WINTER 2017
VOLUME LIII

THE QUARTERLY JOURNAL OF THE GEMOLOGICAL INSTITUTE OF AMERICA

Large Cullinan-Like Diamonds with aSuperdeep Origin
The Dreher Family of Gem Carvers
Akoya Cultured Pearls from Australia
A Chart of Ruby Inclusions

Winter 2017
VOLUME 53, No. 4

EDITORIAL
387

The World’s Biggest Diamonds: Windows into the Earth’s Deep Mantle
Duncan Pay

FEATURE ARTICLES
388

The Very Deep Origin of the World’s Biggest Diamonds
Evan M. Smith, Steven B. Shirey, and Wuyi Wang
Explores an exceptional family of diamonds, referred to as “CLIPPIR” (Cullinan-like, Large,
Inclusion-Poor, Pure, Irregular, and Resorbed), that formed in a superdeep environment.

pg. 389404

Gem Virtuosos: The Drehers and Their Extraordinary Carvings
Robert Weldon, Cathleen Jonathan, and Rose Tozer
Examines the artistic heritage of the Drehers, an influential family of gem carvers in IdarOberstein, Germany.

423

Akoya Cultured Pearl Farming in Eastern Australia
Laura M. Otter, Oluwatoosin B. A. Agbaje, Le Thi-Thu Huong,
Tobias Häger, and Dorrit E. Jacob
Characterizes the akoya cultured pearls produced on the eastern shoreline of Australia using
native Pinctada imbricata fucata mollusks.

pg. 417

NOTES & NEW TECHNIQUES
438

Accurate Reporting of Key Trace Elements in Ruby and Sapphire Using
Matrix-Matched Standards
Jennifer Stone-Sundberg, Timothy Thomas, Ziyin Sun, Yunbin Guan, Zachary Cole,
Randy Equall, and John L. Emmett
Presents a group of corundum standards developed by GIA to improve the accuracy andefficiency of its laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS)
instruments.

pg. 426

452

Real-Time Microradiography of Pearls: A Comparison Between Detectors
Stefanos Karampelas, Abeer Tawfeeq Al-Alawi, and Ali Al-Attawi
Compares the image quality provided by real-time microradiographic imaging (RTX) units
fitted with two different detectors: an image intensifier (II) and a flat panel detector (FPD).

CHARTS
457

Inclusions in Natural, Synthetic, and Treated Ruby
Nathan 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 rubies.

pg. 457

REGULAR FEATURES
459

Lab Notes
Cat’s-eye alexandrite with unique inclusion pattern • Lizard skin on deformed diamond• Gota de aceite in a Zambian emerald • Dyed quartzite imitation of ruby-in-zoisite• Synthetic moissanite imitating rough diamond • Two natural sapphires with synthetic
ruby overgrowth466

G&G Micro-World
Aragonite spheres in Ethiopian opal • Twinned calcite inclusion in Burmese ruby• Phenomenal feldspar with iridescent inclusions • Yellow fluid inclusions in red Burmese
spinel • Tourmaline crystals on Burmese ruby • Vesuvianite crystal in ruby • Wollastonite
blizzard in manufactured glass beads • Quarterly crystal: Shattuckite in quartz

pg. 470

472

Gem News International
Facet-grade ruby from Tanzania • Fiftieth anniversary of tsavorite discovery • New azuritemalachite mixture from Peru • Type IIa diamonds with strong phosphorescence • Unusual
growth structure in black diamond • Update on the Foxfire diamond • Coated beryl
imitating emerald • Filled freshwater cultured pearl • Update on dyed hydrophane opal
• Conference reports • Peter J. Dunn (1942–2017) • Errata

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About the Cover
The rough diamond shown on the cover, the 812 ct Constellation, was recovered from the Karowe mine in Botswanain November 2015. It is currently the sixth-largest gem-quality rough diamond ever recorded. It was sold in May 2016
for $63.1 million, the highest price paid for a rough diamond to date. The size, near absence of inclusions, low nitrogen content, shape, and surface texture place it in a special variety known as CLIPPIR diamonds, which are reviewed
in the lead article in this issue. Diamonds such as the Constellation, which grow in a geologically distinct way, convey valuable information about the earth’s deep mantle. Photo by Jian Xin (Jae) Liao.
Printing is by L+L Printers, Carlsbad, CA.
GIA World Headquarters The Robert Mouawad Campus 5345 Armada Drive Carlsbad, CA 92008 USA© 2017 Gemological Institute of America
All rights reserved.
ISSN 0016-626X

The World’s Biggest Diamonds:
Windows into the Earth’s Deep Mantle
For geoscientists and gemologists alike, the origins of large, high-clarity, and relatively purediamonds, like the Cullinan and the 812.77 ct Constellation on the cover of this issue, have long
been an enigma. In a December 2016 Science article, a team of researchers led by GIA’s Dr. Evan
Smith provided important insights into how these rare and extraordinary gems form deep in theearth’s mantle. That article presented evidence that such Cullinan-like, nitrogen-poor “CLIPPIR”
diamonds contain high-pressure mineral inclusions that are only stable at depths of 360–750 km(approximately 225–465 miles). By contrast, the bulk of gem-quality diamonds form in the base ofcontinental tectonic plates at depths of 150–200 km (95 to 125 miles). Inclusion-bearing CLIPPIR
diamonds constitute only 1 in 10,000 of thosesubmitted to GIA’s laboratories. The inclusions Natural diamonds are science’s best tools
these big diamonds carry—iron-nickel metal
for understanding the depths of the earth.
with minor sulfur and carbon—truly are awindow into the earth’s deeper mantle. In our lead paper, Evan Smith and Wuyi Wang partner with
Steven B. Shirey of the Carnegie Institution for Science to build on the landmark Science article. They provide moredetail on the key features of these remarkable diamonds as well as data on additional samples.
Our second paper, by Robert Weldon, Cathleen Jonathan, and Rose Tozer of GIA’s Richard T. Liddicoat Library,
explores the astonishing work of a multigenerational family of gem carvers: the Drehers of Idar-Oberstein, Germany.
The authors focus on the contemporary craft of Gerd Dreher and his son, Patrick, artisans with an unerring ability tochannel the spirit of the animals they model from high-quality rough gem minerals and richly patterned agates.
In our third paper, Laura Otter, Oluwatoosin Agbaje, Le Thi-Thu Huong, Tobias Häger, and Dorrit Jacob present thefirst gemological characterization of Australian akoya cultured pearls using Raman, photoluminescence, FTIR, andUV-Vis spectroscopy. Unlike many other akoyas, these Australian examples are marketed without any post-harvest
treatments involving dyes or bleaches.
Next, Jennifer Stone-Sundberg, Timothy Thomas, Ziyin Sun, Yunbin Guan, Zachary Cole, Randy Equall, and John
Emmett introduce a set of new reference standards designed to improve the quality of trace element analysis in rubyand sapphire. These standards use corundum substrates rather than the typical silicate glasses produced by the
National Institutes of Standards and Technology (NIST). This important paper documents the development of
corundum sets with precisely known levels of beryllium, magnesium, titanium, silicon, vanadium, chromium, iron,and gallium using secondary ion mass spectrometry (SIMS).
Stefanos Karampelas, Abeer Tawfeeq Al-Alawi, and Ali Al-Attawi provide a comparison of real-time X-ray microradiography (RTX) units fitted with different detectors. Their analysis demonstrates the superior resolving power of aflat panel detector (FPD) over an image intensifier (II) for interpreting fine detail in a pearl’s internal growth structure.
And to complement our emerald and sapphire charts from Winter 2016 and Summer 2017, we present a new one
featuring some characteristic internal features of natural, treated, and synthetic ruby. This chart
is from GIA’s team of inclusion specialists, led by Nathan Renfro and John Koivula.
As always, there’s something for every gemological taste in our Lab Notes, Gem NewsInternational, and Micro-World sections.
Finally, I encourage you to join us for the 2018 GIA Symposium, October 7–9 in Carlsbad,
California. This promises to be an unforgettable learning and networking event. You canregister to attend or submit an abstract for an oral or poster presentation at
symposium.gia.edu.
The Constellation diamond, with a maximum widthof 64 mm, is shown beside a 1 ct round brilliant.
Photo by Jian Xin (Jae) Liao.

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

EDITORIALGEMS & GEMOLOGYWINTER 2017387

FEATURE ARTICLESTHE VERY DEEP ORIGIN OF THE
WORLD’S BIGGEST DIAMONDS
Evan M. Smith, Steven B. Shirey, and Wuyi Wang

Large and relatively pure diamonds like the historic 3,106 ct Cullinan, found in South Africa in 1905,
have long been regarded as unusual based on their physical characteristics. For example, they often exhibit exceptional color and clarity, while routinely qualifying as type IIa, a rare designation of chemical
purity. A new research discovery about these Cullinan-like diamonds is that they contain heretofore unknown, deeply derived inclusions that originate below the continental mantle keel and are thus known
as “superdeep” diamonds (Smith et al., 2016). Originating from a depth between 360 and 750 km, they
reveal information about the conditions within the convecting mantle, beneath the earth’s rigid tectonic
plates. Here we review the previously published findings, compare the Cullinan-like diamonds to themore abundant lithospheric diamond population, and offer evidence from some additional diamondsamples that further verifies their superdeep origin. Cullinan-like diamonds contain minute and rare silicate and iron-rich metallic inclusions surrounded by a fluid jacket composed of methane and hydrogen.
The inclusion compositions suggest that this deep mantle environment contains small pockets of oxygen-deficient metallic liquid out of which the diamonds crystallized. This new and unexpected observation made on the world’s most expensive diamonds is important for understanding the chemical
reactions between mineral assemblages in the deep earth. It shows that deep regions of the mantle contain metallic iron, as opposed to the shallower, more oxidized mantle rocks actively participating inplate tectonics and its associated volcanism.

Diamonds, besides being the most valuable
gemstones for jewelry, are some of the mostscientifically valuable samples of the deep
earth. Interpretation of their included minerals andcrystallization history provides a snapshot of otherwise inaccessible geological processes from morethan 100 kilometers underground and often from billions of years in the past (e.g., Shirey and Shigley,2013). No other mineral sample can provide information for research from such depths and from so longago. Until recently, exceptional gem diamonds suchas the famous Cullinan or Lesotho Promise, with aset of physical characteristics that distinguish themfrom other kinds of diamonds, were enigmatic andhad an unknown origin (Bowen et al., 2009; Gurneyand Helmstaedt, 2012; Moore, 2014). How did they
form? Certainly not like 99% of other gem dia-monds. New research carried out in the last two
years at GIA, the Carnegie Institution for Science,and the University of Padua reveals that these Cullinan-like diamonds form in a geologically special way,
involving metallic liquid and originating from extreme depths in Earth’s mantle well below that ofother gem diamonds (Smith et al., 2016).

RECOGNITION OF A NEW DIAMOND VARIETY

See end of article for About the Authors and Acknowledgments.
GEMS & GEMOLOGY, Vol. 53, No. 4, pp. 388–403,
http://dx.doi.org/10.5741/GEMS.53.4.388© 2017 Gemological Institute of America

As a family, these diamonds tend to be large, inclusion-poor, and relatively pure (usually type IIa), andin their rough state they are irregularly shaped andsignificantly resorbed (figure 1) (Bowen et al., 2009;
Gurney and Helmstaedt, 2012; Moore, 2014; Smithet al., 2016). These characteristics are combined in
the acronym “CLIPPIR” (Cullinan-like, Large, Inclusion-Poor, Pure, Irregular, and Resorbed). Figure 2
shows a broad dataset of assorted diamonds, where
the CLIPPIR population displays these characteristics. Among larger diamonds, there is a striking increase in the prevalence of D color grades and the
proportion of type IIa diamonds, chiefly due to their

388

GEMS & GEMOLOGYEXCEPTIONAL CULLINAN-LIKE DIAMONDSWINTER 2017

Figure 1. Rough CLIPPIR diamonds have physical features akin to the historic Cullinan diamond, which forms the“C” of the CLIPPIR acronym. The size distribution for this variety of diamond is skewed toward large sizes, withthe examples shown here ranging from 14 to 91 carats. In rough form, CLIPPIR diamonds are irregularly shaped
rather than well-formed crystals and sometimes appear to be broken fragments of once larger diamonds. Photo by
Robert Weldon/GIA; courtesy of Gem Diamonds Ltd.

lack of nitrogen. As expected, these larger type IIa diamonds have very few inclusions and consequently
high clarity grades.
Historically, it has been difficult to study these diamonds because of their rarity and high value as
gemstones; they simply cannot be purchased for indepth analysis on a research budget. It is only
through the research program of GIA, where thousands of high-quality gem diamonds were available
to be examined by non-destructive methods such as
Raman spectroscopy and X-ray diffraction, that theircommon inclusion paragenesis and hence their origin was revealed. Here we review in more detail the
key features of diamonds reported by Smith et al.
(2016) as well as some additional CLIPPIR samples
examined since.
An important key to the origin of these diamonds
lies in the special inclusions they contain, composedof iron-nickel metal with minor sulfur and carbon.
At the ambient pressure and temperature underwhich the CLIPPIR diamonds formed, these inclusions were metallic liquids. But now, under surface

conditions, they have cooled and crystallized to a distinctive, rarely seen mineral assemblage. This assemblage includes the rare mineral cohenite, an iron-richcarbide with the formula (Fe,Ni)3C, and the relatively
common iron sulfide mineral pyrrhotite.
Metallic iron-nickel alloy is thought to be createdand stabilized in parts of the deep mantle (Frost et al.,
2004; Rohrbach et al., 2007). Although the normal
amount of metal in these regions of the mantle islikely about 1% or less, it is expected to regulate andlimit the local activity of oxygen (Frost et al., 2004).
Oxygen availability is a key planetary parameter resulting from the earth’s large-scale geologic evolution(Rohrbach and Schmidt, 2011). It controls, along withtemperature and pressure, the basic mineral composition of the planet’s interior, how this varies withdepth, and the composition of melts generated. At
the pressure and temperature conditions near and at
Earth’s surface, rocks almost never contain metallic
iron. Also, these shallower rocks are affected by magmatism associated with plate tectonics and by interaction with Earth’s atmosphere and hydrosphere,

EXCEPTIONAL CULLINAN-LIKE DIAMONDSGEMS & GEMOLOGYWINTER 2017389

Prevalence of D color grade

Clarity grade distribution:
Largest 1000 of 3.5 million diamonds

Proportion of type IIa

1650

D color surpasses E
for larger diamonds

4

Type I

40
30

COUNT

8

% TYPE IIA

D/E RATIO

200
12

2.0

20

150

Type IIa

100
50

10

1.3 %
0

0

Sa
m
3. ple5 om f
di i l l i o
am n
on
La
ds
rg
es
La t 10rg00
e
La st 500rg
es
La t 1
rg 00
es
t5
0

c
2– t
3
c
3– t
4
c
4– t
5
5– ct
10
10 ct
–2
0
>2 ct
0
ct

1–
2

<1

ct

0

I3

I2

I1

SI2 SI1 VS2 VS1 V VS2 V VS1 IF

FL

Fewer inclusions/blemishes

Figure 2. Systematic deviations of properties suggest that CLIPPIR diamonds become more prevalent among largersized diamonds. Left: Diamonds over 5 carats show an increasing incidence of D color grades in a random sample
of 4.2 million diamonds graded by GIA; shown is the ratio of D color (colorless) to E color (not quite perfectly colorless) grades awarded. Center: In a similar dataset of 3.5 million samples, the proportion of type IIa diamonds (nitrogen-deficient, high-purity) also increases dramatically when considering only the larger diamonds. Right: Among a
set of large diamonds, all over 15 carats, those qualifying as type IIa have markedly higher clarity and dominate theflawless grade category. (GIA clarity abbreviations: FL = flawless, IF = internally flawless, VVS1/2 = very very slightly
included 1/2, VS1/2 = very slightly included 1/2, SI1/2 = slightly included 1/2, and I1/2/3 = included 1/2/3)

which occur at relatively oxidizing conditions. These
conditions completely mask the ambient conditionsin the earth’s deep interior, which can be revealed in
the mineralogy of CLIPPIR inclusions. It is coincidental but agreeably fitting that the world’s mostvaluable diamonds as gemstones have now taken on
exceptional scientific value.

Nitrogen is all around us every day, making up 78%of the air we breathe and forming an essential element for life on Earth. Nitrogen behavior inside theearth, especially in minerals and fluids deep in the
mantle, is less understood, but nitrogen is thought
to be recycled into the mantle by plate tectonic activity. In the mantle, it is an ingredient in the diamond-forming fluids for the most common
diamonds, known as type I. As such it is the mostabundant trace element in diamond, where it substitutes for carbon atoms in the crystal structure.
Since the advent of studies to understand the geological conditions for diamond growth and formation, diamonds have become one of the important
tools that can help geologists trace the deep cycling
and behavior of nitrogen.

The nitrogen content of diamond can vary greatly
for several reasons, including variable supply of nitrogen in diamond-forming fluids, variable partitioning
into the diamond, and variable partitioning into acompeting nitrogen-bearing phase. Diamonds with
no appreciable nitrogen-related absorption in the 800–
1400 cm–1 range in infrared spectroscopy are classically defined as type IIa (Wilks and Wilks, 1994). Notethat the abundance of nitrogen in diamond is a continuous range without a sharp division. The continuous range means that the 5–20 ppm nitrogenconcentration threshold that marks the boundary inclassification between type IIa (nitrogen-deficient) andtype I (nitrogen-bearing) has no basis in mineralogy
but rather is based on analytical sensitivity. Analytical sensitivity has shifted to lower thresholds overtime, as instrumentation has improved.
The type IIa designation of chemical purity is usually regarded as a desirable gemological trait that is
associated with high clarity and color, and it has
proven convenient for scientific classification of diamond (see review by Breeding and Shigley, 2009).
With one exception, the CLIPPIR diamonds of thisstudy are type IIa. The relationship between CLIPPIRand type IIa diamonds likely applies to larger unstudied populations, as shown by the disproportionate

390

GEMS & GEMOLOGYNITROGEN AND THE DISTINCTION BETWEENTYPE IIA AND CLIPPIR DIAMONDSEXCEPTIONAL CULLINAN-LIKE DIAMONDSWINTER 2017

number of large, high-quality diamonds that are typeIIa (figure 2). It is important to bear in mind, however,that not all type IIa diamonds are classified as CLIPPIR, and vice versa. Some lithospheric diamonds
from peridotitic and eclogitic host rocks, for example, can also have very low nitrogen concentrations
and be considered type IIa (e.g., Stachel and Harris,
2009; Gurney et al., 2010; Moore, 2014).

2013, in Moore, 2014). However, a search of the literature reveals that the only consistently reported inclusion is visually identified graphite. In fact, theCullinan diamond itself was described as having asmall round, black inclusion in the center, which
was intentionally bisected with the first cleave of therough diamond by Joseph Asscher in 1908 (Crookes,
1909). Of course, the finished Cullinan gemstones
are essentially flawless and free of inclusions (Scar-ratt and Shor, 2006). What few inclusions are to befound in rough CLIPPIR diamonds are usually eliminated during cutting and polishing, making thesearch for inclusions all the more difficult among
polished goods.
Our recent study (Smith et al., 2016), comprising atargeted subset from hundreds of thousands of faceted
diamonds as well as a small number of offcuts
trimmed from rough diamonds during cutting andfaceting, documented 53 inclusion-bearing CLIPPIR diamonds that establish a specific inclusion assemblage
that deviates from known lithospheric or sublithospheric suites. Thirty additional faceted stones havesince been studied and now yield observations on a
total of 83 diamonds, summarized in table 1 (see also
data supplement at www.gia.edu/gems-gemology/
winter-2017-worlds-biggest-diamonds; for methods,
see Smith et al., 2016). Past visual descriptions of inclusions in these types of diamonds mention flat,
black features, interpreted as graphite. Our work has
shown that these are graphitic rosette fractures thatsurround and sometimes conceal a much smaller
non-graphitic inclusion (figure 3) somewhat reminiscent of sulfide inclusions.
In the center of the black fractures, the inclusion
nucleus itself is different from that of a typical sulfide
inclusion. In contrast to lithospheric diamonds,
where black fracture rosettes are typically associatedwith sulfide inclusions, CLIPPIR diamonds haveblack fractures surrounding many inclusions, suchthat even silicates can have a superficial resemblance
to “common” sulfide inclusions (figure 4A; see also
figures S2 and S3 in Smith et al., 2016). The fractures
are likely due to the higher stresses that build up
around most superdeep inclusions when they are exhumed from the mantle.
The most common inclusion identified in CLIPPIR
diamonds is a metallic iron-nickel-carbon-sulfur mixture. While most of these inclusions can only be studied remotely through the diamond by Raman
spectroscopy, all inclusions that can be examined directly by other microanalytical techniques such as
scanning electron microscopy (SEM), electron microprobe analysis, and/or X-ray diffraction (XRD) are similar metallic Fe-Ni-C-S mixtures. In our experience,these metallic inclusions differ from sulfide inclusions,which also have metallic luster but are smoother, moreequant cuboctahedral shapes, isolated rather thangrouped, and far less magnetic. The sulfide inclusions
sometimes have brassy colors and identifiable sulfide
mineral Raman features, and they have not yet beenfound to have coexisting fluid. In contrast, the Fe-Ni-

EXCEPTIONAL CULLINAN-LIKE DIAMONDSGEMS & GEMOLOGYSOLIDIFIED IRON-NICKEL METAL:A NEWLY RECOGNIZED INCLUSION TYPE
Although inclusions are scarce in CLIPPIR diamonds, with the right approach they can be sought
and studied. By leveraging a high-volume diamond
grading service like that of GIA to find prospective
samples for examination, it was possible to cull out
enough of the rare inclusion-bearing CLIPPIR diamonds to look at their features as a group. In the past,
the only reported inclusions in CLIPPIR diamonds
were flat black inclusions with round boundaries,
previously assumed to be flecks of graphite (Bowenet al., 2009; Moore, 2014). Rarely, some inclusions
have been suspected to be sulfides, as they can resemble common pyrrhotite and pentlandite inclusions in lithospheric diamonds (Bowen, pers. comm.,

In Brief• Unusually large and pure diamonds like the 3,106 ct
Cullinan have a special geological origin, much deeper
in the earth’s mantle than most other gem diamonds.
• Many of the world’s biggest high-clarity, D-color diamonds belong to this special variety known as CLIPPIR
diamonds.
• Newly recognized iron-rich metallic inclusions in these
diamonds provide insight into the makeup of the deep
earth.
• There is still much to be learned from the study of diamonds, which are an invaluable “window” into the unseen world deep beneath our feet.

WINTER 2017391

C-S metallic inclusions often have step-faced surfaces,
strong magnetism, and elongate and irregular shapes,
grouping into chains, and routinely possess a coexisting fluid phase (again, see figure 3).
Specifically, these inclusions are accompanied bya thin, invisible fluid layer of methane (CH4) andlesser hydrogen (H2) trapped at the interface between
the solid inclusion and surrounding diamond (figure5). Detailed analysis of the inclusions reveals thatthey are made up of cohenite ((Fe, Ni)3C), interstitial
Fe-Ni alloy, segregations of Fe-sulfide, and minor occasional Fe-Cr oxide, Fe-oxide (likely wüstite), and Fephosphate (Smith et al., 2016). We interpret the minoroxides as evidence of small amounts of oxygen evenin these relatively oxygen-poor conditions, because
all the inclusions examined were carefully selectedfrom unaltered diamonds that had no surface-reaching fractures. This assemblage of minerals is inter-

preted to have crystallized during transport to the surface from the molten metallic liquid that was trapped
during diamond growth at depth. The metal contains
very limited amounts of oxygen, which indicates that
CLIPPIR diamonds form under reducing conditionsin the mantle. Metallic Fe-Ni-C-S melt inclusions
such as these have not been described previously, although rare, isolated occurrences of native iron, ironnickel alloy, and iron carbide inclusions have beenfound in other diamonds (Sharp, 1966; Jacob et al.,
2004; Kaminsky and Wirth, 2011; Mikhail et al.,2014). Coincidentally, the German mineralogist Emil
Cohen, for whom cohenite is named, might have encountered one of these Fe-Ni-C-S melt inclusions inan 80 ct rough diamond in South Africa 140 years ago,
though he described the inclusion as “specular iron”
or hematite based on color, luster, and form (“Iron indiamonds,” 1877).

Figure 3. Examples of the typical appearance of metallic Fe-Ni-C-S inclusions in CLIPPIR diamonds. A: Two parallel <111> oriented chains (field of view 2.34 mm). B: Backlit inclusion chain (field of view 1.42 mm). C: Elongate
metallic inclusion with a round black fracture of {111} orientation that obliquely cuts the <111> elongation direction of the inclusion (field of view 1.42 mm). D: A less elongate metallic inclusion with a small irregular tail on
the lower left (field of view 1.42 mm). Photos by Evan M. Smith.

A

B

C

D

392

EXCEPTIONAL CULLINAN-LIKE DIAMONDSGEMS & GEMOLOGYWINTER 2017

TABLE 1. Summary of inclusions observed in 83 CLIPPIR diamonds.
No. ofdiamonds

Largest in group

Inclusion assemblage

Inclusion properties

Mineralogy

60

30.13 ct

Metallic Fe-Ni-C-S (inferred to
be primary melt inclusions)

Magnetic, silver/black color, opaque,grouped in <111> chains, CH4 fluid
jacket (22 also had detectable H2 in
Raman); associated with healed
cracks; alters to red-brown (hematite).

Cohenite (Fe,Ni)3C + Fe-Ni
alloy + pyrrhotite + minor
phases15

32.88 ct

Calcium silicate phases withoriginal perovskite structure
inferred (CaPv)

Colorless, transparent, often withdroplet-like satellite inclusions
defining lobes of localized healed
cracks; one diamond had inclusions
with CH4 + H2 fluid jackets but no
indication of metal.

CaSiO3-walstromite ± larnite(β-Ca2SiO4) ± CaSi2O5-titanite ±wollastonite ± perovskite(CaTiO3)

4

10.21 ct

CaPv + metal

Colorless, transparent, with opaque,magnetic, metallic-luster droplet-like
satellite inclusions with detectable
CH4; note that the silicate and metal
co-occur rather than appearing as
discrete separate inclusions.

CaSiO3-walstromite ± larnite(β-Ca2SiO4) ± CaSi2O5-titanite +Fe-Ni-C-S phases

2

10.21 ct

Majoritic garnet + metal

Pale orange, transparent, with opaque,magnetic metallic phase partly
occupying inclusion space, with
detectable CH4 ; note that the garnet andmetal co-occur rather than appearing as
discrete separate inclusions.

Low-Cr majoritic garnet ± FeNi-C-S phases ± retrograde
clinopyroxene, plagioclase,
olivine1

4.41 ct

CaPv + majoritic garnet + metal

Pale orange, transparent garnet
inclusions with distinct metallic
opaque regions exhibiting strong
magnetism, with detectable CH4; onecolorless, transparent calcium silicate.

Majoritic garnet with metallic
component + CaSiO3walstromite

1

10.17 ct

CaPv + majoritic garnet

Two colorless transparent calcium
silicate inclusions; one pale orange,transparent garnet inclusion.

CaSiO3-walstromite + majoritic
garnetCombines results from 53 diamonds in Smith et al. (2016) and 30 additional diamonds (see supplement at www.gia.edu/gems-gemology/winter-2017-worldsbiggest-diamonds). Average diamond mass is 6.1 ct, with 13 of them >10 ct. Note that most recorded masses are for the cut diamond and original mass of rough is
unknown (also see data S1 in Smith et al., 2016).

The metallic inclusions (figures 3 and 5) have asilvery metallic luster with variable coating of patchy
black graphite (as identified with Raman spectroscopy—a technique that can help identify minerals using a focused laser). They are bound by
sharp-edged, flat cuboctahedral faces as well as complex stepped faces, and are often elongate in one dimension corresponding to a <111> vector withrespect to the host diamond crystal. Inclusions near
the surface of the diamond are noticeably magnetic
when brought near a small rare-earth magnet suspended from a thread. Magnetism can be helpful forrecognizing these inclusions but is not definitivesince some other kinds of inclusions can be magnetic, such as sulfides or the metallic flux trapped in
HPHT (high-pressure, high-temperature) synthetic
diamonds. Raman spectroscopy, while of limited usefulness in identifying these inclusions since they are

dominated by metals and carbides (both of which areinactive or weakly active in Raman), is good at revealing sulfides, which yield distinctive Ramanpeaks. We therefore take the general lack of Raman
response from the inclusions with metallic luster as
additional evidence that they are multi-phase metallic assemblages in which iron sulfide is a partial component rather than wholly sulfide mineralinclusions, which would have a distinctive Raman
response.
Taken together, the metallic inclusions’ consistent shape, texture, grouping, magnetism, lack ofclear Raman response, and other features justify extending the microprobe and XRD results (Smith etal., 2016) to the majority of inclusions in the faceted
samples that have been studied. It is unlikely thatsome of the metallic inclusions were misidentified
sulfide inclusions. Furthermore, it is important to

EXCEPTIONAL CULLINAN-LIKE DIAMONDSGEMS & GEMOLOGYWINTER 2017393

R AMAN SPECTR A
larnite (ȕ-Ca2SiO4)
CaSiO3-walstromite

660

32.88 ct

859
890

981

1042

1112
1086 1178

845

125
150

A

CaSi2O5-titanite

610

5 mm

RELATIVE INTENSITY

100 μmB
669

10.21 ct

999

CaSiO3-walstromite
128
1059
153

966
100 μm

C

921

5 mm

10.17 ct

Majoritic garnet
860

360
510

564

1051

644

100 μm
200

400

600

800

1000

5 mm

1200

RAMAN SHIFT (cm–1)

Figure 4. Raman spectra representative of the silicates in CLIPPIR diamonds. Spectra are offset vertically to avoid
overlap. A: The principal silicate phase CaSiO3-walstromite is accompanied by Ca2SiO4 and CaSi2O5 in a small
colorless inclusion with a large graphitic fracture in a 32.88 ct D-color type IIa diamond. The middle spectrum
shows CaSiO3-walstromite alone, with peak positions noticeably shifted due to high remnant pressure inside theinclusion, on the order of several gigapascals (Anzolini et al., 2017). B: This CaSiO3-walstromite inclusion in a
10.21 ct light pinkish brown type IIa diamond is a good example of the main part of the inclusion being accompanied by many smaller satellite inclusions, presumably from inclusion rupture/expansion during inversion from
CaPv. C: Majoritic garnet in the bottom spectrum was observed in a 10.17 ct D-color type IIa diamond. Note this10.17 ct sample contained both majorite and CaSiO3-walstromite, and the bottom two spectra were actually bothcollected from this diamond. Photomicrographs by Evan M. Smith, face-up diamond photos by Jian Xin (Jae) Liao.

note that sulfide (pyrrhotite) appears to have been exsolved from the Fe-Ni-C-S mixture, suggesting thatthe original metallic liquid would have dissolved any
sulfide minerals in this geologic environment, making it unlikely that discrete sulfide mineral grains
would be available to be trapped as inclusions.
The fluid jacket with hydrogen and methane surrounding these inclusions is detectable with Raman
spectroscopy, although the fluid is not uniformly distributed over the inclusion interface (figure 5).
Methane (CH4) is most easily detected and has a peakat 2918 cm–1, while hydrogen (H2) is generally lessabundant but has its main peak at 4156 cm–1 (Smithet al., 2016). Peaks may be shifted by a few wavenumbers due to residual pressure inside the inclusions(Frezzotti et al., 2012). Methane is present at the inclusion-diamond interface in all metallic and mostsilicate inclusion assemblages in every CLIPPIR diamond and is often accompanied by hydrogen. The
fluid is not thought to have existed as a free fluid
phase while the diamond grew. Rather, it is interpreted to have formed as a result of hydrogen atoms
exsolving out of the metallic liquid, and perhaps tosome extent the silicates as well, forming CH4 and H2
by reacting with the surrounding diamond (Smith andWang, 2016).

394

GEMS & GEMOLOGYEXCEPTIONAL CULLINAN-LIKE DIAMONDSSILICATE INCLUSIONS IN CLIPPIR DIAMONDS:EVIDENCE FOR DEEP ORIGIN
The second most abundant inclusion is a mix of calcium silicates interpreted as retrogressed CaSiO3-perovskite (CaPv), a perovskite-structured high-pressuremineral stable at depths beyond about 360 km (seebox A and Brenker et al., 2005). The most common

WINTER 2017

BOX A: POST-ENTRAPMENT RECRYSTALLIZATION OF INCLUSIONS
Diamond excels at preserving trapped inclusions byvirtue of its physical strength and chemical inertness.
Even if they are protected and isolated, however, someinclusions may nevertheless recrystallize in response to
the ambient temperature and pressure, especially whena diamond is transported to surface. This is true of themetallic Fe-Ni-C-S inclusions in CLIPPIR diamonds,
which are thought to be trapped as a homogenous melt
but later unmix into multiple phases (figure A-1). Textures within these metallic inclusions are essentially igneous, reflective of solidification and crystallization
processes.
In addition to the crystallization of trapped melt inclusions, solid mineral phases can also undergo postentrapment changes. Some minerals are only stable deepin the earth, at elevated pressure and temperature, andbecome unstable under conditions at the earth’s surface.
This is an important concept for inclusions in diamondbecause it explains how mineral inclusions can change
after being trapped in a diamond. A mineral inclusion
trapped very deep in the earth can undergo retrogression
or inversion on its way to surface, meaning the inclusions we observe might be the breakdown products ofsome original high-pressure phase. When minerals break
down, they are said to have undergone retrogression if
the breakdown results in multiple phases, or inversion
if the result is a single mineral phase. For example, thehigh-pressure mineral CaSiO3-perovskite could undergo
retrogression to produce two complementary minerals,
larnite (β -Ca2SiO4) and CaSi2O5-titanite, or inversion to
produce a single mineral, CaSiO3-walstromite. In eithercase the bulk composition remains unchanged. Often,

high-pressure phases are known mainly from experimental work and are referred to by their crystal structure. For
example, the mineral perovskite (CaTiO3) has a closely
packed cubic crystal structure that is emulated by calcium silicate at high pressures, and this phase is called“perovskite” (broadly) or CaSiO3-perovskite.

breakdown product of CaPv is CaSiO3-walstromite(figure 4). Other calcium silicate phases encounteredare larnite (β-Ca2SiO4), CaSi2O5-titanite, and, lesscommonly, wollastonite (CaSiO3). All four phases are
sometimes found together (metastably) in a single inclusion. If the inclusion contains sufficient titanium,
it can be present as perovskite (CaTiO3). Although it
is still unclear, there may be two possible CaSi2O5
polymorphs in retrogressed high-pressure calcium
silicate inclusions, corresponding to monoclinic andtriclinic structures that have been observed in highpressure experimental products (e.g., Kubo et al.,1997). Two different sets of Raman features havebeen interpreted as CaSi2O5-titanite. One signatureencountered, as in figure 4, resembles monoclinic titanite (CaTiSiO5) with its prominent 890 cm–1 band(see also database S3 in Smith et al., 2016). Another

Raman signature corresponding to a synthetic
CaSi2O5 sample (figure 2 in Nasdala et al., 2003) has
also been observed in CaPv inclusions (Nasdala et al.,
2003; Anzolini et al., 2016; Smith et al., 2016).
The CaPv inclusions are colorless and transparent, with surface textures ranging from flat-faced,sharp cuboctahedra to more ragged-looking irregularsurfaces, especially for larger inclusions. Some inclusions have small opaque portions that are magnetic,
interpreted as traces of metallic liquid trapped alongwith the silicate inclusion. Many CaPv inclusions
possess small droplet-like satellite inclusions, all of
the same mineralogy, grouped in one or more tabular
lobes that appear to have been introduced from themain inclusion outward along localized cracks (figure
4B). The satellite inclusions are interpreted as the
byproduct of pressure buildup sufficient to rupture

EXCEPTIONAL CULLINAN-LIKE DIAMONDSGEMS & GEMOLOGY

Fe-sulfide (pyrrhotite)
Fe-Ni metal alloy

cohenite (Fe-carbide)

Fe
Ni
S

50 µm

Figure A-1. An exposed polished metallic Fe-Ni-C-S inclusion. This inclusion was originally a homogeneous
molten metal, but as it cooled and solidified the mixture crystallized into three separate phases: cohenite, FeNi alloy, and Fe-sulfide. It is shown here as anenergy-dispersive X-ray elemental map from an electron
microscope, with the three phases colored according towhere iron, nickel, and sulfur are more strongly concentrated. Fe (red) is concentrated in cohenite, Ni (blue) in
Fe-Ni alloy, and S (yellow) in Fe-sulfide. The host diamond is a 2.14 ct offcut from a larger type IIa diamondfrom the Letšeng mine, Lesotho (sample Letseng_889, inclusion F). For methods, see Smith et al. (2016).

