Lab Notes
Editors
Thomas M. Moses | Shane F. McClure | Sally Eaton-Magaña

DIAMOND
Etch Features Reveal theMorphology of Diamond
Natural monocrystalline diamonds
formed in the earth’s mantle have
two major growth forms: octahedronand cube. It has been suggested that
diamond growth habit depends on
multiple factors, including crystallization temperature, growth rate,
and the degree of carbon supersaturation in the diamond-forming
fluids (J.W. Harris et al., “Morphology of monocrystalline diamond andits inclusions,” Reviews in Mineralogy and Geochemistry, Vol. 88, No.
1, 2022, pp. 119–166). If a diamond
forms under changing conditions, it
might not have a regular octahedral
or cubic morphology but a combination of both. In some cases, diamonds
grow without any well-defined crystal faces and are referred to as “irregular diamonds” (see examples in R.
Tappert and M.C. Tappert, Diamonds in Nature: A Guide to RoughDiamonds, Springer-Verlag, Berlin,
2011, p. 28). While octahedral or
cubic faces cannot always be identified visually in irregular diamonds,
the morphology can be inferred byetch features left on the diamond by
fluids in the mantle or during kimberlite eruption. Trigons and tetragons are the most common of these

Editors’ note: All items were written by staff
members of GIA laboratories.
GEMS & GEMOLOGY, Vol. 59, No. 3, pp. 356–369.
© 2023 Gemological Institute of America

356

LAB NOTESTrigons

Tetragons

Figure 1. Table (left) and pavilion (right) views of a chameleon diamondwith visible trigons and tetragons. The trigons and tetragons are shown inmore detail in figures 2 and 3. The diamond measures 1.28 cm in length.

etch features—restricted to octahedral
and cubic crystal faces, respectively.
The Carlsbad laboratory recently
examined a 2.00 ct Fancy browngreenish yellow diamond with both
trigons and tetragons on its surface(figure 1). The trigons were locatedwithin a small indented natural near
the table facet, while the tetragons
were preserved within an indented
natural at the culet (figures 2 and 3).
Co-occurring trigons and tetragons
are very uncommon and indicate anirregular morphology, characterized
by both octahedral and cubic growth.
This stone was identified as achameleon diamond. For such a classification, the diamond must include agreen color component, show phosphorescence to short-wave UV, andchange from a greenish color to a yellow or orange color with gentle heatingor when kept in the dark for an extended period (C.M. Breeding et al.,“Natural-color green diamonds: A
beautiful conundrum,” Spring 2018
G&G, pp. 2–27). These diamonds typically have a broad visible absorption
band centered at approximately 480
nm and are referred to as “480 nm
band diamonds.” A study on roughyellow diamonds from Canada showedthat all of those colored by the 480 nm
absorption band have irregular morphology (M.Y. Lai et al., “Yellow diamonds with colourless cores –evidence for episodic diamond growth
beneath Chidliak and the Ekati mine,
Canada,” Mineralogy and Petrology,
Vol. 114, 2020, pp. 91–103), suggesting

GEMS & GEMOLOGYFALL 2023

Pointed-bottom trigon
with circular etch pit

Flat-bottom trigon

Figure 2. Flat-bottom and pointed-bottom trigons (surface features restricted to an octahedral crystal face) preserved on an unpolished portionof the diamond. A circular etch pit overprinting a pointed-bottom trigon
indicates a late-stage diamond dissolution event that postdated the formation of the trigon. Field of view 1.26 mm.

that diamonds with the 480 nm absorption band may form under changing conditions in the mantle.
Trigons on diamond have two
major morphologies: either a flat bottom or a pointed bottom (pyramidal).
The type of trigon is primarily dependent on the temperature and pressure atthe position where diamond dissolu-

tion occurs, as well as on the carbon dioxide and water contents in the fluidthat etches diamonds. Experimental
work indicates that fluids with higher
carbon dioxide content tend to produce
pointed-bottom rather than flat-bottom trigons (Y. Fedortchouk, “A new
approach to understanding diamondsurface features based on a review of

Figure 3. Tetragons (surface features restricted to the cubic crystal face)preserved at the culet of the diamond. Field of view 1.26 mm.

