as visible red fluorescence using
DiamondView imaging (figure 18,
right), but there was no detectable fluorescence with long-wave UV. With
careful DiamondView imaging, subtle
CVD striations were visible throughthe table facet. In the DiamondView
images, there were no apparent growthinterfaces showing multiple growth
events, and no apparent seed crystal
remnants were observed. Also, PL
spectroscopy of both samples showedvery weak but detectable silicon-vacancy centers at 736.6/736.9 nm.
The Lightbox CVD lab-grown diamonds, due to their price point andmanufacturer, will likely be highly visible in the trade. The pink and blue
samples, as evidenced by De Beers’ literature, have an appearance that is unusual among natural-color diamonds
and are unlikely to ever be perceived
as a natural-color product. However,the colorless Lightbox samples arereadily identifiable as CVD-grown diamonds by spectroscopic techniques,
DiamondView imaging, and their distinctive internal inscription.
Sally Eaton-Magaña

20000

0
550

600

650

700

750

800

WAVELENGTH (nm)Cat’s-Eye Brazilian Paraíba
TOURMALINE
A vivid shade of tourmaline varying

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LAB NOTESGEMS & GEMOLOGYWINTER 2018

Figure 20. This 0.51 ct Paraíba tourmaline from Brazil displays sharp
chatoyancy.

from “neon” blue to greenish blue,
caused by copper and manganese, wasdiscovered in Brazil in the 1980s. Recognized as “Paraíba” tourmaline in
the gem trade, it is still highly sought
after, even though tourmalines exhibiting this “Paraíba” color are now
more accessible from localities suchas Nigeria and Mozambique.
Recently, GIA’s Bangkok laboratory received a vivid blue tourmalinewith chatoyancy (figure 20), weighing 0.51 ct and measuring 5.89 × 4.19
× 2.46 mm. Standard gemologicaltesting resulted in a spot refractive
index reading of 1.64 and a specificgravity of 3.05. Microscopic examination revealed diagnostic irregulartwo-phase inclusions, trichites, andacicular (needle-like) features. The
sharp cat’s-eye effect was caused byan included layer of fine parallel
growth tubes positioned just above
the base of the cabochon. The phenomenon of chatoyancy enhances its
rarity and value.
LA-ICP-MS was used to perform
an elemental analysis. The sample
showed high Cu ranging from 7289 to
10544 ppmw, as well as 9494–10441
ppmw Mn, 114–133 ppmw Ga, 55–65
ppmw Pb, 39–48 ppmw Fe, 14–20

ppmw Zn, and 0.6–0.5 ppmw Sr. Thevery high concentration of Cu as wellas the results for Ga (<250 ppmw), Pb(<100 ppmw), and Sr (<10 ppmw) supported its Brazilian origin (J.E. Shigley
et al., “An update on ‘Paraíba’ tourmaline from Brazil,” Winter 2001
G&G, pp. 260–267; A. Abduriyim etal., “Paraíba-type copper-bearing tourmaline from Brazil, Nigeria, andMozambique: Chemical fingerprinting by LA-ICP-MS,” Spring 2006
G&G, pp. 4–21; Z. Sun et al., “A simplified species classification for gemquality tourmaline by LA-ICP-MS,”
submitted for publication). Copperbearing tourmaline of this color istypically referred to in the trade as“Paraíba” tourmaline.
Cat’s-eye Paraíba tourmaline is notnew, though fewer than 10 have been
submitted to GIA laboratories. The
combination of well-developed chatoyancy, transparency, pleasing vivid
blue color, and Brazilian origin makethis a rare and noteworthy gemstone.
Vararut Weeramongkhonlert

PHOTO CREDITS
Robison McMurtry—1, 5, 11, 18 (left); Garrett
McElhenny—2, 3; Nicole Ahline—4; Hollie
McBride—6; Sood Oil (Judy) Chia—7; Joyce
Wing Yan Ho—8; Claire Malaquias—10; Towfiq
Ahmed—12; Jonathan Muyal—13; Shunsuke
Nagai—15; Sally Eaton-Magaña—18 (centerand right); Nuttapol Kitdee—20

For online access to all issues of GEMS & GEMOLOGY from 1934 to the present, visit:

gia.edu/gems-gemology

LAB NOTESGEMS & GEMOLOGYWINTER 2018

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DIAMONDS FROM THE DEEP
WINDOWS INTO SCIENTIFIC RESEARCH
Karen V. Smit and Steven B. Shirey

How Do Diamonds Form in the Deep Earth?
Carbon is one of the most important elements on ourplanet, which led the Geological Society of London toname 2019 the Year of Carbon. Diamonds are a main hostfor carbon in the deep earth and also have a deeper origin
than all other gemstones. Whereas ruby, sapphire, andemerald form in the earth’s crust, diamonds form many
hundreds of kilometers deep in the earth’s mantle. Colored
gemstones tell scientists about the crust; gem diamonds
tell scientists about the mantle. This makes diamonds
unique among gemstones: Not only do they have great
beauty, but they can also help scientists understand carbon
processes deep in the earth. Indeed, diamonds are some ofthe only direct samples we have of the earth’s mantle.
But how do diamonds grow in the mantle? While Hollywood’s depiction of Superman squeezing coal captured
the public’s imagination, in reality this does not work. Coalis a crustal compound and is not found at mantle pressures.
Also, we now know that diamond does not prefer to form
through direct conversion of solid carbon, even though thepressure and temperature conditions under which diamond
forms have traditionally been studied experimentally as
the reaction of graphite to diamond.
Generally, two conditions are needed for diamond formation: Carbon must be present in a mantle fluid or meltin sufficient quantity, and the melt or fluid must become
reduced enough so that oxygen does not combine with carbon (see below). But do diamonds all grow by the samemechanism? What does their origin reveal about their
growth medium and their mantle host rock? Surprisingly,
diamonds do not all form in the same way, but rather they
form in various environments and through varying mechanisms. Through decades of study, we now understand that
diamonds such as the rare blue Hope, the large colorlessCullinan, and the more common yellow “cape” diamonds
all have very different origins within the deep earth.
Diamonds Form from Fluids in the Mantle That Migrate
Due to Plate Tectonics
Diamond is a metasomatic mineral that forms during migration of carbon-bearing fluids, which means that it forms
from fluids and melts that move through the mantle. Dia-

GEMS & GEMOLOGY, VOL. 54, NO. 4, pp. 440–445.
© 2018 Gemological Institute of America

440

DIAMONDS FROM THE DEEPmonds can form in both peridotite and eclogite (box A) inthe cratonic lithospheric mantle, as well as their higherpressure equivalents in the much deeper transition zone
and lower mantle (box B). Regardless of a diamond’s formation depth, many diamond fluids and melts appear to be related to the recycling of surficial material into the deep
earth or to deep melting processes when tectonic plates
split apart, or rift, to form new oceans. Both processes occur
as part of the geologic cycles that accompany plate tectonics
or, in ancient times, some type of pre-plate tectonics.
Since diamonds come from deep and otherwise inaccessible regions, they can be used to study many largerscale tectonic processes in earth that cannot be studied anyother way. Diamonds reveal processes such as early craton
development, craton growth and stabilization processes,
tectonic processes that can modify and destroy the cratonic
lithosphere, and deep subduction (box B) into the lower
mantle that may reintroduce volatile elements into thedeep earth. This makes the study of diamond source fluids,
as well as inclusions in diamond, a powerful way (if not
the only way) to study the deep earth cycles of many elements such as carbon, nitrogen, boron, sulfur, and oxygen.
How Do Lithospheric Diamonds Form?
Lithospheric diamonds (box B) often contain detectable nitrogen, implying that they crystallize from carbon- and nitrogen-bearing (C-N-bearing) fluids. Through the study of
diamonds from many different localities, we now know that
there are subtle differences in the compositions of these CN-bearing fluids and melts. These differences manifest aschanges in the type of carbon and nitrogen compounds contained in these fluids. “Oxidized” hydrous fluids and melts
can contain CO3, CO2, and N2, whereas more “reduced” hydrous fluids contain CH4, NH3, and minor H2.
Traditional models for diamond formation from fluids
in the mantle invoke either carbonate (CO3) reduction or
methane (CH4) oxidation to remove the elements bonded
to carbon. Both these mechanisms require some oxygen
exchange with the surrounding rocks—peridotite or eclogite (box A)—at the site of diamond precipitation so that elemental carbon can be produced to crystallize diamond.
Sometimes peridotite has a limited capacity to exchange
oxygen, and we now know that cooling of hydrous fluids
containing methane (CH4) and carbon dioxide (CO2) is analternative way to precipitate diamonds in these rocks (figure 1; Luth and Stachel, 2014; Smit et al., 2016; Stachel etal., 2017).

GEMS & GEMOLOGYWINTER 2018

BOX A: ROCK TYPES IN THE MANTLE
Figure A-1. Red-purple
garnet (with Cr-pyrope
compositions) and brightgreen clinopyroxene (with
Cr-diopside compositions)separated from a crushed
peridotite rock. Photos by
Karen Smit/University ofAlberta.

Peridotite. Peridotite is the predominant rock type in the
mantle. It contains the minerals orthopyroxene, clinopyroxene, and olivine (figure A-1). Peridotite also contains
an aluminous phase that can be either spinel or garnet,
depending on depth. At the higher pressure conditionsin the diamond stability field, the aluminous phase is always garnet (figure A-1). Peridotite melts to form basalt
at mid-ocean ridges and ocean islands. This melting removes the basaltic melt from peridotite, leaving theresidual peridotite depleted in elements such as Ca, Al,
and Fe. This is because the melt moves upward to dikes
that eventually feed shallow magma chambers. Lherzolite, the most fertile peridotite, has not undergone significant melt depletion and will contain somecombination of the minerals listed above. With high proportions of melt depletion, clinopyroxene is eventually
exhausted in the residual peridotite, resulting in the
clinopyroxene-free rock known as harzburgite. Witharound 40–50% melting, orthopyroxene is also exhausted and olivine dominates the peridotitic assemblage. After these high degrees of melting where most of
the Ca, Al, and Fe have been lost, the residual peridotite
becomes the most depleted dunite. Importantly, both depleted harzburgite and dunite can be re-enriched by passing melts that could reintroduce many of these minerals
and convert depleted peridotite back to fertile lherzolite.

tle through subduction (Jacob, 2004). Despite theirscarcity in the lithospheric mantle (estimated to be lessthan 1%), eclogites are often sampled by kimberlites and,due to their frequent recycled origin, can provide important insights into the role of subduction in the assemblyof cratonic keels and recycling of surficial components
into the deep earth.

Figure A-2. Bimineralic eclogite containing pale green
clinopyroxene and orange-red garnet (Victor mine,
Canada). This eclogite rock was sawed into a thin section(30 µm thick) and polished so that it could transmit lightand be studied under a microscope. Photo by Karen
Smit/University of Alberta.

Cpx

Grt

Eclogite. Eclogite is another rock type in the lithosphericmantle, a bimineralic rock consisting of a sodium-richclinopyroxene (known as omphacite) and garnet with pyrope (Mg-rich), grossular (Ca-rich), and almandine (Ferich) components (figures 3 and A-2). There are two mainmodels for the origin of eclogites in the lithosphericmantle: as high-pressure mantle melts or as former
oceanic crust that has been recycled back into the man-

1 cm

Unfortunately, gem-quality diamonds almost nevercontain any trapped source fluids that can directly indicate
how they formed. However, there are so-called fibrous diamonds (figure 2) that grow much more rapidly than gem-

quality diamonds, and even coat earlier gem diamondcores, allowing them to trap abundant fluids. Fibrous diamonds from all over the world, including Canada, West
Africa, Siberia, and South Africa, have compositions that

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441

BOX B: WHERE DO DIAMONDS FORM IN THE EARTH?
Natural diamonds typically form 150–200 km below thesurface of the earth. Diamond formation does not occur
everywhere at these depths, but only below the oldest continents that have been stable for billions of years; theseareas are known as cratons (see figure 2 in Summer 2018
Diamonds from the Deep). This is because these old cratons all have thick continental roots with cool temperature
profiles conducive to diamond formation that geologists
term “continental lithospheric mantle.” Diamonds thatform within these continental roots are known as lithospheric diamonds and are carried up to the surface of theearth by rare volcanic eruptions known as kimberlites.
Other diamonds form much deeper in the earth, in
sublithospheric regions of the mantle, below these continental roots. So-called superdeep diamonds form at

depths much greater than 200 km, in areas of the mantle
known as the transition zone (410 to 660 km below theearth’s surface) and lower mantle (> 660 km). After formation they are transported to shallower depths in the mantle, likely through mantle convection cells, and then alsobrought to the surface by kimberlite eruptions. Earth’s
mantle convection associated with plate tectonics is responsible for both the availability of fluids necessary toform diamonds and the return of diamonds to the surface.
Ocean floor is thrust deep into the mantle by the process
known as subduction and carries diamond-forming fluids
in its seawater-altered minerals and rocks. Mantle convection return flow also causes hot mantle to rise to shallower levels and melt, generating the kimberlites thatdeliver diamonds to the surface.

are different mixtures of three end-member fluid compositions: carbonate-like, silica-rich, or salty (e.g., Navon et al.,
1988; Izraeli et al., 2001, 2004; Schrauder and Navon, 1994;
Smith et al., 2012; Weiss et al., 2013; Timmerman et al.,2018).
The origins of fibrous diamonds and their fluids are still
debated. Some researchers argue that fibrous diamonds
may be related to the kimberlite magmas that transport diamonds to the surface. If so, fibrous diamonds could formright before the kimberlite eruption to the earth’s surface,which would make them much younger than many gemquality diamonds that may have resided in the mantle formillions to billions of years. One study, however, linked
the full range of fluids in some fibrous diamonds from
northern Canada to subducting oceanic lithosphere, concluding that the original subducting fluid was related to>200-million-year-old recycled sea water (Weiss et al.,2015). This implies that some fibrous diamonds could have
longer mantle residence times and are not necessarily always related to kimberlite eruption.