WINTER 2017395

16.36 ct

9.56
6 ct

30.13 ct

200 ȝm

5 mm

5 mm

100 ȝmINTENSITY (ARB. UNITS))

30,000DDD

588, H2

15,000200 ȝm

2916, CH4

D
25,00020,0005 mm4155, H2x10

10,000
5000
0
0

500

1000

1500

2000

2500

3000

35
500

4000

4500

–1

RAMAN SHIFT (cm )Figure 5. Metallic Fe-Ni-C-S inclusions with a representative Raman spectrum. All three CLIPPIR diamonds
shown are type IIa. The faceted diamonds (left and center) are D-color and Fancy yellow-brown, respectively. The
rightmost sample is a more heavily included offcut trimmed from an even larger, potentially D-color diamond.
The Raman spectrum shows the typical lack of diagnostic mineral peaks (within the 100–1200 cm–1 range) coupledwith methane (CH4 ) and molecular hydrogen (H2 ). Diamond Raman features are marked “D.” Face-up faceted diamond photos (16.36 ct and 30.13 ct) by Jian Xin (Jae) Liao; other photos by Evan M. Smith.

the surrounding diamond, followed by injection ofinclusion material out into the crack. A large volume
increase of about 30% is estimated to accompany the
inversion from CaPv to CaSiO3-walstromite (Anzolini et al., 2016). The cracks have healed, and the
diamond between individual satellite inclusions is
optically continuous. Although this initial crack ishealed, the main inclusion and sometimes even thesatellite inclusions are each surrounded by agraphitic black fracture (figure 4B), an indication offurther inclusion expansion during exhumation fromthe mantle by the erupting kimberlite. As a diamondis transported to the surface, the confining pressure
acting on it gradually decreases and there is less pressure pushing in on its inclusions. In this situation,some inclusions push out against the diamond host,potentially causing a buildup of elastic strain andbrittle rupturing around the inclusions. It is also possible that the surrounding diamond can deform plastically, thereby reducing the tendency for brittle
failure. Such inclusions demonstrate the complex
histories of brittle, elastic, and plastic deformation

the host diamond can endure in response to inclusion pressure during ascent to surface.
An additional inclusion phase found was lowchrome majoritic garnet, a high-pressure form of garnet containing excess silica (figure 4C). The garnets
are a pale orange color, again surrounded by large
graphitic fractures, and sometimes have a coexisting
magnetic, metallic component. The garnet provides
a convenient maximum depth of derivation, since it
is not stable deeper than about 750 km (Wijbrans etal., 2016). Silicate inclusion phases therefore bracket
the depth between 360 and 750 km, overlapping theregion of the mantle known as the mantle transition
zone, which marks the transition between the upper
mantle and lower mantle.
Examples of former CaSiO3-perovskite (CaPv) andmajoritic garnet inclusions coexisting with a metallic component and CH4±H2 demonstrate a close association between the metal-only inclusions and thesilicate-dominated inclusions and confirm that they
are derived from a common, very oxygen-poor settingin the mantle. The best-studied example, since it

396

GEMS & GEMOLOGYEXCEPTIONAL CULLINAN-LIKE DIAMONDSWINTER 2017

could be polished and examined in cross section withelectron microscopy, is in one of the large diamond
offcut samples from the Letšeng mine in Lesotho. In
it, two majoritic garnets were observed, each trappedwith a Fe-Ni-C-S metallic component alongside thegarnet (fig S4 in Smith et al., 2016). The metallic accompaniments were a mixture of iron-carbide, Fe-Ni
alloy, and Fe-sulfide, similar to the metallic inclusions seen in other diamonds containing no silicates.
Again, CH4 was present.
The silicate inclusions found in CLIPPIR diamonds are comparable to inclusions that have been
described before in other sublithospheric diamonds(see summaries by Stachel et al., 2005; Kaminsky,
2012; Harte and Hudson, 2013). Here, these silicate
inclusions are consistent with a mafic (eclogitic) hostrock affiliation in the sublithospheric mantle. In the
CLIPPIR diamond suite, however, the inclusion assemblages are somewhat different because they areassociated with metal and the reduced volatiles
methane and hydrogen.

A

B

z

<1
11
>
Inc

lus
io

ns

y
5 mm

x

C

D
Subsurface inclusion><111

CRYSTALLOGRAPHIC ORIENTATION OF
METALLIC INCLUSIONS IN CLIPPIR DIAMONDS

0.5 mmIn addition to their surprising metallic nature, themost common inclusions in CLIPPIR diamonds also
have a spatial distribution that is striking. The metallic inclusions are often spatially grouped in one ormore chains, all parallel to a single <111> vector (figure 6). This is a line oriented perpendicular to an octahedral {111} plane. Individual chains can waver
slightly, with jogs and discontinuities, but can reachseveral millimeters in length. When multiple metallic inclusion chains are present, they are often paralleland define a pervasive linear fabric with no tendency
to radiate from the center or otherwise align to any
obvious diamond growth pattern. Instead the chains
define a lineation within the diamond. The uniform,
parallel, and crystallographically controlled orientation of the chains suggests they are like an overprinted fabric established after diamond growth.
Cathodoluminescence or UV luminescence imaging
sometimes reveals bright curviplanar features where
the linear extension of an internal chain pierces thediamond surface. Figure 6 shows an example of thesefeatures extending radially from the point where an
inclusion chain vector meets the polished surface.
These otherwise invisible features are interpreted ashealed cracks with roughly {110} orientation, of
which there are three potential {110} plane orientations that intersect along the chain-defining <111>

Figure 6. Metallic inclusions in CLIPPIR diamonds often
occur in linear chains. A: Long, discontinuous inclusion
chain in a 2.05 ct D-color type IIa diamond. B: Sketch
showing a volume of diamond with multiple parallel<111> inclusion chains. Healed cracks of imperfect {110}orientation (blue) can be seen on the surface, at points
where chain-defining vectors exit the diamond. C: DiamondView UV luminescence image revealing healed
cracks related to a subsurface metallic inclusion in a
15.25 ct D-color type IIa diamond. Also visible are weblike dislocation networks. D: The same area shown in visible light, with blue traces drawn over the invisible healed
cracks and the <111> vector extending from the inclusion,
circled where the vector pierces the diamond surface. E:
DiamondView image showing a <111> inclusion chain
just below the surface, within the plane of the page, andtwo related healed cracks of {110} orientation running parallel to the inclusions. Two sets of finely spaced {111} slip
traces are also seen, overprinting and cross-cutting the<111> vector and healed cracks. Photos by Evan M. Smith.

EXCEPTIONAL CULLINAN-LIKE DIAMONDSGEMS & GEMOLOGYE

Healed cracks
parallel to chain<111> Inclusion chain

0.5 mmWINTER 2017397

BOX B: DIAMOND DEFORMATION AS A WAY TO MAKE <111> CHAINS
Metallic inclusions in CLIPPIR diamonds frequently
occur as chains of a few inclusions, aligned in a <111>
crystallographic orientation (figures 3A, 3B, and 6). These
chains are challenging to explain, but here we consider
that they may be a consequence of diamond deformationin the mantle. At the elevated temperatures in theearth’s mantle, diamond can deform plastically, though
it can still develop cracks under high stress. If the 3-Dstress is non-uniform and causes plastic deformation
within the diamond, there will be a concentration ofstress at the liquid metallic inclusions, where dislocation
movement is interrupted and the inclusion itself is astrengthless fluid. Under these conditions, cracks mightdevelop locally at the inclusion site. Given that thegeometry of a <111> vector can be produced by the intersection of two or three {110} planes, the next step isto consider whether or not the diamond could crack on
a {110} plane in a systematic way. In fact, brittle failureon {110} planes has been experimentally produced in diamond at elevated temperatures, concurrent with plastic
deformation on {111} planes (Brookes et al., 1999). In thisdeformation experiment, the {110} cracks were parallelto the compressional axis.
Bulk plastic deformation of the diamond may have
led to stress concentration and brittle failure localized at
the metallic melt inclusions. The single <111> vector expressed by the chains could correspond to the directionof maximum compressive stress, resolved to the diamond lattice. At the inclusion site, {110} cracks can develop parallel to the compressional axis, like thoseobserved by Brookes et al. in their deformation experiment. It would be possible to develop two or three symmetrically equivalent {110} cracks, such that theintersection of the cracks defines a short-lived dilatant<111> channel along which metallic melt inclusions canredistribute. In other words, the chains may be a redistribution of primary liquid metallic Fe-Ni-C-S inclusions, along a strain-controlled <111> direction, during
brittle-plastic deformation of the diamond in the mantle.
Redistribution of melt inclusions provides immediate
local stress relief conducive to crack closure and healing.
In two diamonds, the metallic inclusions have been observed as a planar group arranged in a {110} orientation,interpreted as a rare case of metallic liquid redistributed
into a single planar {110} crack rather than the linear intersection of two or more cracks. Compared to the solid
silicate inclusions, the metallic inclusions may be prone
to this deformation-induced redistribution simply because they were in a liquid state. Inclusions containing
both Fe-Ni-C-S metal and silicate trapped together do
not exhibit the linear spatial distribution, possibly because the solid silicate portion strengthened the inclusion. It is very unlikely that the metallic liquid could
have originated outside the diamond and penetrated into
fine, parallel <111> channels. The graphitic {111} fractures currently visible around the Fe-Ni-C-S inclusions
postdate this deformation.
The interpreted scenario of melt inclusion redistribution suggests these diamonds were deformed deep
enough that the metallic inclusions were still liquid andhad not unmixed. Development of the {110} healed
cracks in the diamond likely predates the development
of dislocation networks because dislocation networks
appear to conform to the cracks rather than being crosscut by them. These two observations suggest that the development of <111> chains may have occurred in a
discrete deformation episode at depth in the sublithospheric mantle. This deformation could be related tomantle convection and deep plate tectonic processes, orsome other physical mechanism.

vector (see box B). The observations suggest that primary metallic melt inclusions were rearranged into
chains during deformation of the host diamond at
depth in the mantle. The significance is difficult tointerpret without more detailed knowledge of the deformation behavior of diamond in the mantle, but
likely speculation would relate diamond deformation
to the pervasive deformation of mantle host rockthat accompanies mantle convection.

Much of our knowledge of the earth comes fromstudying rocks near its surface, yet the deeper interiorremains wholly inaccessible. While the continuous

action of plate tectonics and the magmatism causedby it allows geologists to relate plate deformation andvolcanism to Earth’s deeper interior, magmas react,
crystallize, and degas on their way to the surface,which changes their composition. The inevitably
modified magmas make it difficult to discern the true
nature of solid deeper mantle except by inference. It
is well known that the increase in temperature andpressure with depth in the earth causes some minerals
to break down and new minerals to form that are only
stable at the more extreme pressure and temperature
conditions. When considering the deep interior of theearth, this effect is fundamental. High-pressure experiments are used by scientists in the field of mineral

398

GEMS & GEMOLOGYMETAL IN THE MANTLE: WHAT DOES IT MEAN?

EXCEPTIONAL CULLINAN-LIKE DIAMONDSWINTER 2017

LithosphereDiaamond-bearing kimberlite eruption

Core

CLIPPIRdiamondg
pwellingUptlemantleOceanosphereContinental lith

Mant
le

here
osp
lith
ic
~ 2 5 0 km

660 kmAmountof metal(wt.%)
0.5

1

Oxygenfugacity
(∆IW)
0 +2

Metal
saturation
depth

Metal

Figure 7. Cross section of the uppermost 1,000 km of the earth (center) illustrating the origin of CLIPPIR diamonds, shown as large blue diamond symbols. Smaller black diamond symbols indicate other varieties of diamond formed mainly in the continental lithosphere. Oceanic lithosphere subducted into the mantle provides therocks necessary to explain the CaPv and majoritic garnet inclusions. CLIPPIR diamonds are thought to grow fromliquid metal. Following growth, they may be carried upward with thermally or chemically buoyant upwelling
mantle material and entrained in a kimberlite eruption to the surface. Profiles at the right show how the amountof metal in the mantle is expected to increase with depth starting from 250 km down, reaching up to approximately 1 wt.% below 660 km and buffering oxygen fugacity to reducing conditions (ΔIW, log units relative to theiron-wüstite buffer). Profiles after Rohrbach and Schmidt (2011).

physics to predict what kinds of mineral assemblages
will occur even within the lower mantle. One important prediction to come out of these considerations ofmineral physics is the idea that there is a depth,
around 250 km, below which metallic iron might become one of the stable phases within deep mantle
rocks (Frost et al., 2004). This prediction for metallic
iron is fundamental to understanding the basic properties of the mantle. We know that at the bottom of
the mantle it is in direct contact with the iron-nickel
metal of the core, whereas at the top of the mantle,
iron metal is not even stable during mantle melting.
What happens, mineralogically speaking, in between?
The mechanism thought to be responsible is the
progressive increase in the capacity for silicate minerals to host Fe3+ (iron with a 3+ oxidation state) relative
to Fe2+ at high pressures (Ballhaus, 1995; Frost et al.,2004). The preference for Fe3+ in certain minerals
under extreme pressure induces a disproportionation
reaction, whereby valence electrons in the existing
Fe2+ atoms are redistributed according to the reaction
3Fe2+ → 2Fe3+ + Fe0. The Fe3+ is partitioned into the silicates, but the Fe0 separates into its own metallic
phase. Iron disproportionation is thought to generate
up to about 1 wt.% metal in the lower mantle (Frostet al., 2004; Rohrbach et al., 2007). Nickel, carbon, sul-fur, and other elements are expected to dissolve into
this metallic phase. This prediction is based on experiments (Bell et al., 1976; Ballhaus, 1995; Frost et al.,
2004; Rohrbach et al., 2007; Rohrbach and Schmidt,
2011) but has never before been verified by actual observation of mineral grains.
The Fe-Ni-C-S melt inclusions in CLIPPIR diamonds are interpreted to be samples of such a metallic liquid, thereby confirming the fundamental
process of Fe2+ disproportionation at depth (Smith etal., 2016) and providing evidence for a metallic liquidmechanism for diamond formation. This is the reason why CLIPPIR diamonds are so significant forearth science. The metal has large-scale implications
for the behavior and evolution of the mantle over geologic time because it will influence the storage andcycling of the many elements that dissolve into it,such as oxygen, carbon, nitrogen, and hydrogen. The
tendency for metallic iron to react with oxygen is expected to regulate or buffer the oxygen fugacity (thechemical availability of oxygen in the mantle) andmaintain reducing conditions in the ambient mantle
below about 250 km depth (figure 7). The projected
low oxygen fugacity below 250 km, shown in figure
7, is a direct consequence of Fe2+ disproportionation(Rohrbach and Schmidt, 2011).

EXCEPTIONAL CULLINAN-LIKE DIAMONDSGEMS & GEMOLOGYWINTER 2017

399

GEOLOGICAL ORIGIN OF CLIPPIR DIAMONDS
The consistent association of the mineral assemblages found in CLIPPIR diamonds with metal andmethane, and its limitation to the CLIPPIR category,indicate that these diamonds form in a unique way.
The CaPv and majoritic garnet inclusions, as well as
the light carbon isotopes of the diamonds themselves, imply an association with subducted eclogite
at extreme depths, likely within 360–750 km in theconvecting mantle (Smith et al., 2016). This is much
deeper than other gem diamonds, nearly all of whichcontain much more nitrogen (type I) and form in thelowermost parts of thick, old continental lithosphereat depths of 150–200 km. This extreme depth is,
however, within the range of other rare “superdeep”
diamonds in the sublithospheric mantle (figure 7).
The source of the carbon that crystallized into diamond is also important. Carbon has two stable isotopes, 13C and 12C, whose ratio varies according to thesource, such as ambient mantle carbon or subducted,
organic carbon. Variably light carbon isotopes in
CLIPPIR diamonds, having 13C/12C ratios lower thanthe convecting mantle (Smith et al., 2016), suggest
derivation from organic carbon (e.g., Kirkley et al.,
1991; McCandless and Gurney, 1997), which implies
the carbon was originally sourced at Earth’s surface
and then subducted.
CLIPPIR diamonds, as described above, appear togrow in close association with metallic liquid in the
sublithospheric mantle. In this deep environment, themetallic Fe-Ni-C-S melt inclusions are hypothesized
to represent small retained traces of the actual growth
medium (Smith et al., 2016). Experiments and routine
HPHT synthetic diamond growth processes show thatiron-nickel mixtures are effective media at elevatedtemperatures and pressures, similar to the conditionsin the deeper mantle. Diamond growth from metallic
liquid could help explain the large size of CLIPPIR diamonds and their near-complete lack of nitrogen. Interestingly, the CH4 ± H2 fluid jackets surrounding
inclusions in natural CLIPPIR diamonds are a feature
also seen in metal/carbide inclusions in HPHT synthetic diamonds (Smith and Wang, 2016), further supporting their interpretation as primary melt
inclusions. Natural CLIPPIR diamonds may havecrystallized inside small pockets of molten metallic
liquid in Earth’s deep mantle (figure 7). Small dropletsof this metallic liquid would have occasionally been
trapped within the diamonds as they grew, preserving
the inclusion assemblages that we now sample.
As shown in figure 7, the eclogitic host rocks responsible for the silicate inclusions in CLIPPIR dia-monds likely represent a basaltic crustal layer of theoceanic lithosphere that was subducted into thedeeper underlying mantle. Below a depth of approximately 250 km, iron disproportionation can lead tometal saturation in mantle rocks. Both eclogite andthe surrounding peridotite, including the mantle portion of the oceanic lithosphere, have the potential togenerate metal by disproportionation. The source ofthe metal can be constrained by its bulk composition,roughly estimated as Fe0.61–0.75Ni0.10–0.13C0.15–0.20S0.05–0.12
based on the measured composition and relative
cross-sectional area of cohenite, Fe-Ni alloy, and Fesulfide exposed in four polished inclusions (Smith etal., 2016). The modest Ni/(Ni+Fe) ratio (<0.2) is lower
than the 0.3–0.5 range proposed for metal compositions precipitating in upper mantle peridotites(Rohrbach et al., 2014). Combined with the notionthat the metallic liquid should be nearly immobile,
tending to become trapped as disconnected dropletsin the intergranular spaces of silicate mantle rocks(Rohrbach and Schmidt, 2011; Rohrbach et al., 2014),
it is tempting to infer that the metal was generated
locally, within the eclogitic host rocks where the diamonds grew. However, the observed Ni/S andNi/(Ni+Fe) ratios in the inclusions are significantly
higher than expected for equilibrium with eclogite(e.g., Ni/S=0.3 and Ni/(Ni+Fe)=0.02 reported for a
metallic inclusion found in eclogitic garnet [Jacob etal., 2004]). To explain this discrepancy, the metal
could have formed in equilibrium with peridotite(e.g., Zhang et al., 2016) and subsequently migrated
into the eclogite before diamond crystallization occurred, but this scenario would imply significant
metal precipitation, segregation, and liquid metal mobility in order for large diamonds to ultimately crystallize. If metal in the mantle is typically distributed
along grain boundaries in silicates at low abundancesof around 1%, then segregation and mobilization of
the liquid metal may rely on deformation of surrounding rocks. However, other rock types or localized irregular rock compositions within the proposed
growth setting of subducted oceanic lithosphere
could also play a role in the metal and diamond formation. Further inclusion analyses and experimental
constraints are needed to clarify the exact provenanceof the metal.
Metallic iron has already been suggested to play arole in the formation of other types of superdeep diamonds, by its proposed ability to reduce subductedcarbonate species (CO32–) to diamond (C), also called“redox freezing” (Rohrbach and Schmidt, 2011). It is
not clear how or even if carbonate would be involved

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in CLIPPIR diamond growth since an oxygen-deficient
mantle region is a prerequisite for metallic inclusions.
But the expected high calcium content of carbonate
might be one explanation for the abundance of CaPv
inclusions as a reaction byproduct (Walter et al., 2008;
Bulanova et al., 2010; Harte and Richardson, 2012;
Thomson et al., 2016). Alternatively, other forms of
subducted carbon such as abiogenic, organic carbon
could be involved where carbonate does not play a significant role. The main point here is that metallic FeNi-C-S inclusions clearly show that the metallic
iron-rich phase plays the key role for CLIPPIR superdeep diamond formation.
Once formed, CLIPPIR diamonds, like other sublithospheric diamonds, require some mechanism totransport them upward to be sampled by kimberlite
magmatism and brought to surface where they aremined. The mechanism is uncertain but may involve
thermochemically buoyant, ascending solid mantle
that is part of the general upwelling associated withmantle convection (figure 7) prior to being entrainedin erupting kimberlite. The dynamic action of the
mantle may be cryptically recorded in the crystal
strain in CLIPPIR diamonds. There is a remarkably
strong association between CLIPPIR diamonds anddislocation networks (De Corte et al., 2006) that canbe better understood in light of the present study. This
web-like feature, rare in other diamonds, is visible incathodoluminescence or UV fluorescence imaging inalmost all 83 CLIPPIR samples examined (e.g., figure
6C). The network is interpreted as a dislocation structure arising from plastic deformation followed by recovery (Hanley et al., 1977). The high temperatures
afforded by a sublithospheric origin as well as the minimal nitrogen contents in CLIPPIR diamonds are conducive to the development of dislocation networks.
These diamonds have witnessed severe conditions in
the deep mantle—a likely consequence of mantle convection. Earth’s mantle convects in the solid form, introducing strain on the scale of the mineral lattice at
extremely high pressure. Despite their often exquisite
gem quality, these diamonds have an internal structure that preserves evidence of this strain and theirjourney from the deep mantle to the surface.

It has long been recognized that a curiously high proportion of large, gem-quality diamonds are type IIa,an otherwise rare designation. But now we havelearned that these special gems, termed CLIPPIR diamonds, actually form in a unique way, in a different
part of the mantle compared to other kinds of dia-monds. Many inclusion-free, nitrogen-deficient diamonds, especially those with dislocation networks,
are expected to belong to the CLIPPIR category (figure 2). The “superdeep” (i.e., sublithospheric) originof CLIPPIR diamonds, which leaves them free of inclusions associated with shallower, lithosphericmantle diamond host rocks, helps explain why exploration geologists and miners have never been able
to correlate these diamonds with traditional indicator minerals (Bowen et al., 2009; Gurney and Helmstaedt, 2012). The rarity and extraordinary value thathave made research study prohibitive over the years
also contributes to this fact. Indicator minerals suchas chrome-rich pyrope and ilmenite, the fragmentsof diamond host rocks from the lithospheric mantle
keels of Archean continents, are useful for finding
lithospheric diamonds. CLIPPIR diamonds, however,originate deeper in the mantle, far below the lithosphere where these indicator minerals are not stable
and cannot be included. Finding CLIPPIR diamonds
is all the more difficult. Predicting their ore grade,even in promising mines, requires large bulk sampling and carries great uncertainty.
Large and pure diamonds are nevertheless ahighly sought prize. Prior to the study by Smith et al.
(2016), there was no accepted model describing how
these large type IIa diamonds form in nature. We can
now appreciate that these exceptional diamonds arecoincidentally some of the most scientifically valuable samples of our planet’s interior. They are a window into the deep convecting mantle, providing a
glimpse through the shroud of Earth’s tectonic plates
and surface magmatism.
Previous experiments and theory have predicted
for many years that parts of the deep mantle below
about 250 km contain small amounts of metallic
iron and have limited available oxygen. Now, themetallic inclusions and their surrounding methaneand hydrogen jackets in CLIPPIR diamonds provide
physical evidence to support this prediction. This isa key observation for our understanding of planet
Earth, having broad implications for its geologic evolution through time, such as the behavior and cyclingof carbon and hydrogen, which are the primary fluxes
for rock melting and the generation of new crust.
Confirming the existence of metallic iron containing
nickel, carbon, sulfur, and other elements as a discrete liquid also impacts our understanding of theseismic velocity and thermal and electrical conductivity of the mantle, as well as the way it deforms
and flows. This result is a sign that there is still muchto be learned from diamonds and their inclusions.

EXCEPTIONAL CULLINAN-LIKE DIAMONDSGEMS & GEMOLOGYCONCLUSIONSWINTER 2017401

ABOUT THE AUTHORS
Dr. Smith is a research scientist, and Dr. Wang is vice president ofresearch and development, at GIA in New York. Dr. Shirey is asenior scientist in the Department of Terrestrial Magnetism of theCarnegie Institution for Science in Washington, DC.

ACKNOWLEDGMENTS
The authors thank GIA’s Ulrika D’Haenens-Johansson and PaulJohnson for assistance with sample selection, Alex Balter for help
handling data for figure 2, and Jian Xin (Jae) Liao for acquiring
face-up images of the diamonds in figures 4 and 5. This work
was completed with the support of GIA’s Liddicoat Postdoctoral
Research Fellowship program.

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

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EXCEPTIONAL CULLINAN-LIKE DIAMONDSGEMS & GEMOLOGYWINTER 2017403

FEATURE ARTICLESGEM VIRTUOSOS: THE DREHERS AND
THEIR EXTRAORDINARY CARVINGS
Robert Weldon, Cathleen Jonathan, and Rose Tozer

The German towns of Idar and Oberstein (now Idar-Oberstein) have a rich history of gem cutting andcarving, notably in agate. The profession continues to be passed on from one generation to the next, as
it has been for over five centuries. One of these families, the Drehers, has worked with gem materials
for 13 generations. Gerd Dreher apprenticed gem carving with his father starting in 1955, while Gerd’sson, Patrick, began his apprenticeship in 1988. While they carve individually, occasionally they work
together as a team. The family creates fine carvings from agates and from single crystals of high-quality
rough gem minerals. These unique pieces are extraordinarily detailed and utilize natural color zoning
to achieve a remarkably lifelike effect.

V

iewed from any direction, the gem carvings by
the father-and-son team of Gerd and Patrick
Dreher are remarkably lifelike. Agate toads appear bumpy, glistening, and slippery. Brimming withpersonality, their eyes appear to follow the viewer
around the room. A carved tiger lily emerges frombanded agate (figure 1) as a velvety, dappled flower,
its petals enticingly curling inward. And on the backsof these petals, details of the flower’s physiognomy
are scrupulously maintained. Much like the gem materials from which they are carved, these works are
one-of-a-kind creations.
Decades of experience between the two impartsvirtuosity to their work, as well as a sense of humor
often depicted in the subjects. Today, Gerd is globally
acknowledged as a master of the craft, while Patrick
has emerged from the younger generation, adding
new carving techniques to the family repertoire. Thisenhances the formidable range of skills that havebeen passed down through the Dreher family for 13
generations.
Following in the path of their ancestors, theDrehers’ ability to render the anatomy of flora andfauna in astonishing detail demands an intimate
knowledge of their subject matter, not to mention adeep understanding of the characteristics and attrib-

utes of the gem materials they carve. The Drehers
study rough gem material, sometimes for years. Fromthese observations they conceive a three-dimensional outcome and then set to work bringing thestone to life (figure 2). A growing collection of diamond-sintered tools, and a thorough understandingof how to use them, underpins their closely guarded
lapidary techniques.

IDAR-OBERSTEIN’S GEM INDUSTRY

See end of article for About the Authors and Acknowledgments.
GEMS & GEMOLOGY, Vol. 53, No. 4, pp. 404–422,
http://dx.doi.org/10.5741/GEMS.53.4.404© 2017 Gemological Institute of America

An understanding of the environment that gave riseto the Dreher dynasty—as well as hundreds of othercelebrated practitioners of the lapidary arts—is essential to appreciating their story. Idar and Oberstein (figure 3), two picturesque German towns separated by
the Nahe River in the state of Rhineland-Palatinate,
were united in 1933 to form Idar-Oberstein.
This area in southwestern Germany, nestled in the
Hunsrück mountain range, became famous for its
agate and quartz deposits, as well as its residents’ expertise in gem-related professions such as mining andcutting and more recently goldsmithing. Idar lore suggests that agate nodules and quartzes, such as chalcedony, jasper, carnelian, and petrified wood, werediscovered by farmers as they plowed their fields centuries ago (figure 4). Agate mining and cutting flourished there for at least five hundred years. Some believe
the Romans who conquered the region used Idar’sagates more than two thousand years ago. A cameo
found at Hidera, a Roman settlement in the mountains
above present-day Idar, suggests this ancient glyptic

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GEMS & GEMOLOGYGEM CARVINGS OF THE DREHER FAMILY

WINTER 2017

Figure 1. This Gerd Dreher lily carving (2005) is from a single piece of Brazilian agate and measures 11.0 cm inlength. His skills are on exhibit through his use of the material and his technique, such as the curled petals that
demonstrate a wealth of detail even on their undersides. The leaf, stamen, and enameled pistil accents arecrafted from 18K gold and set with diamonds. Patrick Dreher’s citrine mouse (2015), 6.0 cm in length, shows attention to the animal’s stance and demeanor as well as fine detail in the carving of the fur. Photo by Robert
Weldon/GIA, courtesy of the William F. Larson family.

use of its agates (Rapp, 2002). Other scholars dispute
the Roman connection, but there is agreement that thedeposits were mined during the Middle Ages. Cuttersworked with gem materials from the area, and by the
fourteenth century the region’s agate cutting industry
was established (Ball, 1931). Traditionally, the gem cut-

GEM CARVINGS OF THE DREHER FAMILYGEMS & GEMOLOGYWINTER 2017405

Figure 2. Natural bands of color in a single piece ofjasper were used to accentuate Gerd Dreher’s 1993
carving of an orangy red toad sitting on a green leaf
(left). The small cross section to the right shows how
he used the gem’s natural color banding to create theeffect. The finished piece measures 10.20 cm inlength. Photo by Robert Weldon/GIA, courtesy ofLeslie Hindman Auction House.

ting trade has been centered in Idar, with jewelry manufacturing and related professions evolving in neighboring Oberstein and other hamlets (Frazier, 1978).

Figure 4. This agate with an amethyst-lined cavity exhibits banding that is typical of the Hunsrück deposit
near Idar-Oberstein. The slice measures 27.94 cm inlength. Photo by Robert Weldon/GIA, courtesy ofFriedrich August Becker Edelsteine.

In the early days of the agate cutting industry in
Idar, water from nearby rivers—the Nahe, the Idarbach, and others—provided energy used to turn massive sandstone wheels for cutting (Frazier, 1978).
Large wheels, up to three meters in diameter, wereused to shape the agate’s exterior. Cutters from thearea developed a technique in which they lay stom-

Figure 3. Left: The town of Oberstein as it looked in the late 1700s. The picturesque Schloss Oberstein (the castle
at the top of the hill) and Felsenkirche (the church built into the wall of the mountain) have changed little since
this engraving was made. Colorized by Robert Weldon, from Collini (1776), courtesy of the Richard T. Liddicoat
Library and Information Center. Right: Oberstein, as photographed in late 2015, bears a remarkable similarity to
the sketch from nearly 250 years ago. Photo by Robert Weldon/GIA.

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GEM CARVINGS OF THE DREHER FAMILYGEMS & GEMOLOGYWINTER 2017

ach-down on a wooden bench. This position, with
their feet pressed against the floor, or against a blockof wood nailed to the floor, gave them the necessary
leverage to push the gem material against the rotating wheel and cut it (figure 5). The first record of awater mill used to grind stone was in 1454 (Gerdt,2017). A Grinder’s Guild document dating back to1609 bears witness to the profession, including
strong advice to its members: “No stranger must acquire the trade of a grinder, but the craft must be
handed down from father to son” (Hadley, 1984).
It was long, difficult work that demanded physical strength. Smaller wheels were used to refine theinterior—to hollow out preform bowls, for example.
Accounts passed down through the Dreher family

In Brief• Idar and Oberstein, two German towns united in 1933,
have an agate carving tradition that dates back to theMiddle Ages.
• The Dreher family has been involved in the agate
trade near Idar-Oberstein for 13 generations. The
modern Dreher family, believed to have carved animal figures for Fabergé in the 19th century, has produced three-dimensional carvings for five generations.
• Modern carving tools allow for much greater detail inhardstone carving.
• The Drehers’ superb library of animal images takenfrom various angles and studies of live animals gives
their carvings exceptional detail and realism.

note that agate cutters rose at 4:00 a.m. and went to
the water mills in Vollmersbach to await their turnat the wheel. Much of the work had to be donearound farming obligations since cutting alone
could not support the tradesmen. Throughout thesmall artisan workshops of Idar, family secrets
learned at the cutting wheel were passed down
through generations. Gem carving techniques andindividual styles evolved with specific creative refinements and specialties that in many cases could
be attributed to different carvers or their families(Dreher, 1979).
Gem cutters later developed foot-powered devices
to cut the agates, which was followed by the adventof electric-powered engines to turn the spindles.
These refinements allowed cutters to sit uprightrather than lying on their stomachs. One technique
did not change: While in many other parts of theworld the gem material is held stationary and thecraftsman moves a flexible tool around it to form thedesired shape, Idar’s cutters have always held thegem rough, as steadily as they can, in two hands.

GEM CARVINGS OF THE DREHER FAMILYGEMS & GEMOLOGY

Figure 5. Top: This engraving from a 1776 book by
Colosimo Collini, who explored the agate mining regions of southern Germany, shows a water millcross-section in Oberstein along the Nahe River. The
river current rotates the water wheel, which turns ageared axis. The gears turn the large sandstone
wheels used to grind and form agate. Bottom: Another engraving illustrates in detail the arduous cutting process practiced by the German agate cutters,
who used their bodies and the wheel to work the object. Courtesy of the Richard T. Liddicoat Library
and Information Center.

WINTER 2017407

Figure 6. Gerd Dreher shapes the preform of the jasper
toad seen in figure 2. Gerd and Patrick Dreher bothuse a fixed-spindle technique while holding the gemmaterial in their hands, a carving technique that has
been used in Idar-Oberstein for centuries. Courtesy of
the Dreher family.

This practice continues today. The gem is moved
around a fixed spindle, progressively grinding down
the material. A wide variety of diamond tools aremounted on these spindles, depending on the effectthat is needed, and the speed can range from 3,000 to
11,000 revolutions per minute (rpm). According toPatrick Dreher, both the spindles and the diamond
tools are manufactured in Idar-Oberstein to each cutter’s specifications. Gradually, the process reveals thecarver’s vision (figure 6).
A dramatic change in the supply of agate andquartz occurred in the early nineteenth century. The
Hunsrück deposit was nearing depletion following
centuries of exploitation. The resulting decline incenturies-old mining traditions could have spelled
the end of Idar’s cutting trade. Fortunately, between
the 1820s and 1850s, German explorers and farmers
homesteading in southern Brazil found new andvastly richer sources for agate and quartz along theborder with Uruguay. The agate and quartz were discovered the same way they had been in Idar centuries
before: by plowing the fields. Starting in 1825, shipments of the rough gem material made their way to
Idar. The quantity and quality of the Brazilian agate
surpassed anything that had been known from theHunsrück deposit. According to a Scientific American report from the time, up to 300 tons of agate
were shipped each year to Idar and Oberstein, where

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some 6,000 people were employed in the trade(“Where agates come from,” 1882). Other Brazilian
gems such as quartz, tourmaline, topaz, and beryl
were eventually imported, greatly expanding thetown’s offerings. The variety and availability of gem
materials brought new opportunities and challenges
for the cutting center.
Germany exported much of its new material to
French artists in the mid-1800s, during the waning
days of Romanticism. Paris was a magnet for artistsof all disciplines, including fine art stonecutters andgem engravers. The new Brazilian agate spurred a revival of gem engraving and carving, enabling cuttersto create cameos, intaglios, and seals using its multicolored layers for relief (Lindemann, 2017).
Young craftsmen from Idar began flocking toParis, learning refined engraving and cameo carving
techniques from Parisian masters. The start of theFranco-Prussian War in 1870, however, hastened theGermans’ return to their native land. These artists,
who now had abundant raw imported material athome, were soon able to surpass the skills they hadlearned in France. With the sudden influx of skilled
carvers, Idar’s renaissance as a gem center was wellon its way. Many artists formed engravers’ guilds
upon their return, with more than 230 members in
Idar and Oberstein (Pauly, 2012). The guilds helped
train apprentices and enabled members to hone theircutting and carving skills. They also established astable pricing structure for products. These developments cemented Idar-Oberstein’s modern role as acenter for agate cutting and engraving. The newskills acquired in Paris also prepared the cutters forthe development of three-dimensional carving.

THE DREHER DYNASTY
Accounts suggest that one of the most admired cutters and engravers in nearby Vollmersbach during thelate 1800s was Wilhelm Dreher (1840–1900). His
meticulous work was widely commissioned both inGermany and internationally. An agate bowl of Wilhelm’s, weighing 43 kilograms, was sent to Frenchemperor Napoleon III (Dreher, 1979). Other items
were sent to British royalty. One of Wilhelm’s sons,possibly Karl (1861–1943), produced a lapis lazuli
bowl for Emperor Nicholas II of Russia in the early
1900s. While the whereabouts of the bowl are unknown today, its sale was documented in the Dreher
family history (Dreher, 1979). Karl Dreher’s work, andthat of other German artists at the time, marked the
beginning of Idar’s three-dimensional gem-carving
tradition.

GEMS & GEMOLOGYWINTER 2017

Wilhelm’s son Karl was the first in the modernline of Drehers (figure 7) who developed skills as
gemstone carvers, instead of simply cutters. As ayoung man he trained under a master carver who had
returned from Paris, learning how to carve cameos,
monograms, and other ornaments. These skills
greatly expanded the Drehers’ repertoire as they
began to add engraving and carving to their skills.
With the increased exposure to international carving
styles and art movements, the family’s worldview
began to expand as well.
Meanwhile, Karl Wild, a contemporary of Karl
Dreher who was related to the Dreher family, saw
opportunities outside of Idar and traveled to Russia,
acquiring the nickname “Russ-Karl.” There he not
only sold finished carvings and objects of art by Karl
Dreher and others from Idar but also took orders andbrought back raw materials (such as Russian lapis
lazuli) to be carved. The lapis lazuli bowl mentioned
earlier is one such piece.

THE DREHERS DURING THE ERA OF FABERGÉFigure 7. Three generations of Drehers (clockwisefrom top): Hermann Dreher (1886–1960), Karl Dreher(1861–1943), and a young Paul Dreher (1910–1968).
Courtesy of the Dreher family.

The Dreher lineage has been traced back to 1620,
but the family believes their ancestors began working with gems from the region much earlier. Some
details were recorded in birth, marriage, and deathcertificates. Dreher activities were also gleaned fromproperty ownership records, particularly with regard
to lapidary mills the family bought, owned, or soldover time.
Unfortunately, many Idar and Oberstein records
before 1620 were destroyed during the Thirty Years’War (1618–1648), a religious conflict in central Europe. This period witnessed considerable devastationof churches and the loss of parish records. Destruction of records was repeated in both World Wars,leading to ambiguities about the provenance of some
important unsigned works of art, where the craftsmen cannot be verified with certainty. This was true
for the Drehers and many other notable agate cutting
families in Idar.

GEM CARVINGS OF THE DREHER FAMILY

The Dreher family, like many others in Idar, reliedprimarily on a series of brokers to sell their work.
One notable gem dealer was Moritz Stern, whobrought specific orders to Idar from abroad. These orders were placed with the town’s best carvers.
Among those who recognized Idar’s lapidary talent,
and who would soon use Stern’s services, was Carl
Fabergé, who developed an appreciation for hardstone cutting while traveling through Florence, Dresden, and Idar in the late 1880s (von Habsburg, 1988).
Fabergé was also influenced by Japanese netsuke1
carvings, amassing a collection of some 500 pieces.
These were popular items from sixteenth-century
Japanese clothing.
As a result of these influences, lapidary orders
coming into Idar at the turn of the twentieth century
included specific requests from Fabergé in St. Petersburg. Fabergé developed small plaster models of animals, which were supplied to the gem cutters andreplicated in stone (Adams, 1988). These works were
either assembled pieces or objects made from a single piece of stone. After the finished pieces were returned to Fabergé, his workmasters would apply
embellishments such as gold legs and feet (Wild,
1981). Patrick Dreher credits these Fabergé orders

1
Netsuke refers to a toggle or button adorned with a miniature carving, often depicting animals, made from ivory, wood, lacquer, bone,or metal.