LAB NOTESGEMS & GEMOLOGY

experimental and natural diamondstudies,” Earth-Science Reviews, Vol.
193, 2019, pp. 45–65). Both forms of trigons were observed on the chameleon
diamond we examined, as well as a circular etch pit overprinting a pointedbottom trigon (figure 2). Unlike
pointed-bottom trigons, circular pits
are typically created by fluids with low
carbon dioxide contents, indicating alate-stage etching event after the formation of the trigon.
The combination of surface features provides clues for the morphology of diamonds in rough form, as
well as the interactions between diamonds and fluids throughout theirjourney from mantle residence to theearth’s surface.
Mei Yan Lai and Matthew Hardman

Natural Diamond with Unusual
Phosphorescence
Phosphorescence spectroscopy showsthat natural type IIb diamonds canhave two broad phosphorescencebands: one centered at 500 nm that appears greenish blue and one centered at
660 nm that appears red. Generally,
one of these phosphorescence bands isdominant. In the Hope diamond, forexample, the phosphorescence initiallyappears orangy red and transitions to
red as the subordinate greenish blue
phosphorescence fades away (S. EatonMagaña et al., “Using phosphorescence as a fingerprint for the Hope andother blue diamonds,” Geology, Vol.
36, No. 1, 2008, pp. 83–86). Occasionally, the faster-decaying greenish
blue phosphorescence band will transition to the slower-decaying red band
(Spring 2007 Lab Notes, pp. 47–48).
Recently, a 0.90 ct diamond with
D color and I1 clarity was submitted
to GIA’s laboratory in Ramat Gan, Israel, for a diamond dossier report. Infrared (IR) absorption spectroscopy
indicated that the natural diamond
was nominally type IIa. However,photoluminescence (PL) spectroscopy
revealed that the diamond containedboron-related features, including the648.2 nm peak attributed to a boron
interstitial (B. Green, “Optical and

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Figure 4. These deep-UV (<225 nm) phosphorescence images of the table (left) and pavilion (right) in a 0.90 ct
D-color natural diamond with very low boron showed localized areas of the 500 nm (greenish blue) and 660
nm (red) bands.
magnetic resonance studies of point
defects in single crystal diamond,”
PhD thesis, University of Warwick,2013), along with the observed phosphorescence. These features indicatedthat the diamond did contain boron,
but below the detection level of IR absorption spectroscopy. The distinctive
aspect was that both the red andgreenish blue phosphorescence werelocalized and visible within the sameimage (figure 4).
The phosphorescence is attributed
to donor-acceptor pair recombination.
For the 500 nm band, this recombination has been identified as interactions
between boron acceptors and isolated
nitrogen donors (J. Zhao, “Fluorescence, phosphorescence, thermoluminescence and charge transfer insynthetic diamond,” PhD thesis, University of Warwick, 2022), while the660 nm band is attributed to boron acceptors and unknown donors that arelikely related to plastic deformation(S. Eaton-Magaña and R. Lu, “Phosphorescence in type IIb diamonds,”
Diamond and Related Materials, Vol.
20, No. 7, 2011, pp. 983–989). PL maps
were collected on the table and pavilion with 455, 532, and 785 nm excitation; only an undefined PL feature at
813 nm showed an apparent increaseon the pavilion within the red-phosphorescing region (figure 4, right).
Type IIb diamonds grown by highpressure, high-temperature (HPHT)
methods almost always show the 500358