Figure 1. We now have evidence for a wider range of diamond source fluid compositions in both the lithosphereand sublithosphere that do not include any carbonate components. Both peridotitic and eclogitic diamonds fromthe lithosphere are now known to also precipitate from non-carbonate-bearing fluids. The Marange cuboctahedral
diamonds formed from water-rich fluids that contain both methane and carbon dioxide (Smit et al., 2016), andthe Zimmi eclogitic diamonds crystallized from water-rich fluids that are more reduced and contain significant
methane (Smit et al., 2019), similar to fluids indicated for peridotitic diamonds from the Cullinan mine (Thomassot et al., 2007). Photos by Joshua Balduf and Karen Smit/GIA.

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DIAMONDS FROM THE DEEPGEMS & GEMOLOGYWINTER 2018

Figure 2. A fibrous cubic diamond (1.3 × 1.3 mm) from Wawa (Superior craton, Canada) that has been cut throughthe middle and polished into a double-sided plate (right). Fibrous diamonds such as this example typically contain a darker rim of fluid inclusions that have compositions ranging between carbonate-rich, saline-rich, and silica-rich. Fluids similar to those in fibrous diamonds have been found along twin planes in gem-quality diamonds
from Voorspoed and Venetia (Jablon and Navon, 2016). Photos by Evan Smith/University of British Columbia.

Fluids similar to those in fibrous diamonds have beenfound along twin planes in rare gem-quality diamonds fromSouth Africa, indicating that some gem-quality diamonds
may have similar formation conditions to fibrous diamonds(Jablon and Navon, 2016). However, fluid inclusions in gemquality diamonds are actually very rare, and source compositions and the nature of reactants to make diamond must
be inferred from the covariation of carbon isotope composition and nitrogen content, either in individual diamonds
or diamond suites (Deines, 1980; Stachel et al., 2009). These
carbon isotope studies suggest that gem-quality diamonds
may form through varying mechanisms, though they typically involve hydrous carbon-bearing fluids that also contain oxygen and hydrogen (either as CO3, CO2, or CH4).
Carbon isotope studies can infer whether a diamondsource fluid is “oxidized” or “reduced” (see above) but do
not reveal the fluid’s full elemental composition. Diamonds are comprised mostly of carbon, and any other elements present in the diamond are normally at incredibly
low abundances that are difficult to measure. For this reason, trace element data for gem-quality diamonds are only
now being realized with improvements in analytical sensitivity. But the available trace element data for gem-quality diamonds do appear to show many compositional
similarities to fluid-rich fibrous diamonds (Krebs et al.,2019), further suggesting that fibrous and gem-quality diamonds crystallize from similar types of mantle fluids.
Sublithospheric Diamonds:
The Product of Very Deep Subduction

stellation diamond from Karowe mine in Botswana; Smithet al., 2016). Some superdeep diamonds are plastically deformed, making them pink or brown (e.g., diamonds fromthe Juina area in Brazil). Rarely, they can contain someboron imparting a blue color (e.g., the Hope diamond;
Smith et al., 2018). Based on studies of inclusion-bearing
superdeep diamonds, we now know that they cannot allform in the same environment and that they must crystallize from a wide variety of source fluids and melts that all
relate to different aspects of very deep subduction (box B).
Many superdeep diamonds, such as those from the Juina
and Machado River areas in Brazil, preserve inclusion evidence for their crystallization from carbonate-rich fluids (figure 3; Walter et al., 2008; Bulanova et al., 2010; Burnham etal., 2016; Thomson et al., 2016). These CO3-rich source fluids likely derive from oceanic lithosphere that was deeply
subducted into the mantle transition zone (box B). CLIPPIR
diamonds (figure 4) are now also known to crystallize frommetallic melts in the deep earth that are associated insteadwith reduced carbon (CH4) and hydrogen (Smith et al., 2016).
These diamonds have carbon isotopic compositions that are
unlike those expected for the mantle, but rather indicate anultimate source for the carbon in the oceanic lithosphere, as
do other superdeep diamonds. The third kind of superdeep
diamond, boron-containing blue diamonds, are also related
to deeply subducted oceanic lithosphere (figure 4; Smith etal., 2018). In this case, however, the source for the boroncontaining fluids is likely to be altered peridotite in the
deeper portions of the subducted lithosphere.

So-called superdeep diamonds that form in the sublithospheric mantle (box B) contain very little nitrogen and are
relatively pure, making them nearly colorless (e.g., CLIPPIR diamonds such as the Cullinan diamond and the Con-

Our Fluid Understanding of How Diamonds Form:
Future Studies of Diamond-Forming Fluids

DIAMONDS FROM THE DEEPGEMS & GEMOLOGYOur understanding of the fluids from which diamonds form
is improving with advances in the sensitivity of analytical

WINTER 2018

443

Figure 3. Before 2016, the majority of diamonds were thought to crystallize from fluids and melts that containedcarbonate. For example, the diamonds contained in Jericho eclogites (Slave craton, Canada; left) have covariations
in carbon isotopic composition and nitrogen content that indicate carbonate-rich source fluids/melts (Smart et al.,2011). Similarly, the trace element compositions of inclusions in Juina superdeep diamonds (right) also indicate
their formation from carbonate-rich fluids or melts in the deep mantle (Walter et al., 2008; Bulanova et al., 2010;
Thomson et al., 2016). Photos by Katie Smart/University of Alberta and Galina Bulanova/University of Bristol.

techniques. Most diamonds are only comprised of carbon,
with less than a few parts per million of nitrogen, boron, andother trace elements. Many elements that scientists are interested in detecting in diamond are currently not able to bemeasured accurately. With improved analytical techniquesthat can measure the very low concentrations of trace ele-ments in diamonds, we may be able to better understandthe different origins for diamond source fluids.
Future work will also reveal how the different diamondforming environments relate to each other. Our understanding of the origin of lithospheric diamond source fluids isbetter developed than it is for sublithospheric diamonds.

Figure 4. Although some superdeep diamonds have been shown to crystallize from carbonate-rich melts (figure3), there are also some rare superdeep diamonds that crystallize from boron-rich fluids and reduced metallic
melts, both variably associated with subducted oceanic lithosphere (Smith et al., 2016, 2018). On the left is a
29.62 ct boron-containing rough blue diamond, and on the right is the 812.77 ct rough Constellation diamond,
which contained metallic inclusions. Photos by Jian Xin (Jae) Liao/GIA.

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DIAMONDS FROM THE DEEPGEMS & GEMOLOGYWINTER 2018

This is because they contain much more nitrogen that canbe studied along with carbon, and sometimes they are foundstill trapped within their peridotite or eclogite host rocks(figure 3). Since superdeep diamonds contain little or no nitrogen, and are never found within their original superdeep
mantle host rocks, they provide less information about thegeological conditions by which they formed. We do know,
however, that the carbonate-rich fluids, metallic melts, andboron-rich fluids in superdeep diamonds all relate in some
way to deeply subducted material from the earth’s oceanic
lithosphere. But the challenge remains for geologists to predict where these domains, all with different oxidation states,
occur in the deep earth. Current diamond exploration models have a near-exclusive focus on lithospheric diamonds, so
geologists still need to do some work to figure out how to
explore for potentially high-value superdeep diamonds.

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Blundy J., Gobbo L. (2010) Mineral inclusions in sublithospheric diamonds from Collier 4 kimberlite pipe, Juina, Brazil:
subducted protoliths, carbonated melts and primary kimberlite
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160, No. 4, pp. 489–510.
Burnham A.D., Bulanova G.P., Smith C.B., Whitehead S.C., Kohn
S.C., Gobbo L., Walter M.J. (2016) Diamonds from the MachadoRiver alluvial deposit, Rondonia, Brazil, derived from bothlithospheric and sublithospheric mantle. Lithos, Vol. 265, pp.
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Deines P. (1980) The carbon isotopic composition of diamonds: relationship to diamond shape, colour, occurrence and vapour
deposition. Geochimica et Cosmochimica Acta, Vol. 44, pp.
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Letters, Vol. 187, No. 3-4, pp. 323– 332.
Izraeli E.S., Harris J.W., Navon O. (2004) Fluid and mineral inclusions in cloudy diamonds from Koffiefontein, South Africa.
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Jacob D.E. (2004) Nature and origin of eclogite xenoliths from kimberlites. Lithos, Vol. 77, No. 1-4, pp. 295–316.
Krebs M.Y., Pearson D.G., Stachel T., Laiginhas F., Woodland S.,
Chinn I.L., Kong J. (2019) A common parentage – low abundance trace element data of gem diamonds reveals similar fluids to fibrous diamonds. Lithos, Vol. 324-325, pp. 356–370.
Luth R.W., Stachel T. (2014) The buffering capacity of lithosphericmantle: implications for diamond formation. Contributions toMineralogy and Petrology, Vol. 168, No. 5, p. 1083.
Navon O., Hutcheon I.D., Rossman G.R., Wasserburg G.J. (1988)
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Mah D., Daniels D. (2009) The origin of high-MgO diamondeclogites from the Jericho Kimberlite, Canada. Earth and Planetary Science Letters, Vol. 284, No. 3-4.
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Heaman L.M. (2011) Diamond growth from oxidized carbon
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Earth’s lower mantle. Nature, Vol. 560, pp. 84–87.
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in inclusion-bearing diamonds. Lithos, Vol. 112S, pp. 625–637.
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as multi-component systems. Earth and Planetary Science Letters, Vol. 473, pp. 44–51.
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Walter M.J. (2016) Trace element composition of silicate inclusions in sub-lithospheric diamonds from the Juina-5 kimberlite:
Evidence for diamond growth from slab melts. Lithos, Vol. 265,
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Timmerman S., Jaques A.L., Weiss Y., Harris J.W. (2018) N-d13Cinclusion profiles of cloudy diamonds from Koffiefontein: Evidence for formation by continuous Rayleigh fractionation andmultiple fluids. Chemical Geology, Vol. 483, pp. 31–46.
Walter M.J., Bulanova G.P., Armstrong L.S., Keshav S., Blundy J.D.,
Gudfinnsson G., Lord O.T., Lennie A.R., Clark S.M., Smith
C.B., Gobbo L. (2008) Primary carbonatite melt from deeply
subducted oceanic crust. Nature, Vol. 454, pp. 622–625.
Weiss Y., Griffin W.L., Navon O. (2013) Diamond-forming fluids
in fibrous diamonds: The trace-element perspective. Earth andPlanetary Science Letters, Vol. 376, pp. 110–125.
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(2015) Highly saline fluids from a subducting slab as the source
for fluid-rich diamonds. Nature, Vol. 524, p. 339.