GEMS & GEMOLOGYWINTER 2017409

Figure 8. Fabergé representatives provided plaster models, such as the toad on the left, as a sample for German
carvers in the Idar region to reproduce in agate. The Drehers have kept this plaster model for generations. Photo by
Patrick Dreher, courtesy of the Dreher family. Right: Gerd Dreher’s multicolored jasper toad (1985), measuring 6.5
cm in height, was carved from the family’s Fabergé plaster keepsake. Photo by Robert Weldon/GIA, courtesy of
the William F. Larson family.

with changing the family’s focus from the simple
cutting of agates toward carving in more artistic
forms. Karl Dreher’s son, Hermann (1886–1960), is
one of the artists who provided carvings purchased
by Fabergé. The Drehers say these works were faithfully carved from plaster models provided by Fabergé
craftsmen (figure 8, left; Ovchinnikov, 2017). Although these models were considered worthless
after the hardstone work was done (figure 8, right),
and most were lost to time and history, the family
managed to keep one such model.
This period marks the earliest shift to three-dimensional gem carvings. The Dreher family maintains only two such early carvings in its possession:

the rock crystal bowl seen in figure 9, and the figureof a gem carver with a bowl in figure 10.

Figure 10. Paul Dreher’s figure of a gem carver holding
a bowl (1935) is another of the earlier pieces in the
Dreher collection. Photo by Robert Weldon/GIA,
courtesy of the Dreher family.

Figure 9. This rock crystal quartz bowl by Hermann
Dreher, ca. 1910, is one of the oldest items in the family’s possession. Photo by Robert Weldon/GIA, courtesy of the Dreher family.

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Even with family members brokering some of thebusiness, the hardstone carvings went unsigned andwere subsumed under the Fabergé name. The venerable Russian firm relied to some extent on outside
vendors for a variety of goods they could not manufacture themselves. The items supplied had to be of
the highest caliber and craftsmanship, reflecting expertise simply not found in Russia at the time.
German lapidary craft is acknowledged in the
Fabergé literature. References indicate that the firstcarved hardstone animals likely came from Idar. In
Fabergé, Dr. Géza von Habsburg writes: “Fabergé
took up the search for hardstone carving outside of
Russia… [H]is journey led him to Idar-Oberstein, alittle town specialized in the cutting and engravingof Brazilian agate.” Von Habsburg singles out theGerman carver Alfred Heine, working for the Wolff
Company, who “produced stone animals for
Fabergé.” He goes on to say that “Fabergé’s numerous commissions brought about a new flowering forthe old stone cutting center” (von Habsburg, 1988).
This is also acknowledged by Russian experts. “It isa well-known fact that the Idar-Oberstein masters
made large quantities of carvings for Fabergé,” said
Galina Gabriel, a member of the International Association of Art Critics and the Russian Union of
Artists who spoke at the 2015 International Fabergé
Conference in St. Petersburg.
After 1908, Fabergé acquired the Woerffel factoryin St. Petersburg to handle the firm’s lapidary needs.
Orders for the carved animals, commissioned throughFabergé and originally carved in Idar, consequently
slowed in Germany. After World War I (1914–1918),
such carvings came to an abrupt halt. Widespread social unrest in Russia culminated in the 1917 Russian
Revolution and the execution of Emperor Nicholas II
and his family in July 1918. Fabergé lost all of its
wealthy Russian patrons. The firm was nationalized,
closing its doors in November 1918 (Snowman, 1962;
Faber, 2008). The destruction of records in both Germany and Russia left a gap in the full understandingof Idar carvers’ links to Fabergé. Nonetheless, theseeds had been sown for the growth of some of theworld’s greatest three-dimensional gem carvers.

Figure 11. Paul Dreher (1910–1968) working in his
studio. Courtesy of the Dreher family.

like deer and a large, sinuous puma are two Paul
Dreher carvings owned by the family (figures 12 and13). In homage to his innovations, the firm today

Figure 12. Viewed from any angle, this Paul Dreherdoe (1957) is remarkably lifelike. These realistic
pieces marked a new design direction in animal carvings for the Dreher family. Photo by Robert
Weldon/GIA, courtesy of the Dreher family.

MASTER CARVERS: FROM FATHER TO SON
Having learned the trade from his father, Hermann,
Paul Dreher (1910–1968; figure 11) was third in a lineof carving masters. The absence of influence from
Fabergé or any other major buyer provided Paul withgreater creative latitude, allowing him to render animal sculptures with rich variations. A delicate, life-

GEM CARVINGS OF THE DREHER FAMILYGEMS & GEMOLOGYWINTER 2017411

Figure 13. This puma by Paul Dreher (1965) shows exquisite overall form and beauty in its smoothness, but
without the nuanced details that diamond-sinteredtools would later allow. It measures 32.5 cm in length.
Photo by Robert Weldon/GIA, courtesy of the Dreher
family and the Deutsches Edelsteinmuseum.

bears the name Paul Dreher Edelsteine und Gravuren(Paul Dreher Precious Stones and Engraving).
Aside from his large, single-stone carvings, Paul
Dreher also experimented with combinations of several carved gem materials in composite sculptures.
These animal figures became very popular and wereof such exceptional quality that they were sometimes misidentified as Fabergé pieces. According toGerd Dreher (2012), “We were rather surprised to see
two original carvings made by my father in the second edition (1962) of the book The Art of Carl
Fabergé by A. Kenneth Snowman.” The mistake issomewhat understandable: Unsigned pieces by the
Drehers, and others in Idar-Oberstein, continued tobe sold through brokers or dealers. The style once inspired by Fabergé had endured for decades, long after
the legendary company had ceased to exist.
Why did the pieces go unsigned? The brokers had
the luxury of travel and fluency in languages used ininternational commerce. They often presented thepieces as a shared Idar-Oberstein quality brand. Basedin Idar-Oberstein and abroad, these brokers sold thecarvings internationally or in some cases passed
them along as examples of their own work (P. Dreher,
pers. comm., 2017). This was considered normal
business practice. There were positive and negative
effects of this business model. On one hand, carving
families in Idar-Oberstein did not have to concern
themselves with marketing and sales. They could
concentrate on producing the work and take the time
to develop new skills. The obvious drawbacks, how-ever, were that the carvers did not receive recognition, build a reputation, or understand their own
market. This business arrangement lasted well into
the career of Gerd Dreher. The unfortunate result
was that the Dreher name was not widely recognizedoutside of Idar-Oberstein.
Gerd Dreher, born in 1939, was trained by his father starting at the age of 16, in the time-honored local
tradition of passing these skills from father to son (see“Idar-Oberstein’s Gem Industry” section above). Between the 1960s and 1980s, Gerd followed a path sim-

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GEMS & GEMOLOGYGEM CARVINGS OF THE DREHER FAMILY

Figure 14. “Love Birds” (1979) was created during
Gerd Dreher’s early years, when he carved various
stones and composited them to form a whole sculpture. The birds are carved from aventurine quartz,
black agate, and yellow jasper with obsidian tailfeathers. They are perched on a base of preserved petrified wood. The piece measures 25.40 cm tall. Photo
by Robert Weldon/GIA, courtesy of Leslie Hindman
Auction House.

WINTER 2017

Figure 15. “Red Baron”(Gerd Dreher, 2015) is amostly rubellite tourmaline toad that gradually transitions to green
tourmaline toward thebase. The toad measures 7.10 cm in height
and weighs 280 g (1,400
ct). Photo by Robert
Weldon/GIA, courtesyof the William F. Larson family.

ilar to that of his father, carving various gem materials,
often in ways that could be composited to create animal figures such as the one in figure 14.
After Gerd Dreher took over the family business,he realized the need to change how his carvings werebrought to market. He finally began to sign Dreher
animal carvings in the 1970s, and collectors quickly
seized upon the crisp logo they saw etched along theedges of the artwork. Dreher carvings began toemerge from relative obscurity.
He observed that his artwork would benefit fromcarving single pieces of gem material—demonstrating what can be done with a single gem—albeit withaccents, or an occasional quartz base to help a carving stand upright. Accents include gold fins for fish,feathered crests for birds, and tails for various animals. These accents are carved in wax and then castin gold. Eyes are also added features, and they are
sufficiently unique as to require particular attention.

They are made from small translucent to opaquesections of agate, or black agates cut as cabochons.
The translucent areas are lined internally with goldleaf. This results in the shimmering appearance seenin an amphibian’s eye (figure 15) or the brilliant, darkstare of a mouse. Both appear startlingly similar toreal eyes.
By 1980, much finer diamond-sintered tools became available. “It allowed us to carve mammals,
reptiles, and amphibious creatures with much finer
detail than before,” Patrick Dreher recalls. These
tools could also cut faster. But as Gerd Dreher cautioned his son, who was an apprentice by then, “Thetools are not meant for us to produce faster. We will
only use them to produce better.” Elaborate carving
techniques they continue to master show refined, individual detail in fur, where even single strands canbe identified (see box A). Varying degrees of carving
depth create selected areas of translucency or opacity,

GEM CARVINGS OF THE DREHER FAMILYGEMS & GEMOLOGYWINTER 2017413

BOX A: THE DREHERS AND THE GEM CARVING PROCESS
Idar-Oberstein’s artists exert far more control over the
shape, symmetry, details, and final polish of finished workthan they did fifty years ago, thanks largely to modern diamond-sintered tools. The speed of cutting (the revolutions per minute of the spindle) has also increased.
However, the Drehers prefer to use today’s tools to increase the quality and fine detail of the work, rather thanto improve turnaround time. The family has maintained
their proprietary secrets, but they continue to use the traditional technique of holding the gem material against aspindle to grind away gem material. The following images
and short descriptions provide a step-by-step progression
resulting in a final carved object of art.

• An agate nodule (figure A-1) is carefully chosen andsliced using a diamond saw into an angular, blocked
shape, from which the subject size and dimensions
are determined. The Drehers sometimes sketch theanimal onto the flat surfaces of the agate using apencil or marker. This helps them to visualize thefinished carving and determine how the material’scolor zoning will define the animal’s characteristics

Figure A-1. The first step in carving is to saw the agate
nodule, revealing the interior banding and zones ofcolor. Photo by Robert Weldon/GIA, courtesy of the
Dreher family.

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GEM CARVINGS OF THE DREHER FAMILY

and personality. Gerd and Patrick Dreher use color
zoning in a single block of agate to determine how
the animal will be posed. Both the agate and dozensof photos of the subject—in this case, a mouse—arestudied to ensure anatomical correctness.
• In the second photo, Gerd Dreher has defined thethree-dimensional object (a mouse), including theoutlines of its tail and ears. All of the aspects of thecreature’s demeanor, stance, and position have been
carved into the agate (figure A-2). The Drehers use
4–6 cm diamond-sintered tools at this stage, spinning at 8,000–9,000 revolutions per minute (rpm),with continuous water drip for cooling and cleaning.
Patrick Dreher explains, “This step is one of themost difficult states, because you have to cut away
a lot of material; but you can’t cut too much because
you cannot get it back if there is a mistake.” This
stage is also critical for observation: The artist must
frequently pull away from the grinding to assess thematerial, sketch new drawings, study color separations, and correct any mistakes. In agates, the color

Figure A-2. Once the concept for a mouse subject is conceived, large sections of the agate are removed in the initial carving stage. Photo by Robert Weldon/GIA, courtesyof the Dreher family.

GEMS & GEMOLOGYWINTER 2017

borders are sometimes hard to see, which may require a redesigned mouse if color patterns are off.
• At this stage, the mouse has much finer characteristics, with translucent ears and more pronounced
facial characteristics and tail (figure A-3). The
Drehers generally use smaller diamond-sinteredtools at this stage, varying from 5 mm to 2 cm. Different steps in carving require an assortment of tools
and shapes as the carver exerts variable speeds (between 8,000 and 14,000 rpm) with a continuous
water drip. The carver determines the thickness andfineness of the piece by varying the applied pressure.
At this stage, the object, which must now have theanimal’s correct proportions, begins to appear lifelike.
• Gerd Dreher finishes this mouse (figure A-4) bycarving extremely detailed strands of fur, defining
the translucency and delicacy of the ears, adding
small dimples denoting the mouse’s whiskers, andfashioning the characteristics of the rock the mouseis standing on (consider that the mouse and rock onwhich he stands are all one piece). At least three degrees of polishing occur: pre-polish, fine polish, andhigh polish. Additionally, some sandblasting takes
place on the rock portion for a different degree of
texture. These polishing details are performed withsmall brushes and diamond powder (grits not disclosed). The powder is mixed with oils to create
slurry, which can easily be cleaned with water.
Dreher leaves small divots in the carving in whichto place the animal’s eyes, which are carved fromblack agate and prepared separately, then glued into
place (figure A-4). Other accents may be added at
this time as well, such as a gold tail or gold-feathered
crests. Paraffin is never used to finish off the carvings, ensuring they will last for generations withproper care and handling. Both carvers serve as eachother’s quality control, Patrick Dreher adds. “It isalways great to have a new pair of eyes look at something. But this I know is true: If my father says it isfinished, it is finished!”

Figure A-3. Smaller tools are used for additional definition and detail. Photo by Robert Weldon/GIA, courtesy of
the Dreher family.

Figure A-4. The final step is to carve minute details including fur, dimples, and muscles, and to polish the finished product. Photo by Robert Weldon/GIA, courtesy of
the Dreher family.

GEM CARVINGS OF THE DREHER FAMILYGEMS & GEMOLOGYWINTER 2017415

from books or magazines for reference. The photographs also feature animals that are live-captured by
the Drehers to act as models for the carvers. It is the
Drehers’ impressive collection of images andsketches that gives the family a depth of understanding about their subjects that few other carvers enjoy.
Patrick Dreher recalls that on one occasion he waslooking for a “preening” mouse. He could not photograph the desired pose in a captured mouse until atiny bit of strawberry jam was strategically smearedon a small patch of the mouse’s fur. It had the intended effect: The mouse soon went to work cleaning himself. The photographs, which are taken frommultiple angles, help the Drehers interpret and in-

Figure 17. This Gerd Dreher chameleon (2000), measuring 12.4 cm tall and weighing 2,390 ct, was carved
from a single crystal of gem-quality Brazilian green
beryl. Photo by Robert Weldon/GIA, courtesy of Silverhorn Jewelers.

Figure 16. Gerd Dreher’s evocative, softly undulating
carved agate (2004) emulates coral. With delicately
carved translucent agate fins, the fish appears to swim
through the coral. The piece measures 25 cm high andweighs 1,960.8 g (9,804 ct). Photo by Robert Weldon/
GIA, courtesy of the William F. Larson family.

which often evoke comparisons with actual animals.
Ears on a mouse or rabbit are strikingly thin andtranslucent, yet they still exhibit the detailed dimples
and folds seen in a live animal. Advancements in thequality of the tools, merged with a deep understanding of the subject’s appearance, imbue the creatureswith stunning personalities (figures 16 and 17). Art
critic Galina Gabriel considers the present generationof Drehers consummate masters, and Gerd specifically the “world’s most prestigious gemstone carver”(Gabriel, 2015; Gabriel, 2017).

THE DREHER PHILOSOPHY
Neatly categorized shoeboxes line the walls of thetiny Dreher studio, packed with photographs andsketches of fauna in various poses. Some are copied

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GEM CARVINGS OF THE DREHER FAMILYGEMS & GEMOLOGYWINTER 2017

Figure 18. A startled mouse (1997) assesses his options from inside an upturned mushroom. Carved by
Gerd Dreher from smoky quartz, it measures 12.4 cm
wide. Photo by Robert Weldon/GIA, courtesy ofLeslie Hindman Auction House.

corporate three dimensions into the finished object.
These live animals fulfill their role as models, resulting in carvings such as the startled mouse (figure 18).
After that, they are carefully released back into thewild, unaware that their likenesses are sought by collectors around the world.

The Drehers carve a variety of rough gem material ranging from 5 to 9 on the Mohs hardness scale,though their stated preference is always agate. They
appreciate agate’s toughness but also its wide-ranging color variations, which guarantee distinctive
works of art. Carving into the layers of color zoningin agate provides the “canvas” and opportunity forthree-dimensionality. Dreher carvings also appear
regularly in rock crystal quartz, ruby-in-zoisite,
beryl, topaz, rhodonite, obsidian, and tourmaline,
among other gem materials. Here, too, the Drehers
use color zoning in single crystals to their advantage,or to reveal a story in the carving.
Collectors generally supply the raw material in
crystal form or as rough chunks. It is always valuable
and often extremely rare. One notable example is atoad (figure 19) carved from a single piece of Brazilian
tourmaline crystal provided by California gem mineral collector William Larson.
“This piece came to us in colors of black, red,green, and black again,” Patrick Dreher recalls. “As
we began to remove the black material, we saw a thinlayer of blue we hadn’t seen before. This increased thevalue and became the head of the toad. The pink andred colors that emerged became the body of the toad,and the green color became the feet. This ‘Queen of
the Toads’ is the most valuable piece we have evercarved.”Patrick, born in 1970, apprenticed with his father,in keeping with the family’s tradition. “My father isFigure 19. This particolored tourmaline(2013) revealed its richcolors as it was being
cut. Gerd Dreher did
not know at the outsetthat the toad’s head
would be blue. It measures 10.8 cm tall andweighs 1,226 g (6,130
ct). Photo by Robert
Weldon/GIA, courtesyof the William F. Larson family.

GEM CARVINGS OF THE DREHER FAMILYGEMS & GEMOLOGYWINTER 2017417

Figure 20. Gerd
Dreher’s “Three Young
Birds” (2006), a carving
in Ukrainian heliodor,
incorporates part of thenatural beryl face inthe base. The accentsare 18K gold. The piecemeasures 11.5 cm talland weighs 922 g (4,610
ct). Photo by Robert
Weldon/GIA, courtesyof Silverhorn Jewelers.

the best teacher I could possibly get,” he says. Bothwork together at their home-based studio. “It’s notlike a traditional job where you go home after work.
I’m home already. And my boss is also my father!”
Patrick explains that he was exposed to the craft as a
toddler, with ample opportunities to absorb his father’s carving methods. Actual hands-on work beganby the age of 18. In 1997, Gerd and Patrick traveled
to Rio Grande do Sul, Brazil’s southernmost state,and brought back 3.5 tons of handpicked agate rough,which they continue to work with to this day.
The 1980s and ’90s also provided incredible new
gemstone finds, such as large beryl crystals from
Ukraine that were available after the fall of the Soviet
Union. Gem materials were also emerging from Brazil
and from newer sources such as Afghanistan, East
Africa, and Madagascar. This gemstone windfall dovetailed nicely into the family’s growth, with two
decades of some of the finest, largest, single-crystal
gem materials that had been found in the twentiethcentury. A young bird’s nest lavishly carved from anenormous hexagonal Ukrainian green heliodor (figure20) exemplifies the era. Sensitive to the beauty of thegeometric etched pits on the crystal, Gerd Dreher left
one face of the beryl intact with the gem’s natural surface. Similarly, a mouse carved from African ruby andzoisite (figure 21) illustrates the massive ornamental
materials beginning to emerge from Africa at the time.
Patrick says that he and his father consistently
carve 12–20 new works every year, each of which
may take 300–400 hours to complete. Father and son
work both independently and collaboratively on

pieces and continue to find new collectors to supply
them with exceptional gem material.

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GEMS & GEMOLOGYGEM CARVINGS OF THE DREHER FAMILY

Figure 21. Gerd Dreher’s ruby-in-zoisite mouse (1993),
carved from a single piece of rough, has sapphire
cabochon eyes and an 18K gold tail. It measures 6.8
cm tall and weighs 246 g (1,230 ct). Photo by Robert
Weldon/GIA, courtesy of Silverhorn Jewelers.

WINTER 2017

BOX B: DREHER CARVING QUALITY FACTORS

Figure B-1. Gerd
Dreher’s “Tree Frog”(2002) was carved fromchrysoprase and meticulously worked so thatthe frog’s feet would
curve to grasp the gold
accents. The base of thecarving is rock crystal
quartz; the stem of thepond reed is 18K gold.
The combined artwork
weighs 1,032 g. Photo
by Robert Weldon/GIA,
courtesy of theDeutsches Edelsteinmuseum.

Quality of the Rough: The rough gem material must be extraordinary and rare, such as larger agates with unusual
color banding and strength of color. This allows for the development of a themed finished carving. In transparent
gems, the material is often crystalline and devoid of any obvious inclusions, resulting in clean, luminous carvings.
Quality of the Carving: The carving must maintain lifelike
proportions throughout, and symmetry from all viewing
angles should be comparable to an actual animal’s appearance (figure B-1).
Details: Dreher carvings are studies in minute detail. How
are these details rendered? Does the fur of a bear overlap?
Are the ears of a mouse fine and translucent?
Use of Material: The Drehers sometimes spend years looking at a rough gemstone before starting to carve it. Considerable thought, planning, and execution go into the useof the gem’s color zoning to convey lifelike features, or to
distinguish an animal from its environment.

before the 1980s, expressing the material, the know-how,the demand, and the tools that were available at the time.
Single-Gem Carvings: Large single-crystal carvings reflect
the company’s change in artistic direction and philosophy
in the 1980s. Single-gem carvings reveal not only the rarityof the gem material but also the Drehers’ ability to rendera complete three-dimensional carving from it.
Accents: Gold accents, such as tails and feathers, carvedeyes and quartz bases, are used in both composite andsingle-gem carvings (figure B-1).

Figure B-2. Unlike their Idar-Oberstein predecessors, the Drehers started signing their contemporary work in 1975. The signature on theleft is that of Gerd Dreher, while Patrick
Dreher’s initials are seen on the right. Photos
by Robert Weldon/GIA.

Uniqueness: Dreher carvings are always original works ofart. Though some poses might be similar, no two carvings
are identical; there is always variation because they arecarved in different materials and at different times.
Signatures: Contemporary work is signed by Patrick or
Gerd Dreher. In figure B-2, “GD” is Gerd Dreher and “PD”
is Patrick Dreher.
Composite Works: Some Gerd Dreher carvings are composites of various gem materials. This generally dates a piece

GEM CARVINGS OF THE DREHER FAMILYGEMS & GEMOLOGYWINTER 2017419

Figure 22. This hippopotamus in citrine (2015) shows
Patrick Dreher’s mastery in rendering the animal,
which exhibits a highly polished, glistening surface.
It measures 12.0 cm long and weighs 526 g (2,630 ct).
Photo by Robert Weldon/GIA, courtesy of theWilliam F. Larson family.

Patrick’s own mastery of the craft was realized ina dramatic fashion when, after decades of apprenticeship, he detailed a plan to carve a rounded but com-pletely smooth and glassy hippopotamus out of citrine
quartz. “It cannot and should not be done—you’ll be
wasting material,” his father chided. Nevertheless,
Patrick was steadfast in his resolve, and his father ultimately agreed the piece was masterful (figure 22).
Patrick has since carved a number of importantpieces, including a starfish from a strawberry quartz
specimen that in its rough state had concealed a secret. It was not until he began the removal of unwanted or damaged sections that the strawberryquartz revealed pale amethyst and colorless rock
crystal quartz in the layers beneath. The color variations in the amethyst became a coral reef on an ocean
floor of rock crystal (figure 23).
Inside their home studio, the Drehers take turns
at the spindle. A collection of diamond-sinteredtools, in different sizes and numbering in the hundreds, await their turn at the workstation. These
tools, and the skilled use of them, bring out extremely fine detail. With a few exceptions, it is thisdetail that defines the present era. In his day, Paul
Dreher carved unique large items like the puma anddeer, in which the personality came to life in thecarvings’ well-defined but smooth, soft surfaces, reflecting a mastery that was limited only by his tools.
Today’s carvings have generally lost that smoothness

Figure 23. Patrick
Dreher’s strawberryquartz starfish (2014),
carved from a crystal
similar to the one
shown on the right, revealed layers ofamethyst and rock crystal as he carved into thestone. The “strawberry” portion of thesingle piece became theshiny starfish, resting
upon an amethyst
coral. The rock crystal
quartz section wascarved as the ocean
floor. The starfish measures 13.6 cm tall andweighs 1,279.50 g(6,397.50 ct). Photo by
Robert Weldon/GIA,
courtesy of the William
F. Larson family.

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GEM CARVINGS OF THE DREHER FAMILYGEMS & GEMOLOGYWINTER 2017

Figure 24. Gerd andPatrick Dreher in theirstudio. Courtesy of the
Dreher family.

in favor of extraordinary detail, attention to realism,
and quality (see box B).

CONCLUSIONSFor centuries, the German towns of Idar and Oberstein have been known for agate cutting. Joined as
one town before World War II, the region developed
into a cutting and carving center for colored gem-

ABOUT THE AUTHORS
Mr. Weldon (rweldon@gia.edu) is director, Ms. Jonathan(cjonathan@gia.edu) is a research librarian, and Ms. Tozer(rtozer@gia.edu) is senior librarian at the Richard T. Liddicoat
Gemological Library and Information Center in Carlsbad, California.
ACKNOWLEDGMENTS
The authors wish to thank the Dreher family for giving us the opportunity to interview them, for helping us understand their history,
and for opening the doors to their house and studio to photographcarvings. We thank Anette Fuhr, director of the Deutsches Edelsteinmuseum in Idar-Oberstein, for our interview with her and her
permission to photograph selected pieces from the museum.

GEM CARVINGS OF THE DREHER FAMILY

stones. Two of its principal carvers, Gerd and Patrick
Dreher, can trace their family’s association withagate back thirteen generations, with the last five involved in three-dimensional gem carving. Father andson (figure 24) are considered by many to be theworld’s greatest living gem carvers, and their work
continues to be acquired by collectors around theworld.

Thanks also to Dieter Hahn, chairman of the Foundation of theDeutsches Edelsteinmuseum, for his insights into the history of theIdar-Oberstein region. GIA has assembled a large collection ofphotos of Dreher carvings over nearly a decade, starting whengem dealer Michael Ridding of Silverhorn Jewelers (Santa Barbara, California) brought the Dreher carvings to our attention in
2009, and we thank him. We are grateful to Leslie Hindman Auctioneers (Denver) for allowing us to photograph a major collectionof Dreher carvings prior to their sale. Gem and mineral dealer Bill
Larson and his sons, Carl and William, all of Pala International (Fallbrook, California), introduced us to the Dreher family. We thankthem for accommodating our ongoing requests to photographtheir growing collection of Dreher carvings.

GEMS & GEMOLOGYWINTER 2017421

REFERENCES
Adams T. (1988) Fabergé’s use of oriental motifs. M.A. thesis, San
Diego State University. https://archive.org/details/FabergesUseOfOrientalMotifs
Ball S.H. (1931) Historical notes on gem mining. Economic Geology, Vol. 26, No. 7, pp. 681–738, http://dx.doi.org/10.2113/gsecongeo.26.7.681
Collini C.A. (1776) Journal d'un voyage qui contient differentes
observations mineralogiques: particulierement sur les agates,
et le basalt. Avec un détail sur la maniere de travailler lesagates. C.F. Schwan, Mannheim, Germany [in French].
Dreher E. (1979) Einer Schleiferfamilie mit Tradition uber drei
Jahrhunderte. In K. Schultheiss, Ed., Heimatkalender desLandkreises Birkenfeld. Gemeinsam Verlegt von Arbogast, Otterbach, und Klebes, Baumholder, Germany, pp. 139–144.
Dreher G. (2012) Die Gestaltung von Tierfiguren aus Schmuckstein im Raum Idar-Oberstein nach 1950. In Gravierte Kostbarkeiten = Reznyye Sokrovishcha = Carved Treasures:
Precious Stone Carvings from St. Petersburg and Idar-Oberstein at the German Gemstone Museum. Stiftung Deutsches
Edelsteinmuseum, Idar-Oberstein, Germany.
Faber T. (2008) Fabergé’s Eggs: The Extraordinary Story of the Masterpieces that Outlived an Empire. Random House, New York.
Frazier S. (1978) The gem cutting industry of Idar-Oberstein Part
II: Origins. ULW [United Lapidary Wholesalers] Show News,
Vol. 2, No. 3, pp. 6–27.
Gabriel G. (2015) Lapidary centers of modern Russia. International
Fabergé Museum Conference, Fabergé Museum, St. Petersburg.
——— (2017) Homage. In W. Lindemann, W. Larson, and E. Schneider, Dreher Carvings: Gemstone Animals from Idar-Oberstein.

Arnoldsche Art Publishers, Stuttgart, Germany, pp. 230–231.
Gerdt O. (2017) Idar-Oberstein – A gemstone of Europe. In W. Lindemann, W. Larson, and E. Schneider, Dreher Carvings: Five
Generations of Gemstone Animals from Idar-Oberstein.
Arnoldsche Art Publishers, Stuttgart, Germany, pp. 8–13.
von Habsburg G. (1988) Fabergé. Habsburg, Feldman Editions,Geneva.
Hadley W. (1984) A new look at Idar-Oberstein. Rock & Gem, Vol.
14, No. 10, pp. 48–51.
Lindemann W. (2017) Gerd and Patrick Dreher - The art of stonecutting today. In W. Lindemann, W. Larson, and E. Schneider,
Dreher Carvings: Gemstone Animals from Idar-Oberstein.
Arnoldsche Art Publishers, Stuttgart, Germany, pp. 14–23.
Ovchinnikov M. (2017) The Dreher family cultural code. In W.
Lindemann, W. Larson, and E. Schneider, Dreher Carvings:
Gemstone Animals from Idar-Oberstein. Arnoldsche Art Publishers, Stuttgart, Germany, pp. 34–41.
Pauly H.U. (2012) Hans-Ulrich Pauly. In Gravierte Kostbarkeiten= Reznyye Sokrovishcha = Carved Treasures: Precious Stone
Carvings from St. Petersburg and Idar-Oberstein at the German Gemstone Museum. Stiftung Deutsches Edelsteinmuseum, Idar-Oberstein.
Rapp G. (2002) Archaeomineralogy. Springer-Verlag, Berlin.
Snowman A.K. (1962) The Art of Carl Fabergé. Faber & Faber,
London.
Where agates come from (1882) Scientific American, June 3, p.
352.
Wild K.E. (1981) Ueber die nachbildung Fabergésche Figuren in
Idar-Oberstein. Goldschmiede-Zeitung, No. 2, pp. 108–109.

More on Dreher Carvings
Interviews and photo galleries capture the lifelike detailand painstaking process followed by Gerd and Patrick
Dreher. Visit www.gia.edu/gems-gemology/winter-2017gem-virtuosos or scan the QR code to the right.

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GEM CARVINGS OF THE DREHER FAMILYGEMS & GEMOLOGYWINTER 2017

FEATURE ARTICLESAKOYA CULTURED PEARL FARMING IN
EASTERN AUSTRALIA
Laura M. Otter, Oluwatoosin B. A. Agbaje, Le Thi-Thu Huong, Tobias Häger, and Dorrit E. Jacob

Akoya cultured pearls have been produced on the eastern shoreline of Australia since approximately
1999 using Pinctada imbricata fucata mollusks native to New South Wales. Unlike many of their Japanese counterparts, Australian akoya cultured pearls are harvested after 18 months of growth and marketedwithout any post-harvest treatments involving dyes or bleaches. This study presents the first gemologicaland mineralogical characterization of Australian akoya cultured pearls using Raman, photoluminescence, FTIR, and UV-Vis specular reflectance spectroscopy. Raman and FTIR spectroscopy identified
the major mineral phase aragonite as well as some organic compounds. While Raman spectroscopy revealed polyene-related pigments with bands occurring at 1134 and 1532 cm–1, FTIR spectroscopy
showed sulfate- and polysaccharide-associated groups occurring at around 1200 and 1115 cm–1, respectively. UV-Vis spectroscopy revealed broad spectral features that provide insight into the distinct
bodycolors and enable discrimination from some non-akoya saltwater cultured pearls from P. margaritifera, P. maxima, and P. mazatlanica bivalves, while separation from other untreated akoya pearls is notpossible. Production processes are examined to better understand the modern, sustainable, and environmentally friendly pearl farming operations in Australia.

T

he Pinctada imbricata fucata mollusk has long
been used to produce akoya cultured pearls, dating back to the pioneering work in the early
1900s by Japanese entrepreneur Kokichi Mikimoto(Strack, 2006). This bivalve is distributed widely
across Asia and also occurs on the eastern coast ofAustralia (Gifford et al., 2004), where it is used to produce untreated and sometimes vibrantly colored cultured pearls (figure 1). With Pinctada imbricata
fucata populations readily available on New South
Wales’s Central Coast region between Sydney andthe city of Lake Macquarie, a local enterprise called
Broken Bay Pearls with expertise in farming of edible
Sydney rock oysters (Saccostrea glomerata) has been
culturing akoya pearls since 2003 (figure 2). The climate in New South Wales is ideally suited for pearl
culturing using Pinctada imbricata fucata. It is located approximately the same distance from theequator as the southern Japanese pearl farms, and its
very similar seasonal variations of water temperature
optimize nacre quality during the cultivation process(Strack, 2006; Gilbert et al., 2017).

Australia was originally known for its large-scale
production of silver- and gold-colored natural andcultured South Sea pearls from Pinctada maxima(Scarratt et al., 2012 and references therein), which
are valued for their large sizes of up to 20 mm in di-Figure 1. A bracelet showing naturally colored blue,
cream, yellow, and silver akoya cultured pearls fromBroken Bay Pearls. Photo courtesy of Broken Bay
Pearls Pty Ltd.

See end of article for About the Authors and Acknowledgments.
GEMS & GEMOLOGY, Vol. 53, No. 4, pp. 423–437,
http://dx.doi.org/10.5741/GEMS.53.4.423© 2017 Gemological Institute of America

AUSTRALIAN AKOYA CULTURED PEARLSGEMS & GEMOLOGYWINTER 2017

423

A

²

N

B
WamberalGosford

Calga

Erina

Kariong
N o r th e r n
Te r r ito r y

Brisbane Water
National Park

Qu e e n s lan d
We s t e r n
Aus t ralia

Woy Woy
S o u thA u s tr a lia

Umina Beach

Ne w S ou th
Wal esGreat Australian
Bight

Box Head
Brooklyn

Pearl Beach
Patonga

V ic to r i a
0

C

3 km

D

Figure 2. The map of Australia (A) indicates the location of the Broken Bay Pearls farm near Woy Woy in New
South Wales, on the southeastern shoreline (B). The akoya pearl farming operation near Woy Woy (C) and some of
the long-line systems for juvenile Pinctada imbricata fucata that are held nearby (D). For scale, the wooden jetty
shown in C and D is 1.5 meters wide. Photos by Laura Otter.

Hatchery and Spat Production. For about a decade,the hatchery facilities located at NSW Fisheries, Port
Stephens Fisheries Institute (PSFI) have supplied Broken Bay Pearls with young Pinctada imbricata fucata. Broodstock are collected from both the farmand in the wild and selected based on nacre color andshell shape. Priority is given to stock with more convex shells, which allow for larger nuclei to be implanted during seeding. These parents are brought tothe hatchery, where spawning is induced by increasing water temperatures by about 4°C. Eggs and sperm
are mixed in 1,000-liter tanks. They are kept at 24–
26°C until they develop into larvae (figures 3A and3B) after 20–24 hours; water temperature, feeding
protocols, and stock density are regulated as needed(O’Connor et al., 2003). The larval cycle takes approximately three weeks before they are ready to settle from the water column and attach to a substratesuch as mesh screens or bags.
After settlement, these spat are retained until
reaching approximately 1.5 mm in size, whereupon
they are transferred from the hatchery in Port

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GEMS & GEMOLOGY

ameter (Strack, 2006). Australian akoya cultured
pearls have yet to receive comparable attention in
the gemological community. This study aims tocharacterize the occurrence of akoya cultured pearls
in eastern Australia and presents what is believed tobe the first thorough gemological and mineralogicalcharacterization through Raman, photoluminescence (PL), ultraviolet-visible (UV-Vis), and Fouriertransform infrared (FTIR) spectroscopic analysis.

AUSTRALIAN AKOYA CULTURED PEARLSWINTER 2017

Stephens to the pearl farm near Woy Woy (figure 2).
Here, they are placed in 0.5 mm mesh bags (figure 3C)
attached to several parallel long-line systems about
200 meters in length and situated at a depth of 4 meters below the low tide water level. As the juvenile
Pinctada imbricata fucata bivalves grow, they areprogressively transferred to larger mesh bags or cages
that are cleaned regularly to ensure good water flow.
Broken Bay Pearls is currently the only akoya
pearl farm on the New South Wales coastline. Several small islands act as a barrier between the open
ocean and the farm, creating a well-protected baythat is ideally suited for pearl farming. This area
within the estuary provides stable salinity, nutrient
availability, and high levels of dissolved oxygen,
which are key factors for the long-term development
and cultivation of a healthy stock.
Seeding and Maintaining of Australian Akoya Pearl
Oysters. The juvenile pearl oysters are maintained on
the farm until they are approximately two years old
with shell heights of about 7 cm. Similar to otherfarms, the mollusks are cleaned with high-pressurecleaners every two to four weeks (Gifford et al., 2004).
It is common practice to condition the pearl oysters for several weeks before seeding by reducing their
physiological fitness. At Broken Bay this is achievedby stocking the mollusks at high density within barnacle-overgrown wicker baskets that restrict waterflow and food availability. Other farms, such as thosein Southeast Asia, cover the mollusks with fabric toachieve the same effect (Hänni, 2007). Either way,
they respond to food shortage by ceasing gamete production that would otherwise interfere with the seed-ing process (Hänni, 2007). This conditioning strategy
allows the seeders at Broken Bay Pearls to process theanimals without having to apply relaxant drugs to immobilize them (Acosta-Salmón et al., 2005).
The bivalves are seeded in the austral summer
month of February using only shells of suitable size
(shell height larger than 7 cm) and fitness. This ensures acceptance of the bead, fast recovery from sur-

In Brief• Gem-quality akoya bead cultured pearls have been
produced on Australia’s eastern shoreline since 1999,
with environmentally friendly strategies to achieve sustainable farming.
• A wide variety of colors occur naturally besides the traditional white and silver. These cultured pearls are marketed without the application of bleaches or dyes.
• Australian retailers have embraced these akoya cultured pearls as locally manufactured jewelry becomesincreasingly popular in the country.
• This work suggests that colored akoya cultured pearls
produced by P. imbricata fucata can be differentiatedfrom pearls from other species such as P. margaritifera,
P. maxima, and P. mazatlanica using UV-Vis spectroscopy.

gery, and a greater chance for successful pearl growth.
The production of cultured pearls requires two typesof mollusk broodstock. Donor mollusks are selected
for nacre color and quality and are sacrificed in theseeding process to extract the mantle tissue graft thatis later inserted with the bead. The host animals, on

A

C

B

AUSTRALIAN AKOYA CULTURED PEARLSGEMS & GEMOLOGY

Figure 3. Australian Pinctada imbricata fucata larvae, shown here at anage of about 25 hours (A)with approximately 200µm shell size, are rearedin 1,000-liter polyethylene tanks at the nursery(B). After 24 days, thelarvae mature to spatwith approximately 1.5mm shell lengths. They
are transferred to longline systems and kept in
0.5 mm nylon mesh bags
(C). Photos by Wayne A.
O’Connor.