LAB NOTES

nm phosphorescence and occasionally a separate orange phosphorescence band centered at 580 nm. In a
few instances, HPHT-grown diamonds have shown the 500 and 580
nm bands simultaneously in different
portions of the diamond (Eaton-Magaña and Lu, 2011; Spring 2023 Gem
News International, pp. 155–156).
This is the first time the authors
have seen spatially distinct observations of red and greenish blue phosphorescence in a natural diamond, an
unusual find.
Sally Eaton-Magaña,
Evelina Goldort, and Dani BinyaminType IIa diamonds typically display a blue fluorescence pattern underdeep UV as a result of “band A” fluorescence or the N3 defect in the stone(U.F.S. D’Haenens-Johansson et al.,“Synthesis of diamonds and theiridentification,” Reviews in Mineralogy and Geochemistry, Vol. 88, No. 1,
2022, pp. 689–753). High amounts ofnitrogen vacancy (NV) centers cancause red fluorescence in diamonds;

Figure 5. This 3.58 ct natural typeIIa diamond with H color and SI2
clarity displayed a unique fluorescence pattern when exposed todeep-UV light.

Natural Type IIa Diamond with
Unusual Red Fluorescence
Distribution
The Carlsbad laboratory received anatural type IIa diamond with some
unusual characteristics. As part of thestandard data collection, the diamondtype was determined by Fouriertransform infrared (FTIR) spectroscopy and deep-UV fluorescence
images collected using the DiamondView instrument. The DiamondView
images revealed predominantly red
fluorescence on one side of the diamond and blue fluorescence on theother. This 3.58 ct pear modified brilliant diamond had H color and received an SI2 clarity grade due tocavities, chips, and a feather (figure 5).

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PL SPECTRAINTENSITY

Red-fluorescing region
Blue-fluorescing region

NV0

NV–
Raman line

560

580

600

620

640

WAVELENGTH (nm)Figure 6. 514 nm PL spectra collected on the pavilion of opposite sides of the stone. The spectrum plotted in red
corresponds with the red-fluorescing region, and the blue spectrum corresponds with the blue-fluorescing region,
with Raman lines at 552 nm scaled as equal. Spectra are offset vertically for clarity. PL analysis spots are circled in
the deep-UV fluorescence images.
however, this is rare in type IIa stones,
as they are defined by nitrogen concentrations low enough to be undetectable by FTIR (Summer 2016 Lab
Notes, pp. 189–190). The NV centers
can be detected in a negative charge
state (NV–, zero-phonon line at 637nm) or a neutral state (NV0, zerophonon line at 575 nm). Photoluminescence (PL) testing revealed muchhigher concentrations of both NV
centers in the red-fluorescing region of
the stone (figure 6). This distribution
could have occurred if traces of isolated nitrogen were concentrated in
one growth area of the stone.
PL mapping using 532 nm laser
excitation (figure 7) displayed the relative intensities of these defects, demonstrating the wide distribution of theNV centers in opposite sides of thetable and crown facets of this diamond. Analysis of this interesting fluorescence feature demonstrated that
nitrogen could have been distributed
unevenly in a relatively pure type IIa
diamond when it initially formed.
Taryn Linzmeyer andBarbara Whalen

151

NV0 intensity

NV– intensity

Figure 7. False-color 532 nm PL map showing the Raman-normalized peak area of NV0 (left) and NV– (right). The
maps were compiled from 47,040 spectra. The pronounced gradient in NV centers across the diamond resulted
in the different fluorescence color observations (see figure 6 insets).

00

LAB NOTESGEMS & GEMOLOGYFALL 2023

359

Figure 8. The etch channel in this CVD laboratory-grown diamond extends across the table facet into the crown. Field of view 7.19 mm.