DIAMONDS FROM THE DEEPGEMS & GEMOLOGYWINTER 2018445

EditorNathan Renfro

Contributing Editors
Elise A. Skalwold and John I. Koivula

Rose in Demantoid from Madagascar
Garnets have been known since antiquity. However, it
was only during the late nineteenth century that the green
variety demantoid—named for its “diamond-like” luster—was discovered in the Ural Mountains of Russia. A
few decades later, Fabergé and other jewelers helped demantoid gain more exposure and popularity. Today demantoid garnet is found in various deposits around theworld, including Russia, Namibia, Italy, Iran, Afghanistan,and Madagascar.
The authors recently examined a 0.33 ct round brilliant
demantoid from Antetezambato, Madagascar—a skarn-related deposit—that was of particular interest for a large inclusion resembling a flower (figure 1). Further microscopic
examination revealed the inclusion to be a growth blockage followed by a large etch tube.
The observed shape immediately evokes a flower in repose. The subtle oblique illumination also reflects a shadow
on the opposite facet, adding more three-dimensionality tothis “still-life” image. Finally, the use of Rheinberg illumination (Fall 2015 Micro-World, pp. 328–329) enhances thecolors and gives the inclusion a suitable rose red color.
Even though horsetail inclusions are the more heraldedinternal feature of demantoid, the beautiful flower inclusionin this demantoid specimen from Madagascar proves once

more that the exploration of the microscopic world in gemstones will always reserve for us endless surprises.
Jonathan Muyal
GIA, Carlsbad
Pierre-Yves Chatagnier
Tsara International, Paris

Lepidocrocite in Boulder Opal
The term “boulder opal” is used to describe gem-quality
opal that fills in the pore spaces and cracks of its ironstone
host. When cut, some of that ironstone matrix is includedin the finished stone, often to add structural support to delicately thin veins of opal (R.W. Wise, “Queensland boulder

Figure 1. A negative crystal growth blockage followedby an etch tube is observed in a faceted demantoid
from Madagascar. The use of Rheinberg illumination
gives the inclusion a red color reminiscent of a rose.
Photomicrograph by Jonathan Muyal; field of view
1.99 mm.

About the banner: An iris agate from Nipomo, California, shows vibrantdiffraction colors. Photomicrograph by Nathan Renfro; field of view 11.51
mm. Courtesy of the John Koivula Inclusion Collection.
Editors’ note: Interested contributors should contact Nathan Renfro at
nrenfro@gia.edu and Jennifer-Lynn Archuleta at jennifer.archuleta@gia.edu
for submission information.
GEMS & GEMOLOGY, VOL. 54, NO. 4, pp. 446–451.
© 2018 Gemological Institute of America

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MICRO-WORLDGEMS & GEMOLOGYWINTER 2018

database showed that these inclusions were the iron hydroxide mineral lepidocrocite. Energy-dispersive X-ray fluorescence testing revealed only the presence of iron, which
was consistent with the Raman results. This is the firsttime the authors have encountered a lepidocrocite inclusion in boulder opal.
Nathan Renfro
GIA, Carlsbad
Bona Hiu Yan Chow
GIA, Hong Kong

Prismatic Rutile in Quartz
Figure 2. This boulder opal contains a layer of needlelike lepidocrocite inclusions along the interface between the opal and the ironstone matrix. Photomicrograph by Nathan Renfro, field of view 0.96 mm.

opal,” Spring 1993 G&G, pp. 4–15). The authors recently
examined a boulder opal, presumed to be from Australia,that showcased some interesting inclusions along the interface between the opal and ironstone matrix. Microscopic observation revealed a carpet of minute needle-likeinclusions radiating outward from the ironstone into thesurface opal layer (figure 2). Where some of the inclusions
broke the surface, they showed a submetallic luster in reflected light. In order to identify these unusual inclusions,
we used Raman spectroscopy to analyze some of the surface-reaching needles. Raman spectroscopy and comparison with the reference spectra from the RRUFF mineral

Rutile, a mineral composed mainly of titanium dioxide(TiO₂), is a common inclusion in quartz in the form of profuse acicular hair-like crystals (E.J. Gübelin and J.I. Koivula,
Photoatlas of Inclusions in Gemstones, Vol. 1, ABC Edition, Zurich, 1986). These golden needle inclusions are appreciated as a pleasing feature, giving their name to thevariety known as rutilated quartz.
However, prismatic single rutile crystal inclusions inquartz remain an underappreciated feature, often synonymous with “flaws.” They are rarely showcased by the lapidary. Nevertheless, we observed a 21.27 ct cushion-cut
rock crystal quartz that displayed a large, well-formed rutile crystal inclusion (figure 3) under the table.
The protogenetic inclusion showed a black-silver color
with adamantine to submetallic luster, a well-formed
tetragonal (“stubby”/blocky) prismatic crystal habit withfine striation along its length (parallel to the c-axis), andsmooth pyramidal termination faces. Cyclical twinningsuch as twin knee/sharply angled twins on [011] and parallel twinning crystal growth along the length were also
observed (again, see figure 3).

Figure 3. Left: Depending on the viewing angle, these two rutile crystals in rock crystal quartz seem to be touchingeach other. In the foreground is a black-silver prismatic crystal, and below on the right is a shadowed, fragmented
piece, seen in diffuse/fiber-optic illumination. Right: The use of Rheinberg illumination gives warmer colors to therutile crystals and the background. Photomicrographs by Jonathan Muyal; field of view 14.52 mm.

MICRO-WORLDGEMS & GEMOLOGYWINTER 2018447

Very close below, in the background, was another rutile
crystal inclusion, this one a fragmented piece. At firstglance, it could be mistaken for part of the main crystal inclusion described above. Nevertheless, this rutile fragment
adds details to the overall visual composition.
Rheinberg illumination (Fall 2015 Micro-World, pp.
328–329) using blue and yellow filters provided additional
contrast. Lighting technique is critical in photomicrography. Here it dramatically enhanced the inclusion scene, offering alternative vibrant colors for aesthetic purposes.
This rock crystal quartz had preserved and beautifully
highlighted a prismatic rutile crystal inclusion, like a collector mineral specimen in a display window. Such a large
inclusion specimen also provides valuable mineralogicalinformation for the gemologist.

of the crystal that it reached. We suspect that the crystal
was originally more opaque and of darker color or filledwith a dark substance. It is possible that the drill hole wascreated so that the crystal could be cleaned out with acid,minimizing its appearance. We can only guess at the intentions of the treater, who might have gotten the ideafrom the laser drilling of diamonds.
Although the exact process may remain a mystery,
this inclusion indicates an unusual treatment in ruby andsapphire.

Jonathan Muyal and John I. Koivula
GIA, Carlsbad

Recently, the New York laboratory received for origin determination a ruby whose unusual lathe-like inclusions
caught the authors’ eyes. The inclusions were long, prismatic, and transparent, often accumulating in small bundles throughout the stone (figure 5). Luckily, a few needles
broke the surface, allowing laser Raman spectroscopy toidentify the mystery inclusions as sillimanite, an aluminosilicate mineral that forms in high-grade metamorphic
rocks, including the amphibolite facies. With a chemical
formula of Al2SiO5, sillimanite, a polymorph of andalusite
and kyanite, is frequently found with ruby.
Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) of the host ruby revealed a particularly high iron concentration of 7100–7410 ppmw. The
combination of the elemental composition and inclusions
indicates the stone is from an amphibolite host rock, a nonclassic metamorphic formation (NCL). NCL ruby sources

Drill Hole in Heated Pink Sapphire
While testing a faceted pink sapphire in our laboratory, we
looked at its internal features and determined that it wasa heat-treated stone from Myanmar. As we examined thesurface of the 14.75 × 13.02 × 8.82 mm sapphire, we noticed an unusual feature: a large round drill hole extending
from the surface into a crystal or negative crystal within
the stone (figure 4). Note that this drill hole did not extend
through the sapphire, as one might see in a bead. This
stone was faceted, so it is unlikely that the person who
drilled into the stone intended to create a bead.
What seems more likely, given the placement of thedrill hole, is that it was drilled to minimize the appearance

E. Billie Hughes
Lotus Gemology, Bangkok

Sillimanite in Ruby

Figure 4. A drill hole ina heated pink sapphirefrom Myanmar, seen
with diffuse brightfield
and fiber-optic illumination. Photomicrograph by E. Billie
Hughes; approximate
field of view 5 mm.

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Figure 5. Bundles offine sillimanite needles
clash within their rubyhost. Photomicrograph
by Tyler Smith; field ofview 1.76 mm.

include East African countries such as Mozambique, Madagascar, and Tanzania, as opposed to classic metamorphic
sources such as Burma and Vietnam.
Such a high density of these inclusions is rarely observedin stones submitted to GIA. Sillimanite itself is not a particularly uncommon mineral, especially in amphibolite hostrocks, so why has it been missing from previously analyzed
East African rubies at GIA? Due to its preferred habit ofdensely packed needles, sillimanite in ruby likely affects
transparency, potentially resulting in non-gem-qualitytranslucent to opaque rubies. Such stones are not frequently
submitted to GIA. It is refreshing to see less common mineral inclusions in the lab, as they provide a greater understanding of East African rubies.
Virginia Schneider and Tyler Smith
GIA, New Yorkand wispy secondary flux fingerprint inclusions, as well as
strain bands like graining aligned parallel to the c-axis, allcommon features of Gilson synthetic emerald. The numerous growth striae resulted from inner strain, caused by periodic growth interruptions or slight changes in chemicalcomposition when the growth tank was recharged(Sinkankas, 1981; R. Diehl, “Neues zum Thema ‘Synthetischer Smaragd’: Besuch bei Pierre Gilson,” Zeitschrift
der Deutschen Gemmologischen Gesellschaft, Vol. 26, No.
2, 1977, pp. 61–75).

Figure 6. This 2.73 ct Gilson synthetic emerald cabochon displays a sharp “cat’s-eye” phenomenon. Photoby Kevin Schumacher.

Gilson Cat’s-Eye Synthetic Emerald
In the early 1960s, French ceramist and engineer Pierre
Gilson succeeded in growing and producing flux synthetic
emerald of commercially marketable quality. By the mid1970s, it was reported that Gilson commanded 95% of
the world market in synthetic emeralds (J. Sinkankas,
Emerald and Other Beryls, Chilton Book Company, Radnor, Pennsylvania, 1981, p. 308). While the Gilson factoryis no longer active, the material is still occasionally encountered in the trade and in gemological laboratories.
The authors recently examined one example, a 2.73 ct
cabochon that was of particular interest for its chatoyancy (figure 6).
Gilson synthetics are often grown from seed plates ofslices of natural beryl positioned parallel to the c-axis.
Microscopic examination of the specimen revealed veils

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449

Figure 7. The parallel arrangement of a network of primary flux inclusions is responsible for the cat’s-eye effect.
Photomicrograph by Jonathan Muyal; field of view 2.77 mm.

Also parallel to the c-axis (the basal pinacoid of the original crystal), we observed a plane of tubes (figure 7) that was
responsible for the chatoyant effect. This plane of numerous
elongated bubbles/cavities containing the primary flux—
and possibly minute phenakite crystals—was located near
the base of the cabochon. This oriented plane of primary
flux tubes also appears to result from the variation of conditions during growth.
The micro-world of flux-grown Gilson emerald has already been captured extensively (E.J. Gübelin and J.I.
Koivula, Photoatlas of Inclusions in Gemstones, Vol. 3,
Opinio Publishers, Basel, Switzerland, 2008). But the interest of this specimen is its clever fashioning, with theplane of the coarse primary flux residue—which a lapidary
would normally want to remove—oriented close to thebase and parallel to it, turning this into a chatoyant specimen. In fact, this is the first time a Gilson flux-growncat’s-eye emerald has been encountered by the authors.
Jonathan Muyal and Pierre-Yves ChatagnierZircon Cluster in Ethiopian Sapphire
Ethiopia is a known producer of opal, emerald, and commercial-grade sapphire. In March 2018, a GIA team collected a 1.911 ct blue sapphire from the Ch’ila mining areain the Tigray region. The inclusion scene shows a clusterof small transparent euhedral crystals with high relief.
Raman spectroscopy identified the smaller crystals as zircon, but the clusters also contain some larger roundedmonazite crystals (figure 8). Zircon is a common inclusion

Figure 8. A very densecluster of euhedral zircon associated with alarger rounded crystalof monazite, viewed
under brightfield illumination. Photomicrograph by Charuwan
Khowpong; field ofview 1.75 mm.

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in blue sapphire, usually associated with metamorphic
sources such as Myanmar, Sri Lanka, or Madagascar. Zircon inclusions from those deposits typically have morerounded shapes (E.J. Gübelin and J.I. Koivula, Photoatlasof Inclusions in Gemstones, Vol. 3, Opinio Publishers,
Basel, Switzerland, 2008, pp. 188–308). The sapphire deposit in northern Ethiopia is related to alkali basalt, similar
to the deposits in Australia, Nigeria, or Thailand. Thesesources rarely show clusters of euhedral zircon crystals.
The presence of these zircon clusters might help to separate Ethiopian sapphire from other basalt-related sapphiresources.
Charuwan Khowpong
GIA Bangkok

Quarterly Crystal: Bubble in Fluorite
The very lightly etched green fluorite crystals that comefrom the Rogerley mine, located in Rogerley Quarry,
Weardale, County Durham, England, are well known forthe beautiful bright fluorescence they display. Rogerleymine fluorite is highly fluorescent, turning bright bluishwhite on exposure to long-wave ultraviolet radiation.
The fluorescent fluorite from this locality will also takeon a purplish color in sunlight. This effect, known as “daylight fluorescence,” appears to be unique to fluorite fromthe Weardale area. Research has shown that this intense
fluorescence is due to an elevated rare-earth element (REE)content, including the elements cerium, lanthanum,
neodymium, samarium, and yttrium.
The Rogerley fluorite specimen shown in figure 9
measures 17.68 × 17.38 × 13.50 mm and weighs 41.98 ct.
What makes this specimen the subject of this issue’s“Quarterly Crystal” is the presence of an eye-visible primary fluid inclusion with a moving gas phase. Along theinterface, where the two growing crystals came together,

Figure 9. This 41.98 ct cluster of transparent green fluorite cubes contains a large primary two-phase fluidinclusion that was trapped between the cubes as they
developed. Photo by Diego Sanchez.

negative space was created. This form of primary fluid inclusion hosts fluid remnants that were present when the
fluorite was growing. When comparing the two photomicrographs in figure 10, the movement of the gas phase canbe clearly seen. Fluid inclusions like this are not at all common in fluorite.
John I. Koivula
GIA, Carlsbad

Figure 10. In this registered pair of images, the movement of the gas phase in the fluorite cluster can be easily seen.
Photomicrographs by Nathan Renfro; horizontal field of view 6.54 mm.