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A

B

C

D

E

F

Figure 4. These photos
show the steps involvedin the seeding of Australian akoya pearls. A:
The outermost part ofthe mantle lobe is cut
from a donor mollusk.
B: The outer epithelial
tissue is separated fromthe darker marginal
mantle part using ascalpel. C: The outerepithelial tissue is cut
into small, approximately 2 × 2 mm tissue
grafts (saibo). D: An incision is carefully madein the gonad, while thebivalve is affixed to anoyster stand. E: The 6
mm beads are manufactured from American freshwater mussel
shells. F: Tissue andbead are inserted into
the gonad. Photos by
Laura Otter.

the other hand, are selected for fitness and health toenable optimal proliferation of the tissue graft into anacre-producing pearl sac (Hänni, 2012). The twoAustralian seeders at Broken Bay Pearls were trainedby Japanese specialists who also visit regularly during
harvests. Each year they insert several thousand
beads—exact numbers remain confidential—together with tissue grafts. Two beads are inserted permollusk.
Tissue grafts are prepared following the Japanesemethod. First, the outermost part of the mantle lobe
is removed from the donor (figure 4A) and the outerepithelial tissue is carefully separated from thedarker marginal mantle tissue (figure 4B). Then theouter epithelial tissue is cut into approximately 2 ×
2 mm pieces, known as the saibo or graft (figure 4C).
The gonad in the donor mollusk is opened (figure
4D), and each tissue graft is carefully inserted into
the mollusk together with a 6 mm bead manufactured from American freshwater mussel shells (figure4E). Graft and bead are carefully placed in contact
with each other (figure 4F). Since the gonad tissue itself is unable to produce pearls, the bead must be accompanied by the mantle tissue graft. Following theseeding process, the graft proliferates to form a pearlsac, fully enclosing the bead (Hänni, 2012) and pro-

426

GEMS & GEMOLOGYAUSTRALIAN AKOYA CULTURED PEARLSWINTER 2017

TABLE 1. Characteristics of natural-color cultured pearls from Pinctada imbricata fucata bivalvesfrom eastern Australia.
PhotoaSample no.

Diameter (mm)Weight (ct)

Bodycolorb

Hueb

Overtoneb

BBP01

7.3

3.01

Light yellow

Green

Yellow

BBP02

6.7

2.20

Light yellow

Orange

Gold

BBP03

7.0

2.51

Dark yellow

Orange

Green

BBP04

6.9

2.48

Dark yellow

OrangeGold, orange

BBP05

6.9

2.50

Orange

Brown

Pink

BBP06

7.5

3.03

Pinkish orange

Green

Pink

BBP07

7.4

2.90

SilverBlue

Blue, pink

BBP08

6.8

2.31

White

Silver

Pink

BBP09

7.2

2.66

White

Cream

Pink

BBP10

7.0

2.49

Silver

Green

Blue

BBP13

7.9

3.56

Green

Silver

Pink

BBP14

7.7 × 8.2

3.65

Green

SilverBlue

BBP11c6.7

2.00

Dark blue

Green

Silver, blue

BBP12

7.2

2.48

Silver (darker than BBP07
and BBP10)

GreenBlue, pinka

Images not to scale. Bead sizes are 6 mm for all specimens shown.
Bodycolor, hue, and overtone were determined by visual examination. Bodycolor descriptions follow the GIA scheme (https://www.gia.edu/pearl-description),but extending the scheme was necessary to incorporate the large range of color in these samples.
cColor was found to vary from blue on one side to silver with only a blue hue and overtone on the other. All spectroscopic measurements were taken from theblue side.
b

Harvesting and General Farming Procedures of Australian Akoya Cultured Pearls. After seeding, thePinctada bivalves are returned to the long-line systems in bags or cages, where their food supply is nolonger restricted. Their metabolic activity increases,
and the production of nacre needed for shell growthand pearl development returns to normal. Hence, thebulk of pearl growth occurs during the austral summer months (December to February), when the ani-mals have an increased metabolism and food is abundant. In contrast, a finer and therefore more lustrous
outermost layer of nacre is deposited in austral winter(June to August), when colder temperatures slow
down metabolic and biomineralizing processes(Gilbert et al., 2017).
Bead rejection rates are approximately 10%, whichis relatively low compared to farms in the Federated
States of Micronesia (28%) or southwest India (14%),
while recent rejection rates from Japan were not available in the literature (Kripa et al., 2007 and references
therein; Cartier et al., 2012). Broken Bay Pearls generally allows a longer cultivation time of 18 months
to achieve a thicker nacre, compared to the standard
6–12 months in Japan (Strack, 2006). The longer cultivation time results in a nacre layer around the beadmeasuring approximately 0.8 mm, estimated frompearls used in this study (see bead sizes and diametermeasurements in table 1) as well as verification measurements on a cross section of a low-quality pearl.

AUSTRALIAN AKOYA CULTURED PEARLSGEMS & GEMOLOGY

ducing calcium carbonate, causing the deposition ofnacre onto the bead (Jacob et al., 2011). Hence, therelative position between tissue graft and bead aswell as the position within the pearl sac determine
the eventual shape of the pearl: In the ideal case,when tissue graft and bead are in tight contact, around pearl is formed. Near-round, semi-baroque, orbaroque pearls are formed by an irregular contact between bead and graft that results in cavities or evenloose beads (Hänni, 2012; Otter et al., 2014).

WINTER 2017

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A

B

C

Figure 5. The steps involved in the process of
harvesting Australianakoya pearls. A: Bivalves are removed
from their cages. B: The
separator cleans thepearls from the tissues.
C: Separated pearls arecollected by opening avalve at the bottom of
the machine. D: Wooden
revolving drums areused to wash the pearls
in a saltwater solution.
E: A selection of the
day’s harvest with therange of colors displayed at the front. Photos by Laura Otter.

D

E

This is high compared to Japanese akoya, whose nacre
thickness averages only 0.2 mm in the northern islands and rarely exceeds 0.3 mm in the warmer waters of the southern islands (Strack, 2006).

The pearls are harvested in the austral wintermonths of June and July. Following the Japaneseakoya culturing tradition, pearl oysters at Broken Bay
Pearls are generally not seeded a second time but are

428

GEMS & GEMOLOGYAUSTRALIAN AKOYA CULTURED PEARLSWINTER 2017

removed from their cages (figure 5A) and sacrificed
by cutting through the adductor muscle. A motorized separator (figure 5B) reduces the soft tissues tosmall pieces while the relatively heavy pearls collectat the bottom of the machine and are extracted by
opening a valve (figure 5C). Adhesive organic remains are removed by using a suspension of salt infreshwater (figure 5D), while walnut shells are used
to buff the pearls, a common practice in Japan. The
pearls are spread out on cloth for air drying in sunlight (figure 5E), which could be understood as a minimal maeshori1 luster enhancement, depending on
how strictly this is defined. However, it is emphasized here that no color- or luster-improving substances or processes are otherwise applied—e.g.,dyes, bleaches, or alcohol, which are traditionallyused for Japanese akoya (Gervis and Sims, 1992).
After drying, the pearls are graded for quality, color,luster, shape, and size.

Figure 6. This silver pendant features a round 7.5mm silver akoya pearl from Broken Bay. The silver
disk is etched with a pattern resembling the reflection of the moon on the rippling ocean. Photo courtesy of AngelRock Jewellers.

Figure 7. Naturally white cultured pearls from Broken
Bay: two necklaces, a pair of stud earrings, and threeloose pearls. Photo courtesy of Percy Marks Jewellers.

The farm in Broken Bay produces several thousand pearls per year, and about 50% are of gem quality. The average size ranges from 6.5 to 8 mm and invery rare cases up to 10 mm. Keshi pearls also occur
as a result of the seeding process, as the fragile epithelial cells of the mantle tissue can be injured or
separated and develop into small pearl sacs that produce an additional though unintended small pearl(Hänni, 2006). Broken Bay pearls are cultured in awide range of colors. Bodycolors include the traditional akoya silver and white (figures 6 and 7, respectively), though light and dark yellows appear almost
as frequently and blues are also occasionally seen(again, see figure 1). Intense orange bodycolors (as in
BBP05 and BBP06, table 1) occur very rarely. Overtones range from orange, pink, silver, white, silvergreen, and cream through yellow to gold.
The two seeders at Broken Bay have noticed a difference in the respective proportions of silver towhite, yellow, and blue bodycolors they produced(figure 8). After tracing back and comparing their in-

1
Maeshori treatment aims to enhance a pearl’s luster. This can involve
different chemical (e.g., alcohol or salty solutions) or physical (e.g.,heating and cooling) treatments. It is traditionally applied to Japaneseakoya cultured pearls, often in combination with dyes or bleaches.

AUSTRALIAN AKOYA CULTURED PEARLSGEMS & GEMOLOGYWINTER 2017429

% GEM-QUA
ALITY HARRVVEST (2016)

50

40

30

20

10

0

White/silver

Yellow/gold
Yellow/goldSeeeder 1

Seeder 2

Blue

Figure 8. Broken Bay’s
two seeders tag their own
cages of freshly seeded bivalves to track the proportions of bodycolors
produced. The proportionof white, yellow, and blue
bodycolors is seen to vary
between the seeders, andthis is attributed to slightvariations in the selection of appropriate tissue
graft. The red line shows
the overall abundance ofeach bodycolor as an average of both seeders.
Photo by Laura Otter.

Ave
erage

The lead author attended Broken Bay’s annual pearl
harvest in June 2016 to obtain pearls for this study.
The mollusks were brought to the farm by boat andtaken from the nets and opened by hand. After extraction from the separator, the pearls were spreadout on a cloth and examined. The author visually determined a wide range of bodycolors, including yel-low, silver, white, cream, orange, blue, and light silver-green of various shades and intensities (again, see
figure 5E). A total of 14 saltwater cultured pearls
were selected as representative of each bodycolorgroup for the present study. The pearls were found to
be mostly round (samples BBP01 to BBP13) to semiround (BBP14) in shape. They measured 6.7–8.2 mm
in diameter with an average of 7.2 mm, while theirweight varied from 2.0 to 3.7 ct (table 1).
Raman spectra of each pearl were collected atroom temperature using a Horiba Jobin Yvon
LabRAM HR Evolution confocal spectrometer with
473 nm laser excitation. All Raman spectra wererecorded in the 100–2000 cm–1 range using a spectral
acquisition time of 12 seconds and four accumulations. A grating with 1800 grooves/mm was usedwith a slit width of 100 µm to ensure a high spectral
resolution of approximately 0.8 cm–1. PL spectra
were collected using the same instrument, althoughmeasurement conditions were adjusted to a spectral
acquisition time of eight seconds and five accumulations per cycle, with 532 nm excitation wavelength. Data were collected in the 537–710 nm range
using a grating with 600 grooves/mm to achieve
higher intensities at a spectral resolution of approximately 2 cm–1.
Mid-FTIR spectra were recorded with a Thermo
Scientific Nicolet iN10 infrared microscope using a
149 × 149 μm aperture and an acquisition time of fiveseconds per spectrum. All data were collected with
16 scans per spectrum in the range of 675–3970 cm–1
using a liquid-nitrogen-cooled MCT-A detector sys-

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GEMS & GEMOLOGY

dividually seeded bivalves, which had been color
coded on their cages, the seeders concluded thatwhile cutting and preparing the tissue grafts, theyeach favored slightly different colored tissue pieces,thus influencing the harvested colors.
It is understood that modern pearl farming yields
many positive consequences for the local ecosystem.
The exceptionally high filtering capabilities of thePinctada species, up to 25 liters per gram of dried tissue each day, effectively remove heavy metals, organic
pollutants, and nutrient overloads from coastal environments (Gifford et al., 2004). Hence, pearl farming
reduces turbidity and eutrophication—i.e., the excess
supply of nutrients coupled with high biomass loads.
Turbidity is reduced by the long-line systems, with
their many large cages that act as a barrier for nearsurface currents. Eutrophication is reduced by the highfilter-feeding capacities of the bivalves. Furthermore,
the timber-free long-line systems prevent entanglement of dolphins and other marine species. Following
these environmentally friendly principles, Broken Bay
Pearls has been successful in supplying a wide rangeof Australian wholesalers and jewelers each year.

MATERIALS AND METHODSAUSTRALIAN AKOYA CULTURED PEARLSWINTER 2017

RESULTS AND DISCUSSION

tem and a spectral resolution of 4 cm–1. A background
spectrum was collected in air before each sample
spectrum. Raman, PL, and FTIR data were collected
at Macquarie University’s Department of Earth andPlanetary Sciences in Sydney.
UV-Vis spectra were recorded 16 times per sample
in the 380–800 nm range using a Leica Orthoplan microscope in combination with a Leica MPV-SP UVVis spectrophotometer at Johannes Gutenberg
University in Mainz, Germany. Microscope-based
UV-Vis data acquisition is generally performed without the use of an integrated sphere accessory, which
made it necessary to collect all spectra in specular reflection mode with well-defined incident and reflected light angles (2° in this study). Specularreflection mode uses a thin plate of polished aluminum as reference material, since it has higher reflectance properties than BaSO4 or Spectralon, which
are only used when data collection is performed indiffuse reflection mode. All spectra were collectedusing 32× magnification by focusing on the surfaceof each pearl. Some individual samples (namely
BBP05, BBP07, BBP11, and BBP12) yielded reflectancevalues greater than 100%, which made it necessary
to focus slightly subsurface.

Raman Spectrometry. Figure 9 presents seven representative Raman spectra of Australian akoya cultured
pearls across the range of bodycolors as outlined intable 1 (yellow, orange, silver, white, green, and blue).
The most prominent peaks are assigned to aragonite(black lines), the crystalline calcium carbonate polymorph generally associated with lustrous pearls of thePteriidae family (e.g., Jacob et al., 2011; Wehrmeister
et al., 2011; Hänni, 2012). Among these, the highestintensity band was observed at 1085 cm–1, as well asa doublet with peak centers at 701 and 705 cm–1,
which are assigned to ν1 (symmetric stretching) andν4 (in-plane bending) modes of the carbonate anion(CO32–) in aragonite (e.g., Urmos et al., 1991). The
small peak at 1462 cm–1 is identified as ν3 (in-plane
asymmetric stretching); due to its low intensity, thispeak is not observed equally well in all pearls. In addition, aragonite lattice modes were observed between 170 and 300 cm–1 (Urmos et al., 1991). All
pearls showed virtually identical peak centers, intensities, and backgrounds except for the darkest one(BBP11), which had a slightly increased background(again, see figure 9). This is due to a stronger contribution of luminescence in the background signal, pos-

R AMAN SPECTR A
1085

701

705
1462
1532

INTENSITY

1134

BBP14
BBP11
BBP09
BBP08
BBP06
BBP03
BBP01
200

400

600

800

1000

1200

1400

1600

1800

Figure 9. Raman spectraof seven Broken Bay
akoya cultured pearls
from Pinctada imbricata
fucata normalized to thehighest-intensity peak at
1085 cm–1 and offset forclarity. The selection
shows a cross section of
bodycolors ranging fromlight yellow (BBP01,
BBP03), orange (BBP06),
white (BBP08), silver(BBP09), and dark blue
(BBP11) to green(BBP14). The spectra
show identical bands foraragonite (black lines),
while two remaining
peaks are attributed topigments (red lines).

RAMAN SHIFT (cm–1)

AUSTRALIAN AKOYA CULTURED PEARLSGEMS & GEMOLOGYWINTER 2017431

sibly related to pigments contributing to the pearl’sdark blue color.
Peaks of weaker intensity (figure 9, red lines) corresponded to distinct bands of pigments (polyenes)
consistent with previously published values (e.g.,
Karampelas et al., 2007; Soldati et al., 2008; Karampelas et al., 2009; Bersani and Lottici, 2010). These
include peaks at 1134 and 1532 cm–1 that belong to
the stretching modes of the C-C single bond (ν2) and
C=C double bond (ν1) in the polyene chain biomolecule, respectively. Samples with darker bodycolors
such as dark blue (BBP11), orange (BBP06), and dark
yellow (BBP03) displayed the highest intensities forboth pigment-related peaks, while green (BBP14),
white (BBP09), and light yellow and yellow (BBP01)
pearls exhibited much lower intensities. For thewhite specimen BBP08, the peaks were undetectable.

as well as discrete peaks, caused by vibrationalmodes of the carbonate ion, at 552 nm (in-planebending, ν4), 565 nm (symmetric stretching, ν1), 577
nm (in-plane asymmetric stretching, ν3), and 630 nm(caused by ν1 + ν3; Xu and Poduska, 2014). The four
PL bands had positions similar to those previously
published for cultured pearls from Pinctada maxima,
Pinctada margaritifera, Pinctada mazatlanica, andPteria sterna, at 620, 650, and 680 nm; however, theweak band at 585 nm has not been described forthese species (Miyoshi et al., 1987; Kiefert et al.,
2004; Karampelas et al., 2011; Karampelas, 2012). It
should be noted that all bands appear less defined forthe akoya pearls than for those produced by Pinctada
maxima, Pinctada margaritifera, and Pteria sterna.
PL features in pearls are generally thought to result
from organic compounds within the nacre composite
material (Karampelas et al., 2007). This is consistent
with our observation that the relative PL intensity
correlated with color intensity in the specimens andstronger pigment-related Raman bands (figure 9).

Photoluminescence Spectrometry. All PL spectra
showed virtually identical features in the yellow to
red region at 585, 610, 625, and 685 nm (figure 10).
Sharp peaks in the spectra resulted from the Raman
effect and occurred independently of the PL bands.
These included features in the 538–540 nm region(vibrational properties of the aragonite lattice modes),Mid-FTIR Spectrometry. The most prominent features
observed in the spectra of cultured pearls from Australian Pinctada imbricata fucata were caused by the

PHOTOLUMINESCENCE SPECTR A
BBP11
BBP06
BBP14
BBP01
BBP03
BBP09
BBP08
610

625

INTENSITY

585

685

540

560

580

600

620

640

660

680

700

WAVELENGTH (nm)WA

432

AUSTRALIAN AKOYA CULTURED PEARLSGEMS & GEMOLOGY

Figure 10. Uncorrected
photoluminescence (PL)spectra of the sevenakoya cultured pearls
whose Raman spectra
are shown in figure 9.
Spectra are offset forclarity while maintaining their original orderof relative PL intensities. All spectra show
identical features at585, 610, 625, and 685
nm, with varying
amounts of luminescence that correlatewith the color intensityof the samples. Peaks inthe 538–540 nm region
as well as at 552, 565,
577, and 630 nm originate from the Raman
effect of aragonite.

WINTER 2017

FTIR SPECTR A

700
712

1792
877

REFLE
REFLECT
ECT
TA
ANCE

REFLE
ECT
TA
ANCE

1115 1080
1200

1447
7

1474
2400

2200

2000

1800

1600

1400

1200

1000

800

600

1350

1300

WA
AV
VENUMBER (cm–1)

1250

1200

1150

1100

1050

1000

WA
AVENUMBER
VENUMBER (cm–1)

Figure 11. Left: The mid-FTIR spectrum of an orange sample from Broken Bay Pearls (BBP05) shows bands at 700,
712, 877, 1447, 1474, and 1792 cm–1 that are characteristic for aragonite and were found in all other samples.
However, this sample also shows several weak peaks in the 1000–1350 cm–1 region (red box in A). Right: Enlargement of this region reveals several small peaks at around 1200 and 1115 cm–1 that are assigned to sulfate andpolysaccharide groups of the organic component. The weak band at 1080 cm–1 results from stretching vibrationsof the carbonate.

intrinsic vibrational modes of the aragonite crystal lattice (figure 11, left), namely ν4b and ν4a at 700 and 712
cm–1 (internal modes), ν2 at 877 cm–1 (out-of-planebending mode), and ν3 at 1447 cm–1 (in-plane asymmetric stretching). Strong absorption bands in the 1600–
1400 cm–1 range resulted from several closely spaced
peaks at 1570, 1525, 1488, 1474, and 1440 cm–1 (Andersen and Brecevic, 1991; Xu and Poduska, 2014). The
highest-intensity band at 1474 cm–1 was previously
found to result from a combination of the lattice mode
peaks at 220, 263, 290, and 700 cm–1 (Andersen andBrecevic, 1991; Xu and Poduska, 2014). A weak bandat 1792 cm–1 was caused by a combination of the ν1 andν4a modes, while ν1 (symmetric stretching vibration)
was observed in figure 11, right (an enlargement of the
red box in figure 11, left). Three other bands in figure
11 (right) can be attributed to different organic compounds in nacre: Broad bands at around 1200 and 1115
cm–1 likely resulted from S-O of sulfate and C-O ofpolysaccharide groups, respectively (Marxen et al.,1998). The peak at 1080 cm–1 is assigned to the symmetric stretching vibration (ν1) of CO32–.
UV-Vis Spectrometry. The pearls were grouped into
different UV-Vis spectra with similar characteristics.
For better readability, overlapping spectra were offset
by adding or subtracting each measured intensity

value with a fixed offset value expressed as a percentage relative to the original measured intensity (figure12). The specimens shown in figure 12A consist of
two pearls of a rather cooler shade of yellow, whichmight result from green hues and/or overtones(BBP01 and BBP03), plus silver (BBP10) and green(BBP14) samples. They are characterized by a slight
spectral trough in the blue-green to yellow region between 450 and 600 nm (except for BBP01) and have a
sharp drop in relative intensity from approximately
645 nm onward. The light yellow specimen BBP01(table 1) has the brightest bodycolor, which correlateswith the highest relative intensity. Of the two pearlsin figure 12B, one has a light silver bodycolor with ablue hue and overtone (BBP07) and the other a dark
blue (BBP11) bodycolor with green, blue, and silver
hues and overtones (hues and overtones determinedby visual observation). The spectrum of the dark blue
pearl (BBP11) shows two distinct troughs at 425–530
nm (blue to green region) and 550–625 nm (green toorange region), while the silver specimen (BBP07) has
a trough at 425–625 nm. Both pearls display a sharp
drop in reflectance at 625 nm. A lower intensity overthe full spectral range is responsible for the dark colorof BBP11; specimen BBP07 shows a similar pattern,
but at an overall higher relative intensity that corresponds to its brighter color. Figure 12C shows spectra

AUSTRALIAN AKOYA CULTURED PEARLSGEMS & GEMOLOGYWINTER 2017433

UV-VIS SPECULAR REFLECTTANANCE SPECTR A

A

B

BBP07 +5%
BBP11 0%

REFLLECTTAANCEREFLLECTTA
ANCE

BBP01 +20%
BBP10
0%
BBP03 –5%
BBP14 –10%

400

450

500

550

600

650

700

750

800

400

450

500

WA
AVELENGTH
VELEN
NGTH (nm)

C

550

600
0

650

700

750

800

WA
AVELENGTH
VELENGTTH (nm)D

BBP09 +15%
BBP08 +10%
BBP02 –10%
BBP04 –10%
BBP12 –10%

REFLECTTA
ANCEREFLECTTA
ANCE

BBP05 +10%
BBP06 0%BBP13 –5%

400

450

500

550

600

650

700

750

800

400

450

WA
AVELENGTH
VELENGTH (nm)

500

550

600
0

650

700

750

800

WA
AVELENGTH
VELENGTTH (nm)Figure 12. UV-Vis specular reflectance spectra of 14 Australian akoya samples normalized to the reflectance yieldof a polished aluminum plate. Some spectra are offset for clarity, with offset values provided in the legends.

for the pearls with orange bodycolor (BBP05 and
BBP06) as well as for a green specimen with warm
pink and silver hues and overtones (BBP13). These
specimens exhibit distinct absorption features between 400 and 475 nm and between 600 and 800 nm
that correspond to the blue region and the orange to
red region, respectively. At 800 nm, relative intensities drop to below 55%. Lastly, figure 12D shows
spectra for pearls that exhibit white (BBP08 and
BBP09), dark silver (BBP12), and yellow bodycolors(BBP02 and BBP04). Note that the pearls with yellow
bodycolor from figure 12D have orange and golden
hues and overtones, while the other yellow specimens in figure 12A show green and yellow hues andovertones. Their spectra lack distinct absorption features and differ only in relative intensity.

Altogether, each pearl’s bodycolor is strongly dependent on its specific absorption features and relative intensities, which are produced by different
combinations of pigments present in the organic
compound of the nacre (Soldati et al., 2008; Karampelas et al., 2009; Karampelas, 2012). The bodycolor
was found to correlate with the overall relative intensity of the PL spectra (figure 10), where the dark
blue specimen (BBP11) exhibited the highest relative
PL intensity, while the yellow, white, and silver samples had the lowest.
Although the pearls from this study show a wide
variety of spectral features, they can be differentiatedfrom untreated pearls of some other species: Gray,yellow, and black pearls from Pinctada margaritifera
as well as gray, yellow, and green pearls from Pinc-

434

GEMS & GEMOLOGYAUSTRALIAN AKOYA CULTURED PEARLSWINTER 2017

tada mazatlanica show a distinct trough at 700 nm
that is not present in any of the akoya pearls from thisstudy. In those pearls, the feature is associated withthe presence of pigments (Miyoshi et al., 1987; Elen,
2002; Karampelas et al., 2011; Cartier et al., 2012).
Further, dark gray pearls from both Pinctada margaritifera and Pinctada mazatlanica show an absorption
feature at 405 nm that is known to result from uroporphyrin pigments (Homkrajae, 2016, and reference
therein). Yellow pearls from Pinctada maxima show
a broad trough from 310 to 510 nm, with individualabsorption features centered at 360 and 430 nm. Thisdistinguishes them from the Pinctada imbricata fucata pearls from this study, which also show various
absorption features at higher and lower wavelengths(table 2). While discrimination between naturally colored pearls across different saltwater species appears
promising, naturally colored white akoya pearls remain indistinguishable from untreated white pearls
produced by other mollusks, due to the absence ofcharacteristic spectral features. Also, the discrimination of naturally colored akoya cultured pearls produced in eastern Australia from others of different

geographic origin is considered beyond the capabilityof this method.

CONCLUSIONS
We have presented a description and characterizationof akoya cultured pearls from the Central Coast region of New South Wales in eastern Australia. Apartfrom the absence of bleaching or dyeing procedures,the pearls are cultured following the Japanese tradition. Their natural variety of bodycolors ranges fromlighter and darker golden yellows to different shades
and intensities of orange and blue to the classic silver
and white. These colorful akoya pearls can be used
to create modern, nature-inspired jewelry (see figures
1 and 6) as well as classic pieces (figure 7).
Raman and FTIR spectroscopy verified the mainmineral phase as aragonite (figures 9 and 11), and pigment-related Raman bands were observed at 1135
and 1530 cm–1. These belong to stretching modes of
the C-C single bond and C=C double bond of thepolyene chain biomolecules. These peaks were foundto have the highest intensities for samples withdarker bodycolors, such as dark blue, orange, and yel-

TABLE 2. Summary of color and corresponding absorption centers of untreated cultured pearls from P. fucata,
P. margaritifera, and P. maxima.
Mollusk species

P. imbricata
fucataP. margaritifera

Pearl bodycolor

Absorption centers in specific range (nm)350–450

450–550550–650

650–800

Silver

None

None

~550a

775

Yellow (cool hue and overtone)

None

None

~550a

c.a.b

Yellow (warm hue and overtone)

None

None

None

c.a.

References

This study

White

None

None

None

c.a.

Orange

430

None

None

~720a

Green

~430a

None

~550a

~720a

Silver with strong blue overtone

None

513

None

c.a.

Dark blue

None

510

580

~750a

White and silver

None

None

None

None

Elen (2002)

Gray

None

460, 495

None

700

Karampelas (2012)

Yellow

None

None

None

700

Elen (2002)

Black

405

495

None

700

P. maxima

Yellow

360, 430

495

None

None

Elen (2002)

Gray

None

460, 495

None

None

Karampelas (2012)

P. mazatlanica

Dark gray

405

None

None

700

Yellow to green

~358a

~423a

None

700

White and silver

None

None

None

None

Homkrajae (2016)aApproximate peak center due to a very broad or indistinct featurec.a. = continuous absorptionb

AUSTRALIAN AKOYA CULTURED PEARLSGEMS & GEMOLOGYWINTER 2017435

low (figure 9, red lines). The pearls showed four
rather indistinct PL bands in the yellow to red regionof the electromagnetic spectrum (figure 10), whichwere similar to the band positions observed for Pinctada maxima, Pinctada margaritifera, Pinctada
mazatlanica, and Pteria sterna bivalves (though not
as prominent). FTIR spectroscopy of an intense orange pearl revealed the presence of sulfates and polysaccharides representative of organic compounds(figure 11). Lastly, UV-Vis specular reflectance spec-

troscopy showed several absorption features in thevisible range that result from the pearls’ different
bodycolors, hues, and overtones (figure 12, A–D).
This technique was found to be useful in discriminating between diverse colorful akoya pearls fromthis study and cultured pearls from Pinctada margaritifera, Pinctada mazatlanica, and Pinctada maxima bivalves (table 2), while akoya pearls from otherlocations as well as white specimens from various
species are likely not distinguishable.

ABOUT THE AUTHORS
Ms. Otter (laura.otter@hdr.mq.edu.au) and Mr. Agbaje are PhD
candidates at the Macquarie University Department of Earth andPlanetary Sciences in Sydney. Dr. Huong is postdoctoral researcher at the Institute of Earth Sciences, Karl Franzens University in Graz, Austria. Dr. Häger is a scientist at the Centre for
Gemstone Research at Johannes Gutenberg University in Mainz,
Germany, and lectures at the Gemstone and Jewelry Design Department at the University for Applied Sciences in Idar-Oberstein.
Dr. Jacob is professor of earth sciences and biomineralization at
Macquarie University.

questions. Dr. Jennifer Rowland is kindly thanked for skillful editing of the final manuscript. We thank Ursula Wehrmeister, Dilmi
Herath, Michael Förster, Christoph Lenz, and Matthew A. Kosnik
for many enriching discussions. Dr. Wayne O’Connor, center director for aquaculture at the Port Stephens Fisheries Centre,
NSW Department of Primary Industries, is kindly acknowledged
for insightful comments on an earlier draft. Furthermore, we thankCeleste Boonaerts from AngelRock Jewellers, Cameron Marksfrom Percy Marks Jewellers, and Wayne O’Connor for providing
photographs. This work is part of the lead author’s PhD thesis;
she is supported by an Australian Government International Postgraduate Research Scholarship (IPRS). Mr. Agbaje is supported
by a Macquarie University Research Excellence Scholarship, and
Dr. Jacob is financially supported by the Australian ResearchCouncil via a Future Fellowship and a Discovery Grant. Lastly, we
thank three anonymous reviewers for providing very constructive
and valuable comments.

ACKNOWLEDGMENTS
We gratefully acknowledge Ian and Rose Crisp as well as Peter
Clift from Broken Bay Pearls Pty Ltd for the opportunity to visit
their pearl farm during seeding and harvest season, and for providing all the pearls shown in this study and answering all our

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AUSTRALIAN AKOYA CULTURED PEARLSGEMS & GEMOLOGYWINTER 2017437

NOTES & NEW TECHNIQUESACCURATE REPORTING OF
KEY TRACE ELEMENTS IN RUBY AND SAPPHIRE
USING MATRIX-MATCHED STANDARDS
Jennifer Stone-Sundberg, Timothy Thomas, Ziyin Sun, Yunbin Guan, Zachary Cole, Randy Equall, and John L. Emmett

See end of article for About the Authors and Acknowledgments.
GEMS & GEMOLOGY, Vol. 53, No. 4, pp. 438–451,
http://dx.doi.org/10.5741/GEMS.53.4.438© 2017 Gemological Institute of America

ment detection techniques used today for analyzingmineral species—electron microprobe, X-ray fluorescence (XRF), secondary ion mass spectrometry(SIMS), laser-induced breakdown spectroscopy (LIBS),
and laser ablation–inductively coupled plasma–massspectrometry (LA-ICP-MS)—require standards foreach trace element of interest. Essentially, these sophisticated and expensive instruments that allow us
to quantify the trace elements in gems can only be
as accurate as the standards used. With gemologicallaboratories issuing origin reports for ruby, sapphire,
and other gems, it is essential to have a high level ofcertainty associated with the quantitative determination of trace element chemistry. The standard’s“matrix,” the material that it is comprised of, matters a great deal: Matching both the composition andstructure of the standard to those of the sample being
analyzed will yield the most accurate results(Sylvester, 2008). For example, trace levels of vanadium in ruby (or any of the colors of sapphire) aremost accurately quantified by comparing against apiece of single-crystal corundum with a known levelof vanadium in it as opposed to some other material
containing vanadium, such as silicate glass.
However, commonly used standards such as
those produced by the National Institute of Standards
and Technology (NIST) are generally not available inmatrix-specific forms, so silicate glasses such as NIST
Standard Reference Materials (SRM) 610 and 612 are
frequently applied. As the silicate glass matrix differs
significantly from the crystalline alumina matrix ofsapphires and rubies in both composition and structure, what is known as a “matrix effect” can occur.
This effect leads to inaccuracy for many of the key
trace elements characterized. A potential outcome ofcalibrating an instrument with a matrix different
from the sample to be measured is the enhancement
or suppression of trace element levels detected(Strasheim and Brandt, 1967). Furthermore, NIST
SRM 610 and 612 glasses are not certified for manyof the trace elements they are being used for, as is thecase for corundum, and both have been shown to

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GEMS & GEMOLOGY

To improve the accuracy and efficiency of traceelement analysis in ruby and sapphire, standards
sets containing matrix-matched corundum withtargeted levels of beryllium, magnesium, silicon,
titanium, vanadium, chromium, iron, and gallium were created. Ultra-high-purity corundum
was also incorporated as a “true matrix zero.” To
our knowledge, these sets contain the most accurate standards for the key trace elements incorundum today. The standards were designed tocover the optimal range of the main trace elements typically characterized in natural ruby andsapphire. Additionally, we were able to accurately quantify silicon in corundum by success++fully resolving the 28Si peak from the 27Al1H
peak using the superior mass resolving power of
secondary ion mass spectrometry (SIMS) as compared to laser ablation–inductively coupledplasma–quadrupole mass spectrometry (LA-ICPQMS).

To correctly assign geographic origin (Emori and
Kitawaki, 2015; Sutherland et al., 2015), formation history (Peucat et al., 2007), and color mechanisms (Emmett et al., 2003) in ruby and all colors ofsapphire, accurate key trace element data is an essential component. As magnesium, titanium, vanadium,
chromium, iron, and gallium are found in all natural
sapphire in varying amounts, these trace elements
are identified as the key trace elements for natural
corundum. Additionally, beryllium is significant toquantify, as the presence of this trace element can indicate treatment. The various quantitative trace ele-

NOTES & NEW TECHNIQUESWINTER 2017

02-1032-01

07-0687-01

YOGO 7NIST 610

UHP BLANK
99-113-05 E

Figure 1. One of GIA’s
new LA-ICP-MS corundum calibration standards sets (set number
1); the epoxy disk containing the set is 1.5
inches in diameter. NIST
SRM 610 and 612 glass
standards are included
to account for trace andnon-trace elements, suchas those found in inclusions, that were not incorporated into thesynthetic sapphire crystals grown for standards.
Photo by Jennifer StoneSundberg.

NIST 612

demonstrate variability (Pearce et al., 1997). Of the
key trace elements normally analyzed in corundum,
these glasses are only certified for iron and chromium(certificates of analysis from NIST are available athttps://nemo.nist.gov/srmors/certificates/view_certGIF.cfm?certificate=610 and https://nemo.nist.
gov/srmors/certificates/view_certGIF.cfm?certificate=612). Another drawback to the NIST glasses forcorundum: Aluminum is present at low concentrations (around 1 wt.%) in the NIST glasses but is amajor element in corundum (around 52.9 wt.%). The
projection from low concentration to high concentration from the standards to unknowns can introduce significant error—projections work best whensimilar concentrations are compared between standard and unknown.

Due to concerns regarding composition and structure matrix effects, GIA decided years ago to generate
corundum standards for its LA-ICP-MS instruments(Wang et al., 2006). After a decade of use for both production and research applications, new standards sets
have been created to further improve accuracy (discussed in the Background section) and efficiency. To
optimize the new standards sets for regular laboratory use, each individual set contains a minimum
number of standards (in our case, four pieces ofcorundum and NIST SRM 610 and 612 glasses embedded in epoxy—see figure 1), reasonably capturing
the range of interest for each key trace element to bequantified. As there is a need to characterize many
samples routinely for origin reporting, efficiency isparamount. We reduced calibration time by combining as many trace elements as possible into single
standards. We accomplished this by growing “multidoped” synthetic corundum crystals. Instead of having only one or two of the trace elements of interestin a single standard, we worked with FLIR's crystal
growth group, Scientific Materials of Bozeman, Montana, to produce highly uniform Czochralski-grownsingle crystals of corundum containing up to six intentionally doped trace elements (figure 2). To incorporate beryllium into the standards, slices from oneof these custom-grown crystals were diffused withberyllium for 100 hours at 1800°C in pure oxygen,generating one standard in which seven trace elements can be calibrated at the same time. Beyond re-

NOTES & NEW TECHNIQUESGEMS & GEMOLOGYIn Brief• New corundum standards have been developed for
improved accuracy and efficiency in trace element
quantification using LA-ICP-MS.
• A true matrix-matched zero was introduced to further
minimize matrix effects.
• The GIA research collection was used to establish
meaningful target levels of the trace elements of interestfor the standards.

WINTER 2017439

Figure 2. Crystal boules
grown by Scientific Materials for multi-doped
corundum standards:
sample 02-1032 (top)and sample 07-0687(bottom). Both crystals
were doped with Mg, Ti,
V, Cr, and Ga in different amounts; only 021032 was successfully
doped with Fe. Crystal
02-1032 is 40 mm in diameter by 150 mm inlength at diameter, andcrystal 07-0687 is 30
mm in diameter by 150
mm in length at diameter. Photos courtesy of
Scientific Materials.

ducing instrument calibration time, this approach of
fewer individual measurements in the calibration
cycle also enhances accuracy, precision, and repeatability, as there is less chance for instrument signal
drift, and therefore more accurate conversion of instrument signal into trace element concentrations.
Even with this approach, it was impossible to incorporate all of the trace elements of interest into thesynthetically grown crystals at levels that best represented what is found in natural corundum. As wewere unable to produce a standard for mid-range tohigher iron levels and moderate silicon concentrations with Czochralski growth, we selected a seriesof natural sapphires from Yogo Gulch, Montana.