LABORATORY-GROWN DIAMOND
CVD “Etch” Channel
GIA’s New York laboratory recently
examined a diamond that had beengrown via chemical vapor deposition(CVD) and processed using a high-pressure, high-temperature (HPHT) treatment. Standard grading procedures
identified it as a 4.00 ct H-color cushion modified brilliant with SI1 clarity.
The diamond was identified as HPHT
processed primarily due to the green
fluorescence observed in the stone (seeFigure 9. Dark residue is visible insome parts of the channel, as seen
through the pavilion. The appearance of the residue is similar tothat of graphitized carbon but
could also be attributed to nondiamond carbon. Field of view
1.99 mm.

360

LAB NOTES

figure 10), while distinct fluorescent
growth layers across the table and pavilion confirmed its CVD origin.
While GIA regularly receives
CVD-grown diamonds submitted forlaboratory-grown diamond reports,
this particular example exhibited aunique characteristic. An etch channel–like structure was plainly visible
across the table of the stone, a feature
not observed in CVD laboratorygrown diamonds at GIA so far. The
channel broke the surface of the tableand extended across the stone, ending
near a pavilion facet on the other side
(figure 8). When viewed under highmagnification, a dark residue (figure9) was observed around parts of thechannel. This residue was not present
throughout the channel and appeared
to be opaque. Close to the surfacereaching channel on the table facet
were multiple smaller channels contained within the diamond. The surface-reaching opening of the channel
was imaged with a scanning electron
microscope (SEM), which revealed ajagged, slit-shaped entrance, suggesting that the shape of the channel extending throughout the diamondstructure was similar in nature (figure11). Some fragmentary material
trapped just inside the entrance of the
opening appeared to extend into thechannel itself. This fragmentary ma-

GEMS & GEMOLOGY

Figure 10. DiamondView imaging
revealed that the channel was
surrounded by blue-fluorescing
dislocation bundles extending across the growth layers of the CVD
diamond.

terial could have been the same typeof opaque residue observed in someareas of the channel.
Fluorescence imaging with the
DiamondView instrument also revealed the presence of this channel,
which could be discerned by the bluefluorescing line of dislocation bundles
following the channel’s path (figure10). These dislocation bundles appeared almost perpendicular to thegreen-fluorescing growth layer boundaries, suggesting the channel was

Figure 11. A secondary electron
SEM image showed the finer
structure of the channel opening,
revealing a jagged, slit-like feature. Field of view 16 μm.

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PL SPECTRA
NV0

Typical CVD
This CVD

INTENSITY

NV–

SiV–

600

650

700

750

466

WAVELENGTH (nm)

467

468

469

470

WAVELENGTH (nm)Figure 12. The PL spectra for a 1.40 ct CVD-grown diamond are shown in red. Left: The 514 nm PL spectrum reveals relatively weak NV centers and no detectable silicon. For comparison, the 514 nm PL spectrum for a morecommonly observed as-grown CVD (purple) shows much stronger NV centers and detectable silicon. The Ramanlines (not shown) are scaled as equal. Spectra are offset vertically for clarity. Right: Many locations on the CVDgrown diamond were analyzed with 457 and 633 nm excitation to verify whether the 468 nm center or the SiV–
center could be detected; this very weak peak of the 468 nm center was only detected at the culet.

created by exploiting weaker dislocation bundles that propagated throughthe diamond during CVD growth.
The presence of this channel in a
CVD laboratory-grown diamond andthe shape of the channel opening wereunlike any natural etch channel opening or laser drill hole opening previously seen. It is unclear whether thischannel was created during initial
CVD growth or during HPHT processing. The opaque residue visible insome parts of the channel as well as
the material visible at the channel surface could point to the presence ofgraphitized carbon, suggesting thechannel was a byproduct of HPHT
treatment, or it might indicate thepresence of non-diamond carbon,
which is a common feature found in
untreated CVD laboratory-grown diamonds. In summary, the residue mayarise from either the CVD growth process or post-growth treatment. Because this feature has not previously
been documented at GIA, futurestudies may help determine the mechanism of action that could createchannels in CVD-grown diamonds.
Elina Myagkaya