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Contributing Editors
Emmanuel Fritsch, University of Nantes, CNRS, Team 6502, Institut
des Matériaux Jean Rouxel (IMN), Nantes, France (fritsch@cnrs-imn.fr)
Gagan Choudhary, Gem Testing Laboratory, Jaipur, India(gagan@gjepcindia.com)
Christopher M. Breeding, GIA, Carlsbad (christopher.breeding@gia.edu)

COLORED STONES AND ORGANIC MATERIALSNatural emerald with inclusions along three directions. Recently, Guild Gem Laboratories received a 10.48 ct sugarloaf
emerald (figure 1) for identification and origin determination. The refractive index (approximately 1.58) and specificgravity (approximately 2.80) fell within the range for beryl,and Fourier-transform infrared (FTIR) testing confirmed it
as natural emerald. Additionally, energy-dispersive X-ray fluorescence (EDXRF) analysis revealed Fe, V, and Cr contents
consistent with those in Zambian material.
The stone showed interference colors when placed
under a polariscope with the bottom facing up. With aconoscope, the optic axis of this emerald was determined
to be perpendicular to the bottom. Using the microscope,
we found thin platy inclusions arranged in three directions
intersected with each other at 60/120 degree angles (figure2). Those inclusions were mainly dark brownish and transparent with well-formed rectangular shapes, some ofwhich exhibited a light bodycolor resembling an unhealed
fracture. Evenly distributed reflective light could be seenat certain angles. We deduced that those inclusions had relatively smooth surfaces, which means that their original
crystal faces were not corroded during the emerald’s formation. Further observation revealed hexagonal inclusions
in the basal plane. Owing to uneven development during
their crystalline formation, several of them were nearly triangular in shape. Their sides were parallel to the directionof the platy inclusions (figure 3, top). We also found distinct
growth lines near the bottom of the sugarloaf perpendicular
to the c-axis. These platy inclusions appeared to be con-Figure 1. This 10.48 ct sugarloaf emerald from Zambia shows a vivid and highly saturated green color.
Photo by Yizhi Zhao.

centrated sparsely in a thin layer with a thickness around
1.5–2.0 mm, as shown figure 3 (bottom). The sparseness of

Figure 2. Platy inclusions in the emerald in three directions, intersecting at 60/120 degree angles viewed along
the c-axis. Photo by Yujie Gao; field of view 2.8 mm.

Editors’ note: Interested contributors should send information and illustrations to Stuart Overlin at soverlin@gia.edu or GIA, The Robert MouawadCampus, 5345 Armada Drive, Carlsbad, CA 92008.
GEMS & GEMOLOGY, VOL. 54, NO. 4, pp. 452–469.
© 2018 Gemological Institute of America

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Hexagonal prismatic crystal of emerald

c-axisc-axisBasal plane

Figure 3. Top: The hexagonal inclusions in the basal
plane are parallel to the orientation of the platy inclusion described in figure 2. Field of view 3.1 mm. Bottom:
A thin layer exhibiting growth lines is perpendicular to
the emerald’s c-axis. Photos by Yujie Gao.

Figure 4. Proposed illustration of hexagonal inclusions
in the basal plane and platy inclusions along the prismatic faces. Illustration by Yujie Gao.

the oriented inclusions resulted in the absence of asterism
or cat’s-eye phenomena.
Considering the optic axis, we concluded that the platy
inclusions grew along the hexagonal prismatic emerald
faces, with the hexagonal platy inclusion parallel to thebasal plane, as illustrated in figure 4. However, it is still
unclear whether they were syngenetic or exsolution, since
their well-preserved shapes showed little evidence of corrosion and there was insufficient evidence of exsolution.

Under ultra-short-wave UV excitation, the 0.30 ct K-L
diamond with faint brown color, mounted in an 18K goldprong setting (figure 5), showed strong blue fluorescenceand strong greenish blue phosphorescence that lasted forapproximately eight seconds (figure 6). Infrared absorption
spectroscopy showed low concentrations of the hydrogenrelated peak (3107 cm–1) and nitrogen impurities in the B
aggregates at 1174 cm–1 (figure 7), indicating a type IaB diamond (C.M. Breeding and J.E. Shigley, “The ‘type’ classi-

Yujie Gao (peter.gao@guildgemlab.com) and Kai Li
Guild Gem Laboratories, Shenzhen
Darwin Fortaleché
Guild Gem Laboratories, Hong Kong

Figure 5. This 0.30 ct K-L diamond with faint browncolor, mounted in an 18K gold prong setting, is anominal type IaB diamond with detectable uncompensated boron. Photo by Wenqing Huang.

DIAMONDS
Nominal type IaB diamond with detectable uncompensated boron. In recent years, nominal type IaAB and IIa diamonds with transient 2800 cm–1 FTIR absorption peaks
arising from uncompensated boron produced under UV radiation have been reported (J. Li et al., “A diamond with atransient 2804 cm–1 absorption peak,” Journal of Gemmology, Vol. 35, 2016, pp. 248–252; Winter 2016 Lab Notes,
pp. 412–413). The National Center of Supervision and Inspection on Quality of Gold and Silver Products recently
examined a type IaB diamond that exhibited instantaneous
2803 cm–1 FTIR absorption shortly after exposure to an
ultra-short-wave (< 230 nm) UV source.

GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2018453

Figure 6. DiamondView
imaging shows blue fluorescence (left) andgreenish blue phosphorescence (right) in thenatural type IaB diamond. Images by Wenqing Huang.

fication system of diamonds and its importance in gemology,” Summer 2009 G&G, pp. 96–111); prior to ultra-shortwave UV excitation, we were unable to detect the presenceof the B center. No boron-related absorption was detected
before UV radiation exposure, due to uncompensated B
concentrations below the detection level of the FTIR spectrometer. But shortly after ultra-short-wave UV exposure,the transient boron-related absorption peak was recorded
at 2803 cm–1 (again, see figure 7). Nitrogen-related peaks
were detected at 415.7, 428.5, 439.0, and 452.4 nm using
photoluminescence (PL) spectroscopy (figure 8); the peakat 415.7 nm belongs to the zero-phonon line (ZPL), while
the others belong to its associated phonon replicas (A.M.

Figure 7. The FTIR spectra reveal low concentrationsof the hydrogen peak (3107 cm–1) and nitrogen impurities in the B aggregates (1174 cm–1) (blue line). Shortly
after ultra-short-wave (< 230 nm) UV exposure, thetransient boron-related absorption was recorded at2803 cm–1 (red line). Spectra have been offset vertically for clarity.

Zaitsev, Optical Properties of Diamond: A Data Handbook, Springer-Verlag, Berlin, 2000). PL and FTIR spectra
confirmed the diamond’s natural origin.
The generally accepted mechanism for interpreting thephosphorescence in type IIb diamonds is donor-acceptor
pair recombination processes involving boron and otherdefects (P.J. Dean, “Bound excitons and donor-acceptor
pairs in natural and synthetic diamond,” Physical Review,Vol. 139, 1965, pp. A588–A602). Boron is deemed as theacceptor in the model, where the donor is believed to be
nitrogen related, either as isolated nitrogen, aggregated nitrogen, or a plastic deformation–related defect (S. EatonMagaña and R. Lu, “Phosphorescence of type IIb
diamonds,” Diamond and Related Materials, Vol. 20,
2011, pp. 983–989; E. Gaillou et al., “Boron in natural typeIIb blue diamonds: Chemical and spectroscopic measurements,” American Mineralogist, Vol. 97, 2012, pp. 1–18).

Figure 8. The photoluminescence spectrum of thesample excited at room temperature with a 405 nm
laser reveals an N3 center with its zero-phonon line
(ZPL) at 415.7 nm and its associated phonon replicas
with peaks at 428.5, 439.0, and 452.4 nm.

FTIR SPECTRA
PL SPECTRUM

Before UV excitation
After UV excitation

452.4
439.0

3107

1332
2803

3000

2500

2000

1500

1174

INTENSITY

ABSORBANCE

428.5

ZPL
415.7

1000

450

WAVENUMBER (cm–1)

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WAVELENGTH (nm)GEMS & GEMOLOGYWINTER 2018

NORTH
KOREA

Pyongyang
Beijing

CHINA

Seoul

TianjinYellow
SOUTH
Sea
KOREA

Xi'an
ShanghaiChengduHangzhouEast China Sea

Chongqing

TaipeiQinglong

TAIWAN

Pacific
Ocean

Macau

VIETNAM
Hanoi

Hong KongN

0

250 km

When almost all of the boron impurities received electrons
from donors, almost no uncompensated boron (B0) was left
behind, and therefore no boron-related absorption peaks
were recorded. When the diamond was exposed to ultrashort-wave UV excitation, some of the compensated boron
converted to an uncompensated state due to a chargetransfer process between compensated boron and ionizeddonors, which could be recorded before the phosphorescence decayed. This mechanism is also suitable for interpreting the observed phenomenon of this specimen.
Natural diamonds with long-lasting phosphorescence
under UV excitation are typically type IIb or chameleon diamonds (J.M. King et al., “Characterizing natural-color typeIIb blue diamonds,” Winter 1998 G&G, pp. 246–268; T.
Hainschwang et al., “A gemological study of a collection ofchameleon diamonds,” Spring 2005 G&G, pp. 20–35). It israre to find diamonds of other types, especially type IaB diamonds, showing this phenomenon. Finding a detectable, if
temporary, B0 defect in a type IaB diamond is also unusual.
Wenqing Huang, Yijing Liu, and Shujia Dong
National Center of Supervision and Inspection on
Quality of Gold and Silver Products
Nanjing, China

Figure 9. Qinglong, the site of the Guizhou Jade deposit, is located in southwestern China.

Dongjuan Chao
Jiangsu Daocun Industrial Development Co. Ltd.
Nanjing, China

clay minerals are often found in the micro-cracks or small
holes in the gem material.
Guizhou Jade is translucent to opaque, with a refractive
index of about 1.54 (spot reading), a specific gravity of 2.62,
and a Mohs hardness of 6.5–7. According to the infrared

Guizhou Jade from Qinglong, China. A green-blue quartzite
produced in the Qinglong antimony deposit, in southwestern Guizhou Province, is called Guizhou Jade in the trade.
The source area is located in the middle of the YunnanGuizhou Plateau at 25°N latitude, rising 1,600 meters(5,250 ft) above sea level (figure 9). This material was discovered in the 1950s, when the antimony deposit was economically more important to the area. The accompanying
blue quartzite was only commercially mined as a decorative
material. Later, it was used as a gem material, and it has
been popular in Chinese jade markets since about 2011 (figure 10).
In June 2018, the authors went to the source to inspect
the antimony deposit and conduct exploration and collection for Guizhou Jade in the mine. The host rocks aremainly pyroclastic (breccia) rocks, breccia clay rocks of the
Dachang layer, and bio-limestones of the Maokou Formation. The Dachang layer is the main ore-bearing layer of
the antimony deposit, which is a set of pyroclastic andchemical deposits, and subjected to alteration to siliceousand clay rocks (J.C. Cao, “The dyeing mechanism andcause of Guicui,” Acta Mineralogica Sinica, No. 3, 1983,
pp. 183–192).
The authors observed that in the mine, this material
has a close relationship with stibnite. It is mostly developed in the interlayer fissures, fracture zones, and areas
where brecciation has taken place. The material occurs as
blocks and/or veins (figure 11). In the ores, there are calcite- and gypsum-filled cracks and voids. Green or white

GEM NEWS INTERNATIONAL

Figure 10. This Guizhou Jade ornament, typical in the
Chinese jade markets, stands about 11 cm high.
Photo by Yushan Dai.