BACKGROUND
Original and Next-Generation Corundum Standards
Sets. The first corundum standards sets GIA createdfor its LA-ICP-MS instruments focused on accuracy
by using matrix-matched standards. These sets consisted of seven different corundum standards: one
high-iron natural sapphire and six syntheticallygrown sapphire crystals with either one or two intentionally doped trace elements each. A need for increased accuracy, better targeting of trace elementlevels in natural ruby and sapphire, and enhanced efficiency led to the development of the current generation of standards sets. To this end, we focused on
the following criteria while minimizing uncertainty:
1. Using corundum that clearly displays highly
uniform levels of the trace elements of interest

440

NOTES & NEW TECHNIQUES

2. Capturing the appropriate ranges of the trace elements in our standards by matching them tolevels occurring naturally in sapphire and ruby3. Developing a high-purity blank sample torepresent the absence of trace elements incorundum
4. Using the most accurate methods available forcorundum as the basis of our calibration work
Uniformity of Trace Elements in the Standards. Fora standard to produce accurate and reproducible results, it must be extremely homogenous (even more
so for a spot method such as LA-ICP-MS than for abulk method). Czochralski-grown synthetic crystalsof corundum and other matrices are known for their
exceptional crystal quality, including highly uniform
distributions of trace elements. Demand in the 1960s
for ruby crystals suitable for lasers led to the refinement of the Czochralski technique for the production of commercial solid-state lasers (Harris, 2004).
For this reason, we chose the Czochralski techniqueas our growth method. As mentioned above, producing Czochralski-grown corundum with mid-range tohigh levels of iron and moderate levels of silicon was
not practical, so we sourced extremely uniform Yogo
sapphire crystals (shown in figure 3) from Eric Braunwart of Columbia Gem House (Vancouver, Washington). Surprisingly, we found with SIMS that inaddition to iron, several of the other key trace elements of interest for corundum—including Mg, Si,Ti, and Ga—were as uniformly distributed in the natural Yogo sapphires as they were in the Czochralski-

GEMS & GEMOLOGYWINTER 2017

grown material. We have confirmed that silicon andnickel are also present in Yogo sapphires in amounts
up to 26 and 12 ppma, respectively, and are likewise
homogenously distributed.
Targeting the Trace Element Levels in the Standards.
To best determine the concentrations of trace elements in unknown samples, it is optimal to havestandards that contain similar to somewhat higher
levels of the same trace elements. We attempted tocreate standards with concentrations at the 50th percentile or higher of the key trace elements found innatural sapphire and ruby based on data from the GIA
research collection. GIA has been gathering and cataloging natural ruby and sapphire from identified
sources worldwide as part of its reference collection
effort. The purpose of this collection is to carefully
document material from each accessible source andto produce detailed information on the inclusions andtrace element chemistry by location (Chapin et al.,2015; Pardieu and Vertriest, 2016). This collection
contains over a thousand samples and is one that GIA
adds to each time its field gemologists visit a uniquemining area of commercial interest or significance.
The collection includes basalt-related sapphire, metamorphic sapphire, marble-hosted ruby, high-iron
ruby, and additional types of corundum beyond these

Figure 3. One of the slices of Yogo sapphire selected
for its uniformity of blue color. The slice weighs 0.117
grams and measures approximately 5.8 × 7.6 × 0.9
mm. The small dots are laser ablation spots. Photo by
John L. Emmett.

TABLE 1. Key trace elements in natural corundumfrom GIA’s reference collection.

Traceelement

Levels of natural occurrence (ppma)
Sapphire
Ruby
50th
75th
50th
75th
percentile
percentile
percentile
percentile

Mg

50

75

40

100

Ti

55

100

50

85

V

5

10

15

100

Cr

2

5

900

1300

Fe

210

620

325

845

Ga

20

25

10

15

four categories. The samples measured include gem
and non-gem quality, and for the key trace elements,
the data was quantified using the original corundum
standards sets. For our purposes, we are limiting thediscussion to these key trace elements that are foundin the corundum matrix, and not those found in inclusions.
Using data from the GIA reference collection, we
considered the entire range of each key trace element
detected, with the 50th and 75th percentiles presented in table 1. It is worth noting that the highest
levels detected can be considerably higher than the75th percentile levels reported. For beryllium, where
we were interested in detecting diffusion treatment(Emmett et al., 2003), we targeted around 60 ppma, alevel sufficient to distinguish between diffused samples (where the surface of the gem can show significant beryllium levels) and undiffused samples (withberyllium levels that are undetectable or very low,such as 1–2 ppma).
Introduction of a Matrix-Matched Zero. The newstandards sets address accuracy in part by incorporating a true matrix-matched “zero”—a piece ofultra-high-purity sapphire containing essentially no
detectable trace elements. Using this approach ofdefining the zero signal point for each of the trace elements as the pure matrix instead of a backgroundof solely helium gas minimizes matrix effects, as interferences will be eliminated and the zero point of
the calibration line will now be far more accurate(Lin et al., 2016). Standard undoped colorless sapphireand high-purity alumina powders used commerciallystill contain several ppmw of various trace elements
such as chromium, titanium, magnesium, and iron.
For example, high-purity alumina with a 5N designation (meaning “five nines,” or 99.999% purity) stillcontains up to 10 ppmw combined trace elemental

NOTES & NEW TECHNIQUESGEMS & GEMOLOGYWINTER 2017

441

Step 1

Starting Material

Calibration Method

Standard

A BC

Rutherford backscattering spectrometry(RBS) for quantifying
Ti, V
V,, Cr, Fe, and Ga(consensus SIMS
results for Be, Mg,
and Si)

The ion implants are
now ready to use as
calibration standards
for secondary ion mass
spectrometry (SIMS)

Ion implant wafers: one sapphire wafer
each for Be, Mg, Si, Ti, V
V, Cr, Fe, and Ga

02-1032-01 07-0687-01
A

Step 2

A

B

C

A

B

C

A

B

C

B

F

E

D

F

E

D

F

E

D

C

G

H

I

G

H

I

G

H

I

SIMS for Be, Mg,
Si, Ti, V
V,, Cr, Fe,
and Ga levels andpoint-to-point
variation

The four sapphire pieces to be calibrated: high-purity baseline, two multi-doped
Czochralski-grown, and natural Y
Yogo
ogo sapphire

NIST 610

YOGO 7
UHP BLANKNIST 612
LA-ICP-MS calibration
standards sets
assembled

Figure 4. The process outline used to create the new corundum calibration standards.

Ensuring Accuracy. As mentioned earlier, the accuracy of the measurements obtained from standardsdependent quantitative analytical techniques employedby many research laboratories is limited by the adequacy of the standards used. To improve the accuracyof the new standards sets over the original sets, many
steps were taken to develop a highly accurate calibration methodology with minimal combined uncertainty (figure 4). We sought a method based on firstprinciples for determining the levels of the trace elements of interest in our standards. In other words, we
wanted a way of determining trace element levels incorundum that did not require referencing the levelsof those same trace elements in some other standard(i.e., a noncircular method). This led us to an approach
used by the geology community in which individual
ion implant doses verified by Rutherford backscattering spectrometry (RBS) are used to calibrate the SIMS
apparatus prior to measuring final samples (Burnett
et al., 2015). As the concentrations of the ion implants
arrived at from the voltage and current settings areaccurate to only about 30% (Burnett et al., 2015)—an
unacceptable level of uncertainty for our purposes—
the actual dosing levels achieved for each ion-implanted wafer were determined through multiple RBS
characterizations (or for the lighter isotopes 9Be, 24Mg,
and 28Si where this was not practical, through amethod described below). RBS is a nondestructive
first-principles (standardless) quantitative analyticaltechnique that is capable of 1% absolute accuracy(Colaux and Jeynes, 2014). SIMS was chosen as ourtechnique for performing the ultimate calibration
work on the final corundum standards, as it is a precise technique with fine mass-resolving power capable of quantifying all of the elements of interest to us.
As trace elements are not distributed with absolute uniformity in synthetic sapphire, and each natural Yogo sapphire slice will have its own
composition, nine points on all individual pieces for

442

GEMS & GEMOLOGY

impurities. For our purposes, it was important to obtain undoped sapphire of significantly higher purity—ideally 6N or better. To accomplish this, themost refined single-crystal sapphire known to us was
acquired from Chandra Khattak of the former Crystal
Systems Corporation (sold to GT Advanced Technologies in 2010). The single-crystal sapphire wasmaterial that had been recrystallized multiple times
using the heat exchanger method (HEM) to further
reduce the impurity levels found in the original aluminum oxide raw material (Khattak and Schmid,
2001).

NOTES & NEW TECHNIQUESWINTER 2017

each standards set were characterized by SIMS (seefigure 4). Simply put, the same standard type in eachstandards set has its own unique set of values. Thisis quite a departure from the SRM NIST 610 and 612
glasses, where most researchers refer to published tables for the concentrations of the trace elements (certified and uncertified) contained within any piece ofa particular series of NIST glass, of which there arethousands of pieces worldwide (Pearce et al., 1997).
For example, the chromium level in a Czochralskigrown corundum crystal is nearly uniform from top
to bottom, but its distribution coefficient will resultin pieces from the bottom of the crystal having levels
slightly lower than those from the top. To label theentire crystal as having a single chromium concentration would result in inaccuracy. As SIMS can easily
quantify not only differences between the top andbottom of the crystal, but also point-to-point differences across areas less than one square millimeter,
we made sure to quantify the levels of chromium (andall of the other trace elements) individually for eachseparate standard piece from each source. These characterized standards were now ready to be assembled
into finished sets for GIA’s LA-ICP-MS instruments.
To most accurately report data based on our new
corundum standards, it is necessary to calculate thetotal uncertainty in the final values for each trace element in each standard, factoring in all measurement
and instrument errors and uncertainties. We accounted
for all of the sources of errors and uncertainties to thebest of our ability and combined them via the root sumof the squares method following the NIST-referenced
INC-1 (1980) recommendation reached by the Working Group on the Statement of Uncertainties, approved by both the International Committee for
Weights and Measures (CIPM) and the International
Bureau of Weights and Measures (BIPM).

MATERIALS AND METHODS
Crystals for Standards. Crystal Growth. As mentioned, we selected the Czochralski method, known
for producing crystals of high quality with uniform
doping of trace elements, to grow synthetic sapphire
crystals containing the key trace elements for ourstandards. After many crystal growth runs to best understand the doping characteristics of each trace element of interest, two final crystals were grown by
Scientific Materials to provide material to be used inour standards sets. These two samples were both
doped with the trace elements Mg, Ti, V, Cr, Fe, and
Ga. Crystal 02-1032 had lower concentrations of Mg,

NOTES & NEW TECHNIQUES

Ti, and Cr and higher concentrations of V, Fe, and Ga;
crystal 07-0687 had lower concentrations of V, Fe,
and Ga and higher concentrations of Mg, Ti, and Cr(figure 2 top and bottom, respectively). Pieces fromcrystal 02-1032 were subsequently diffused with Be
for a period of 100 hours at 1800°C in pure oxygen toprovide a standard for this trace element. From eachof the two boules, seven polished slices measuring 8
× 10 × 2 mm were fabricated by Scientific Materials.
These seven pieces from each boule constitute onlya small fraction of the total available material for thetwo boules.
Both crystals were grown directly from the melt
at approximately 2050°C and pulled from iridium
crucibles using seeds at an orientation 60° off the caxis (the growth direction was perpendicular to then-plane, to facilitate growth of more defect-free material). The raw materials used were 5N purity powders of Al2O3 and dopant metal oxides. After the
powders were loaded into iridium crucibles, the crystals were grown in a nitrogen atmosphere containing
3,000 ppmw oxygen. The crystals were pulled at an
extraction rate of 0.015 inches (0.38 mm) per hour.
The final size of crystal 02-1032 was 40 mm in diameter by 150 mm in length at diameter. The final sizeof crystal 07-0687 was 30 mm in diameter by 150
mm in length at diameter.
Magnesium, titanium, and vanadium were “wellbehaved ions” under the growth conditions used, inthat they did not exhibit vaporization and their incorporation into the crystals was predictable basedon our knowledge of their distribution coefficients.
For chromium, iron, and gallium, some vaporization
was noted and they were less predictably incorporated into the grown crystals under the conditions
used. Therefore, maintaining well-controlled growth
conditions to reduce variability was critical.
Ultra-High-Purity Corundum. The ultra-high-purity
corundum was obtained from the former Crystal Systems, which employed the HEM technique for producing UV-grade sapphire. To enhance the purity ofthe material, the sapphire was recrystallized multiple
times (C. Khattak, pers. comm., 2003). Ultimately,
we determined a combined total ppma level of lessthan 0.5 for the key trace elements in this material.
Seven finished pieces were fabricated from this material by Scientific Materials.
Yogo Sapphire. Several polished slices of highly uniform light blue Yogo sapphire crystals were carefully
selected by Eric Braunwart of Columbia Gem House.

GEMS & GEMOLOGYWINTER 2017

443

TABLE 2. Consensus SIMS and RBS results in the ion-implanted corundum wafers.
Isotope

Implanter target
dose (at/cm2)

Average of measured
fluence (at/cm2)

Combined uncertainty formean and measurements% combined uncertainty formean and measurements

91.00 x 1015

1.22 x 1015

3.55 x 1013

2.90%

24

1.00 x 1014141.00 x 10

4.60 x 10

12

4.60%

28

1.00 x 1015

1.32 x 1015

8.45 x 1013

6.40%

48

1.00 x 1015151.03 x 10

7.06 x 10

13

6.85%

51

1.00 x 1015

1.09 x 1015

5.46 x 1013

5.03%

52

15

15

5.00 x 10

13

4.46%

13

5.15%
5.02%

Be
Mg
Si
Ti
V
Cr

1.00 x 10
1.00 x 10

1.10 x 10

5.68 x 10

691.00 x 1015

1.05 x 1015

5.29 x 1013

Fe
Ga

15

1.12 x 1056

15

We obtained seven for our standards sets. Yogo sapphires are known for mid-range to high iron content
and exceptional color uniformity (Mychaluk, 1995;
Emmett et al., 2017), which we expected would correspond to trace element uniformity (figure 3).

used for our wafers was 200 KeV for all isotopes except 9Be, which used an energy of 100 KeV. For all
wafers, the tilt angle between the ion beam and thewafer surface normal was 7°.

Ion Implant Standards Creation. The first step wasto create a separate calibration standard for each traceelement of interest in a corundum matrix. This was
accomplished at INNOViON Corporation (San Jose,
California) using ion implantation, a method that allows one to precisely control the concentration (dose)and depth profile of a specific amount of a trace element to be placed into a matrix (Ryssel and Ruge,1986). Single isotopes of 9Be, 24Mg, 28Si, 48Ti, 51V, 52Cr,
56
Fe, and 69Ga were implanted separately into theirown two-inch-diameter high-purity corundum wafer
on top of a four-inch-diameter silicon wafer (except
in the cases of 24Mg and 28Si, in which their two-inchdiameter corundum wafers were placed on top of
four-inch-diameter gallium arsenide wafers). The
four-inch silicon or gallium arsenide wafers functioned as witness samples for the ion implantation
process. The target dose (or “fluence”) for each isotope was 1.00 × 1015 at/cm2 (except 24Mg, which targeted a 1.00 × 1014 at/cm2 dose). The implant energy

Verification of the Ion Implant Dosing. For the key
trace elements that are significantly heavier than thematrix elements aluminum and oxygen (Ti, V, Cr, Fe,
and Ga), RBS was used to determine the actual dosing. The RBS technique can determine the concentrations with depth of isotopes in a matrix of lighter
elements by bombarding a sample with a beam ofhigh-energy particles and measuring the number andenergy of backscattered ions (Verma, 2007). For those
key trace elements that are close in mass or lighter
than aluminum and oxygen (Be, Mg, Si), the ion implant dosing had to be verified by a consensus-dosing
approach using comparisons to well-characterized
existing implants.
The implant doses of the heavier isotopes 48Ti, 51V,
52
Cr, 56Fe, and 69Ga were characterized by RBS at
Evans Analytical Group (EAG) in Sunnyvale, California; the Ion Beam Laboratory at the University at
Albany, State University of New York (SUNY); andthe Tandetron Accelerator Laboratory of the University of Western Ontario (UWO) in London, Ontario.
++
For all measurements, a He ion beam with energy
between 2 and 3 MeV was used.
To characterize the ion implant standards lighter
than or close in mass to Al (9Be, 24Mg, and 28Si), EAG
determined “consensus doses” (doses based on several verifications) using SIMS and their multiple reference standards for Be in Si, and Mg and Si in GaAs.
When these lighter ions were implanted in their sapphire substrates, they were simultaneously implanted into larger-diameter “witness” substrates ofsilicon or gallium arsenide that the sapphire substrates were placed on top of. These witness samples

444

GEMS & GEMOLOGYStandards Characterization. Our pursuit of accuracy
led us to create the standards sets using a two-step
approach: First, create highly controlled and measurable standards (ion implants) to calibrate extremely
precise instrumentation (SIMS), and then use thestandardized SIMS to calibrate selected corundum
pieces to be incorporated into final product standards
sets (see figure 4). The steps taken to create the SIMS
calibration standards and then the final productcorundum calibration standards for GIA’s LA-ICPMS instruments are listed below.

NOTES & NEW TECHNIQUESWINTER 2017

BOX A: SIMS RSF AND TRACE ELEMENT CONCENTRATION DETERMINATIONWith the RBS “dose” or “fluence” values Ψ (units ofatoms/cm2), SIMS RSF values—the conversion factors
between SIMS data for a particular element in a sample
and its concentration—can be determined in the following way.
We first sputter the ion implant standards with SIMS
to collect the counts of the implanted ion and matrix ion.
This implanted ion, or “ion of interest,” is also referred toas the “secondary ion of interest.” We express the ion counting rate of the implanted isotope as I(x)1, which is also thecurrent of the implanted isotope. Similarly, the ion counting rate of the matrix isotope—in the case of a corundum+
matrix this would be 27Al —is expressed as I(m)1, which isalso the current of the matrix isotope. The RSF (units ofatoms/cm3) can be determined using the relationship
RSF = Ψ/∫(I(x)1/ I(m)1)dx
where dx is the depth profile in angstroms and is determined by the product of the sputtering rate (S) in
angstroms per second and the time interval in seconds
recorded during the SIMS analysis:dx = Sdt

were then measured with SIMS and directly compared to the existing reference standards produced
and used by EAG. These standards served as calibrators for the SIMS to determine the doses in our witness samples. For Be, Mg, and Si, EAG had three,four, and five existing standards, respectively. We assumed that the doses in the witness samples wereidentical to those in the actual sapphire substrates,
which was shown to be true for the heavier implants
for titanium, vanadium, chromium, iron, and gallium that each had silicon witness samples underthem during the implantation process.

The sputtering rate is the ratio of the simulated peak
depth to the peak time in seconds:
S = Peak depth/Peak time
We attempted peak depth determination by both
physical measurements and calculation with “Stopping
and Ranges of Ions in Matter” (SRIM). Because of thesmall non-flat-bottom craters in sapphire, large uncertainties exist in physical depth measurements. The peak
depths are currently calculated with SRIM, before moreaccurate depth measurements can be achieved.
Once the RSF values for each trace element in thematrix have been determined, the atomic concentrations—n(x)—of these trace elements in other samples
can be determined using the product of the RSF with theratio of the secondary ion counting rates:
n(x) = RSF × (I(x)2)/(I(m)2)
where I(x)2 is the secondary ion counting rate, or currentof the trace element isotope in a sample, and I(m)2 is thesecondary ion counting rate, or current of the matrix iso+
tope—in our case, 27Al .

SIMS signal for a particular trace element in a defined
matrix under defined conditions into concentrations(see box A for a more detailed description). Our determined RSF values were then applied to data collected on the pieces of corundum that are now in our
corundum standards sets under the same controlled
set of operating conditions to accurately quantify
these same trace elements. The RSF values for eachtrace element were determined from a series of two
to four spots on the appropriate ion implant standard,
verified in two separate measurement sessions on
nonconsecutive days. The concentration values withcombined uncertainties for each piece of corundum
incorporated into the standards sets were obtainedwith SIMS based on averaging nine spots per piece.

Calibration of the SIMS and Characterization of the
Final Standards. SIMS is a highly sensitive and precise quantification technique for elements from Be
to U (Benninghoven et al., 1987). The technique produces elemental depth profiles by sputtering samples
with a primary beam of either oxygen or cesium ionsand then analyzing the secondary ions formed witha mass spectrometer. Once the doses in the ion implant standards were accurately characterized, thesestandards were measured with SIMS under a controlled set of conditions to determine “relative sensitivity factors,” or RSF values, for each traceelement of interest to be characterized in corundum(Laufer et al., 2011). The RSF simply converts the

SIMS Instrument Description and Operating Conditions. The CAMECA IMS 7f-GEO at Caltech(Pasadena, California) is a magnetic sector type SIMS
instrument with dedicated options for geoscience applications. Modified from the CAMECA IMS 7f-Auto,
it is equipped with double secondary Faraday cups forhigh-precision stable isotope analysis. The primarycolumn consists of a duoplasmatron source; a microbeam Cs ionization source; a primary beam massfilter; fully automated slits and apertures; ion optics(lenses, stigmators, and double deflectors) for primary

NOTES & NEW TECHNIQUESGEMS & GEMOLOGYWINTER 2017445

LA-ICP-MS MASS SCANSIMS MASS SCAN
4000

1000

Si+

27

Al1H+

INTENSITY (×1000 CPS)INTENSITY (CPS)

28

100

10

1

0.1
27.970

27

Al1H+

Si+

3500

28

N14N+

14

3000
2500
2000
1500
1000
500
0

27.97527.98027.98527.99027.99528.000

27.55

27.65

ATOMIC MASS UNITS
+

27.75

27.85

27.95

28.05

28.15

28.25

28.35

ATOMIC MASS UNITS+

Figure 5. Left: 27Al1H interference to 28Si for sapphire using SIMS. At a mass resolving power (MRP) of 3,000, the++27
Al1H interference (mass of 27.98936 amu) to 28Si (mass of 27.97692 amu) can be separated, allowing accuratequantification of Si in corundum. During SIMS measurements, the magnetic field is set to collect signals only+
from the center of the 28Si peak. Right: For comparison, the LA-ICP-MS instrument described in the Materials and+++Methods section cannot resolve the 27Al1H interference to 28Si for sapphire (or even the further away 14N14N interference). This mass scan shows that the peak width of 28Si is 0.7 amu (vs. around 0.01 amu for SIMS), which means+++that the peak includes the combination of 14N14N (mass of 28.00615 amu), 28Si , and 27Al1H .

beam focusing and rastering; and a high-accuracy primary Faraday cup combined with a fast beam blanking system for monitoring the primary beam intensity
during measurements. The secondary ion optics arecontinuously adjustable from –10 to + 10 kV, with acontinuously adjustable imaged field and a dynamictransfer system that optimizes transmission for an analyzed area up to 500 × 500 µm2. The Nier-Johnson
double-focusing mass spectrometer has fully adjustable position and width on automated entrance
and exit slits, automated contrast and field apertures,a spherical electrostatic analyzer for energy filtering,an automated continuously adjustable energy slit, anda laminated electromagnet (120 mm radius) for fastpeak switching. The detection system consists of anelectron multiplier, double Faraday cups, and a microchannel plate assembly.
RSF values for the elements of interest in corundum were determined through SIMS depth profilingof the implant standards. Because sapphire is an insulator and depth resolution is not a concern for thistask, an O– primary beam, which can minimize sample charging during measurement, was used to acquire
depth profiles of the implant standards. Matched analytical conditions were then used to determine the element concentrations of the non-implant samples.
Specifically, the O– primary beam current has a potential of –13 KeV, a current of approximately 15 nA, anda size of about 15 µm. Positive secondary ions of 8.5

KeV were generated by the primary beam, rastering an
area of 50 × 50 µm2 on sample surfaces. To avoid crateredge effects, a field aperture was inserted on the secondary ion path so that only the signals from the center 20 µm2 area were detected. The positive secondary
ions collected were 9Be, 24Mg, 27Al, 28Si, 46Ti (samples),48
Ti (implants), 51V, 52Cr, 56Fe, 69Ga (implants), and 71Ga
(samples). All secondary ions except 27Al were measured with an electron multiplier (EM). 27Al was measured with a Faraday cup because of its high intensity.
The reason for measuring 46Ti instead of 48Ti on samples is to avoid possible unresolvable interference
from 48Ca (0.187% natural abundance of all Ca),
whereas the isotopic abundance of 46Ca is only
0.004%. The reason for measuring 71Ga instead of 69Ga
on samples is to avoid possible unresolvable interferences from 56Fe13C, 57Fe12C, and 53Cr16O, as Fe and Cr
are both potentially present in the samples. Becauseof the high 48Ti fluence of the implant standard, thepossible 48Ca interference has no significant contribution to its 48Ti depth profiling results. The mass spectrometer of the SIMS was set at a mass resolving
power (MRP) of 3,000 for all the measurements, which
is sufficient to resolve all possible interferences to the+masses of interest, especially the 27Al1H interference(mass = 27.98936 unified atomic mass units, or amu)+
to 28Si (mass = 27.97692 amu) with an MRP of 2,251,
which is significant due to the abundant Al in sapphire (as shown in figure 5). The lowest concentrations

446

GEMS & GEMOLOGYNOTES & NEW TECHNIQUESWINTER 2017

TABLE 3. RSF values for SIMS in corundum.
in ppma we could detect with confidence for the key
trace elements were 0.0003 for Be, 0.0002 for Mg, 0.2
for Si, 0.007 for Ti, 0.007 for V, 0.003 for Cr, 0.0006 for
Fe, and 0.0005 for Ga.

Isotope

Testing Standards and Samples with LA-ICP-MS. To
examine the differences in using NIST glasses versus
our new corundum standards for LA-ICP-MS calibration, we used a Thermo Fisher Scientific iCAP Qc
ICP-MS and a New Wave Research UP-213 laser ablation unit with a frequency-quintupled Nd:YAG
laser running at 4 ns pulse width. Ablation wasachieved using a 55-µm-diameter circular laser spot,a fluence (energy density) of approximately 10 J/cm2,
and a 15 Hz repetition rate. The internal standard
used was 27Al with a value of 529,200 ppmw calculated and rounded from pure corundum. The dwell
time of each laser spot was 40 seconds. The lowest
concentrations in ppma we can detect with confidence by LA-ICP-QMS are 0.5 for Be, 0.1 for Mg, 0.5
for Ti, 0.05 for V, 0.2 for Cr, 3.5 for Fe, and 0.01 for Ga.

RESULTS AND DISCUSSION
Verification of the SIMS Calibration Standards. A
summary of the consensus SIMS results from EAG
for the actual doses of 9Be, 24Mg, and 28Si as well as
the RBS results from the three labs (EAG, SUNY, and
UWO) for the actual doses of 48Ti, 51V, 52Cr, 56Fe, and69
Ga in corundum are given in table 2. All values arepresented with their combined uncertainties in termsof actual values and as a percentage of the determined
doses. It is clear that verifying the ion-implanted
doses was important in that the actual doses varied

RSF (atoms/cm3)

%RSD

Be

1.99 x 1023

2.42%

24

Mg

3.12 x 1022

1.30%

28

Si

2.87 x 1023

2.05%

48

Ti

5.08 x 10

22

1.10%

51

V

8.73 x 1022

3.60%

52

Cr

5.87 x 10

22

1.99%

56

Fe

8.37 x 1022

0.94%

Ga

22

5.76%

9

69

5.31 x 10

from the target doses from as little as zero to as muchas 32%. The combined standard uncertainties at thispoint contain the uncertainties in the measured fluence values with each RBS measurement (or consensus SIMS measurement) and in calculating the meanvalues from the multiple RBS measurements for eachfluence.
Determined RSF Values for SIMS. The RSF values
with their relative standard deviations (RSD) are
given in table 3. These values allow us to accurately
calculate the actual concentrations of the key traceelements in our final standards originating from thecustom-grown multi-doped crystals, the Yogo sapphire slices, and the ultra-high-purity blank sapphire.
Measured Values for the Final Corundum Calibration Standards. Using our RSF values, we calibrated
the SIMS apparatus and determined the concentrations of the key trace elements in our new corundum
standards based on nine separate points each. The

TABLE 4. Range of ppma values within the seven calibrated pieces of eachcrystal standard type with nine-point RSD value ranges from SIMS.
Trace element

02-1032-01 to 07

07-0687-01 to 07

Be

56–71

2–10%

––

––

––

Yogo-01 to 07

––

Mg

24–26

1–4%

75–82

1–2%

(85–104)(1–7%)

––

22–26

1–5%

Si

––

––

––

Ti

40–44

1–3%

106–115

1–4%(76–104)(1–8%)

1–3%(3–12)(1–12%)

V

39–43

1–3%

7–8

Cr

84–88

1% or less

599–621

1–2%(3–26)(4–93%)(1–6%)

1200–1410

1–2%

2–4%

12–14

2–3%

Fe

34–36

1–8%

(2–3)

Ga

84–91

1–4%

2–4

“—” indicates level too low to calibrate, and “()” indicates that the trace element in the particular standard is not
being used for calibration purposes. Gray cells indicate RSD ranges unacceptable for calibration purposes. Note that
all of the trace elements in the Yogo sapphire are remarkably uniform except for chromium and vanadium.

NOTES & NEW TECHNIQUESGEMS & GEMOLOGYWINTER 2017447

ranges for each key trace element by crystal typewith relative standard deviation ranges in the newstandards sets are presented in table 4. These can becompared to the targeted ranges of values in table 1.
The homogeneity achieved in the crystal growth andnaturally present in the Yogo sapphires are demonstrated by the low RSD values accompanying theconcentration ranges for those trace elements used
for calibration purposes. Looking at the range of values by trace element within a standard type underscores the significance of individually calibratingeach piece from the same source.
Table 5 presents the final data with total combined uncertainty (includes all measurement uncertainties from all steps) for the first standards set
imaged in figure 1. As mentioned, high uniformityof the trace elements within the crystals is necessary
to improve accuracy and reproducibility while minimizing uncertainty. For each standard, we used
SIMS to collect nine uniformly distributed spots
across the entire surface. We found that the relative
standard deviations representing the point-to-point
variations in the calibrated levels of trace elements
within our standards ranged from less than 0.5% tono more than 10%. The highest variation was in the
diffused beryllium in the 02-1032 crystal pieces. The
lowest variations were in the chromium in the synthetically grown crystals and in the iron in the Yogo
sapphire slices (all 2% or less).

SRM 610 and 612 glasses, we compared values determined for one of our standards sets (set 7), first using
our RSF values with SIMS and then with LA-ICP-MS
using a different corundum standards set (set 1), andfinally with LA-ICP-MS using NIST SRM 610 and 612
glasses separately. Additionally, we used the new
corundum standards set 1 separately from NIST SRM
610 and 612 glasses to measure a series of other samples using LA-ICP-MS. We were not able to measure
this set of samples on SIMS but plan to do so with additional samples in the future. As shown in table 6,
using the new standards calibrated by SIMS in the LAICP-MS instrument provided agreement within lessthan 10% of SIMS for standards set 7. Looking at calibrating the LA-ICP-MS with NIST 610 and 612 ascompared to the matrix-matched standards, trends in
differences between the measured samples for eachtrace element can be seen. For Be, Ti, V, Fe, and Ga,
NIST SRM 610 and 612 glasses produce values consistently lower than the corundum standards. For Mg,
NIST SRM 610 and 612 glasses produce values higher
than the corundum standards. For Cr, the trend is not
so clear, but the differences are within less than 10%of each other.
Accurate Quantitative Reporting of Silicon in Sapphire Using SIMS. Using SIMS with an MRP of
3,000, we were able to completely separate the++27
Al1H interference from 28Si (a mass scan around28
Si, collected on a sapphire with 22 ppma Si, at achamber vacuum level of approximately 2 × 10–9 torr;
see figure 5), allowing us to accurately quantify Siconcentration in corundum. The quantitative reporting of silicon in sapphire is a problem for many of thePreliminary Comparison of LA-ICP-MS Data Using
the New Standards Versus NIST SRM 610 and 612
Glasses. To grasp the significance of matrix effects for
key trace element reporting in corundum using NISTTABLE 5. Trace element concentration values (in ppma) with total combined uncertainty incorundum calibration standards set number 1 (see figure 1).
02-1032-01

Uncertainty

07-0687-01

Uncertainty

Yogo-07

Uncertainty

Be

68.5

4.4%

––

––

––

––

Mg

25.3

5.1%

76.0

4.8%

––

––

Si

––

––

––

––

23.9

7.6%

Ti

44.4

7.6%

111

7.2%

––

––

V

42.5

6.3%

7.41

6.3%

––

––

Cr

87.6

5.0%

599

5.2%

––

––

Fe

36.8

5.4%

––

––

1240

5.5%

Ga

86.3

7.7%

3.32

8.6%

12.4

8.0%

Trace element“—” indicates a trace element that was not present or not being used for calibration purposes within a standard.

448

NOTES & NEW TECHNIQUESGEMS & GEMOLOGYWINTER 2017

TABLE 6. Comparison of LA-ICP-MS quantitative ppma data using matrix-matchedcorundum standards and NIST SRM 610 and 612 glass standards.
Trace element

SIMS

LA-ICP-MS
set 1—newstandards

LA-ICP-MS
NIST 610

LA-ICP-MS
NIST 612

02-1032-07

Be

56

56

48

44

77524

Be

69

46

46

02-1032-07

Mg

25

25

26

30

07-0687-07

Mg

76

77

81

95

Yogo-01

Mg

104

107

113

133

67293

Mg

7.6

8.0

9.6

02-1032-07

Ti

43

46

42

43

07-0687-07

Ti

106

110

101

103

76965

Ti

69

64

60

4.4

4.0

3.8

43

38

38

7.9

6.7

6.7

106

91

94

Sample67923

Ti

02-1032-07

V

41

07-0687-07

V

7.2

69501

V

02-1032-07

Cr

86

86

84

83

07-0687-07

Cr

614

619

585

577

67925

Cr

1324

1384

1403

02-1032-07

Fe

36

33

29

14

Yogo-01

Fe

1353

1359

1142

552

67295

Fe

37

24

10

SD1

Fe

4039

2992

1177

02-1032-07

Ga

91

88

83

86

07-0687-07

Ga

3.8

3.5

3.3

3.4

Yogo-01

Ga

12

12

11

11

SD1

Ga

38

36

38

67292

Ga

312

272

306

Nine spots were used in both instruments.

LA-ICP-MS instruments used in gemological labs
today, as they may not be capable of removing interferences and background from the isotope of interest,
consequently yielding erroneously high results (Shen,
2010; Emmett et al., 2017). Using other techniquessuch as electron microprobe and XRF is not practical,
as the detection limits for Si in corundum are ordersof magnitude too high. LIBS with an intensified
charge-coupled device (CCD) combined with a Czerny-Turner spectrometer might be more suitable
than electron microprobe and XRF, but the limits ofdetection again for Si in corundum appear to be well
above the 1 ppma range we are interested in.
Consider that the MRP for separating 28Si+ (mass of+
27.97693 amu and 27Al1H (mass of 27.98936 amu) is2,251. The MRP of the instrument for a particularmass is the ratio of the isotopic mass of interest to thepeak width at half maximum. To determine the mass
resolution required to separate a particular isotope
from a close-in-mass interference, we take the massof the isotope of interest and divide by the absolutevalue of the difference between that isotopic mass and+the mass of the interference of concern. Here, for 28Si
27
1 +and Al H , the MRP is: 27.97693/(|27.97693 –
27.98936|) = 2,251. The MRP of quadrupole mass spectrometers used in many laboratories at atomic mass
28 is around 40 at normal resolution and tops out
around 90 at high resolution. The required 2,251 MRP
far exceeds the capability of these commercial “desktop” ICP-QMS used in a number of gemological labo-

NOTES & NEW TECHNIQUESGEMS & GEMOLOGYWINTER 2017449

ratories. One could consider trying to determine the
Si trace element concentration using the 29Si isotope(mass of 28.97649 amu), which has a much lower natural abundance (4.7% abundance vs. 92.2% abundance for 28Si). However, the signal from such a
low-abundance trace element would be very difficult
to quantify and distinguish from traces of Si thatmight be present due to quartz elements in the torch
assembly. Even if one could correct for these possible
problems, there are still close-in-mass interferencessuch as 28SiH and 29N-N (28.98475 and 29.00318 amu,
respectively) that require finer MRP (3,508 and 1,085,
respectively) than the quadrupole detector is capable
of. We decided to test measuring trace levels of siliconin corundum using a magnetic sector field ICP-MS
paired with a 193 nm LA unit. This work is still ongoing, but signal intensity for our spot size of choice
is proving to be an issue for either 29Si or 28Si at themedium mass resolution option (4,000–5,000 MRP)to quantify the levels of silicon we found in our Yogo
sapphire samples using SIMS (22–26 ppma).
For further context, the use of the high-purity“blank” sapphire containing essentially no trace elements allows the LA-ICP-MS operator to see atwhat masses erroneous quantities of trace elements
may be detected. Where there is an inexplicable signal compared to what is expected for the matrix
alone, one can assume the signal originates fromsources including interferences from plasma products, other contaminants, and residual atmosphericcomponents. In an alumina substrate, where Si concentration is very low, the dominant peak at mass 28+
is 27Al1H , which varies accordingly with the H contents (vacuum level) available during measurements.
To illustrate this further, we measured our ultrahigh-purity synthetic sapphire blank using the laser
ablation–inductively coupled plasma–quadrupole
mass spectrometer (LA-ICP-QMS) calibrated with
NIST SRM 610. We found erroneous and highly varying levels of both 28Si and 29Si in our high-purity
blank of 1136 ± 333 ppma and 1062 ± 182 ppma, respectively (using SIMS, the 28Si level was below 1ppma). This could help to explain in part the highlevels of Si in corundum reported in previous literature using LA-ICP-MS and NIST SRM 610 or NIST
SRM 612 standards (Peretti and Gunther, 2002;
Peretti et al., 2003; Sutherland et al., 2015). After run-ning a full mass scan from beryllium to uranium on
the high-purity blank standard, also using NIST SRM
610 as a standard, we found that several trace elements beyond 28Si and 29Si would similarly be reported at erroneously high levels. These included 11B(around 50 ppmw), 43Ca (around 350 ppmw), 46Ti
(around 2 ppmw), 56,57Fe (up to 18 ppmw), 67Zn
(around 50 ppmw), 95Mo (around 0.4 ppmw, though
this trace level may be contamination from the HEM
crystal growth process), and 116,117,118,120Sn (around 0.5
to 2.5 ppmw).