GEMS & GEMOLOGYWINTER 2018455

Figure 11. Left: In the mine, Guizhou Jade is mostly developed in the interlaminar fissures and closely related tostibnite. Right: Guizhou Jade, which develops between layers of stibnite, is massive and can be seen in some small
holes in the surface. Photos by Yushan Dai.

spectrum, the main constituent mineral is quartz, and its
infrared spectrum matches the α-quartz standard infrared
spectrum, including several obvious absorption peaks at
1172, 1124, 1085, 798, 781, 540, and 478 cm–1 (figure 12).
Quartzite is generally cryptocrystalline. Its colors range
from light green-blue to dark green-blue. The most soughtafter color is ocean blue, as shown in figure 10.
UV-Vis-NIR absorption spectra (figure 13) of both samples show an obvious 415 nm absorption band and a strong
absorption band at 590–620 nm, located in the blue-green
range of visible light. The absorption intensity of the lightcolored sample is significantly lower than that of the deepcolored sample. The 415 nm absorption band is caused by
4
A2g→4T1g transition and 4A2g→4T2g transition of Cr3+. The
strong absorption band at 590 to 620 nm is caused by chargetransfer between Fe2+→Ti4+ and 4A2g→4T2g transition of Cr3+

(J. Liu, “The color formation of common green quartz jade,”
Ming Ri Feng Shang, No. 3, 2017, pp. 368–371).
High-quality Guizhou Jade is rich in color and loved bycollectors. It has been widely used in necklaces, bracelets,
earrings, and other items.
Yushan Dai and Xuemei He
School of Gemmology, China University of Geosciences
Beijing

SYNTHETICS AND SIMULANTS
Single HPHT synthetic diamond mixed in natural diamond ring. Recently, a ring with 195 mounted colorlessand near-colorless stones (figure 14) was submitted toDubai Central Laboratory for identification. The ring con-Figure 13. The UV-Vis-NIR spectra of both Guizhou
Jades show a 415 nm absorption band and a strong
absorption band at 590–620 nm.

Figure 12. The infrared spectrum of a Guizhou Jade
sample.

IR SPECTRUM

UV-VIS-NIR SPECTRA

1.0
1085

50

1124

Dark sample
Light sample

REFLECTANCE

1172
478

0.6

0.4
798 781
0.2

540

REFLECTANCE (%)

0.8
40

30

20

10

0.0
2000

1800

1600

1400

1200

1000

800

600

400

100

200

–1

WAVENUMBER (cm )456

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400

500

600

700

800

900

WAVELENGTH (nm)GEMS & GEMOLOGYWINTER 2018

Figure 14. The ring with 194 natural diamonds andone HPHT-grown specimen. Photo by Nazar Ahmed
Ambalathveettil.

Figure 15. These metallic flux inclusions that are associated with feathers show high reflection in oblique
light. Photo by Nazar Ahmed Ambalathveettil.

tained round-brilliant-cut diamond melee arranged inrows. Testing with the DiamondSure instrument identified
194 of them as natural diamond, and the remaining melee
was referred for further testing.
The sample’s setting in the ring restricted us to FTIR
spectroscopy in reflection mode to determine its identity.
Solid metallic inclusions were revealed under the microscope (figure 15). The specimen displayed strong yellow
and moderate greenish yellow fluorescence under longwave UV and short-wave UV, respectively (figure 16). The
inclusions and fluorescence suggested HPHT-grown diamond, which generally shows a stronger fluorescence reaction to short-wave UV than to long-wave UV. The vast
majority of HPHT synthetics in the “colorless” range exhibit no detectable fluorescence to long-wave UV (S. EatonMagaña et al., “Observations on HPHT-grown synthetic
diamonds: A review,” Fall 2017 G&G, pp. 262–284), but
this one showed strong fluorescence under long-wave UV.

The stone was further examined with DiamondView
imaging and photoluminescence (PL) spectroscopy. Strong
yellowish green fluorescence and blue phosphorescencewere observed with the DiamondView, but the growth
sector pattern typical of HPHT-grown diamond was not
visible because of the stone’s size. PL spectroscopy showednickel-related peaks at 882/884 nm. Based on these results, we concluded that this was an HPHT laboratorygrown diamond.
We later learned that the customer had given the ringto a jewelry repair shop to replace a broken diamond,
which may account for the single lab-grown specimen.
This is a good example of the need for vigilance in every
stage of diamond jewelry making.
Nazar Ahmed Ambalathveettil (nanezar@dm.gov.ae),
Nahla Al Muhari, and Sutas Singbamroong
Gemstone Unit, Dubai Central Laboratory
United Arab Emirates

Figure 16. The laboratory-grown diamond fluoresced yellow under long-wave UV (left) and greenish yellow undershort-wave UV light (right). Photos by Nazar Ahmed Ambalathveettil.

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Figure 17. This sapphire that was treated with heat and pressure contained small birefringent crystals (left) thatwere nearly invisible with unpolarized light, as seen in the brightfield image (right). Photomicrographs by Nathan
Renfro; field of view 1.81 mm.

TREATMENTS
Microscopic observations of blue sapphires treated withheat and pressure. In recent months, sapphires treatedunder heat and pressure have been documented in the trade.
This material is reported to be treated under pressure of 1
kbar at temperatures between 1200 and 1800°C by HB Laboratory Co. Ltd. of Korea (H. Choi et al., “Sri Lankan sapphire enhanced by heat with pressure,” The Journal of theGemmological Association of Hong Kong, Vol. 39, 2018,
pp. 16–25). This process is used to improve blue colorationand potentially heal any fractures within the stones.
GIA acquired from Sri Lankan gem dealer Imam Faris of
Imam Gems (Pvt) Ltd. six samples that were said to havebeen treated under the conditions mentioned above. The
samples were examined using a standard gemological microscope to look for any unusual features resulting from thistype of treatment. Five of the six sapphires showed a featurethat to our knowledge has not been reported before. Viewed
in polarized light (figure 17, left), planes of small crystallites
were observed as bright spots against a dark backgroundwhen the host corundum was in the extinct position. But
under unpolarized light (figure 17, right), the crystallites
were either invisible or nearly so, and only visible from a
low-relief interface between the crystallite and the hostcorundum. Due to the extremely low relief of these inclusions, the author speculates that these inclusions are corundum crystals that originated from fractures and were healed
by recrystallization of the corundum. While it is certainly
possible to have birefringent crystals of corundum in untreated corundum, the consistent observation of the planesof birefringent crystals by the author suggests that this feature could be a useful indicator for corundum treated withheat and pressure. These preliminary observations offersome interesting clues, but further research will be needed
to fully characterize corundum treated with this technique.

Emeralds filled with epoxy resin: DiamondView observations. Emeralds from all sources routinely contain surfacereaching fissures, and as a result are subjected to clarity
enhancement processes (oiling or resin filling) to improvetheir appearance. The quantity and variety of emerald-filling substances undoubtedly affects the final market value(M.L. Johnson et al., “On the identification of various
emerald filling substances,” Summer 1999 G&G, pp. 82–
107). Recently, the Lai Tai-An Gem Lab received a stone—reported as an emerald by the client—for identification
services, with a request to focus on the degree of clarity enhancement. DiamondView imaging allowed us to visually
explain the degree of filling in a way the client was quickly
able to understand.
The transparent emerald-cut stone weighed 16.15 ct
and measured 16.80 × 14.07 × 9.48 mm. It exhibited a lightto medium green saturation and contained white hazy inclusions that were visible to the eye (figure 18). Standard

Figure 18. This 16.15 ct emerald was filled with epoxy
resin. Photo by Lai Tai-An Gem Lab.

Nathan Renfro
GIA, Carlsbad

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IR SPECTRUM

Figure 19. When viewed through a gemological microscope, “blue flashes” characteristic of resin-filled
emeralds are clearly visible. Photo by Lai Tai-An
Gem Lab; field of view 8.8 mm.

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ABSORBANCE UNITS

gemological testing revealed an RI of 1.570–1.575, an SGof approximately 2.66, and a weak yellowish green reaction
under long-wave ultraviolet radiation. Magnification with agemological microscope revealed fluid and three-phase inclusions typical of natural emeralds. When turning the specimen, “blue flashes” characteristic of resin-filled material
were seen within many of the fissures (figure 19). These results confirmed that the stone was a natural, clarity-enhanced emerald. Infrared spectrometry was subsequently
performed to analyze the filling in more detail. Epoxy resin
peaks at 3061, 3040, 2965, 2930, and 2870 cm–1 (figure 20)
confirmed the epoxy resin treatment of the stone, as indicated by the initial microscopy.
Although it may not be difficult for experienced gemologists to identify various emerald-filling substances using
high-end equipment like Fourier-transform infrared (FTIR)or Raman spectroscopy, we wanted to check on the suitability of another tool to assist in identifying fillers and tohelp see the extent and degree of filling applied. We turnedto the DiamondView and obtained some interesting images for this clarity-enhanced emerald.
The stone’s surface was first observed in different directions under the DiamondView’s visible light source
until obvious surface-reaching fissures appeared. Subsequent exposure to the unit’s ultra-short energy UV lightclearly revealed the epoxy resin filler within the fissures asa series of blue lines extending over the entire surface
against the beryl’s orange-fluorescing bodycolor. The more
severe (quantity in relation to width and depth) the treatedfissures were, the stronger the blue reaction (figure 21). The
results of this simple test show how the DiamondView
may be applied. Although the DiamondView cannot precisely identify the fillers, it does provide a means of detection that can be applied to a variety of gems. The optionof ultra-short-wave radiation should be considered, as

5.0
4.5
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2930

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2870
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3061

3040

3.0
2.5
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3200

3000

2900

2800

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2600

WAVENUMBER (cm–1)

Figure 20. Characteristic epoxy resin peaks were detected at 3061, 3040, 2965, 2930, and 2870 cm–1 withFTIR spectrometry.

there may be concerns about the color and structural durability of host and fillers that have not been fully taken into
account.
Larry Tai-An Lai (service@laitaian.com.tw)
Lai Tai-An Gem Laboratory, Taipei
Coated pink synthetic moissanite. The French Gemmological Laboratory (LFG) recently received a 0.41 ct pink stone
resembling a pink diamond (figure 22) for identification. The
surface of the stone showed numerous patches (figure 23),
casting doubts about the natural origin of its color.

Figure 21. Surface-reaching fissures with greater concentrations reveal a stronger blue reaction whenobserved in different directions under the DiamondView’s visible light (left) and when exposed to theunit’s ultra-short-wave UV energy (right).

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Figure 22. This 0.41 ct pink stone was revealed to bea coated synthetic moissanite. Photo by Aurélien
Delaunay.

Under the microscope, these flakes showed metallic
luster. Furthermore, the pink color appeared concentrated
at the surface. Some unevenness in the color was observed
due to scratches of this film. When observed through thecrown, the gem showed a clear doubling of its edges, indicating an anisotropic material. These observations confirmed the client’s doubts that the gem was a pinkdiamond (figure 24).
The sample was analyzed using infrared, UV-visible,
and Raman spectrometers. All the spectra collected indi-

Figure 23. Metallic flakes on the surface raised questions about the origin of the pink color. Photomicrograph by Aurélien Delaunay; field of view
approximately 1.8 mm.

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Figure 24. Doubling of the edges, observed near thecrown in this synthetic moissanite. Photomicrographby Aurélien Delaunay; field of view approximately
3.4 mm.

cated a synthetic moissanite coated with a colored film.
Chemical study of this film acquired with an EDXRF spectrometer revealed that iron and titanium were responsible
for the color of the calcium-rich film.
This is the first example the LFG has seen of synthetic
moissanite coated with a thin colored film. This type oftreatment is not rare with topaz, quartz, diamond, or tanzanite. Gemologists must remain vigilant because thistreatment can be performed on all gems, natural or synthetic.
Aurélien Delaunay
Laboratoire Français de Gemmologie (LFG)
Paris
Synthetic moissanite coated with diamond film imitating
rough diamond. A transparent yellowish octahedral (sawable) crystal (figure 25) weighing 5.35 ct was submitted asa rough diamond to the Far East Geological Institute (FEGI)for examination.
The faces of the octahedron showed a stepped appearance, and the edges had parallel grooves and combinationalsurfaces. The faces and edges were smooth except for one
face where mechanical damage was noticeable. Initially, thespecimen was examined using conventional gemological instruments. It was inert to long-wave UV (365 nm) andanisotropic. Thermal conductivity testing indicated diamond. Tests for electrical conductivity were not convincing,however: Some areas (mostly on the edges) corresponded todiamond, but others (on smooth faces and dimples) indicatedsynthetic moissanite. There were no inclusions associatedwith natural diamond. Only small parallel needle-like inclusions, typical for synthetic moissanite, were found usinga gemological microscope (figure 26).

GEMS & GEMOLOGYWINTER 2018

Figure 25. This 5.35 ct sample, submitted as a roughdiamond, was identified as synthetic moissanite
coated with a diamond film. Photo by V. Pakhomova.