450

GEMS & GEMOLOGYNOTES & NEW TECHNIQUESCONCLUSIONSThe need for improved accuracy and efficiency led
GIA to develop new corundum standards sets for its
LA-ICP-MS instruments. These sets:
1. Minimized the number of individual standards
2. Incorporated a true “zero” to represent the matrix background
3. Covered trace element levels that best represent the ranges found in natural ruby and sapphire of the key trace elements Mg, Ti, V, Cr,
Fe, and Ga
4. Contained individual pieces that were calibrated using a highly controlled process basedon, to the best of our knowledge, the most accurate methods technologically available today
Additionally, we were able to calibrate silicon incorundum standards, and with our determined SIMS
RSF value for silicon in sapphire we were able to accurately characterize trace levels of this significant
trace element using the high mass resolving powerof SIMS.
These new standards sets were tailored to ensurehigh reproducibility, minimal calibration time, andless chance of instrument signal drift with fewer individual measurements in the calibration cycle. The
creation of these standards was a lengthy and complex endeavor, incorporating custom crystal growth,
creation of ion implant standards, and utilization of
RBS and SIMS measurement techniques. We consider the end product well worth the effort, as these
new standards allow us to more accurately study
corundum chemistry for the purposes of both basic
research and geographic origin reporting.

WINTER 2017

ABOUT THE AUTHORS
Dr. Stone-Sundberg is a GIA research scientist and a technicaleditor of Gems & Gemology located in Portland, Oregon. Mr.
Thomas is director and design engineering authority at Applied
Materials in Hillsboro, Oregon. Mr. Sun is a staff gemologist at GIA
in Carlsbad, California. Dr. Guan is laboratory director of the Microanalysis Center, Division of Geological & Planetary Sciences, at
the California Institute of Technology in Pasadena, California. Mr.
Cole is director of Scientific Materials in Bozeman, Montana. Dr.
Equall is vice president of laser operations at FLIR. Dr. Emmett isdirector of Crystal Chemistry in Brush Prairie, Washington, and a
consultant to GIA.
ACKNOWLEDGMENTS
This work would not have been possible without the support ofmany individuals. Discussions with Prof. George Rossman at
Caltech were invaluable during the course of the project. Discus-

sions with Dr. Chandra Khattak regarding the high-purity material
were very much appreciated. To help verify our data at various
stages, discussions with Dr. Lyudmila Goncharova of the physics
and astronomy department at the University of Western Ontario,
Dr. Hassaram Bakhru at the State University of New York, Albany, and Dr. Tim West at Evans Analytical Group were mosthelpful. We recently worked with Professor Graham Pearson's
lab on the issue of using sector field ICP-MS technology with
193 nm LA to accurately quantify low levels of silicon in corundum. Some preliminary work with Dr. Mandy Krebs and Dr. Yan
Luo from Prof. Pearson's lab is underway, and results will be included in a future publication. Discussions with Dr. Karl Schmetzer regarding quantification of silicon in corundum were verymuch appreciated. We would like to thank Troy Ardon for creating “AtomicDensityCalculator” software for future SIMS data processing. Finally, the support of GIA management (Tom Moses
and Shane McClure) was essential to see this project to the end.

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Sylvester P.J. (2008) Chapter 5: Matrix Effects in Laser AblationICP-MS. Mineralogical Association of Canada Short Course
Series, Vol. 40, Vancouver, B.C., pp. 67–78.
Verma H.R. (2007) Atomic and Nuclear Analytical Methods.
Springer, Berlin.
Wang W, Hall M., Shen A.H., Breeding C.M (2006) Developing
corundum standards for LA-ICP-MS trace-element analysis.
G&G, Vol. 42, No. 3, pp. 105–106.

NOTES & NEW TECHNIQUESGEMS & GEMOLOGYWINTER 2017451

NOTES & NEW TECHNIQUESREAL-TIME MICRORADIOGRAPHY OF PEARLS:
A COMPARISON BETWEEN DETECTORS
Stefanos Karampelas, Abeer Tawfeeq Al-Alawi, and Ali Al-Attawi

See end of article for About the Authors and Acknowledgments.
GEMS & GEMOLOGY, Vol. 53, No. 4, pp. 452–456,
http://dx.doi.org/10.5741/GEMS.53.4.452© 2017 Gemological Institute of America

of chemicals are necessary for film processing. It
takes approximately 20 minutes to select the film
and secure the pearls to the film cassette. At thesame time, the exposure must be determined assuming an average-sized sample and keeping in mind thatpearls in a strand are often graduated in size and thatspheres require longer exposure times through thecenters than the edges. Next, the film must be developed, fixed, and dried. All told, it is a time-consuming
process.
The last 20 years have seen RTX steadily replacefilm-based radiography in the medical sector, and overthe last decade most gemological laboratories havefollowed this trend by partially or fully adopting RTX.
This method has several important advantages. No
hazardous liquids are needed, and it gives immediateor nearly immediate results, which are easier to store
and share among a team of technicians or in publications and presentations. RTX microradiography also
requires a lower total amount of radiation than filmbased microradiography, though similar X-ray generating tubes may be used without a need to reduce
X-ray scattering. Some gemological laboratories initially employed RTX units with image intensifier (II)technology generally associated with digital cameras
to acquire RTX microradiographs. More recent units
have employed flat panel detectors (FPD), which canbe of larger dimension with high resolution. However,
FPD costs approximately US$25,000, about 40%
more than II units and cameras.
An II is a vacuum tube device that converts invisible X-rays transmitted through the sample into visible light by a cesium iodide (CsI) scintillator. The
visible light is then converted into electrons at thephotoelectric surface and emitted inside the vacuum
tube. The emitted electrons are accelerated and focused by electrodes, which act as an electron lens,
onto the output screen and converted into bright visible light that is captured by a digital camera (figure
1, left; Ide et al., 2015). On the other hand, an FPD isa thin, flat solid sensor where invisible X-rays transmitted through the sample are converted into visible
light, also by a CsI scintillator. The visible light is

452

GEMS & GEMOLOGYOver the past ten years, gemological laboratories
have been replacing film-based microradiography with real-time X-ray microradiography (RTX).
This paper compares the output quality and resolution provided by two RTX units fitted with different detectors: an image intensifier (II) and a flat
panel detector (FPD) using the same type of Xray generating tube. Although the II is faster andless expensive, the images acquired with the FPD
show greater detail of the pearl’s internal growth
structures, making interpretation and consequentconclusions easier to validate.

S

ince the early 20th century, gemological laboratories have been using film-based microradiography
to reveal minute structures that separate natural from
cultured pearls, sometimes alongside other methods
such as Laue diffraction and endoscopy (e.g., Galibourg and Ryziger, 1927; Anderson, 1932; Alexander,
1941; Webster, 1954; Farn, 1980; Hänni, 1983; Poirot
and Gonthier, 1998; Scarratt et al., 2000; Sturman,2009). Today, real-time X-ray microradiography (RTX)
is the foremost testing method for carrying out thisvital work. It can also be paired with the more timeconsuming X-ray computed microtomography forchallenging identifications and research purposes(Karampelas et al., 2010; Krzemnicki et al., 2010).
With film-based microradiography, pearls are
sometimes placed in direct contact with a high-resolution film cassette or immersed in a scatter-reducing liquid (e.g., lead nitrate solution or carbon
tetrachloride, both of which are hazardous). X-ray
scattering may also be reduced by simply surrounding individual pearls with a thin lead sheet or film.
Regardless of the technique, a darkroom and a series

NOTES & NEW TECHNIQUESWINTER 2017

X-raysCsl scintillator

Focusing electrode
X-raysVisible light (weak)Electron beam

Visible light(bright)
TFT drive signal

Csl scintillator
Input surfacePDsurface
Photoelectric
c surfac

TFT switch

Output surface
Electrt ic chaharge
haLow-noise amplifier

Digital video signal

Figure 1. Structures and principles of operation for an II (left) and an FPD (right). Modified after Ide et al. (2015).

converted into an electric charge stored in each photodiode (PD). The signals are read by a thin-film transistor (TFT) switch provided for each pixel andamplified by a low-noise amplifier, undergoing analog-digital conversion to become digital video signals(figure 1, right; Ide et al., 2015).
The quality of the RTX microradiographs depends
on the system’s resolution (usually given in line pairs
per millimeter, or LP/mm), the magnification, andthe exported image size. The images are processed
and initially viewed with software linked to the instrument or, more commonly, third-party software
such as Fiji (ImageJ) or Adobe Photoshop. To view the
microradiographs, a relatively large high-resolution
screen (>20 inch) should be used. For this study, RTX
microradiographs were acquired for the same set ofsamples (figure 2 and table 1) using the two different
systems described above.

MATERIALS AND METHODS
Two undrilled and two drilled samples of various
sizes from different mollusks were selected for thisstudy (figure 2 and table 1): one natural saltwater
pearl, one bead-cultured saltwater pearl, one nonbead-cultured freshwater pearl, and one non-beadcultured saltwater pearl.
Microradiographs were acquired at the Bahrain Institute for Pearls and Gemstones (DANAT) using two
RTX units: a FocalSpot (San Diego, California) Verifier HR FSX-090 and a Pacific X-Ray Imaging (PXI,San Diego, California) GenX-90. The electronics andimaging systems of both units were provided by PXI.
Microradiographic images were collected in the same
direction for each sample. Both instruments have thesame tube type, a Thermo Scientific PXS5-928 witha spot size of <9 microns. The FocalSpot unit has aToshiba E5877J-P1 image intensifier (two-inch andFigure 2. The four samples from this study.
Left to right: three cultured pearls (sample
numbers 19, 21, and 8)
and a natural pearl(sample number 1). The
largest sample is 15.65
mm tall. Photo by
Ghadeer Abdali, ©
DANAT.

NOTES & NEW TECHNIQUESGEMS & GEMOLOGYWINTER 2017

453

TABLE 1. General characteristics of saltwater pearl samples.
Sample no.

Type

Mollusk

Size

Shape

1

Natural saltwater

Pinctada radiata

5.69–5.75 × 5.00 mm

Buttona8

Bead-cultured saltwater

Pinctada fucata

5.14 × 5.23 × 5.50 mm

Ovalb

19

Non-bead-cultured saltwater

Pinctada maxima

11.63 × 12.37 × 15.65 mm

Baroquea

21

Non-bead-cultured freshwater

Hyriopsis species

10.29–10.86 mm

Near-roundbaUndrilled
Drilledbfour-inch options) with >40 LP/mm resolution at highmagnification and a camera with 0.5 MB resolution.
Due to the instrument’s size and the X-ray tube collimator to minimize distortion, the maximum sensi-

In Brief• Most gemological laboratories have been replacing
film radiography with real-time X-ray microradiography (RTX) to separate natural and cultured pearls.
• A comparison of RTX units with image intensifier (II)and flat panel detector (FPD) technology shows that thefirst is more economical and produces faster results.
• An FPD yields images with less noise and greater detailof a pearl’s internal structures, making it more suitable
for their characterization.

tive area is 33 × 33 mm2 (with some areas at thecorners not active, as an II initial field of view isround). The PXI unit has a Perkin Elmer Dexela 1512
flat panel detector with >40 LP/mm resolution at highmagnification, a pixel size of 75 microns, 3072 × 1944
resolution, and a sensitive area of 33 × 33 mm2, reduced from 49 × 56 mm2 due to the X-ray tube filter.

The maximum frame averaging used to decrease
noise was 256 frames for the II and 128 frames for the
FPD. X-radiation of 70–90 kV accelerating voltage and70–90 µA current were used in both instruments withan exposure time of 100–250 milliseconds per frame.
The acquisition times for each microradiographic
image were approximately 10 seconds for the II and
100 seconds for the FPD. The images were exported
as TIF files, with a maximum resolution of 300 KB/8bit grayscale and 6 MB/16-bit grayscale, respectively.
For each sample, microradiographs were taken fromthree directions perpendicular to each other. The images were manipulated with Fiji (ImageJ) version 1.0
using Java 6, an open-source software.

RESULTS AND DISCUSSIONS
Selected radiographs of all four samples are shown infigures 3–6. Microradiographs acquired with the FPD
are provided on the left, while images collected using
the II system are on the right. All images aregrayscale; lighter tones indicate materials with higher
density such as calcium carbonate (usually aragonite
for most gem-quality pearls, as in this study), whiledarker tones represent lower-density materials (usually organic matter, cracks, or cavities/voids). To view

Figure 3. Microradiographs of sample 8, abead-cultured saltwater
pearl from Pinctada fucata, produced with an
FPD (left) and an II(right). The diameter ofthe bead is about 4.5
mm.

454

NOTES & NEW TECHNIQUESGEMS & GEMOLOGYWINTER 2017

Figure 4. Microradiographs of the center ofsample 19 (a non-beadcultured saltwater pearl
from Pinctada maxima),
produced with an FPD(left) and an II (right);
fields of view approximately 7 mm.

the raw original images, visit www.gia.edu/gemsgemology/winter-2017-microradiography-pearls andsee supplementary items S3–S6. Figure 3 presents the
microradiographs of a bead-cultured saltwater pearl
from Pinctada fucata. The implanted bead, which
presents no structure and is almost centered, isclearly indicated by a dark growth line running inside
the edge of the sample and roughly parallel with thisedge in both microradiographs. This line, made up
mostly of organic material, separates the bead fromthe nacre overgrowth (Scarratt et al., 2000). The microradiographs acquired with an II appear less clear
than those produced with the FPD, which allow thegrowth line surrounding the bead to be clearlyviewed. This feature appears less clear in the II along
several parts of the growth line.
Figure 4 presents the magnified microradiographsof the central part of a non-bead-cultured saltwater
pearl from Pinctada maxima. A large irregular darkgray area that allows this sample to be identified isclearly observed in both microradiographs (Krzemnicki et al., 2010). However, the microradiograph acquired with an FPD reveals additional information in
the form of light lines within the dark gray center andgrowth lines around it.

Figure 5 presents magnified microradiographs ofthe central part of a natural saltwater pearl from Pinctada radiata. Both images reveal an “onion-like”
structure with a darker color and a dark spot in thecenter, a characteristic of natural pearls (Scarratt et al.,
2000; Karampelas et al., 2010; Krzemnicki et al., 2010).
Additionally, some dark areas and lines are observed
toward the outer part of the sample. In the microradiograph acquired with the II, the dark center and thevarious growth lines are barely visible. It is very noisy,
and thus further information cannot be revealed. In
the microradiograph produced with an FPD, several
additional lines are observed as well as some radial
structures in the darker part of the sample. These
structures, which likely result from the radial calcite,
appear darker due to the enrichment of organic matterthat is observed in the center of some natural pearls(Krzemnicki et al., 2010).
In figure 6, ring-like growth structures are recordedin the microradiographs acquired with FPD, as well asa weak, elaborate dark gray area in the center that represents a likely “twisted” cavity-related structure observed in some non-bead freshwater cultured pearls(Scarratt et al., 2000; Sturman, 2009). In the microradiographs acquired with II, fewer and less distinct

Figure 5. Microradiographs of sample 1 (anatural saltwater pearl
from Pinctada radiata),
produced with an FPD(left) and an II (right);
fields of view approximately 3.5 mm.

NOTES & NEW TECHNIQUESGEMS & GEMOLOGYWINTER 2017455

Figure 6. Microradiographs of sample 21 (anon-bead-cultured
freshwater pearl from
Hyriopsis species), produced with an FPD(left) and an II (right);
fields of view approximately 9 mm.

growth structures are observed and in the center only
a “hair-like” line is barely recorded. Generally, microradiographs of our samples acquired with an II giveless distinct images with more noise than those acquired with an FPD; this observation is consistent
with previous publications (Baba et al., 2002, 2004).

CONCLUSIONS
RTX microradiography is widely used today bygemological laboratories to separate natural and cul-

ABOUT THE AUTHORS
Dr. Karampelas (stefanos.karampelas@danat.bh) is research director, Ms. Al-Alawi is executive director, and Mr. Al-Attawi is pearl
testing manager at the Bahrain Institute of Pearls and Gemstones(DANAT), based in Manama.

tured pearls. Both II and FPD detectors are used forthis purpose. An II detector produces faster results
than an FPD, and at present the overall cost of an IIbased unit is less. On the other hand, FPD images areless noisy and provide greater detail of the internal
structures in both natural and cultured pearls, making them more suitable for pearl identification. However, an II could be appropriate for other industries,
where the balance between cost and performance isimportant or when quick response is essential.

ACKNOWLEDGMENTS
The authors thank the gemological team of DANAT for their help
with the microradiographs and macro image acquisition. John
Donaldson from Pacific X-Ray (PXI) is thanked for the numerous
fruitful discussions regarding the specifications sheets of each
instrument.

REFERENCES
Alexander A.E. (1941) Natural and cultured pearl differentiation.
G&G, Vol. 3, No. 12, pp. 184–188.
Anderson B.W. (1932) The use of X-rays in the study of pearls. The
British Journal of Radiology, Vol. 5, No. 49, pp. 57–64,
http://dx.doi.org/10.1259/0007-1285-5-49-57
Baba E., Konno Y., Ueda K., Ikeda S. (2002) Comparison of flatpanel detector and image intensifier detector for cone-beam CT.
Computerized Medical Imaging and Graphics, Vol. 26, No. 3,
pp. 153–158, http://dx.doi.org/10.1016/S0895-6111(02)00008-3
Baba E., Ueda K., Okabe M. (2004) Using a flat-panel detector in highresolution cone beam CT for dental imaging. Dentomaxillofacial
Radiology, Vol. 33, No. 5, pp. 285–290, http://dx.doi.org/
10.1259/dmfr/87440549
Farn A.E. (1980) Notes from the laboratory. Journal of Gemmology, Vol. 17, No. 4, pp. 223–229.
Galibourg J., Ryziger F. (1927) Les méthodes d’examen et d’étude
des perles fines et des perles de culture. Revue d’OptiqueThéorique et Instrumentale, Vol. 3, pp. 97–133.
Hänni H.A. (1983) The influence of the internal structure of pearlson Lauegrams. Journal of Gemmology, Vol. 18, No. 5, pp. 386–
400, http://dx.doi.org/10.15506/JoG.1983.18.5.386
Ide H., Yamamoto T., Onihashi H. (2015) X-ray devices contributing to sophistication of X-ray diagnostic systems. Toshiba Re-

view Edition, Vol. 1, No. 1, pp. 39–44.
Karampelas S., Michel J., Zheng-Cui M., Schwarz J.-O., EnzmannF., Fritsch E., Leu L., Krzemnicki M.S. (2010) X-ray computed
microtomography applied to pearls: Methodology, advantages,
and limitations. G&G, Vol. 46, No. 2, pp. 122–127,
http://dx.doi.org/10.5741/GEMS.46.2.122
Krzemnicki M., Friess D., Chalus P., Hänni H.A., Karampelas S.
(2010) X-ray computed microtomography: Distinguishing natural
pearls from beaded and non-beaded cultured pearls. G&G, Vol.
46, No. 2, pp. 128–134, http://dx.doi.org/10.5741/GEMS.46.2.128
Poirot J.P., Gonthier E. (1998) Le contrôle des perles à partir de1929 au Laboratoire Gemmologique Français (du laboratoire
syndical au laboratoire C.C.I.P.). Revue de Gemmologie a.f.g.,
Vol. 133, pp. 26–27.
Scarratt K., Moses T.M., Akamatsu S. (2000) Characteristics of nuclei in Chinese freshwater cultured pearls. G&G, Vol. 36, No.
2, pp. 98–109, http://dx.doi.org/10.5741/GEMS.36.2.98
Sturman N. (2009) The microradiographic structures on non-bead
cultured pearls. www.giathai.net/pdf/The_Microradiographic_
structures_in_NBCP.pdf, Nov. 21 [date accessed: Jul. 8, 2017].
Webster R. (1954) Some unusual structures in pearls and cultured
pearls. Journal of Gemmology, Vol. 4, No. 8, pp. 325–334,
http://dx.doi.org/10.15506/JoG.1954.4.8.325

456

GEMS & GEMOLOGYNOTES & NEW TECHNIQUESWINTER 2017

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

Figure 1. These rubies, a 16.68 mm rough and a 2.72 ct cushion cut, are from Myanmar. Photo by Robert Weldon/
GIA, courtesy of the William F. Larson collection.

F

ollowing the charts for the micro-features of emerald and sapphire—published in Winter 2016 andSummer 2017, respectively—this chart on rubyrounds out G&G’s series on inclusions in the “BigThree” colored stones. Rubies (figure 1) have long
been one of the top gems in the trade, commanding
premium prices. Historically, their popularity has

See end of article for About the Authors.
GEMS & GEMOLOGY, Vol. 53, No. 4, pp. 457–458,
http://dx.doi.org/10.5741/GEMS.53.4.457© 2017 Gemological Institute of America

been critical to the development of color and clarity
treatments (including heating and dyeing, and now
more recently introduced processes) and synthetic
gems. In the early 1900s, over five million carats ofsynthetic ruby were produced annually by the flamefusion, or Verneuil, method (Hughes, 2017).
Innovative new treatments have also played amajor role in satisfying the continued demand forruby. In the early 1990s, gemological laboratories saw
the introduction of chromium-diffused rubies (McClure et al., 1993). In the early 2000s, lead-glass fillingof low-quality rubies reached international markets
and became one of the most widespread—and most

RUBY INCLUSIONS CHARTGEMS & GEMOLOGYWINTER 2017457

problematic—treatments in the gem trade (McClureet al., 2006). Also encountered in the early 2000s wasberyllium diffusion of ruby, which made it possible
to produce pleasing red colors from stones with strong
brown or dark tones that would not respond to traditional heat treatment (Emmett et al., 2003). Rubies
from Songea, Tanzania, for example, were dramatically improved with beryllium diffusion.
Demand has also been met by several new rubydeposits in the last decade. Mozambique has become
the leading producer of gem-quality rubies since thediscovery in Montepuez in 2009. More than two million carats of rough from Mozambique were offeredat the first Gemfields rough ruby auction in 2014
(Lucas and Pardieu, 2014).
The photomicrographs chosen for this chart represent a wide range of features one might encounterin natural, treated, and synthetic rubies when examining them with a gemological microscope. Somefeatures are common, while others are exceedingly
rare. However, all of the images presented provide
the viewer with a tremendous amount of information about the unique micro-world of rubies. For
more on ruby and its inclusions, see our suggested
reading list (http://www.gia.edu/gems-gemology/
winter-2017-suggested-reading-ruby-chart).

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
photo producer for Gems & Gemology, and Dr. Shigley is distinguished research fellow at GIA in Carlsbad.

REFERENCES
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
Hughes R.W., with W. Manorotkul and E.B. Hughes (2017) Ruby
and Sapphire: A Gemologist’s Guide. RWH Publishing,
Bangkok.
Lucas A., Pardieu V. (2014) Gemfields inaugural rough ruby auc-

tion in Singapore. GIA Research News, Jul. 17, www.gia.edu/
gia-news-research-gemfields-ruby-auction-singapore
McClure S.F., Kammerling R.C., Fritsch E. (1993) Update on diffusion-treated corundum: Red and other colors. G&G, Vol. 29,
No. 1, pp. 16–28, http://dx.doi.org/10.5741/GEMS.29.1.16
McClure S.F., Smith C.P., Wang W., Hall M. (2006) Identificationand durability of lead glass–filled rubies. G&G, Vol. 42, No. 1,
pp. 22–34, http://dx.doi.org/10.5741/GEMS.42.1.22

Additional Reading
For a list of references pertaining to inclusions innatural, synthetic, and treated ruby, go to
www.gia.edu/gems-gemology/winter-2017-suggestedreading-ruby-chart or scan the QR code to the right.

458

RUBY INCLUSIONS CHARTGEMS & GEMOLOGYWINTER 2017

Editors
Thomas M. Moses | Shane F. McClure

Cat’s-Eye ALEXANDRITE with
Unique Inclusion Pattern
Chatoyancy is an optical effect caused
by light reflecting off dense concentrations of parallel needles or hollow
tubes in cabochon-cut gem materials.
To maximize chatoyancy, the base of
the cabochon should be cut parallel tothe inclusions to produce an even effect across the dome. In some cases,
the parallel inclusions are not distributed throughout the stone and are only
in zones or narrow bands. In such cases
the cutter must orient the needles
with care to produce a cat’s-eye.
A chatoyant cabochon, weighing
21.22 ct and measuring 17.75 × 17.50
× 6.77 mm, was recently submitted to
GIA’s Tokyo laboratory for identification service. This stone displayed achange of color (figure 1) from brownish green in fluorescent light to brownish purple in incandescent light.
Standard gemological testing resulted
in a spot refractive index (RI) reading of
1.75, a specific gravity (SG) of 3.74, andstrong trichroism. In addition to theseproperties, heterogeneous needle-likeinclusions and infrared and Raman
spectroscopy revealed that the stone
was natural chrysoberyl.
What is notable about this stone isthat all the needle-like inclusions thatcause the chatoyancy are confined toa narrow layer at the very bottom of

Figure 1. This alexandrite cabochon appears brownish green in fluorescentlight (left) and brownish purple in incandescent light (right). The cabochon shows chatoyancy under both forms of illumination due to light reflection from the shallow plane of dense fine parallel needles.

the cabochon (figure 2). The rest of thestone is nearly free of inclusions. The
cutter obviously knew to orient whatmust have been a narrow layer of needles at the bottom of the cabochon sothat the dome would form a complete
cat’s-eye. Some synthetic or imitationstones have an engraved foil backing
or an engraved base to produce a cat’seye or star in much the same way.
Raman spectroscopic analysis indicated that the needle-like inclusions
were rutile (figure 3). While theboundary between the included andFigure 2. A side view of the cabochon, immersed in water, showing the localized inclusions near
the base. Field of view 1.6 cm.

Figure 3. Iridescent minute parallel needles and particles in thealexandrite cabochon. Field ofview 2.0 mm.

Editors’ note: All items were written by staff
members of GIA laboratories.
GEMS & GEMOLOGY, Vol. 53, No. 4, pp. 459–464.
© 2017 Gemological Institute of America

LAB NOTESGEMS & GEMOLOGYWINTER 2017459

Figure 4. A 2.67 ct oval-cut diamond with uneven “lizard skin” surface texture. Close-up views of the pavilion
with reflected light show how the textured pattern continues across facet junctions. Fields of view 3.56 mm (center) and 1.29 mm (right).

inclusion-free areas looks sharp, thestone is not assembled.
Makoto Miura and Yusuke Katsurada

Lizard Skin on Deformed
DIAMOND
Facets that are nearly parallel to a diamond’s octahedral crystal plane
often develop a wavy, rippled appearance called “lizard skin” during polishing (e.g., J.I. Koivula, The MicroWorldof Diamonds, Gemworld International, Northbrook, Illinois, 2000, p.
63). The term is also used more
broadly to describe any bumpy, unevensurface texture that develops on polished diamond facets. It is often attributed to polishing off-grain. Recently,
GIA’s New York lab encountered a2.67 ct type IIa diamond (figure 4, left)
with especially prominent lizard skintexture on multiple facets (figure 4,
center and right). In this case, the texture appears to have developed due toa preexisting deformation fabric or
structure inherent to the diamond itself, rather than merely as a consequence of poor polishing technique.
The surface texture has a pattern
to it, with small bumps appearing toline up in corridors. Some corridors
clearly continue from one facet to thenext (figure 4, right). The continuity
across facets suggests that this texture
is the surface expression of irregularities that actually extend into the volume of the diamond itself. At highmagnification with crossed polarizing
filters, the lizard skin can be seen to460

LAB NOTES

conform to the shape and texture of
the strain pattern within the diamond—that is, the pattern of bumps
and depressions matches up where
the intricate internal dark/light pattern of tatami birefringence meets thepolished surface. This connection
supports the idea that the surface texture is a reflection of underlying crystal imperfections.
Unusual hydrogen- and methanebearing metallic inclusions in this diamond suggest it originated fromextreme depths of about 360–750 km
in the earth’s mantle (E.M. Smith etal., “Large gem diamonds from metallic liquid in Earth’s deep mantle,” Science, Vol. 354, No. 6318, 2016, pp.
1403–1405). In this high-temperatureenvironment, deformation and annealing over a long period of time may
have given the diamond a mosaic crystal structure. This natural phenomenon occurs when heat allows the
crystal to undergo recovery, a processof dislocation reorganization that divides the distorted grain into a mosaic
of smaller, undistorted subgrains without new crystal growth. The subgrains,measuring about 10–30 microns, arelike bricks in a wall; while the wall
may be slightly curved, the individual
bricks are not distorted. These distortions become localized as subgrainboundaries rather than spreading continuously through the crystal. As a result, the subgrains will be oriented inslightly different directions.
Because polishing is so strongly dependent on crystal orientation, if a single facet consists of a mosaic ofsubgrains with varying orientation,
polishing will be uneven. The resulting surface may develop a pattern ofbumps and depressions that mimics
the size and shape of underlying subgrains and, in turn, reflects the diamond’s natural deformation history.
Samples like this one are interestingfor scientists because little is known
about the geological conditions thatlead to the various deformation-related
features seen in natural diamonds.

GEMS & GEMOLOGYWINTER 2017

Evan M. Smith and Paul Johnson

Gota de Aceite in a Zambian
EMERALD
Gota de aceite (Spanish for “drop ofoil”), a rare phenomenon that occurs
in the finest emeralds, is typically associated with Colombian origin (R.
Ringsrud, “Gota de aceite: Nomenclature for the finest Colombian
emeralds,” Fall 2008 G&G, pp. 242–
245). The phenomenon creates aroiled effect caused by irregularity inthe emerald’s internal crystal structure. During the gemstone’s crystallization the growth conditions arealtered, giving rise to rapid columnar
growth. When looking down the
emerald’s c-axis, the outline of thecolumns can be seen. This sometimes
has the appearance of drops of oil, giving rise to the name. The columns
typically have a slightly different
trace element composition from thatof the host emerald. This heterogeneity in trace element chemistry willcause a minor change in the refractive

Figure 5. A muted gota de aceite
effect, with epigenetic ilmenite,in an emerald from Zambia.
Field of view 1.26 mm.

in Colombian emeralds, have also
been documented in emeralds fromcertain mines in Afghanistan, China,
and Zambia (S. Saeseaw et al.,“Three-phase inclusions in emerald
and their impact on origin determination,” Summer 2014 G&G, pp. 114–
132). This emerald shows that
inclusions may not always provide
conclusive proof of origin, but they
can still provide useful information.
Nicole Ahline

Dyed QUARTZITE Imitation of
Ruby-in-Zoisite
The New York laboratory recently received a bracelet composed of translucent multicolored beads that closely
resembled ruby-in-zoisite. Standard
gemological testing of one of theround beads (measuring 8.33 × 8.17mm) revealed an RI of 1.55 for boththe purple and green areas (instead of
approximately 1.76 or 1.69 for rubyand zoisite, respectively) and very
weak red to inert fluorescence in longwave and short-wave ultraviolet light,
respectively. Microscopic observation
revealed fissures and a translucent aggregated/grainy structure, both of

Figure 6. Green to dark green andpinkish purple to dark purple dyeconcentrations were observed in
the fissures and structure of thisquartzite, which resembled rubyin-zoisite. Field of view 9.61 mm.

which contained green to dark green
and pinkish purple to dark purple dyeconcentrations (figure 6).
Although most of the translucent
green and purple aggregate material we
encounter for identification is ruby-inzoisite, the gemological features of thisbead were inconsistent with our expectations. Raman spectra were collected to confirm the identity. Spectrafrom both the purple and green areas
matched quartz (figure 7). Since thematerial was an aggregate, we concluded that it was dyed quartzite.
The Lab Notes section has documented many cases of dyed quartzite

Figure 7. Raman spectra collected from the sample’s purple and green areas
indicated quartz rather than ruby and zoisite. Spectra are offset for clarity.

RAMAN SPECTRARELATIVE INTENSITY (ARB. UNITS)

index of the columns, allowing thestructure to be visible.
The Carlsbad laboratory recently
received a 2.10 ct emerald for origin
determination. The stone had blocky
multiphase inclusions and ilmenite
scattered throughout, along withmica platelets and a very subtle blue
flash effect associated with somesmall feathers. At a certain angle, amuted gota de aceite effect was also
visible (figure 5). The UV-Vis spectrum shows a distinct Fe2+ broad bandat approximately 900 nm. Inductively
coupled plasma–mass spectrometry(ICP-MS) confirmed the stone’s relatively high iron content and indicateda chemical composition consistent
with Zambian origin.
The gota de aceite seen in thisZambian emerald was not exactly thesame as the phenomenon found in
Colombian emeralds. Dendritic ilmenite, an iron-rich mineral, wasfully enclosed in the columnar structure. We believe the epigenetic ilmenite exsolved the increased ironcontent, as Zambian emeralds contain a larger amount of iron than their
Colombian counterparts (J.C. Zwaan
et al., “Emeralds from the Kafubu
area, Zambia,” Summer 2005 G&G,
pp. 116–148).
Until now, gota de aceite has
only been documented in Colombian emeralds and has been an aid inorigin determination. Still, this is
not the first time that an inclusionindicative of a particular origin has
been found elsewhere. Jagged threephase inclusions, traditionally seen

Ruby
ZoisiteQuartzPurple area in the sample
Green area in the sample

6000

4000

2000

0
1000

800

600

400

200

RAMAN SHIFT (cm–1)

LAB NOTESGEMS & GEMOLOGYWINTER 2017461

imitating jadeite, ruby, lapis lazuli,
and sugilite (Spring 1986, pp. 49–50;
Summer 1991, pp. 122–123; Summer
1995, pp. 125–126; Summer 1998, pp.
131–132; Spring 2001, pp. 62–63; andFall 2003, pp. 219–220). But this is thefirst example we have seen ofquartzite being used to imitate rubyin-zoisite. This dyed quartzite provides an intriguing example for
consumers to be aware of when purchasing ruby-in-zoisite.
HyeJin Jang-GreenSYNTHETIC MOISSANITE
Imitating Rough Diamond
The Carlsbad laboratory recently examined a very light green 9.71 ct specimen (figure 8), measuring 11.79 ×
9.69 × 11.61 mm, that was submitted
as a rough diamond. The sample resembled a diamond octahedron, withsurface growth features and a bright
vitreous to subadamantine luster.
Closer examination of its habit andsurface features, along with gemological and advanced testing results, revealed it to be a synthetic moissanite.
The specimen was not a true octahedron, as is typical of a diamond
crystal, but a rectangular bipyramidwith 10 faces (eight triangular andtwo hexagonal side pinacoids on thegirdle). The surface was dimpled, andFigure 8. A very light green 9.71
ct synthetic moissanite crystal,
submitted to the Carlsbad laboratory as a rough diamond. Fieldof view approximately 14 mm.

462

LAB NOTES

Figure 9. Sub-hexagonal etch pits in synthetic moissanite are observed
using differential interference contrast. Field of view approximately 1.44mm.

two of the faces had deep striations resembling growth features in a roughdiamond. Irregularly shaped and subhexagonal etch pits (figure 9), alongwith some dark brown residue, werealso found on the surface. Due to theuneven surface, observation of internal features was limited to somesmall scattered pinpoint inclusions
and a few etch tubes (figure 10). The
surface also made it difficult to see
any doubling effect or a doubly refractive reaction in the polariscope.
Viewed in plane-polarized light, however, a large twinning plane crossed
the crystal diagonally, bluish green on
one side and colorless on the other.
This dichroism served as proof of thestone’s doubly refractive nature, as opposed to singly refractive diamond.
Standard gemological properties ofthe stone offered further evidence of
its true identity, including an overthe-limit refractive index reading, ahydrostatic SG of 3.23, very weak yellow fluorescence in both long-wave
and short-wave UV, and a uniaxial
optic figure. These properties and advanced testing results, including
Fourier-transform infrared (FTIR) and
Raman spectrometry, identified thespecimen as synthetic moissanite. It
is important to note that althoughnatural moissanite exists, it is ex-

GEMS & GEMOLOGY

tremely rare and gem-quality material
has never been found. Natural
moissanite commonly occurs in fragmented pieces and in much smaller
sizes (the largest known specimen
measured 4.1 mm), often with acreamy white or red matrix (Summer
2014 GNI, pp. 160–161). That was not
the case for this 9.71 ct synthetic
moissanite.
Gemological and advanced testing are indispensable tools for revealing the true identity of gems,
especially simulants and imitations
with an appearance that can easily
deceive the general public. While
there is no evidence that this specimen was deliberately deceptive,

Figure 10. Etch tubes extended
from surface etch pits and ended
at the twinning plane. Field ofview approximately 2.30 mm.

WINTER 2017

TABLE 1. Trace elements in two synthetic ruby overgrowth samples,
detected by LA-ICP-MS (avg. concentration in ppmwa).

Figure 11. A thin layer of synthetic ruby overgrowth with flux
particles is distinct from the natural sapphire seed visible in theupper right of the image. Field ofview 1.99 mm.

Element

Concentration in overgrowthStandard deviationCr

32,866

1342

Fe

1231

101.4

Ga

47.6

2.40

Mg

4.92

1.69

Mn

4.55

0.31

Mo

b

bdl

—

Ni

34.9

49.5

Ti

19.06

6.94

Pt

4.03

4.07

Zr

0.41

0.71

a

gemological knowledge is importantin preventing accidental and intentional acts of fraud and preserving the
integrity of the trade.

Six spots examined in total.
bbdl: below detection limit. Detection limit was 0.013 ppmw for both samples.

The New York laboratory recently received two loose red oval mixed cuts
for identification. Standard gemological testing yielded refractive indicesslightly higher than expected forcorundum: 1.778–1.788 and 1.776–
1.787, while a typical RI for corundum is 1.762–1.770. Elevated RIs forchromium-diffused corundum havebeen reported and may be attributed
to higher Cr2O3 concentration at thesurface (S.F. McClure et al., “Update
on diffusion-treated corundum: Red
and other colors,” Spring 1993 G&G,
pp. 16–28). To the unaided eye, thestones appeared to be chromium diffused, displaying red color concentration at the facet junctions, but theirsynthetic component became apparent upon further observation.
Microscopic examination revealed
that planes of minute particles demarcated a thin layer, approximately 0.3
mm thick, of synthetic overgrowthfrom a natural sapphire core (figure11). The presence of intact silk andheat-altered crystal inclusions confirmed the seeds to be natural (figure12). A series of shallow flux-finger-

prints cracking the surface suggested
a flux growth process (figure 13). Portions of the near-colorless core could
be seen in areas where the overgrowth
was cut away during polishing (figure14). These windows showed a sharpboundary without “bleeding” of thesaturated red overgrowth into thenear-colorless seed, which is typicallyobserved in chromium-diffused corundum (McClure et al., 1993). The windows into the near-colorless seed also
indicate that most or all of the redcolor is concentrated in the synthetic
ruby overgrowth.
The overall appearance of the twostones was similar to the now-rare
Lechleitner synthetic overgrowth

Figure 12. A fuzzy heat-altered
crystal inclusion commonly referred to as a “snowball” is surrounded by a discoid fracture,proving the natural origin of thecorundum seed. Field of view
1.26 mm.

Figure 13. Reflective silk inclusions in the natural sapphire seedare visible behind a coarse flux
fingerprint in the synthetic rubyovergrowth, which was cut
through during the fashioning
process. Field of view 3.57 mm.

Figure 14. A portion of the nearcolorless corundum seed is revealed in an area where thesynthetic ruby overgrowth was
cut away during fashioning. Fieldof view 10.85 mm.

Rebecca Tsang

Two Unusual Natural Sapphires
With SYNTHETIC RUBY
Overgrowth

LAB NOTESGEMS & GEMOLOGYWINTER 2017463

Figure 15. A thin layer of synthetic emerald deposited on a near-colorlessberyl seed, a type of synthetic emerald first marketed by Johann Lechleitner in the early 1960s. Field of view 3.57 mm.

emeralds, which are composed of anear-colorless beryl seed with synthetic emerald overgrowth. A sample
with this type of synthetic emerald
overgrowth was coincidentally submitted to the Carlsbad laboratory for
identification around the same time
(figure 15). In addition to emeralds,
Lechleitner also experimented withruby overgrowth on both synthetic
and natural corundum seeds (K.
Schmetzer and H. Bank, “Lechleitnersynthetic rubies with natural seed andsynthetic overgrowth,” Journal of464

LAB NOTES

Gemmology, 1988, Vol. 21, No. 2, p.
95–101), with the most commonly
documented versions containing synthetic seeds (E.J. Gübelin and J.I.
Koivula, Photoatlas of Inclusions inGemstones, Vol. 2, Opinio Verlag,
Basel, Switzerland, 2005, p. 352; Fall2014 Lab Notes, pp. 242–243).
Advanced testing on the synthetic ruby overgrowth layer using
laser ablation–inductively coupledplasma–mass spectrometry (LA-ICPMS) revealed the presence of Cr, Fe,
Ga, Mn, Mg, Ni, Ti, Pt, and Zr (table

GEMS & GEMOLOGY

1). These results, specifically thepresence of platinum, are consistent
with previously reported synthetic
ruby overgrowth (S. Saeseaw et al.,“Analysis of synthetic ruby overgrowth on corundum,” GIA News
from Research, June 10, 2015).
Molybdenum was reported in the primary examination of Lechleitnerovergrowth rubies (Schmetzer andBank, 1988), and its absence here suggests alternative growth conditions
for these samples.
Although this is not the first report of synthetic ruby overgrowth onnatural sapphire seeds (Schmetzer andBank, 1988; C.P. Smith, “Diffusion
ruby proves to be synthetic ruby overgrowth on natural corundum,” Fall
2002 G&G, pp. 240–248), it marks thefirst time the New York and Carlsbad
laboratories have had them submitted
for identification. The resurfacing ofthese vintage overgrowth synthetics
shows that once a material is in the
trade, it is here to stay.
Tyler Smith and Hollie McBridePHOTO CREDITS
1—Shunsuke Nagai; 2 and 3—Makoto Miura;
4—Evan Smith; 5—Nathan Renfro; 6—HyeJin
Jang-Green; 8 –10—Rebecca Tsang; 11–15—
Hollie McBride.

WINTER 2017

Gems & Gemology requires each manuscript submitted for publication to undergoa rigorous peer review process, in which a paper is evaluated by at least three experts in the field prior to acceptance. 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 theirvaluable time to reviewing manuscripts in 2017.

Non-Editorial Board Reviewers
Ilaria Adamo • Donald Burnett • Gagan Choudhary • Zachary Cole • Si and
Ann Frazier • Dan Frost • Artitaya Homkrajae • Richard Hughes • Dorrit Jacob• John King • Maya Kopylova • Glenn Lehrer • Cigdem Lule • Carmel
McDougall • Tetsuji Masaoka • Jana Miyahira-Smith • Lutz Nasdala • Laura
Otter • Karl Schmetzer • Olivier Segura • Sherris Cottier Shank • Elena
Shuchukina • Nicholas Sturman • Ziyin Sun • Rachelle Turnier • Chunhui Zhou

Cast Your Vote for the 2017
Dr. Edward J. Gübelin Most Valuable Article Award
Established in 1981, G&G’s Most Valuable Article Award invites the journal’s
readers to vote on the three most important articles (feature articles, field reports, and charts) from the previous year. Each completed ballot is entered intoa drawing to win a one-year subscription to Gems & Gemology.
To qualify for the drawing, please submit your votes for the2017 MVA Award by Monday, March 12, 2018, either by
mail, by scanning the QR code, or by visiting www.gia.edu/
most-valuable-article-2017

EditorNathan Renfro

Contributing Editors
Elise A. Skalwold and John I. Koivula

Aragonite Spheres in Ethiopian Opal
Recently, the authors examined an 88.51 ct pear-shaped
white precious opal that displayed typical digit patterns andhydrophane behavior (see Fall 2013 Lab Notes, pp. 175–
176). These properties were consistent with opal from theWollo mining area in Ethiopia (see B. Rondeau et al., “Playof-color opal from Wegel Tena, Wollo Province, Ethiopia,”
Summer 2010 G&G, pp. 90–105). The stone also showed
weak whitish blue fluorescence in long-wave UV and wasinert to short-wave UV. No phosphorescence was observed.
In addition to its attractive digit pattern with spectral
play-of-color, this opal hosted a number of unusual inclusions: opaque black octahedrons and translucent spheres.
When viewed with a fiber-optic light, the opaque black octahedrons appeared a dark brassy metallic yellow (figure 1).
Raman analysis identified them as pyrite, which has been

Figure 1. This Ethiopian opal contained an interesting inclusion scene consisting of a string of octahedral pyrite crystals and aragonite spheres.
Photomicrograph by Charuwan Khowpong; field ofview 1.40 mm.

Figure 2. A single pyrite crystal is seen among spheres
and clusters of translucent aragonite inclusions, bothof which were identified by Raman spectroscopy.
Oblique fiber-optic illumination. Photomicrograph by
Charuwan Khowpong; field of view 1.05 mm.

previously reported in Ethiopian opal (N. Renfro and S.F.
McClure, “Dyed purple hydrophane opal,” Winter 2011
G&G, pp. 260–270). Of particular interest is that thetranslucent spherical inclusions (figure 2), which formed
as isolated spheres and clusters, were identified by Raman

About the banner: Modified Rheinberg illumination highlights the crystallographically aligned tension cracks in this topaz crystal. Photomicrograph by
Nathan Renfro; field of view 10.29 mm. Specimen courtesy of John S. White.
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. 53, NO. 4, pp. 466–471.
© 2017 Gemological Institute of America

466

MICRO-WORLDGEMS & GEMOLOGYWINTER 2017

analysis as aragonite. The presence of aragonite spheres inopal is quite uncommon and has not been previously reported in precious opal from Ethiopia.
Ratima Suthiyuth and Charuwan Khowpong
GIA, Bangkok

Remarkable Twinned Calcite Inclusion in
Mogok Ruby
The Mogok Stone Tract in Myanmar (formerly Burma) is
one of the world’s most famous sources of ruby, which
often forms there in a calcite-marble host. Calcite may
occur as an inclusion inside the ruby, as in the example infigure 3. In this stone, the calcite is easy to spot between
crossed polarizers, which reveal polysynthetic twinningplanes that “crisscross” the crystal. While calcite is a common inclusion in ruby, this is the clearest example of calcite twinning this author has seen. Surrounding the calcite
crystal is a dense, angular nest of exsolved rutile silk as
short needles, a typical scene in rubies from this locality.
E. Billie Hughes
Lotus Gemology, Bangkok

New Phenomenal Feldspar from North Carolina
With Iridescent Inclusions
Several varieties of aventurescent feldspar are well known
in the gem trade. Of these, one of the most remarkable isorthoclase from the Hart’s Range area in Australia. This
unique material showcases exsolution platelets ofhematite and ilmenite that display thin-film interferencecolors along the interface between the exsolution productand the feldspar host. Because of its array of colors and thecrosshatch pattern of exsolution platelets, the material’s
trade name is “rainbow lattice sunstone.”
The authors recently examined samples of potassium
feldspar from a relatively obscure source (figure 4) that dis-Figure 3. Viewed between crossed polarizers, an included calcite crystal within an unheated Burmese
ruby displays dramatic twinning planes. Photomicrograph by E. Billie Hughes; field of view 3.90 mm.

played a phenomenon remarkably similar to Australianrainbow lattice sunstone. This new material is reported tobe from the Statesville area of North Carolina and contains
brown and black exsolution platelets of hematite and ilmenite showing thin-film interference colors along the interface with the host feldspar. This deposit was firstreported by George Frederick Kunz (Gems and Precious
Stones of North America, The Scientific Publishing Co.,New York, 1890, p. 164). Chemical analysis of the feldspar
was performed using laser ablation–inductively coupledplasma–mass spectrometry (LA-ICP-MS), and the results
were consistent with potassium feldspar.
Local prospector Ryan Underwood first found samplesof this material as loose crystal fragments and traced themback to their source rock, a metamorphic biotite gneiss.
The crystals are brittle, apparently as a result of metamorphic stresses, and tend to cleave during cutting. As such,material suitable for cutting is rare and finished stones tend

Figure 4. Brown and black exsolution platelets of hematite and ilmenite in feldspar (left) show colorful thin-film interference colors in oblique fiber-optic illumination (right). Photomicrographs by Nathan Renfro; fields of view 3.55 mm.

MICRO-WORLDGEMS & GEMOLOGYWINTER 2017467

Figure 5. This octahedral-shaped negative
crystal in a Burmese
red spinel is filled withcolorless carbonate
crystals, yellow sulfurrich liquid, opaque sulfide crystals, anddiaspore fibers. Photomicrograph by Victoria
Raynaud; field of view
1.20 mm.

to be small (though some large multicrystalline specimens
up to 30 cm in diameter have been recovered). Base colors
include blue-gray, tan, and a pink color apparently induced
by additional fine hematite inclusions.
Stephen ChallenerRaleigh, North Carolina
Nathan Renfro and Ziyin Sun
GIA, Carlsbad

Complex Yellow Fluid Inclusions in
Red Burmese Spinel
Spinel has found new popularity and is now recognized asa birthstone for August. Some of the most desirable stones
come from Myanmar, as they exhibit a pure red color witha light tone, accompanied by extremely high fluorescence
under long-wave UV. Red Burmese spinel can also be foundwith a dark tone and much weaker fluorescence. The main
localities that produce the highly fluorescent spinel are
Namya in northern Myanmar and Man Sin in the Mogok
Valley (V. Pardieu, “Hunting for ‘Jedi’ spinels in Mogok,”
Spring 2014 G&G, pp. 46–57). Clean stones are rare, as the
majority have inclusions consisting of colorless carbonate
crystals and complex multiphase negative crystals. These
complex negative crystals contain a sulfur-rich yellow liquid, opaque metal sulfides, transparent carbonate daughter
crystals, diaspore fibers, and a gas bubble. This unique yellow complex fluid inclusion (figure 5) is only known tooccur in Burmese spinel and therefore serves as a good indicator of this origin.

Tourmaline Crystals on Burmese Ruby
During a GIA field expedition to Mogok, Myanmar, a tiny
but interesting sample was acquired. This 0.552 ct rubywas purchased from local Kanase miners who process thetailings of the larger mines in the Kyatpyin Valley, justwest of the town of Mogok. The ruby is associated withpure white calcite and bluish green tourmaline (figure 6).
Many rubies form in marble, especially in the deposits
related to the Himalayan orogeny (Afghanistan, Tajikistan,
Myanmar, and Vietnam), so calcite as an inclusion or associated mineral with these gems is common. While tourmaline in combination with ruby is not unheard of, it is arelatively unusual combination. LA-ICP-MS chemical
analysis showed that the tourmaline was a Na-Mg-richdravite. Tourmalines are of great interest to geologists be-

Figure 6. Bluish green tourmaline crystals and white
calcite on a Burmese ruby. Photo by Charuwan
Khowpong; field of view 2.48 mm.

Wim Vertriest
GIA, Bangkok
Victoria Raynaud
DANAT, Manama, Bahrain

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MICRO-WORLDGEMS & GEMOLOGYWINTER 2017

Figure 7. This vibrantyellowish green crystal
in a faceted ruby from
Myanmar was identified as vesuvianite.
Photomicrograph by
Nathan Renfro; field ofview 1.20 mm.

cause their isotopic and trace element composition are potentially strong indicators of the formation environmentof the tourmaline and the associated minerals, in this caseruby.
Wim Vertriest and Charuwan Khowpong
GIA, Bangkok

Vesuvianite in Burmese Ruby
It is a pleasant surprise when a gemologist encounters a vibrantly colored crystal in a gemstone, as most gems are either inclusion free or contain inclusions that are weakly
colored due to their small size. When the authors discovered a vibrant yellowish green crystal in a Burmese ruby(figure 7), it was a very welcome sight. Green crystals incorundum are not common but do occur occasionally.
Green spinel and pargasite both occur in gem corundum.
The former, a singly refractive mineral, was ruled out immediately because this inclusion behaved as a doubly refractive mineral when examined between crossed
polarizers. Doubly refractive pargasite remained a possibility. The surprise came when Raman microspectrometry
identified the yellowish green crystal as vesuvianite, also
known as idocrase. To the authors’ knowledge, this is thefirst time vesuvianite has been reported as an inclusion inruby.

terest highlighted in these meetings are of extraordinary naturally occurring minerals and gem materials—some ofwhich have appeared in this column—these rather ordinary
beads were intriguing for the veritable blizzard of translucent colorless needles and short euhedral crystals that filledeach one. They created a beautiful optical effect, especiallywhen illuminated from below (figure 8). Upon acquisition,
the original owner had been told these were Russian synthetic quartz, and indeed their age and azure color suggested
such an origin. It came as a surprise when standard gemological testing (RI of 1.518, SG of 2.47, and the absence ofbirefringence) identified the beads as glass, making the internal scene even more intriguing for its natural appearance.
Raman spectroscopy at GIA’s Carlsbad laboratory identified
the beads as manufactured glass, and the majority of the nee-

Figure 8. Faceted manufactured glass beads measuring approximately 8 mm in diameter. Photo by Robison McMurtry.

Nathan Renfro and John Koivula
GIA, Carlsbad

Wollastonite Blizzard Within Glass
A collection of lovely faceted blue beads was presented toauthor EAS during an annual meeting of inclusion specialists at the 2017 Tucson shows. While most specimens of in-

MICRO-WORLDGEMS & GEMOLOGYWINTER 2017469

Figure 9. Transmitted
light reveals a blizzardof transparent wollastonite needles within
the glass host, an indication of devitrification. Interspersed
among the needles areblocky crystals of diopside. Photomicrographby Nathan Renfro; fieldof view 2.03 mm.

dles as the calcium silicate mineral wollastonite (figure 9).
Additionally, relatively small blocky crystals scatteredamong the needles were conclusively identified as diopside(see Summer 2010 Lab Notes, p. 144).
Inclusions in glass such as wollastonite and diopside
are indicators of devitrification, a process by which various
components of the glass’s composition crystallize out
when subjected to high temperatures and/or changes intemperature. The process varies according to the type ofglass. This may also happen in natural glasses, as with obsidian, resulting in the attractive lapidary material known
as snowflake obsidian, which sports white blooms ofcristobalite crystals on a black background. Devitrified
glass is also sometimes used to imitate natural gems, asseen in manufactured “meta-jade.” The beautiful blue
inner world of these beads makes them a welcome addition
to one’s library of inclusions.
Elise A. Skalwold
Ithaca, New YorkNathan Renfro

The inclusions were situated in the quartz crystals in
the form of phantoms that developed through the deposition of the shattuckite on the surface. Laser Raman microspectrometry identified the phantom layers as
shattuckite. As the quartz continued to grow, the shattuckite was captured as inclusion phantom planes tracing theform of the original quartz host.
Named for the type locality—the Shattuck mine in
Bisbee, Arizona—shattuckite is a medium to deep blue
mineral with a silky luster. A secondary mineral in oxidized copper deposits, shattuckite is often found together
with ajoite, chrysocolla, and malachite, in addition toquartz.
John Koivula

Figure 10. As an inclusion in quartz, shattuckite typically forms aggregates of circular to spherulitic
masses composed of acicular crystals. Photomicrograph by Nathan Renfro; field of view 3.55 mm.

Quarterly Crystal: Shattuckite in Quartz
For our “Quarterly Crystal” in the Micro-World column, weare always searching for unusual crystal specimens that contain interesting mineral inclusions and other micro-features
worthy of description. This quarter’s offering is an intergrown cluster of quartz crystals that play host to a rich blue
deposition of the orthorhombic copper silicate mineral shattuckite, which typically forms aggregates of spherulitic tocircular masses composed of acicular crystals (figure 10). The
41.27 mm long quartz crystal grouping (figure 11) came fromthe Kandesei mine in the Kunene region of Namibia and was
acquired from Jordi Fabre (Fabre Minerals, Barcelona).

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MICRO-WORLDGEMS & GEMOLOGYWINTER 2017

Figure 11. Measuring 41.27 mm and weighing 164.63 ct, this quartz crystal cluster contains a phantom composed of an abundance of deep blue radial concretions of shattuckite, forming a rich blue
felted mat. Photo by Kevin Schumacher.

MICRO-WORLDGEMS & GEMOLOGYWINTER 2017471

Contributing Editors
Emmanuel Fritsch, University of Nantes, CNRS, Team 6502, Institut desMatériaux 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 MATERIALSPreliminary observations on facet-grade ruby from Longido,
Tanzania. With rubies discovered about 100 years ago, theLongido district of Tanzania is one of the longest-known
occurrences in Africa. The deposit is famous for its “rubyin-zoisite,” consisting of large red corundum crystals in a
striking green zoisite matrix, often speckled with black
amphibole spots. The majority is used for carving, but occasionally facet-quality material is discovered (D. Dirlam
et al., “Gem wealth of Tanzania,” Summer 1992 G&G, pp.
80−102).
For this study, 16 transparent rubies (figure 1) were collected during a July 2016 field expedition. The stones wereacquired at the Mundarara mine in Longido and from adealer in a nearby trading post. Most of the rough material
ranged from 1 to 3 ct, although one heavily fractured piece
weighed about 7 ct. Colors ranged from red to purplish red,

Figure 1. Sixteen samples of facet-quality ruby(0.8–7.1 ct) from Longido, Tanzania. Photo by Sasithorn Engniwat.

A

B

C

D

Figure 2. Internal features of ruby from Longido, Tanzania. A: A group of irregular thin films; field of view
1.6 mm. B: An array of reflective platelets with needles; field of view 0.9 mm. C: Short and long needles
together with thin films; bands of fine reflective particles are also seen. Field of view 2.0 mm. D: Angularinternal growth; field of view 4.0 mm. Photomicrographs by Boodsakorn Kongsomart.

very similar to the color of high-quality Mozambican ruby.
Fluorescence was medium red under long-wave UV andweak red under short-wave UV.
The inclusion scenes (figure 2) had features similar to
those of rubies from Mozambique: short needles, particle

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. 53, NO. 4, pp. 472–490.
1 cm

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GEMS & GEMOLOGYWINTER 2017

TABLE 1. Trace element concentrations in rubies from East African deposits.
SourceTrace element (ppma)

CountryMineCr
min-max(avg., SD)Fe
min-max(avg., SD)Ga
min-max(avg., SD)

Mg
min-max(avg., SD)V
min-max(avg., SD)

Tanzania

Longido,facet-grade(n=16)

1604–5059(3300, 791)

62–544(403, 80)

6–10
(7, 1)

7–42(13, 7)

3–25(5, 4)

Longido,carving-grade(n=5)

1839–6235(3760, 1185)

350–868(565, 151)

5–8
(6, 0)

9–130(32, 31)

2–4(3, 0)

Winza,
facet-grade(n=14)

161–1094(583, 295)

405–1596(816, 276)

4–11
(6, 1)

0–118(22, 21)

0–1(1, 0)

Montepuez, Mugloto,
facet-grade(n=14)

506–1737(1167, 318)

851–2034(1534, 243)

5–12
(9, 1)

11–50(24, 10)

2–7(4, 1)

Montepuez, Maninge Nice,facet-grade(n=5)

1886–4941(2868, 813)

261–402(331, 30)

6–9
(7, 1)

19–47(31, 8)

1–6(3, 1)

Didy,
facet-grade(n=21)

33–2698(440, 498)

533–1274(856, 198)

3–17
(8, 4)

0–67(13, 14)

2–17(5, 4)

Andilamena,
facet-grade(n=14)

53–1569(403, 377)

559–1559(1009, 253)

7–21
(14, 4)

19–53(36, 7)

4–29(18, 7)

Zahamena,
facet-grade(n=66)

135–3922(1196, 874)

284–1994(912, 249)

10–30
(16, 4)

13–61(35, 8)

10–100(17, 11)

Chimwadzulu,
facet-grade(n=18)

269–1816(648, 377)

953–2760(1697, 497)

5–15
(8, 3)

10–39(21, 6)1–10(5, 2)

Mozambique

Madagascar

Malawin = number of samples analyzed. On each sample, a minimum of three spots were measured. All the samples were facet grade except those from Longido,
Tanzania, which included both facet and carving grades.

banding, and reflective platelets (V. Pardieu et al., “Rubies from the Montepuez area, Mozambique,” GIA News
from Research, Oct. 1, 2013). The most common inclusions were thin films (figure 2A), a combination of needles and reflective platelets (figure 2B), and particle
banding (figure 2C). In addition, dense particulate planar
clouds were arranged mostly parallel to each other andassociated with short and long needles (again, see figure2C). Internal growth zones (figure 2D) and twinning features were also found. Several types of crystals were identified by Raman spectroscopy, including amphibole,mica, and feldspar. Undetermined opaque metallic inclusions were also observed.
Various advanced analytical techniques were used tocharacterize the properties of the studied rubies. Fouriertransform infrared (FTIR) spectroscopy revealed strong absorption features consistent with boehmite in all samples.
Other minerals that are normally present in ruby, such as diaspore or kaolinite, were not detected in the studied rubies.
The trace element concentrations of these rubies wereanalyzed with laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) and compared to rubyfrom other East African sources (table 1). The rubies from
Longido were extremely rich in Cr and fairly low in Fe
compared to other African sources. The only East African
deposit producing ruby with similar concentrations ofchromophores is Maninge Nice in Mozambique, but the
facet-grade material from Longido has lower magnesium
content on average. Other deposits can be separated from
Longido based on other trace elements (again, see table 1),
although minor overlap cannot be excluded.
While Longido is traditionally known for large ruby-inzoisite specimens, facet-grade rough is also produced andcan yield attractive gemstones. Chemical analysis revealed
an extremely high chromium concentration in both facetand carving-grade ruby. While the internal features of therubies from Longido are quite similar to those of other
African deposits, trace element composition can aid in positively identifying their origin.
Boodsakorn Kongsomart, Wim Vertriest, andVararut Weeramonkhonlert
GIA, Bangkok

GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2017473

Figure 3. A selection from Campbell Bridges’s tsavorite collection, displayed at the 2017 AGTA Tucson Gem
Fair. This collection includes some of the most important pieces found in the past half century. Photo by
Robert Weldon/GIA, courtesy of the Bridges family.

Celebrating 50 years of tsavorite. The year 2017 marked
the 50th anniversary of Campbell Bridges’s discovery oftsavorite. At the 2017 AGTA Tucson Gem Fair, the Smithsonian Institution hosted a selection of historical pieces
from Bridges’s personal collection to commemorate his
life’s work (figure 3).
Starting in the front row and proceeding from left toright, we begin with two crystals that are some of the firsttsavorites Bridges discovered, near Komolo, Tanzania, in
1967. These are among the first samples that were analyzed to identify this new gemstone.
Next, the tsavorite in matrix represents the 1970 discovery in Taita, Kenya, at Bridges’s GG3 mine. Also represented from this location is a lovely tsavorite “thumbnail”
unearthed in 1971. Some years prior, Bridges was engaged
by Tiffany & Co. as a consultant. He was the first to bringtanzanite to the United States, and was credited with thediscovery of tsavorite in Tiffany ads introducing the gem
to the public in 1974 (figure 4).
The three large tsavorite rough samples weighing morethan 5 grams each were found in 1980 at a source Bridges

christened the Scorpion mine. The vibrant yet rich puregreen to bluish green hue became a well-known characteristic of material from this mine. Over the following four
decades, the Scorpion mine would prove to be the world’s
most prolific producer of fine tsavorite.
The next six rough pieces, weighing 5 to 25 grams,
were recovered in 1992 from the famed Bonanza tunnel
at the Scorpion mine. The Bonanza tunnel is the richest
tsavorite-bearing reef zone at Scorpion and has yieldedsome of the finest pockets the world has seen. The “saddle reef structure,” a series of recumbent folds, is thecharacteristic geological feature identified by Bridges at
the Scorpion mine. This distinctive structure has led tothe mine’s rich and consistent production throughout its
history.
Rounding out the Scorpion mine material in the top left
corner is an extremely rare terminated euhedral tsavorite
crystal in matrix. As tsavorite occurs under very high pressures and temperatures, it is often highly fractured in roughform, making such an unblemished and well-formed specimen a remarkable occurrence.

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WINTER 2017

Figure 4. In this 1973
photo, Campbell
Bridges (right) discusses tsavorite with
Henry B. Platt, former
president of Tiffany &Co. Photo courtesy of
the Bridges family.

Next is an exceptional 31.27 ct oval from Merelaniwith a vivid blue-green color. This tsavorite retains fantastic brilliance even in low lighting, while maintaining a sufficient level of saturation under strong lighting.
Last but certainly not least are two tsavorite cushions.
As to their origin, the Bridges family wishes to preserve anelement of mystery. The 33.55 ct square cushion on theright is a loupe-clean gem exhibiting an exceptional bluegreen color that is well saturated yet extraordinarily vivid.
After a lifetime of dealing with tsavorite, the author considers this one of the finest examples ever produced between 10 and 50 carats.
The largest of the four faceted gemstones in this display is a 58.52 ct cushion. It is another loupe-clean example representing the pinnacle of what is possible intsavorite. It also exhibits a strong blue-green color thatglows in any lighting environment. This is the finest tsavorite above 50 ct observed by this author. Given its oneof-a-kind nature, the Bridges family felt it most appropriate
to name the gem the “Golden Jubilee” in honor of tsavorite’s 50th anniversary.
As tsavorite and the legacy of Campbell Bridges celebrate 50 years, the Bridges family wishes to thank theSmithsonian and the colored gemstone community for
their support throughout the years.

In the top right corner, we have a tsavorite nodule inmatrix that opens a window into the gem’s formation andits associated minerals. This nodule was extracted in its
entirety from the Bonanza reef three decades ago and kept
intact.
On display (again, see figure 3) are tsavorite, surroundedin the matrix by tanzanite, calcite, pyrite, quartz, andgraphite. Tsavorite and tanzanite can occasionally occur
together, though their formation is separated by approximately 100 million years. Tsavorite forms under prograde
metamorphism and tanzanite under retrograde metamorphism.
Keeping guard on this tsavorite bounty are the namesakes of the Scorpion mine. These pewter scorpions weredirectly cast from actual scorpions that patrolled the mine.
Needless to say, it’s advisable to check your shoes in themorning… Also on display is one of Campbell Bridges’s
earliest business cards, from 1967.
In the top row are four extraordinarily fine, loupe-clean
faceted gemstones. None of these were ever on public display before the Tucson exhibit. The first is a lovely 25.10
ct “mint” green grossular garnet, unearthed in 1971 from
Bridges’s GG2 mine in Taita, Kenya. Interestingly, thiscolor of mint green garnet has been found at all of theBridges mines in Tanzania and Kenya over the decades. A
strike may yield both richly colored high-chromium andvanadium-colored saturated tsavorite, as well as the far
lighter, mint green garnet within the same pocket. This variety is most prevalent in Merelani, Tanzania, but also occurs near Komolo, Tanzania, as well as in Taita. While suchmaterial came from all three locations in the early years,
it simply was not marketable back then. It was not until
the 2000s that a real market for these garnets developed.

New azurite-malachite mixture from Peru. Green malachite, Cu2(CO3)(OH)2, is very popular as an ornamentalstone, with huge quantities coming every year from deposits in the Katanga Province of the Democratic Republicof Congo. Blue azurite has a similar chemical composi-

GEM NEWS INTERNATIONALGEMS & GEMOLOGY

Bruce Bridges
Bridges Tsavorite, Nairobi

WINTER 2017475

Figure 5. This polished vein of azurite with malachiteand chrysocolla mined from Cochapata measures 8.5
cm wide. Photo by J. Hyršl.

tion, Cu3(CO2)2(OH)2, but is much more rare. Cabochonsof pure azurite are usually quite dark and not very attractive. A blend of the two is much more appealing for jewelry, but this combination is seldom found. Attractive
azurite-malachite mixtures are known mainly from oldfinds in Bisbee and Morenci, both in the U.S. state of Arizona. There was also a find of malachite-azurite-gypsum
mixture from Peru’s Moquegua region in 2012 (J. Hyršl,“Malachite-azurite from Peru,” Journal of Gemmology,
Vol. 34, No. 7, 2015, p. 564).
Another new azurite-malachite mixture appeared in2016 and was originally described as from Puno, in southeastern Peru. In fact, it is from Cochapata, in the Cotabambas Province about 50 km southwest of Cuzco, situated inhigh mountains. According to a dealer who visited the lo-

Figure 6. These azurite-malachite cabochons, fashioned from Cochapata material, measure up to 31
mm. Photo by J. Hyršl.

Figure 7. A cross-section of a 25-mm-wide malachite
double stalactite from Cochapata. The stalactite on
the right shows malachite with an azurite center.
Photo by J. Hyršl.

cality, there are several outcrops of oxidized copper veins
on a steep hill exploited by artisanal miners. The veins are
up to about 20 cm wide, but the parts most useful for cutting are usually only a few centimeters wide. Several tonsof the rough have already been sold in Lima to foreign dealers, with the largest piece weighing 80 kg.
Deep blue azurite is the main mineral found today in
Cochapata, accompanied by light green malachite and, lesscommonly, light blue chrysocolla (figure 5). The most attractive specimens have malachite with a banded structure, but some possess a brecciated structure (figure 6). The
rarest samples are stalactites of malachite up to 5 cm inlength. Some were sliced perpendicular to the elongatedgrowth direction to prepare very attractive stones with anagate-like structure (figure 7).
Jaroslav Hyršl (hyrsl@hotmail.com)
PragueDIAMONDS
Two natural type IIa diamonds with strong phosphorescence and Ni-related defects. Strong phosphorescence under
UV excitation is rarely seen in natural diamond and normally limited to hydrogen-rich type Ia or type IaA/Ib
chameleons and type IIb diamonds (T. Hainschwang et al.,“A gemological study of a collection of chameleon diamonds,” Spring 2005 G&G, pp. 20–35; S. Eaton-Magaña
and R. Lu, “Phosphorescence in type IIb diamonds,” Diamond and Related Materials, Vol. 20, No. 7, 2011, pp. 983–
989). When seen in other diamond types, an even rarer
occurrence, it is shorter and less intense. Recently, the National Gemstone Testing Center (NGTC) in Beijing encountered two natural diamonds that showed extraordinarilystrong blue phosphorescence and uncommon fluorescencecolors under the DiamondView.

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GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2017

Figure 8. DiamondView
images of two unusual
diamonds (0.18 and 0.30
ct, respectively). Left:
Unevenly distributed
grayish blue fluorescenceand strong blue phosphorescence. Right: Vivid red
fluorescence, strong blue
phosphorescence, and adislocation network canbe seen in the table. Images by Shi Tang.

The diamonds weighed 0.18 and 0.30 ct and were both
graded as E color. Both were type IIa, with neither nitrogen
absorption between 1100 and 1400 cm–1 nor boron-related
absorption in their infrared spectra. Magnification and examination with a standard UV lamp showed no abnormal
phenomena for natural type IIa diamonds. Instead of the
deep blue fluorescence and inert phosphorescence that natural type IIa diamonds typically show in DiamondView
imaging, the 0.18 ct diamond emitted unevenly distributed
grayish blue fluorescence and strong blue phosphorescence,
similar to that of a colorless HPHT synthetic diamond.
The 0.30 ct diamond displayed vivid red fluorescence andstrong blue phosphorescence, which is unusual for a natural colorless to near-colorless diamond (figure 8). Red fluorescence is rare in natural type IIa diamond and seldom
reported (Summer 2016 Lab Notes, pp. 189–190).

Photoluminescence (PL) spectra collected with 532 nm
laser excitation at liquid nitrogen temperature revealed
something even more interesting. Along with the GR1
center emission at 741 nm typically seen in natural typeIIa diamonds, the 883.0/884.7 nm doublet that is related
to nickel impurity appeared in both samples’ PL spectra(figure 9). This doublet, often referred to as the “1.40 eV
center,” is frequently seen in the {111} growth sectors of
HPHT synthetic diamonds produced using Ni-based solvents/catalysts. Ni-related defects are more often seen innatural chameleon and greenish yellow diamonds (W.
Wang et al., “Natural type Ia diamond with green-yellow
color due to Ni-related defects,” Fall 2007 G&G, pp. 240–
243; Summer 2014 Lab Notes, pp. 151–152) but seldomfound in colorless to near-colorless natural diamonds (e.g.,
Spring 2017 Lab Notes, pp. 95–96). For natural diamonds

PL SPECTRA
22,000NV0 center
575 nm

20,00018,000INTENSITY (COUNTS)

0.30 ct sample
0.18 ct sample

850
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550
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16,00014,00012,000

875

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885

890

10,000NV– center
637 nm8000

GR1 center
741 nm6000

Ni-related doublet
883.0/884.7 nm

Figure 9. PL spectra of
the two samples with
532 nm laser excitation.
Both showed weak Nirelated doublets at
883.0/884.7 nm andstrong NV centers at
575 and 637 nm, as
well as the GR1 centerat 741 nm.

4000
2000
0
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WAVELENGTH (nm)GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2017477

PL SPECTRUM

60,000NV0 center saturated
575 nm55,000INTENSITY (COUNTS)

50,00045,000Figure 10. The PL spectrum of the 0.30 ct sample emitted with a 532
nm laser, at higher excitation energy. The NV0
center peak is saturated,and emissions at 648 and
776 nm are clearly seen.

40,00035,00030,00025,00020,000NV– center
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GR1 center
741 nm 776 nm

5000

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WAVELENGTH (nm)with such strong phosphorescence, the presence of Ni-related emissions is unusual.
The PL spectrum of the 0.30 ct sample also presented
an extremely strong NV center at 575 nm, compared to thediamond emission at 572 nm, which explained the reddish
fluorescence in the DiamondView image. In each sample’s
PL spectrum, the relative intensity of NV0 (575 nm) is significantly stronger than that of NV– (637 nm).
Furthermore, when we exposed the 0.30 ct sample tohigher-energy excitation with the 532 nm laser to reveal
more subtle features, the PL spectrum showed moderately
strong emissions at 648/649 nm and 776 nm (figure 10).
According to previous research, PL peaks at 648.2 and776.4 nm are associated with boron in phosphorescing type
IIb natural diamonds (Eaton-Magaña and Lu, 2011). Later
studies ascribed the 648.2 nm defect to a boron-interstitial
complex, while the 776.4 nm peak was assigned to a B-V
complex (S. Eaton-Magaña and T. Ardon, “Temperature effects on luminescence centers in natural type IIb diamonds,” Diamond and Related Materials, Vol. 69, 2016,
pp. 86–95). These emissions may partly explain the strong
phosphorescence of the 0.30 ct sample. Since they were notdetected in the 0.18 ct sample, which also exhibited strong
phosphorescence—the same is true of other phosphorescent natural IIa diamonds the authors have encountered
before—this cannot be the full explanation.
Despite the synthetic-like luminescence color in DiamondView imaging and the Ni-related emissions in the PL
spectra, the samples’ Fourier-transform infrared (FTIR)
spectra, UV-visible spectra, PL spectra, features observed
under the crossed polarizing microscope, and UV reaction
indicated that they are not of synthetic origin. These two

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samples demonstrated the diversity of luminescence andspectral features found in natural diamond. Their identification also highlights the importance of a comprehensive
understanding of diamond origin.
Shi Tang (tangs@ngtc.com.cn), Zhonghua Song,
Taijin Lu, Jun Su, and Yongwang Ma
NGTC, BeijingInteresting growth structure in black diamond. The colorof most black diamonds is attributed to graphite microinclusions or metallic inclusions (S.V. Titkov et al., “AnFigure 11. This 1.03 ct opaque round brilliant cut
with a striking pattern of micro-inclusions was identified as a black diamond. Photo by Yujie Li.