X-ray tomography showed that the inner part of the sample was distinguished by its X-ray density from the outershell, which had a variable thickness from 19 to 115 microns(figure 27). Microprobe analysis with a JEOL JXA-8100 four-

Figure 27. Three-dimensional X-ray tomography rendering of the reconstructed sample. The coloring of
the image corresponds to the degree of X-ray permeability. The green color represents the SiC crystal, andthe blue color represents the film.

1.0
0.8
0.6

Figure 26. Needle-like inclusions in the rough synthetic moissanite sample. Photo by V. Pakhomova.

channel microanalyzer revealed the presence of up to 61
wt.% silicon on some polished faces of the crystal, alongwith titanium in the composition of the surface layer (figure
28 and table 1). Some polished faces showed a diamondchemical signature.
Based on these results, we identified the sample as synthetic moissanite that had been covered with a thin diamond film. Based on the study by T. Teraji et al. (“Chemical
vapor deposition of 12C isotopically enriched polycrystalline
diamond,” Japanese Journal of Applied Physics, No. 51,
090104, 2012, pp. 1–7), the diamond coating was likely applied using polycrystalline diamonds. The top layer was
made of a composite material consisting of metal matrix
and nano-diamond particles.
A diamond imitation such as synthetic moissanite
coated with a thin diamond film is challenging to identify,
since its luster and thermal properties correspond to diamond. Even with a very thin coating that did not exceed
0.001 mm, the sample tested positive for diamond. This

0.4
0.2
0.0

TABLE 1. Electron microprobe analysis of some parts ofthe surface of the “diamond” crystal.
Spectrumzyx

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1 mm

C

O

Al

Si

Ti

Total

1

37.52

1.61

0.12

60.76

0

100

2

46.93

4.96

0.13

47.82

0.16

100

3

37.88

0.59

0.10

61.28

0.15

100

4

8.84

0

0.47

11.90

78.79

100

5

40.74

0

0.07

59.18

0

100

6

41.18

1.25

0.08

57.46

0.04

100

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Sp6

Sp2
Sp5
Sp4
Sp3

Sp1

Figure 28. A fragment of the synthetic moissanite crystal, viewed with the electron probe microanalyzer. The crystal was analyzed on the surface. Spectrum numbers correspond to the analysis numbers in table 1.

GSA 2018 report. The Geological Society of America (GSA)
annual meeting took place in Indianapolis November 4–7.
GIA participated as both exhibitor and technical session
holder. In total, 21 presenters reported new findings on abroad range of research topics. The GIA booth and the twotechnical sessions attracted a large audience with an interest in gemology (figure 29).
The “Gemological Research in the 21st Century” technical program included both poster and speaker sessions.
Seven posters were presented on the second day of the conference (figure 30). Kyle Tollefson (Louisiana State University) and Phillip Ihinger (University of Wisconsin-Eau
Claire) reported their characterization study on watermelon
tourmaline. Their spectroscopic measurements showedthat the chromophores Fe and Mn correlate to green andpink colorations, as expected. The infrared spectroscopy
and microprobe analyses showed similar trends of hydroxyl
occupancy on the V site in this type of tourmaline. Nikita
Kepezhinskas (University of Florida) presented the resultsof petrographic, geochemical, and isotopic analyses ofmoissanite and diamond from the shoshonite dike in eastern Finnmark, Norway. The shoshonite host of these minerals is a type of Mg- and K-rich basaltic rock, which isindicative of a subduction-modified mantle source. This
study proved that carbonate recycling into the lower mantle
through subduction, followed by the formation of superdeep diamonds, moissanite, and other carbides, plays animportant role in the global carbon cycle. Paul Johnson andKyaw Soe Moe (GIA, New York) showed an unusual find of
a natural diamond with a cuboctahedral growth habit. Thisdiamond should alert gem labs to the fact that cuboctahedral growth does not occur just in HPHT synthetic diamonds. This special diamond also indicated a potentiallyvery interesting and uncommon growth history before it
was lifted to the surface of the earth. Richard Berg (Montana
Bureau of Mines and Geology) described significant magmatic splitting of sapphire xenocrysts in basaltic trachyandesite sill. Through extremely careful examination of insitu sapphires in their host rock and advanced instrument
analyses such as SEM, XRD, and EDS, he was able to assemble a sequence of what happened to the sapphires before
emplacement into their current location. Ying Song (China
University of Petroleum) introduced a newly designed anddeveloped computer-vision based intelligent RI measuringsystem. This system aimed to enhance the clarity and efficiency of RI and other optical measurements. Classroom
demonstration, rapid crystal identification, optic axis characterization, and crystal orientation determination are thefour modes currently implemented in this instrument.
Ziyin Sun and coauthors (GIA, Carlsbad) displayed theirstudy on chromophore strength in pyralspite garnet. Since
multiple color-causing elements work singularly or together to color garnets, the authors isolated each of themand performed quantitative study by experimenting withvarious combinations of these chromophores’ UV-Vis-NIR

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application of thin diamond films onto non-diamond material could be an issue for gemologists in the future.
This work was supported by the Russian Foundation for
Basic Research (grant N 16-05-00283) and the Far Eastern
Branch of the Russian Academy of Sciences (N 15-1-2-003).
Vera A. Pakhomova, Dmitrii G. Fedoseev, Svetlana Y.
Kultenko, Alexander A. Karabtsov, Vitaliia B. Tishkina,
and Valentina A. Solyanik
Far East Geological Institute (FEGI FEB RAS), Vladivostok
Vladimir A. Kamynin
Gokhran of Russia, Moscow

CONFERENCE REPORTS

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WINTER 2018

Figure 29. Each year, theGIA booth at the GSA
exhibition hall attracts
participants from allover the world. Here,Paula Rucinski (left)and Dona Dirlam(right) speak with a visitor to the booth. Photo
by Cathy Jonathan.

spectra under different lighting conditions. Aaron Palke andcoauthors (GIA, Carlsbad) reported on a Montana sapphire
study aiming to unravel its gemological mysteries. Basedon their inclusion and geochemical study, the authors proposed a new model of sapphire formation through peritectic melting reactions during partial melting of an Al-richprotolith.
This year’s speaker session attracted 14 presenters frommultiple research institutes and universities (figure 31).
Mike Breeding (GIA, Carlsbad) kicked off the session withan overview of colored diamonds formed at different depths
within the earth. He elaborated on the defects that cause
diamond’s blue, pink, yellow, brown, and green colors. The
audience was given a grand tour of colored diamond formation, from the transition zone all the way to the surface ofthe earth. Next, Sally Eaton-Magaña (GIA, Carlsbad) presented her photoluminescence study on pink diamonds

based on GIA’s uniquely large database. She explained thecause of pink color as a 550 nm absorption band and explored the difference of pink coloration in various diamondtypes. She also showed some visual clues that can help toseparate pink diamonds from different sources. Tyler Sundell (Missouri State University) talked about the feasibilityof using time-of-flight secondary ion mass spectrometry(ToF-SIMS) to image diamonds, especially on their trace-element composition and isotope analyses. Evaluation of thismethod focuses on its spatial resolution and analytical precision. Results show that this method lacks the precision
to quantify carbon isotope values. Karen Smit (GIA, NewYork) presented her research on natural black diamonds
found in the billion-year-old Marange conglomerate (Zimbabwe). Diamonds from this source are full of fractures andcan be easily treated to achieve a more valuable fancy blackcolor grade, which makes identification challenging with-

Figure 30. Richard Bergfrom the Montana
Bureau of Mines andGeology presented his
poster on Montana sapphires at the GSA annual meeting. Photo by
Tao Hsu.

GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2018463

Peter Heaney (Penn State University) explored the reason
behind the striking iridescence displayed by some ochrecolored botryoidal goethite. Dr. Heaney applied focused ion
beam (FIB) milling and scanning electron microscopy (SEM)
to zoom in on the internal structure of this gem. With thesepowerful tools, some subsurface void layers were revealed
to be responsible for the angle-independent iridescence. The
origin of these voids remains a mystery. Barbara Dutrow(Louisiana State University) reported a geochemistry study
on some uncommon tourmaline + corundum–bearing
rocks from Afghanistan’s Badakhshan Province with randomly oriented phlogopites as the matrix. Major, minor,
and trace elements were measured with electron microprobe and laser ablation–inductively coupled plasma–massspectrometry (LA-ICP-MS). The results indicate the involvement of boron-bearing fluids at the beginning of tourmaline growth and continuous infiltration of this fluid. The
bulk composition of this rock is consistent with metasomatism of a clay-containing metacarbonate rock with ametamorphic overprint. Chunhui Zhou (GIA, New York)gave the first-ever pearl presentation in this technical session. Three American freshwater cultured pearls weresliced open and their oxygen isotopes were analyzed using
SIMS, aiming to reconstruct the ambient water temperature when the nacre formed. This method is very useful interms of growth cycle determination and can potentiallyshine a light on pearl origin determination.
Tao Hsu
GIA, Carlsbad

out characterization of the natural stones. Visual observation of graphite grain size and the detection of methane associated with the micro-inclusions are necessary to
distinguish between natural and treated Marange diamonds. Evan Smith (GIA, New York) delivered his researchon carbonatitic melt inclusions he discovered in partiallyhealed cracks within a CLIPPIR diamond (for more on these
diamonds, see Winter 2017 G&G, pp. 388–403). The characterization of these inclusions is consistent with carbonatitic melt, providing direct evidence of this melt’s
existence at mantle depths. Russell Harmon (North Carolina State University) evaluated the potential of handheld
laser-induced breakdown spectroscopy (LIBS) to identify
garnets associated with kimberlites, the host rock of most
diamond deposits. This study aims to test whether this instrument will help diamond exploration in the field. Initial
results showed that it works very well on garnets from theSouth Africa kimberlite field but not as well on some othersamples, especially those from extensive solid solution. Rod
Smith (Geological Survey of Canada) presented field and lab
research on the Banks Island region in the western Canadian Arctic, aiming to find promising diamond-bearing
kimberlite. Based on newly found stream sediments and till
samples, geothermometry data, and Lu-Hf geochronology
results, the research group demonstrated the need to continue the search for potential diamond-bearing kimberlite
in this region and presented a potentially unknown kimberlite glacial dispersal model. Tingting Gu (GIA, NewYork) talked about inclusion studies on type IaB diamonds.
This study offered the first piece of evidence that hydrous
phosphate can subduct to the depth of the transition zone.
It also showed the first ringwoodite found in diamond,
which proved that this diamond formed in the deep mantle.
The second half of the speaker session started withMandy Krebs (GIA, New York), who showed the application of Sr-Pb isotope data to colored gemstones’ country-oforigin determination. The analyses were done by thermal
ionization mass spectrometry (TIMS) to precisely measure
the Sr-Pb isotope compositions in gem corundum for the
first time. The separation is promising for certain sources
but less so for others. Rachelle Turnier (University of Wisconsin-Madison) used Raman spectroscopy to evaluate thedepth of zircon inclusion formation. These zircons are inclusions in corundum sourced from different deposits. Her
study is based on an ideal linear upshift of Raman band of
zircon with increasing pressure. However, many other factors can influence this ideal situation, such as radiation
damage, stress, and internal heterogeneity. With carefulconsideration of these influencing factors, using Raman asa zircon barometer can help to distinguish corundum fromvarious sources. William Nachlas (Syracuse University) presented the three different formation mechanisms for rutilated quartz. These include the overgrowth/entrapment
mechanism, the precipitation mechanism, and the grainboundary migration mechanism, each with different relative timing of quartz and rutile growth. All three mechanisms were reproduced with well-designed experiments.