GEMS & GEMOLOGYWINTER 2017

Figure 12. The “double cross” pattern seen in theblack diamond. This pattern showed that the small
inclusions were restricted to certain sectors, indicating that the diamond crystallized through two separate processes. Photo by Yujie Li; field of view
approximately 4 mm.

investigation into the cause of color in natural black diamonds from Siberia,” Fall 2003 G&G, pp. 200–209), and it
is rare to see dense clouds of micro-inclusions producing a

Figure 13. The pattern as seen in the DiamondView.
The well-developed cuboid growth sectors exhibitedyellowish green fluorescence, while the poorly developed octahedral growth sectors were inert to theshort-wave UV light. The DiamondView also revealed a mixed-habit growth structure.

black appearance (see Spring 2007 Lab Notes, pp. 52–53).
Since November 2016, the National Gemstone Testing
Center (NGTC) in Shanghai has routinely received large
quantities of polished black diamonds. One such stone, a1.03 ct opaque round brilliant (figure 11) that we believed
to have been heat treated, had a striking pattern of microinclusions we had never seen before.
Microscopic observation revealed a “double cross” pattern arising from an abundance of pinpoint-like gray inclusions restricted to certain sectors of the diamond (figure 12).
The outer black cross was oriented in the same direction as
the inner pale cross. The inclusions’ crystalline forms were
too small to resolve at 40× magnification. These small inclusions absorbed a large proportion of the light entering the
diamond, causing the black appearance. The FTIR absorption spectrum confirmed the diamond was type IaAB and
H-rich, with nitrogen-related absorption from 1000 to 1500
cm–1, a graphite-related peak at 1582 cm–1, and H-related IR
peaks at 1405, 2785, 3050, 3107, 3154, 3236, 4169, and 4496
cm–1. We confirmed that the pinpoint-like inclusions weregraphitized hydrogen clouds (see P. Johnson et al., “Hydrogen rich treated black diamonds,” poster presentation at Geological Society of America 2016 annual meeting).
When observed in the high-energy short-wave UV radiation of the DiamondView (figure 13), the bulk of thisblack diamond displayed moderate yellowish green fluorescence. Four small areas were basically inert to UV radiation; these also corresponded to the dark cross.
The unique double cross pattern and the DiamondView
image revealed an interesting growth structure. The diamond apparently underwent two distinct phases of growth,with each phase forming a cross developing from separate
mixed-habit growth with contemporaneous cuboid and octahedral sectors. The well-developed cuboid growth sectors
contained regions with cloud-like light scattering thatcaused the black parts; very poorly developed octahedral
growth sectors with a small amount of inclusions formed
the light cross. The cuboid growth sectors exhibited yellowish green fluorescence, while the inclusion-poor octahedral sectors were inert to the short-wave UV light.
The interesting pattern of inclusions and distinctive
growth features of black diamonds such as this one needs
more attention.
Contributors’ note: This study was supported in part by
the National Natural Science Foundation of China (grants
41473030 and 41272086).
Yujie Li, Hui Xu, Taijin Lu, Zhikun Hu,
and Xinming Wang
NGTC, Shanghai
The Foxfire diamond, revisited. The largest gem-quality
rough diamond found in Canada, reported earlier in Gems
& Gemology (Summer 2016 GNI, pp. 188–189), has revealed remarkable responses to excitation with long- andmid-wave UV light. This 187.63 ct diamond (figure 14)
was extracted from the Diavik mine in the Canadian Arc-GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2017479

Figure 14. The 187.63 ct Foxfire rough diamond.
Photo by Jeffrey Post.

tic in the spring of 2015. Aptly named for the aurora borealis, the “Foxfire” displays unusual fluorescence and phosphorescence behavior upon exposure to ultraviolet light.
As previously reported, this type Ia diamond has a highconcentration of nitrogen impurities, a weak hydrogen-related absorption at 3107 cm–1, and typical “cape” absorption lines.
Exposing this stone to the near-band-gap ultraviolet lightof the DiamondView instrument (about 210 nm) and shortwave UV (253.7 nm) results in only very weak fluorescenceand phosphorescence, as reported earlier. However, exposure
to mid- and long-wave UV (313 nm and 365.0 nm, respectively) produces extremely strong blue fluorescence andstrong, long-lived orangish phosphorescence (figure 15).
Another surprising result of exposing the Foxfire diamond to UV light is a noticeable color change from very
pale yellow to a light brown color (figure 16). Fortunately,

the diamond reverts to its original color in a matter of minutes in ambient room lighting.
We further examined the spectral characteristics of theUV-excited phosphorescence emission with the spectrometer previously used to study phosphorescence from the Hopeand other colored diamonds (S. Eaton-Magaña et al., “Fluorescence spectra of colored diamonds using a rapid, mobile
spectrometer,” Winter 2007 G&G, pp. 332–351; S. EatonMagaña et al., “Using phosphorescence as a fingerprint for
the Hope and other blue diamonds,” Geology, Vol. 36, No.
1, 2008, pp. 83–86). In the present experiments, the UV lightsources employed were mineralogical short-, mid-, and longwave UV lamps. Figure 17 displays the spectral emission between 350 and 1000 nm (approximately 10 nm resolution)
as a function of time after turning off the UV light. The mostintense emission resulted from long- and mid-wave UV excitation, while phosphorescence excited by short-wave UV
was extremely weak.
The spectra of the “orange” phosphorescence reported
above are unusual and distinct from those of other naturaland lab-grown phosphorescent diamonds we have examined. We speculate that the primary mechanism for phosphorescence in diamonds is light emission resulting fromrecombination of electrons trapped at ionized donors andholes trapped at ionized acceptors that are in close proximity
to one another. The long time delay results from the thermal
movement of the trapped electrons or holes to retrap closeenough to one another (P.J. Dean et al., “Intrinsic and extrinsic recombination radiation from natural and synthetic aluminum-doped diamond,” Physical Review, Vol. 140, No.
1A, 1965, p. A352–A386; B. Dischler et al., “Diamond luminescence: Resolved donor-acceptor pair recombinationlines,” Diamond and Related Materials, Vol. 3, 1994, pp.
825–830). In the case of the Foxfire, we cannot identify as
yet the nature of either the acceptors or donors involved.
Similarly, the phenomenon of the observed color change
from light yellow to light brown with UV excitation and the

Figure 15. Left: The Foxfire diamond, photographed in daylight-equivalent lighting. Center: The fluorescence exhibited in a darkened room while the diamond was exposed to long-wave UV. Right: The phosphorescence shownin a darkened room immediately after extinguishing long-wave UV excitation. Photos by Jeffrey Post.

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Figure 16. The Foxfire
under ambient room
lighting, before (left)
and just after exposure
to long-wave UV light(right). Photos by Jeffrey Post.

reversal to light yellow has no detailed explanation yet. Suchcolor changes, or sometimes a lightening of color, are often
observed in natural diamonds. It is speculated that these are
due to charge transfer between various defects (donor or acceptor states) within diamond. Diamond is inherently an insulator where electric charges move very slowly and theirmotion depends on the nature of the defects present, thetemperature of the diamond, and its exposure to light. For
an interesting discussion, see K.S. Byrne et al., “Chameleon
diamonds: Thermal processes governing luminescence anda model for the color change,” Diamond and Related Materials, Vol. 81, 2018, pp. 45–53.
James E. Butler and Jeffrey E. Post
Smithsonian Institution,
National Museum of Natural History
Washington, DC
Wuyi Wang
GIA, New YorkTREATMENTS
Coated beryl imitating emerald. Two major issues related
to emerald are origin determination and the presence andquantity of fillers. An emerald’s value depends in part on
the quality of the stone and treatments applied, so examination with a gemological microscope is an essential partof any analysis.
A pair of earrings (figure 18, top) weighing a total of 84.06
grams was submitted to the Lai Tai-An Gem Lab for identification. The earrings consisted of numerous green drilled
briolettes with a vitreous luster. The client, who claimed
they were natural emeralds, granted permission to remove
one piece to aid in identification. Testing gave a spot RI of
1.57, an SG of 2.67, and an inert reaction to both short-wave
and long-wave UV, consistent with beryl. Microscopic observation revealed liquid, crystal, and two-phase inclusions(figure 18, bottom). Infrared and Raman spectroscopy indicated that the loose stone, along with the similar stones stillin the earrings, were beryl. Epoxy peaks at 3056, 3037, 2964,
2931, and 2872 cm–1 were obtained by FTIR spectroscopy(figure 19). However, the green color was unusual in that it
appeared to be concentrated on the surface, which was confirmed by additional testing.
Magnification with diffused illumination clearly
showed concentrated patches of green color with “colorless” boundaries (figure 20, left), as often seen in diffusion-

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GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2017

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Figure 19. FTIR spectroscopy showed epoxy peaks at
3056, 3037, 2964, 2931, and 2872 cm–1.

Figure 18. Top: The drilled green briolettes mounted in
the pair of earrings submitted for identification. Bottom:
Fluid inclusions, crystals, and two-phase inclusions
proved the stones’ natural origin; field of view 2.6 mm.
Photos by Lai Tai-An Gem Lab.

treated stones such as corundum. Further observation byscanning electron microscopy (SEM) indicated a coating on
the faceted surface (figure 20, right). DiamondView imaging revealed the fluorescence reaction of the underlying

Figure 20. Left: Magnification with diffused illumination clearly showed the concentrated green areas of
the coating and the boundaries of the underlying hostberyl. Photomicrograph by Lai Tai-An Gem Lab; fieldof view 4.4 mm. Right: An SEM image from the specimen. The area labeled A shows the coated layer on
the surface, while B shows facet boundaries without
coating.

A

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GEM NEWS INTERNATIONAL

host beryl where the coating had been worn away at the
facet junctions: When exposed to the ultra-short-wave UVof the DiamondView, the “colorless” areas reacted with astrong orange fluorescence (figure 21). UV-Vis-NIR spectra
revealed differences between the test stone and a reference
emerald. While emerald normally exhibits Cr3+-associatedmain absorption bands at approximately 620 and 430 nm,
the examined samples showed strong absorption bands atapproximately 680 and 360 nm, as well as weaker bands at
620 and 430 nm (figure 22)
Coatings have been applied to various gemstones for
decades, and most of the time they are easy to identify. Although this identification was not particularly challenging,it does show the importance of thoroughly examining jewelry in case treated stones have been incorporated into thedesign.
Larry Tai-An Lai (service@laitaian.com.tw)
Lai Tai-An Gem Laboratory, Taipei
Filled pearl with surface features. Pearl cultivation has
been carried out for more than a century, with newer tech-

Figure 21. DiamondView imaging showed where
the coating had been worn away at the facet junctions. The colorless areas reacted with a strong
orange fluorescence after exposure to the short-wave
UV radiation.

B

GEMS & GEMOLOGYWINTER 2017

UV-VIS -NIR SPECTRA
ABSORPTION COEFFICIENT (cm–1)

0.75

Coated emerald
Reference emerald

430

620 680

0.55

360

0.35

0.15
220

320

420

520

620

720

820

Figure 24. Two fillings displayed a coarse appearance
and lower luster that differed from the rest of the pearl.
Photomicrographs by Lai Tai-An Gem Lab; fields ofview 11.5 mm (left) and 8.6 mm (right).

WAVELENGTH (nm)Figure 22. UV-Vis-NIR spectra show the differences
between a reference emerald, which exhibits significant Cr3+-associated main absorption bands at approximately 620 and 430 nm only (red trace), and theexamined sample, which contains absorption bands
at approximately 680 and 360 nm in addition to the620 and 430 nm bands (green trace).

niques supplying the trade with larger and more consistently round freshwater and saltwater pearls. While natural
pearls are seldom perfectly round, their rarity makes them
desirable nevertheless. The Lai Tai-An Gem Lab recently
had the chance to examine a specimen that was purchasedby the client as a “natural white pearl” (figure 23) while
traveling in the Philippines.

The white baroque pearl measured 20.0 × 19.0 × 13.3mm and weighed 20.60 ct, with an SG of 2.60. It exhibited
pink overtone. Long-wave UV produced a strong chalky
blue reaction. Magnification revealed the typical overlapping platelet structure expected for nacreous pearls, but
two abnormal surface features were also observed. These
two areas displayed a coarse appearance and lower lusterthat differed from the rest of the pearl (figure 24).
We further analyzed the abnormal surface features togather more data for future reference. DiamondView imaging showed a noticeable difference between the nacreous
areas and the filled portions (figure 25). Raman analysis of
the surface features revealed epoxy peaks at 635, 1108, and1604 cm–1 and aragonite peaks at 1084 and 701 cm–1 (figure

Figure 23. This 20.60 ct specimen was purchased by
the client as a “natural white pearl.” Photo by Lai
Tai-An Gem Lab.

Figure 25. The two filled portions of the pearl, shownin visible light (left images) and the DiamondView(right images). The DiamondView reaction showed a
noticeable difference between the nacreous areas andthe filled portions of the pearl.

GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2017483

R AMAN SPECTRUM
2000
1800

1084

INTENSITY (COUNTS)

1600

1604

1400

Figure 26. Raman analysis of the pearl revealed
epoxy peaks at 635,
1108, and 1604 cm–1 andaragonite peaks at 701
and 1084 cm–1.

1200
1000
800

1108
635

600
400

701

200
0
250

450

650

850

1050

1250

1450

1650

1850

2050

2250

–1

RAMAN SHIFT (cm )26). These were consistent with results from FTIR reflectance spectrometry that showed calcium carbonate in
the form of aragonite, with peaks at approximately 878 and1484 cm–1.
X-radiography (figure 27) proved this was a bead-cultured pearl with a pre-drilled nucleus typically used in
freshwater pearl cultivation. The filling was very shallow
due to the presence of mother-of-pearl (not visible). Energydispersive X-ray fluorescence (EDXRF) analysis detected

Figure 27. X-radiography proved this was a bead-cultured pearl. The filling was very shallow due to thepresence of mother-of-pearl (not visible). Image by Lai
Tai-An Gem Lab.

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GEM NEWS INTERNATIONAL

higher levels of manganese, confirming the pearl’s freshwater origin. The result came as a surprise to the client,
who was expecting confirmation of a natural pearl. Suchcoatings and fillings, which we have seen before, show theimportance of obtaining a reliable laboratory report whenpurchasing such a large pearl.
Larry Tai-An Lai (service@laitaian.com.tw)
Lai Tai-An Gem Laboratory, Taipei
Update on dyed hydrophane opal. Dyed purple opals first
appeared in the gem trade in 2011 (N. Renfro and S.F. McClure, “Dyed purple hydrophane opal,” Winter 2011 G&G,
pp. 260–270). Recently, the authors became aware of similar material with vibrant blue and pink bodycolors (figure28). From 2015 to 2017, a jewelry designer reportedly purchased over 500 carats of vivid pink and blue opals from adealer she met at a small regional gem show in California.
The dealer did not disclose that the material was dyed andclaimed that these intense colors were from a new opal discovery in Mexico. This kind of misrepresentation could
damage consumer confidence in all opals.
In July 2017, author EB received the two opals in figure
28 for examination. After determining that they werelikely color treated, he sent both samples to GIA’s Carlsbad
lab for further testing. With permission from the owner,
each opal was cut in half to obtain a control sample and atest sample. The test samples (one blue and one pink) were
soaked in acetone and hydrogen peroxide solutions to determine if their colors were stable. These two opals were
carefully examined and, like the dyed purple material from2011, were consistent with hydrophane opal from Ethiopiathat had been dyed. Both stones displayed a “digit pattern”
play of color (B. Rondeau et al., “On the origin of digit pat-

GEMS & GEMOLOGYWINTER 2017

Figure 28. These two opals (21.75 and 15.12 ct) wererepresented as natural-color blue and pink opal from
Mexico. Photo by Robison McMurtry.

terns in gem opal,” Fall 2013 G&G, pp. 138–146). They
also showed small spots of saturated color at the surface,consistent with dye (figure 29).
Both stones were soaked in acetone to collect some ofthe dye material for color spectroscopic analysis. The acetone with residual dye was measured and artificially concentrated by a factor of 20 by multiplying the very low
absorption values measured. The measurements produced
a spectrum consistent with an organic dye, characterized
by broad band absorption features in both the pink and blue
samples (figure 30). The absorption measurements werethen converted to transmission spectra using GRAMS/AI
spectroscopy software by Thermo Fisher Scientific. Colorspace coordinates were calculated from the transmission
spectra and plotted as a color swatch. The hues produced
were consistent with the bodycolor of each opal, confirming that the spectra represent the organic dye component(figure 30, inset).
The two samples were further tested to see if they
could be restored to their original non-dyed state. As reported by Renfro and McClure (2011), soaking dyed purple
opal in a solution of hydrogen peroxide removed the purple
color. These new pink and blue samples were sliced in halfand one piece of each sample was soaked in 3% hydrogen
peroxide for up to two weeks. Their color saturation was
significantly reduced, with the blue half turning white andthe saturated pink half becoming very light pink (figure 31).
It is possible that more time in the solution would havefurther reduced the pink color. Note that even though thesamples lost their color, the dye molecules were not removed. But the hydrogen peroxide had oxidatively decomposed the dye into different molecules that did not absorb
visible light and therefore could no longer impart color on
the opals. Soaking dyed stones in hydrogen peroxide may
be an effective way to remove the observed color in dyed
opals, returning them to their natural appearance. In our
experience, however, there is a risk of cracking when anyhydrophane opal is immersed in a liquid.
Acetone allowed the removal of enough dye for spectroscopic analysis, proving that the coloring agent is an organic dye. While soaking the opals in acetone did not seemto greatly affect their color, soaking them in a hydrogen
peroxide solution for several weeks removed the artificial
color almost entirely. Upon further examination, we determined that they were originally hydrophane opals with awhite bodycolor, likely from Ethiopia, that were color
treated using an organic dye. These findings reaffirm the

Figure 29. Both the blue and pink opal showed dye color concentrations around pits and scratches on the surface,consistent with hydrophane opal that has been artificially dyed. Photomicrographs by Nathan Renfro; fields ofview 2.34 mm (left) and 1.99 mm (right).

GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2017485

ABSORPTION SPECTRA
0.05

ABSORBANCE (ARB. UNITS)

Blue dye
Pink dye
0.04

0.03

0.02

0.01

0
400

450

500

550

600

650

700

Figure 30. The absorption spectra of the dyes
were collected by firstsoaking the opals in
acetone to remove
some of the dye material. Color swatches
were then calculated
from measurements ofthe dye molecules suspended in acetone to
produce the color
swatches for reference(inset).These swatches
were consistent withthe observed bodycolorof each opal.

WAVELENGTH (nm)

importance of treatment disclosure in the trade. A few unscrupulous industry members could compromise the reputation of dealers selling natural opal as well as those
properly disclosing treated material to their customers.
Edward Boehm
RareSource, Chattanooga, Tennessee
Nathan Renfro
GIA, Carlsbad

Figure 31. The blue and pink opals were confirmed tobe dyed hydrophane opal, likely from Ethiopia. Halfof each stone has been bleached using 3% hydrogen
peroxide solution. Photo by Robison McMurtry.

486

GEM NEWS INTERNATIONALCONFERENCE REPORTS
GSA 2017 annual meeting. The Geological Society ofAmerica (GSA) held its annual meeting October 22–25 in
Seattle. For the fifth year, GIA hosted technical sessions
on gemological research in the 21st century. More than 30
researchers, students, and gem experts from multiple institutions shared their most recent research results (figure
32).
Invited speaker Evan Smith (GIA, New York) presented
the diamond inclusion suite study he carried out over the
past two years. Following his paper published in Science ontype IIa Cullinan-like, large, inclusion-poor, pure, irregular,
resorbed (CLIPPIR) diamonds, Dr. Smith investigated insitu mineral phases in more than 20 extremely rare type IIb
diamonds selected from GIA’s day-to-day grading operations. The identified inclusions indicated that type IIb diamonds can originate from the lower mantle, at depths
beyond 660 km. This surprising result refuted the well-accepted view that almost all superdeep diamonds are small
and not of gem quality. Nancy McMillan (New Mexico
State University) talked about the diamond provenancestudy she performed with Catherine McManus (Materialytics, Killeen, Texas). To ease consumer concerns about conflict diamonds, they conducted multivariate analysis oflaser-induced breakdown spectroscopy (LIBS) on diamonds
from various origins as well as synthetic diamonds. The information provided by LIBS on trace element composition
and the electronic structure of atoms in diamonds aided inprovenance determination. Through infrared (IR) mapping,
Sally Eaton-Magaña (GIA, Carlsbad) and her colleague Troy
Ardon documented the spatial changes of the optical defectcenter B0 (uncompensated boron) in two type IIb diamondsamples: One specimen was irradiated along an edge and

GEMS & GEMOLOGYWINTER 2017

Figure 32. Presenters,
session advocates, andsenior executives from
GIA at GSA’s annual
meeting in Seattle.
Photo by Tao Hsu.

then annealed, while the other was only annealed. The irradiated diamond showed an obvious gradient in B0 acrossthe specimen itself and larger gradient changes during annealing compared to the other sample. These were causedby changes in compensating defects, which were then plotted by photoluminescence (PL) mapping.
The following three presenters from the University ofAlberta shared their intriguing diamond formation research.
Mandy Krebs offered trace element data of fluids trapped in
gem-quality diamonds and compared them to those in fibrous diamonds that have been extensively studied. The results showed clear similarities in trace element patterns inboth categories, which indicates that fibrous diamonds andgem diamonds may share a common origin. Rebecca Stone
reported on diamond growth in saline fluid. She and her colleagues carefully documented diamond growth features
under different salinities using a mixed KCl-NaCl brine system within the diamond stability field. Their series of experiments showed that Na-rich brine is a better medium
for diamond growth than K-rich or Na+K mixed brines.
Robert Luth discussed the partial melting mechanism facilitating diamond formation. He noted that the amount of
diamond formed during this process depends on the lithology being melted and the composition of the fluid. The origin of the C-bearing fluid was also explored.
Following the diamond research presentations, invited
speaker Darrell Henry (Louisiana State University) started
the colored stone session with a talk on gem tourmaline.
He pointed out that tourmaline is a very sensitive mineralthat can incorporate and retain chemical and textural fingerprints from its environment. Paraíba, Paraíba-like, liddicoatite, and “chrome” tourmaline were used to illustrate

this mineral’s incredible scientific value. Aaron Palke (GIA,
Carlsbad) discussed his recent findings on demantoid garnet’s coloration mechanism. The existing theory attributes
the brown coloration of this gem to intervalence chargetransfer between Fe2+ and Ti4+ or Fe3+. Dr. Palke challenged
this interpretation based on recent spectroscopic results
showing insufficient Fe2+ in demantoid to justify this mechanism. Philippe Belley (University of British Columbia) addressed the challenges of modeling spinel deposits. His
potential solutions are based on detailed petrographic andgeochemical studies on 14 samples from exceptionally wellexposed in situ spinel occurrences on Baffin Island in
Nunavut, Canada. Donald Lake (University of British Columbia) compared two beryl occurrences in northern
Canada with Colombian emerald deposits. He pointed outthat in terms of formation environment, these potential
emerald deposits are the first “Colombian-type” sources
outside Colombia. Rachelle Turnier (University of Wisconsin–Madison) presented her study on oxygen isotope fractionation factors in corundum. Oxygen isotope ratios areimportant to understanding corundum genesis and origin
determination. This study empirically calibrated the calcitecorundum oxygen isotope fractionation factor from themetamorphosed karst-bauxite deposits at Naxos, Greece.
GIA’s Jennifer Stone-Sundberg closed this portion of the session with a presentation on matrix-matched corundum
standards development. She explained the importance of
these newly developed standards in accurately determining
trace element concentration and elaborated on the advantages of these standards over other commonly used products.
This year’s poster session attracted 18 presenters, triple
the number from last year (figure 33). Daniel Howell (Uni-

GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2017487

versity of Padua) presented new applications of DiaMap
software in automated and semi-automated mapping of
single substitutional defects (N and B) and micro-inclusionbearing diamonds. Paul Johnson (GIA, New York) reported
the first observation of nickel as the cause of the green
color of an HPHT synthetic diamond. Nickel is commonlyused in the metal flux that produces HPHT synthetic diamond, but it rarely contributes to diamond coloration.
Tyler Sundell (Missouri State University) evaluated the viability of in situ δ13C measurement in diamonds using
time-of-flight secondary ion mass spectrometry (ToFSIMS). Tingting Gu (GIA, New York) shared her study on
micro- and nano-inclusions containing both N and Fe in
type IaB diamonds. Kyaw Soe Moe (GIA, New York) presented the identification features of irradiated and annealed
pink diamonds using IR spectroscopy and DiamondView
imaging. Elizabeth Levy (Louisiana State University) explained how to directly measure Fe2+ and Fe3+ concentration in tourmaline crystals using synchrotron-based X-ray
absorption near-edge spectroscopy (XANES). Cole Mount(New Mexico State University) found that using multivariate analysis of LIBS spectra of tourmaline can remove thenegative influence of chemical zoning on host lithology determination. Ulrika D’Haenens-Johansson (GIA, NewYork) gave her insights on the 812 ct Constellation and twoother large rough diamonds. FTIR and morphology observations indicate that the three could possibly be pieces
from the same rough. Christopher M. Breeding (GIA, Carlsbad) described the first ever co-occurrence of magnesite,
olivine, graphite, and silicon-vacancy defects in natural diamonds and explored the unusual conditions under whichthese diamonds formed. Karen Smit (GIA, New York) discussed the formation of peridotitic diamonds through iso-chemical cooling and eclogitic diamonds through redox
buffering. George Harlow (American Museum of Natural
History, New York) and Rachelle Turnier discovered thatsyenite-hosted sapphires from six different sources show awide range of δ18O values, which indicates scavenging ofsapphire from multiple reservoirs. Troy Ardon (GIA, Carlsbad) used IR mapping, cathodoluminescence (CL) imaging,and hyperspectral mapping to correlate various optical andinfrared point defects in diamonds with strong brown coloration. Susanne Schmidt (University of Geneva) outlined
U-Pb geochronology work done on zircon inclusions in Sri
Lankan sapphires. This study was performed by her former
graduate student Emilie Elmaleh. Ziyin Sun (GIA, Carlsbad) investigated the role of chromophore vanadium in coloration of pyrope-spessartine garnet, using samples
without a color-change phenomenon. Eric Brinza (University of Wisconsin–Eau Claire) described an IR spectroscopic
study on hydrothermal quartz crystal. Different hydroxyl
species concentrations vary both vertically and horizontally through the crystal. Kyle Tollefson, also of the University of Wisconsin–Eau Claire, presented IR and visible
spectroscopic study on coloration of watermelon tourmaline. The results showed that the chromophore was incorporated during crystal growth and could reflect changes in
the growth environment. Dona Dirlam and her coauthors
from GIA’s Richard T. Liddicoat Gemological Library andInformation Center (Carlsbad, California) chronicled thelegendary John Sinkankas, whose collection of books andother publications was acquired by GIA in 1988 to form
the basis of its world-renowned gemological library.
Tao Hsu, James E. Shigley, and Dona Dirlam
GIA, Carlsbad

Figure 33. The GSA annual meeting’s gemological research poster
session featured 18 presenters from all over theworld. Photo by Cathy
Jonathan.

488

GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2017

Figure 34. A gatheringof the presenters at the
fifth World of Gems
Conference, held in
Chicago in September
2017. Photo by Scott
Drucker.

World of Gems Conference. The Gemworld Internationalteam, headed by Richard Drucker, hosted the fifth Worldof Gems Conference September 23–24 at the Loews Hotelin Chicago. The event was bookended by optional classes,
making it an ideal opportunity for attendees to learn about
new topics from a diverse group of international speakers(figure 34) and brush up on their practical gemology skills.
Between presentations, the conference held its first-everposter session. The posters included interactive discussions on jet and the identification of light blue stones using
the polariscope and the conoscope, hosted by Sarah Caldwell Steele (Ebor Jetworks, Whitby, United Kingdom) and
Kerry Gregory (Gemmology Rocks, Weavering, United
Kingdom), respectively.
Invited speaker Emmanuel Fritsch (University of
Nantes, France) opened with a talk about the identificationof melee synthetic diamonds. He noted that while the majority of specimens are not hard to identify, near-colorless
HPHT-treated synthetic melee may still be challenging.
Dr. Fritsch also provided a brief history of synthetic diamond production and the current state of the industry, as
well as basic and advanced methods of separating synthetic
from natural. Isotropy and anomalous double refraction—otherwise known as strain—were covered in some detail,as he considered these very useful identification aids. Jon
Phillips (Corona Jewellery Co., Toronto) reviewed world
diamond production and the output of mines such as Jwaneng in Botswana, which accounts for 15% of total global
production. Meanwhile, Canada’s five operating mines
rank among the top 19 producers. One key takeaway fromhis talk was that De Beers plans to invest US$140 million
on a marketing campaign aimed at women buying diamond jewelry for themselves. This should not be ignoredby jewelers. Mr. Phillips also reflected on the threat of syn-thetic melee in the market. This author (GIA, Bangkok) reviewed the different types of pearls (nacreous and nonnacreous) seen in the market and the various mollusks that
produce them. The presentation detailed the surface structures of a wide selection of non-nacreous pearls and concluded with a summary of the more frequently
encountered treatments. Roland Schluessel (Pillar & Stone
International, San Francisco) provided a comprehensive
look at Burmese jadeite and defined the various types, including the term fei cui (kingfisher) for the vivid green variety. He examined cultural aspects and discussed factors
such as grain size and orientation, which relate to transparency and overall quality. Mr. Schluessel also provided
insight into the different colors and patterns, as well as thedifferences between omphacite and jadeite. Ҫiğdem Lüle
and Stuart Robertson (Gemworld International, Glenview,
Illinois) reported on various gem treatments that provide
enough supply to satisfy market demand. Frequently encountered treatments and the pricing of untreated vs.
treated material were reviewed. Diamond was offered as
an example of a gem where treatments markedly affect theend value, while tanzanite shows little if any price difference between natural and treated material. A very lively
presentation from Kerry Gregory about the daily happenings in the pawnbroking world rounded out day one. Ms.
Gregory discussed some of her experiences saving valuablepieces that would have otherwise been destroyed due tolack of resources, training, and time. She also provided insight into her use of simple yet valuable gemological methods (such as the polariscope and conoscope) in identifying
light blue stones removed from items destined for the melt.
J.C. (Hanco) Zwaan (Netherlands Gemmological Laboratory, Leiden) started the second day with a comprehensive look at the geological formation and gemological

GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2017489

characteristics of metamorphic sapphires from Sri Lanka
and to a lesser extent Montana. The search for a primary
sapphire deposit in Sri Lanka and the discovery at Wellawaya (which Dr. Zwaan was involved with) were illustrated. Subsequent discussions on the use of chemicalplotting in the separation of Sri Lankan and Montana material, from one another and from other sources, showed that
it is beneficial but care is still needed with some cases that
may overlap. Ҫiğdem Lüle followed with a solo talk about
the various natural and “non-natural” black gem materials
and the limitations encountered when testing such materials. She covered black diamonds in some detail, outlining
the differences between the rare naturally colored stones andheated or irradiated specimens. Al Gilbertson (GIA, Carlsbad) reported on the status of GIA’s fancy-cut diamond grading project and showed the challenges faced when producing
a system that takes all variables into consideration and satisfies all opinions. This was reinforced after receiving feedback from 440 participants in six global locations who wereasked to look at various fancy cuts and answer a series ofquestions. Alan Bronstein (Aurora Gems, New York) took
attendees on a journey through the colorful world of fancycolor diamonds, looking at the subtleties of the main colors
available: yellow, orange, pink, red, green, and blue. Mr.
Bronstein was clearly in favor of retaining the original cutof a diamond and not re-cutting it. Chameleon diamonds
were also briefly covered. “Beauty trumps rarity” was Mr.
Bronstein’s motto. Richard Drucker brought the presentations to a close with a look at some challenges that affectthe pricing of gemstones. From the small print in pricing
guides that might not be fully understood by users to gemological reports that raise doubts or cause confusion in appraisers’ minds, it became very apparent that the valuationof some colored stones needed careful thought.
The conference ended with a Q&A session in which
Mr. Drucker opened the floor to all attendees. Topics suchas correct nomenclature and disclosure, brand name coop-eration with items submitted for valuation, and color diamond grading consistency were covered.
Nicholas Sturman
GIA, Bangkok

IN MEMORIAM
Peter J. Dunn (1942–2017). Distinguished mineralogist andauthor Pete Dunn died November 8 at the age of 74. He isbest known for the 134 new mineral descriptions he wrote
over the course of his long career.
Dr. Dunn received his master’s degree and PhD in mineralogy/geology from the University of Delaware in
Newark. Before joining the Smithsonian Institution’s National Museum of Natural History in 1972, he served in the
U.S. Air Force and worked at Boston University as a curator
in the geology department. In addition to characterizing
new minerals, Dr. Dunn published a nine-volume monograph and more than 70 papers on the Franklin–Sterling Hillmining district in New Jersey in a number of scientific publications. In 1987, a member of the clinopyroxene subgroupfrom the Franklin mining district was named “petedunnite” in his honor. A prolific contributor to G&G throughout the 1970s, Dr. Dunn served on the journal’s editorial
review board from its inception in 1981 until 1987. Uponhis retirement from the National Museum of Natural History in 2008, he volunteered at the museum’s information
desk until his death.

ERRATA
1. In the Fall 2017 Lab Note on screening of mounted
melee using the GIA iD100 (pp. 366–367), a citation
directed readers to p. 239 of the Fall 2017 Lab Notes
section. The correct issue is Summer 2017, p. 239.
2. Also in the Fall 2017 Lab Notes section, the inset
photo in figure 4 was taken by Kyaw Soe Moe.

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

gia.edu/gems-gemology

490

GEM NEWS INTERNATIONALGEMS & GEMOLOGYWINTER 2017

MULTIMEDIA HIGHLIGHTS FROM 2017
Visit G&G online (www.gia.edu/gems-gemology) to explore free multimedia
content. Scan the QR codes below with your smartphone or tablet, or use thelinks below.
2017 Dr. Edward J. Gübelin Most Valuable Article Award: Cast
your vote for the three most important articles from 2017, andenter a drawing to win a one-year print subscription to Gems &Gemology. www.gia.edu/most-valuable-article-2017

The Dreher Family’s Extraordinary Carvings: Interviews andphoto galleries capture the lifelike detail and painstaking process
followed by Gerd and Patrick Dreher, the two most recent
standard-bearers of a German carving dynasty. www.gia.edu/
gems-gemology/winter-2017-gem-virtuosos

Colombia’s Emerald Industry: Videos reveal Colombia’s emerald
mining areas and the cutting and trading industry in Bogotá.
www.gia.edu/gems-gemology/fall-2017-colombian-emeraldindustry

The Lomonosov Diamond Deposit: The geology, production, andevaluation process at Russia’s Lomonosov deposit are examinedin videos taken at the source. www.gia.edu/gems-gemology/
summer-2017-lomonosov-deposit

Brazilian Diamonds: Slideshows and videos document this historical diamond source, where large-scale production is expected toresume. www.gia.edu/gems-gemology/spring-2017-braziliandiamonds

2017 Tucson Gem Shows: Watch exclusive videos from ourannual coverage of the gem shows, featuring interviews andinsider insight. www.gia.edu/gems-gemology/spring-2017gemnews-tucson-overview

M ICRO -F EATURES OF R UBYTreatedSynthetic

NaturalA hexagonal cloud results from heat treating this Burmese ruby fromMong Hsu. Field of view 2.97 mm.

A rare inclusion of iolite (cordierite) is seen in this ruby from Greenland.
Field of view 1.42 mm.

Rounded protogenetic crystals of orange spinel are extremely rare in
Burmese ruby. Field of view 3.45 mm.

Rainbow-colored thin-film interference colors are seen along a partiallyhealed fracture in this ruby from Thailand. Field of view 1.10 mm.

Delicately patterned, crystallographically oriented thin-film inclusions
are found in a ruby from Vietnam. Field of view 2.02 mm.

Chevron-shaped graining is diagnostic of the hydrothermal growthmethod used to produce this Tairus synthetic ruby. Field of view 1.22 mm.

A blue and orange “flash effect” is prominent in this lead-glass-filled
ruby. Field of view 2.90 mm.

A very rare crystal inclusion of vibrant yellowish green vesuvianite isseen in this Burmese ruby. Field of view 1.99 mm.

Dark, transparent amphibole crystals are commonly found in Mozambique rubies, such as the one shown here. Field of view 2.62 mm.

Metal sulfide crystals are sometimes observed in rubies from Mozambique. Field of view 1.42 mm.

The intersection of twinning planes can provide a conduit for epigenetic
solutions containing iron compounds to enter the interior of some rubies,
as seen in this example from Mozambique. Field of view 4.35 mm.

Crystallographically aligned yellowish flux residue reveals the synthetic
origin of this Ramaura flux-grown ruby. Field of view 4.74 mm.

Internal diffusion of titanium around a rutile crystal in a berylliumdiffused ruby. Field of view 1.03 mm.

A rare orangy brown crystal of sphalerite floats in its host, a ruby from
Myanmar. Field of view 1.03 mm.

Iridescent exsolution rutile is oriented in three directions in this Burmese
ruby. This “silk” is responsible for creating asterism in gem-quality ruby.
Field of view 1.99 mm.

A field of reflective thin films is indicative of this ruby’s Thai origin. Fieldof view 4.10 mm.

Thin platy inclusions of chromite can be found in ruby from Mozambique. Field of view 1.44 mm.

Curved striae are diagnostic of this flame-fusion synthetic ruby. The
striae are accompanied by several gas bubbles that further reinforce thesynthetic origin. Field of view 3.59 mm.

Heat treating ruby in the presence of flux can help to heal cracks. It canalso leave flux residue trapped inside, as seen in this Burmese ruby.
Field of view 3.10 mm.

This black, blocky crystal with tension cracks, found in a Burmese ruby,was identified as uraninite. Field of view 1.03 mm.

Protogenetic carbonate inclusions are commonly seen in rubies that form
in marble, as this example from Afghanistan shows. Field of view 1.26mm.

The aluminum hydroxide mineral boehmite, seen in this ruby fromGreenland, is often found in corundum. Field of view 1.42 mm.

Inclusions of amphibole crystals and mica in a ruby from Mozambiqueshow birefringent colors when examined in polarized light. Field ofview 1.76 mm.

Platinum crystals are a common feature in Chatham flux-grown synthetic ruby. Field of view 1.70 mm.

Heating of a Thai ruby caused this inclusion to rupture, providing evidence of treatment. Field of view 2.15 mm.

Cross-polarized light reveals an otherwise hidden ruby crystal in a Thai
ruby host. Field of view 3.90 mm.

Carbon dioxide fluid trapped in angular negative crystals in this rubyfrom Tajikistan proves that the stone has not been heat treated. Field ofview 0.288 mm.

This partially healed, iridescent fingerprint in a Thai ruby shows an unusual and irregular curved pattern. Field of view 1.10 mm.

Very rare inclusions of blue lazurite are a welcome surprise in this Burmese
ruby. Field of view 3.46 mm.

Reflective stringers of exsolution flux particles in Kashan flux-grown synthetic ruby are best seen using a fiber-optic illuminator. These oriented
particles are diagnostic of Kashan synthetics. Field of view 1.78 mm.

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

Published in conjunction with Nathan D. Renfro, John I. Koivula, Jonathan Muyal, Shane F. McClure, Kevin Schumacher, and James E. Shigley (2017),“Inclusions in Natural, Synthetic, and Treated Ruby,” Gems & Gemology, Vol. 53, No. 4, pp. 457–458. Photomicrographs by Nathan D. Renfro,
John I. Koivula, and Jonathan Muyal.

© 2017 Gemological Institute of America