Meeting of the International Mineralogical Association.
The 22nd meeting of the International Mineralogical Association (IMA), the first held in Australia and only the second in the Southern Hemisphere, took place in the
Melbourne Convention and Exhibition Centre August 13–
17, 2018. The meeting was hosted by the Geological Society of Australia.
Two technical sessions on gems were presented toabout 100 attendees. The August 13 session, “Sciences Behind Gemstone Treatments,” was chaired by Andy Shen
(China University of Geosciences, Wuhan) and Pornsawat
Wathanakul (Gem and Jewelry Institute of Thailand). The
second day’s session, titled “Recent Advances in Our Understanding of Gem Minerals” and led by Ian Graham(University of New South Wales, Australia), Lee Groat(University of British Columbia, Canada), and Gaston Giuliani (University of Lorraine, France), is detailed below.
The session consisted of 18 oral presentations covering
several gem topics. Frederick Sutherland (Australian Museum, Sydney) opened with a keynote talk on the diversity
in the geochemistry and inclusions of ruby from Myanmar
and eastern Australia. He also discussed the ages of rubyformation through zircon ages and the P-T conditions
through inclusion assemblages.
The other talks concerned different types of gems fromsupergene minerals up to corundum and spinel, including
mining discoveries and activities from ancient and modern

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Figure 31. Presenters, guests, and advocates from the GSA poster and speaker sessions. Left to right: Peter Heaney,
Dona Dirlam, Mandy Krebs, Richard Berg, Mike Breeding, Jim Shigley, Tingting Gu, Tyler Sundell, Rachelle Turnier,Nancy McMillan, Evan Smith, Chunhui Zhou, Barbara Dutrow, and Sally Eaton-Magaña. Photo by Tao Hsu.

ages. Ruslan Kostov (Sofia University of Mining and Geology, Bulgaria) presented the archeological mineralogy of theBalkans through prehistoric (7 to 5 million BCE) gem minerals (nephrite, jadeite, talc, gabbros, jasper, and turquoise)and gold. Lee Groat revealed recent advances in colored
gemstones in Canada, focusing on emerald from Yukon
and blue spinel, sapphire, and scapolite from Baffin Island,
as well as the use of different techniques such as drones for
exploration. Peter Lyckberg (Luxembourg) offered a detailed state-of-the art presentation on the mining of gem
pegmatites in Afghanistan and Pakistan, with amazing
photos of aquamarine, kunzite, indicolite, and spessartine
crystals from deposits in the High Karakoram range. Wim
Vertriest (GIA, Bangkok) discussed the dynamics of gemstone discoveries and the challenges for research on thebasis of timing the life of a deposit and the market perception of the gems’ quality.
Different techniques for source determination of gems
were also presented. Hao Wang (SSEF, Basel, Switzerland)
related the advances in origin determination for gems
using inductively coupled plasma time-of-flight (ICP-TOF)
spectroscopy, with applications for blue sapphires andemeralds. Zhiqing Zhang (China University of Geosciences, Wuhan) used Fourier-transform infrared (FTIR)
characteristics of amber from different areas of the world
for origin determination. Allan Pring (Flinders University,
Adelaide, Australia) related the use of multiple techniqueson 200 opal samples of various origins, showing their similarities and differences. Kemela Wijayanti (Padjadjaran
University, Indonesia) combined petrographic analysis
with scanning electron microscopy (SEM) and X-ray fluorescence (XRF) techniques to characterize green jasperfrom southern Java. Peter Downes (Western AustralianMuseum, Perth) applied multiple techniques on variscite
and associated phosphate minerals from the Mt. Deverell
deposits in the Gascoyne region of Western Australia. Isabella Pignatelli (University of Lorraine) reported on the useof electron microprobe analysis, SEM, and X-ray tomographic images for characterizing trapiche ruby from Luc
Yen in northern Vietnam.
New studies combining fieldwork with mineralogy andgeochemistry were presented for several types of gems.
Philippe Belley (University of British Columbia) discussed
advances in trace-element fingerprinting for blue spinel
and new insights into the origin of cobalt-blue spinel from
Baffin Island in Canada. This author gave an update on gem
demantoid garnet from Madagascar’s Antetezambato deposit, based on new field data, and geochemical analysis of
the most important demantoid deposits worldwide. Simon
Pecover (Pan Gem Resources) coupled tectonic, hydrodynamic, rheologic, and shear-induced crystallization
processes in the formation of opal veins in Australia, showing that the genetic model for the formation of Australian
opal is more complex than previously known. Ahmadjan

GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2018465

Abduriyim (Tokyo Gem Science) used the U/Pb methodon zircon inclusions for determining the formation ages ofsapphires from the New England fields in New South
Wales. Kandy Wang (University of New South Wales) presented data obtained on ruby from Paranesti, Greece, specifying the geographic typing of ruby via oxygen isotopes
and trace elements. Nick Raffan, also of the University of
New South Wales, combined fieldwork with remote sensing, petrographic analysis, and SEM to decipher the sourceof sapphires near tertiary volcanic plugs and Devonian conglomerates from Tomahawk Creek in central Queensland.
Ian Graham related the presence of unusual alluvial sapphires from Orosmayo in Argentina using a multi-analytical approach to uncover their origin.
This session was followed by an evening meeting at the
Gemmological Association of Australia (GAA) House in
Melbourne, under the direction of Margaret Blood, president of the GAA’s Victorian Division, and organized byAndy Shen and Pornsawat Wathanakul. The meeting was
open to all researchers who participated in the two gem
sessions of IMA and to Australian gemologists. The meeting consisted of three hour-long talks by this author on
Colombian emeralds, Lee Groat on spinel and sapphirefrom Baffin Island, and Brendan Laurs (Journal of Gemmology) on pegmatites of Namibia.

Chicago Responsible Jewelry Conference. Held October 21
and 22 at Cinema Row, the Chicago Responsible Jewelry
Conference drew 200 attendees who heard industry experts
discuss safe, sustainable, ethical gem production and jewelry design.
Friday’s session opened with a keynote address byMark Hanna (Richline Group). “Our vision is the creationand maintenance of a responsible, worldwide supply chainthat promotes trust in the global fine jewelry industry,”
Hanna announced. He discussed the ways blockchain
technology is allowing for greater mine-to-market transparency. While there are communication and efficiency issues, as the various blockchains do not yet interact,open-source tracking does seem to be the wave of the future. Following Hanna’s presentation, Rolberto Alvarez ofColombia’s Mina Gualconda reported on the gold mine’s
transformation from a manual operation with mercury extraction (1974–2001) to an environmentally conscious,
Fairmined-branded enterprise, supporting 12 families andusing zero mercury.
Eric Braunwart (Columbia Gem House) moderated thefirst of several panels held during the conference. A groupof gem cutters, representing four continents, discussed locale-based challenges that included the costs of replacing
broken equipment, a lack of cutting knowledge and experience among locals, and recent restrictions on exporting
rough from countries such as Tanzania. Panelists observedthat clients also want corporate social responsibility (CSR)
efforts to extend to cutters and reiterated what has been
said at similar gatherings: The art of cutting involves morethan just faceting a stone. Often cutters say the stones“speak” to them, telling them where to begin and end. The
storytelling that has become part of the jewelry industry’s
outreach to customers should include tales of the cut as
well.
Day one ended with the work of sustainability consultants The Dragonfly Initiative (TDI), which has developed
the Coloured Gemstone Working Group (CGWG) to support the communities impacted by the colored gems sector. TDI’s Sarah Caven posed the question: “Things are not
perfect, and we can maybe never get perfection, but what
can we do to improve transparency and do a better job inthe supply chains?” She explained that the CGWG has created due diligence systems that are adaptable for everything from micro-businesses to large corporations, withcommitments from 12 major luxury jewelry brands. With
corporate partnerships, TDI has also launched artisanal andsmall-scale mining projects in Tanzania, Uganda, Kenya,
and Brazil. Brian Cook (Nature’s Geometry) spoke of his
work as a consultant for TDI, investigating the financial
records and environmental reclamation efforts of alluvial
mining sites in Brazil. He also provided updates on the rutilated golden quartz community he established in Brazil’s
Bahia State.
The first day also featured the premiere of River ofGold, a documentary on illegal gold mining in the Amazon
rainforest. The film shows the environmental devastationand human corruption that results from this form of gold
exploitation. After the screening, sustainable jewelry consultant Christina Miller moderated a Q&A session withproducer Sarah DuPont, joined by Susan Egan Keane (Natural Resources Defense Council) and Nigel Pitman (The
Field Museum).
Day two opened with a panel in which jewelry designers
described how they began working ethically sourced material. Moderated by jewelry designer and metalsmith Alexandra Hart, panelists told of humble beginnings in the
responsible sourcing sphere; Helene Grassin (Paulette à Bicyclette) recalled sharing casting trees with other likeminded Parisian designers in order to afford the cost of
ethically mined gold. The designers noted that their clientele know how to find them and were adamant about balancing bad news with transparency: If the customer cannot
be told honestly that their materials are ethically sourced,
they will often select a different metal or gemstone. They
shared a desire to reach out to independent ethical, environmentally responsible gem suppliers so that designers
and suppliers could join together to create a remarkable
story for clientele. As one panelist stated, “We are the pioneers of creating these relationships.”
Joanne Lebert (Impact) used a case study from the Democratic Republic of the Congo to explain how Impact believes ASM activity should operate. Borrowing the466

GEMS & GEMOLOGY

Gaston Giuliani
University of Lorraine, France

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WINTER 2018

Reagan-era dictum “Trust, but verify” allows the gemstoneor jewelry piece’s story to be told honestly and ethically.
The Clinton campaign mantra “It’s the economy, stupid!”reminds us that producers along the supply chain should beseen as economic actors who have a stake—and a final impact—on the material. Finally, Lebert’s assertion that
Obama focused on the good of the community as a whole
reminds us that men and women in the mining and cutting
sectors benefit differently from CSR efforts, a point examined further by the next speaker. Glenn Lehrer (ColourfulLife Foundation) discussed the importance of giving backto communities that produce and work in the gem and jewelry industry. While the foundation is working in gem communities around the world, Lehrer focused on the schools
it has opened for low-income children in Jaipur, India.
Mothers of the children attending Colourful Life schools
were provided with faceting training to prepare them for
Jaipur’s workforce. He was surprised to learn that the
women rejected at-home training and workshop equipment. Going to school and work was a form of dignity forthem, whereas Western workers often prefer the convenience of working remotely.
The last panel of the conference, moderated by Monica
Stephenson (Anza Gems and iDazzle) focused on artisanalmining. Panelists recounted their personal experiences,challenges, and triumphs in the mining sector. Among the
speakers was Salma Kundi, a tourmaline miner from Tanga,
Tanzania, and secretary general of Tanzanian Women’s
Mining Association (TAWOMA); her group was involved in
the Pact/GIA guidebook project (see below). Where Kundi
comes from, a miner pays for a concession and a license andexploits the deposit with assistance. A mining license costs
about US$400, a high price for a woman, and that does notcover mining and food expenses. Membership in TAWOMA
allows for collective mining, enabling women to pay for licenses. Other challenges include a need to reach buyers beyond their local markets.
Robert Weldon spoke about GIA’s collaboration with
Washington, DC–based NGO Pact to create and distributea rough gem guidebook among Tanzanian miners (Summer
2018 GNI, pp. 245–246). Since early 2017, GIA and Pact
have provided training with the Swahili-language guidebook, which is accompanied by a tray for sorting gemstones
using reflected and transmitted light. Follow-up surveys revealed a $12 social return on investment for every $1 invested in the program. As of October 2018, the guidebook
has reached approximately 1,000 Tanzanian miners. The
final speaker of the day, Yianni Melas (The Gem Explorer),
recounted his experiences as a human rights advocate forgem and jewelry laborers, including a recent 31-day hunger
strike that made international headlines.
Both days also featured a gem boutique, with information on ventures and gemstones available for sale. There
were also optional lunch sessions that elaborated on topics
that will affect the industry’s future, such as the Jewelry
Development Index, the flagship project of the Universityof Delaware’s “Mines, Minerals and Society” program; theMercury-Free Mining Challenge; and TrustChain, a collaboration between industry leaders and IBM to create ablockchain solution. As Mark Hanna said in opening theconference, “The challenge of our unknown future is somuch more exciting than the stories of our accomplishedpast.”The 2019 Chicago Responsible Jewelry Conference isslated for Friday, October 25 and Saturday, October 26.

GEM NEWS INTERNATIONALGEMS & GEMOLOGY

Jennifer-Lynn Archuleta
GIA, Carlsbad
Second World Emerald Symposium. Hosted by Fedesmeraldas (the Colombian Emerald Federation), Acodes (theEmerald Exporter Association), Aprecol (the Emerald Producers Association), Asocoemeral (the Emerald Dealers Association), and Minminas (the Ministry of Mines), thesecond World Emerald Symposium was held in Bogotá October 12–14, 2018.
The inaugural event in 2015 was themed “Be part ofthe change.” Three years later, the emphasis was on sustainability, blockchain, nanotechnology, and traceability.
Does the community share the benefit from the companies? The future of the emerald industry should develop
with the local communities through education, improving
health care and working conditions. These questions/keywords were among the important topics expressed during
this second edition of the symposium.
More than 60 Colombian and international speakers
and panelists presented a wide variety of topics such as
gemology, ethics, government, stakeholders, and marketing before a large audience from around the world and representing all levels in the emerald industry.
Day one began with opening talks by Colombian officials, symposium organizers, and presidents of gem andjewelry associations (ICA, CIBJO, and AGTA). This wasfollowed by geology and mining sessions. Gaston Giuliani(IRD, CRPG, Nancy, France) again offered an exciting talkon world emerald deposits in the 21st century, assessing
current knowledge, types of deposit, and exploration. Lee
Groat (University of British Columbia, Vancouver) spokeon emerald occurrences in Canada’s Yukon Territory andthe challenges for exploration and exploitation. Gian Carlo
Parodi (National Museum of Natural History, Paris) reviewed the species and varieties of the beryl group andshared photos of various rare collector specimens such as
stoppaniite and bazzite.
In the afternoon session on gemology, Gabriel Angarita(CDTEC Gemlab, Bogotá) introduced a new treatment for
emeralds coming onto the market called “Naturalys.” Hecompared it to traditional oil treatment or resin and described its identification. Taijin Lu (NGTC, Beijing) discussed the recently formed Chinese national standard on
emerald grading. Vincent Pardieu (DANAT, Bahrain) spokeon emerald from Madagascar and presented a well-made

WINTER 2018467

video from his most recent field expedition to Madagascar.
Olivier Segura (L'École des Arts Joailliers, Paris) presented
the school, which is supported by Van Cleef & Arpels, andits rich variety of classes such as jewelry history, gouachetechniques, setting, gemology, and more.
Andy Lucas (Guild Gemlab, Shenzhen) talked about educating Chinese consumers on colored gemstones andChina’s potential as a luxury jewelry market. He concluded
by introducing the new education programs offered by the
Guild Institute of Gemology. Alan Hart (Gem-A, London)
reviewed the association’s heritage and long history. He
also presented Gem-A resources such as its library, theJournal of Gemmology, and traditional education andalumni activities across the world.
This first day ended with two panel discussions, with
Ronald Ringsrud and Shane McClure moderating thefirst. Laurent Cartier (SSEF, Basel), Gagan Choudhary(GTL, Jaipur), Rodrigo Giraldo (RGLAB, Bogotá), and Aurélien Delaunay (LFG, Paris) discussed laboratory reports
on emerald treatments and the difficulties in determining
the degree of enhancement. Is it a subjective call? Is afinding of minor, moderate, or significant enhancement
sufficient, or would the addition of more degrees of enhancement on the reports be more accurate and benefit
the industry? These were among the questions exchanged.
A second panel on gemology and origin (figure 32) was
led by Shane McClure with panelists Kenneth Scarratt(DANAT), Taijin Lu (NGTC), and Claudio Milisenda(DSEF German Gem Lab). The group offered a frank dis-cussion of many critical issues on country of origin determination. They also shared the difficulties gem labs encounter in building a reliable dataset to support country oforigin determination. Potential solutions were also proposed.
The second day emphasized stakeholders’ social responsibility, ethics, and marketing. The day began with speakers
from mining companies. Assheton Carter (The Dragonfly
Initiative), Rosie Perkins (FURA Gems), German Forero(Santa Rosa), and Elena Basaglia (Gemfields) talked about
their respective projects on sustainability and developmentof social programs to support local communities. Projects
included modernizing the mines, developing schools, andimplementing health care systems. Independent consultant
Gerardo Vargas concluded the session by discussing the importance of appellation of origin for Colombian emeralds
and how it would benefit and protect the market, increasevalue, develop the industry, and give recognition to Colombian emeralds.
After the lunch break, the session continued with Prida
Tiasuwan (Pranda Group) who offered insight on Thailand’s gem and jewelry industry and its potential as a global
gem and jewelry hub. Pointing at the duty-free, tax-free,and non-VAT trading system for gemstones, he talked
about Thailand as a major center for colored stone education, cutting, manufacturing, and treatment.
Zhao Xin Hua presented information on the Gemstone
Association of China and shared data and statistics on the
Chinese colored gem market. Liu Yi (GAGCC) talked
about the gem and jewelry investment hub opportunities

Figure 32. GIA’s Shane
McClure led the discussion panel on countryof origin. Joining him,from left to right, wereKenneth Scarratt, Taijin Lu, and Claudio
Milisenda. Photo by
Tao Hsu.

468

GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2018

Crowningshieldite

Magnesioferrite
1 mmGraphite

Figure 33. Left: A diamond sample from the Letšeng mine in Lesotho that contains the newly recognized mineralcrowningshieldite, in the area circled in red. Right: Electron microscopy reveals individual grains of crowningshieldite in a fine-grained mixture with other minerals. Photos by Evan M. Smith (left) and Fabrizio Nestola (right).

with China. Next, Laurent Cartier (Gemstones and Sustainable Development Knowledge Hub) explained the organization’s work and discussed the challenges regarding
artisanal mining, short-life deposits, stock management,
and consideration of quality over origin.
The last session was devoted to ethics and corporate social responsibility. Cathlijne Klomp (LVMH) spoke about responsible sourcing of colored gemstones as well as thechallenges and opportunities for creating sustainable value.
Next, Charles Chaussepied (Responsible Jewellery Council)
explained the RJC’s history, role, and mission. This last session was by a panel discussion regarding certifications with
Edwin Molina (APRECOL) and Charles Burgess (Muzo
MTC).
Day three was a half-day exploration of history. Independent jewelry specialist Joanna Hardy spoke on the
Colombian emerald pocket watch from the Cheapside
Hoard, the emerald and diamond parure of Empress MarieLouise of France, and many other important antique emerald jewels. Ronald Ringsrud followed with morestorytelling about people, miners, and emerald adventures.
Ioannis Alexandris (Gemolithos) covered the magnificent
Old Mine emeralds, historical jewelry featuring Colombian
emeralds, and record-breaking auction sales. Gerard Martayan (Schlumberger) reviewed the rediscovery of the fascinating Chivor emerald mine.

Closing keynote addresses by Shri Pramon Agrawal(GJEPC), Carlos Amaya (governor of Boyacá), and Oscar Baquero (Fedesmeraldas) concluded the 2nd World Emerald
Symposium.

GEM NEWS INTERNATIONALGEMS & GEMOLOGY

Jonathan Muyal and Tao Hsu
GIA, Carlsbad

ANNOUNCEMENT
Crowningshieldite: A new mineral. GIA, in collaboration
with researchers at the University of Padova, recently discovered crowningshieldite (figure 33), a new mineral
named in honor of G. Robert Crowningshield (1919–2006),
a pioneering researcher at GIA for more than 50 years. His
many landmark contributions included the detection ofirradiated diamonds, the initial report on General Electric’s facet-quality synthetic diamonds, and the description of “padparadscha” sapphire’s orangy pink to pinkishorange color. Crowningshieldite is a nickel sulfide mineralwith a hexagonal crystal structure and can be regarded as
the high-temperature polymorph of the mineral millerite.
Discovered as an altered inclusion in two diamonds fromthe Letšeng mine in Lesotho, it was accepted as a mineralon September 18, 2018, by the International Mineralogical
Association.

WINTER 2018

469

2018

CONGRATULATIONSThis year, hundreds of readers participated in the 2018 Gems & Gemology
Challenge. Entries arrived from around the world as readers tested their gemological knowledge by answering questions listed in the Spring 2018 issue. Those
who earned a score of 75% or better received a GIA Certificate of Completion
recognizing their achievement. The participants who scored a perfect 100% arelisted below.

G&G Challenge Winners
Australia

United States

Barbara Wodecki

Kenneth Fogelberg

Michael Merritt

BelarusDmitry Stepanenko

FranceSylvie Jacquot

Robert Campbell
Lois A. Henning
Douglas Kennedy
Paul Mattlin
Lisa Neely
Geraldine M. Vest
Ryan Waddell
Colleen Walsh
Kate Waterman
Jana White
Alvin Zimmer

Answers

See pages 54–55 of the Spring 2018 issue for the questions.
1 (d), 2 (a), 3 (a), 4 (b), 5 (c), 6 (a), 7 (d), 8 (a), 9 (b), 10 (c), 11 (d), 12 (a), 13 (b), 14(b), 15 (a), 16 (a), 17 (d), 18 (a), 19 (b), 20 (c), 21 (a), 22 (d), 23 (b), 24 (d), 25 (a)470

CHALLENGE WINNERS

GEMS & GEMOLOGYWINTER 2018M ICRO -F EATURES OF D IAMOND
TreatedSynthetic

NaturalThis cleavage crack shows a bright green “flash effect” when observed
subparallel to the plane of the break against a bright background. This isdiagnostic of clarity enhancement in diamonds. Field of view 3.20 mm.

“Lizard skin” results from polishing a facet that lies nearly parallel to theoctahedral face, which is the hardest crystal direction in diamond. Fieldof view 0.72 mm.

This bright green chromian diopside crystal proves that the host diamond is of peridotitic origin. Field of view 1.33 mm.

Interlocking grains with different crystallographic orientations show
undercutting in this polycrystalline diamond. Field of view 2.88 mm.

An olivine crystal inclusion in diamond shows high-order birefringent
colors in cross-polarized light. Field of view 2.00 mm.

De Beers’ line of CVD laboratory-grown diamonds can be easily recognized by the 300 × 300 micron logo inscribed about 200 microns below
the surface of the table facet.

The pavilion of this diamond was covered with an ultra-thin coatingthat is responsible for the stone’s pink color. The coating is heavily
abraded along facet junctions. Field of view 1.92 mm.

A diamond crystal inclusion in a diamond host is often nearly invisible,
but cross-polarized light reveals significant strain between the inclusion
and host. Field of view 1.36 mm.

This diamond has an octahedral hydrogen cloud in its core. The cloudshows strong yellow fluorescence under long-wave ultraviolet light.
Field of view 5.00 mm.

This differential interference contrast image shows square-shaped
stepped etching along the cube faces of a rough diamond crystal. Fieldof view 2.88 mm.

This negative crystal resulted from partial dissolution and contains a loose
diamond that rattles around in the cavity. It was stained green by radioactive fluids that were present in the host rock. Field of view 4.36 mm.

This HPHT-grown yellow diamond contains large iron-nickel flux inclusions. Graining and colorless zones are also present. Field of view
2.30 mm.

Due to the difficulty of detecting some treatments, such as HPHT
processing, some gemological labs inscribe an indication of treatment on the stone’s girdle. Field of view 2.01 mm.

Rainbow graining, rarely seen in diamonds, results from planar structuraldefects that lead to the vibrant colors seen here. Field of view 1.90 mm.

Sometimes thought to be “carbon spots,” these chromite crystals reveal
their identity by showing orangy brown coloration on thin edges. Fieldof view 2.10 mm.

Sapphires, one of the rarest inclusions encountered in diamond, suggest
an eclogitic origin. Field of view 0.99 mm.

The dense light-scattering accumulations of particles known as hydrogen clouds, which lie along phantom planes in this diamond, produce
a “Maltese cross” pattern. Field of view 6.39 mm.

The girdle may contain information showing that a diamond is manmade, as seen here using differential interference contrast. Field ofview 1.44 mm.

The “umbrella effect” seen here results from cyclotron treatment along
the culet area of a diamond and is diagnostic of artificial irradiationinduced color. Field of view 3.50 mm.

Bright purplish pink chromian garnets are a relatively common type ofcolored inclusion in gem diamonds and indicate peridotitic origin. Fieldof view 1.99 mm.

This unique diamond is host to numerous stellate clouds, which are rarely
seen in such high density in a single stone. Field of view 0.72 mm.

This network of cleavage cracks, seen in a pink diamond with polarized
light, reveals weakness along octahedral planes. Field of view 0.61 mm.

Some of the most recognizable features on the surface of rough diamond crystals are the triangular etch features, known as trigons, that lie
on the octahedral faces. Field of view 1.20 mm.

This flux-grown laboratory-grown diamond contains a large flux-filled
negative crystal. Field of view 1.44 mm.

Internal laser drilling is a technique used to open a cleavage crack neardark inclusions to allow bleaching solutions to enter. Instead of a typicaldrill hole, this treatment is characterized by irregular, wormhole-like channels. Field of view 1.91 mm.

This rare bimineralic inclusion consists of a grayish green omphacite
crystal and a pyrope-almandine garnet. The presence of these minerals
indicates an eclogitic origin. Field of view 1.22 mm.

Deep green radiation staining on the surface of this diamond likely
resulted from radioactive materials deposited by groundwater along theinterface of the diamond crystal and host rock. Field of view 2.40 mm.

This bright blue kyanite crystal is a rare sight in a faceted diamond. The
presence of kyanite suggests that this diamond is from an eclogitic environment. Field of view 2.18 mm.

Thin etch tubes allowed radioactive material to enter the host diamond, causing localized brown radiation halos. Field of view 1.03 mm.

Black carbon inclusions that stand out in high relief are occasionallyseen in CVD-grown diamonds. Field of view 1.42 mm.

This chart contains a selection of photomicrographs of natural, synthetic, and treated diamonds. It is by no meanscomprehensive. The images show the appearance of numerous features a gemologist might observe when viewing
diamonds with a microscope.

Published in conjunction with Nathan D. Renfro, John I. Koivula, Jonathan Muyal, Shane F. McClure, Kevin Schumacher, and James E. Shigley (2018),“Inclusions in Natural, Synthetic, and Treated Diamond,” Gems & Gemology, Vol. 54, No. 4, pp. 428–429. Photomicrographs by Nathan D. Renfro,
John I. Koivula, Jonathan Muyal, and Shane F. McClure.

© 2019 Gemological Institute of America