LAB NOTESCVD-Grown Diamond with Few
Diagnostic Features
Diamonds grown by chemical vapor
deposition (CVD) have evolved rapidly in the last two decades. However, the vast majority submitted
to GIA for reports still show several
diagnostic features such as the silicon vacancy or SiV– defect (a doublet
at 736.6 and 736.9 nm) and/or the
468 nm peak when analyzed by photoluminescence (PL) spectroscopy.
Additionally, most CVD diamonds
have distinctive fluorescence images
when analyzed by deep UV with the
DiamondView instrument.
Therefore, it was interesting to analyze a 1.40 ct E-color, VVS2 type IIa
diamond submitted for a laboratorygrown diamond report. Initial PL datacollection did not show either the SiV–
center or the 468 nm peak. The features observed were a 3H peak at 503.5
nm using 455 nm excitation and relatively weak nitrogen vacancy (NV)centers at 575 (NV0) and 637 (NV–) nm
using 514 nm excitation (figure 12,left). The stone showed weak anomalous birefringence indicating strain;
while this observation is helpful in

GEMS & GEMOLOGY

confirming whether a diamond isgrown by high-temperature, high-pressure (HPHT) methods, such birefringence cannot distinguish between
natural and CVD origins. The deep-UV
fluorescence image showed only deep
blue coloration, which appeared generally comparable with the vast majority of natural type IIa diamonds (figure
13, left). Therefore, many of the standard markers of CVD origin were notpresent even when examined using advanced methods. Careful analysis of
the fluorescence image revealed somedistinct differences from the majorityof natural diamonds, namely thepatchiness of the fluorescence withsome inert regions.
Many models of the DiamondView
instrument include a series of filtersthat permit fluorescence imaging inwhich portions of the visible spectrum
are blocked out. Using these filters, theblue portion of the visible spectrum
was blocked in order to observe
weaker underlying fluorescence features. With the orange long-pass filter
blocking wavelengths less than 550
nm, NV-related fluorescence clearly
showed the striations indicative of

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Figure 13. Left: The deep-UV (<230 nm) fluorescence image showed blue coloration (due to the presence of dislocation bundles) that appeared nominally similar to DiamondView images of natural type IIa diamonds. Right:
When the fluorescence was filtered by an orange long-pass filter that blocked wavelengths below 550 nm, theNV-related fluorescence and the striations indicative of CVD growth became apparent.

CVD growth (figure 13, right). Also,
several locations of the diamond wereanalyzed with PL spectroscopy to determine if either the 468 nm center or
the SiV– could be detected. Only at theculet was a small 468 nm feature observed (figure 12, right).
The author concluded that thiswas a CVD-grown diamond with noevidence of post-growth treatment.
This example is a noteworthy indicator that as CVD growth methods
improve, telltale defects are being
minimized or eliminated entirely.
Careful examination of all data, both
spectroscopic and fluorescence imaging, is needed to provide accurate
origins for diamond.

and an outer diameter of 20.32–20.40
mm. The ring was produced by Dutch
Diamond Technologies in collaboration with the Belgian jewelry store
Heursel, established in 1745.
This laboratory-grown diamondring was cut from an 8.54 ct plategrown by chemical vapor deposition(CVD). Laser cutting produced a nearperfect circular ring, as demonstratedusing digital imaging analysis to measure its inner and outer circumferences(figure 15).
The manufacture of a solid singlecrystal diamond ring is a complex andchallenging process. Once material isremoved from the crystal, very fine
fractures and imbalanced strain canhave severe consequences, and the ringcan shatter. Processing can take more

Figure 14. The 4.04 ct ring fashioned from a single-crystal CVDgrown diamond.

Figure 15. OpenCV software wasused to draw perfect circles fromthe center of the ring, marked bya green dot.

Sally Eaton-Magaña

Solid Laboratory-Grown SingleCrystal Diamond Ring
Carved single-crystal diamond rings
are rare, with few examples to reference (see Spring 2020 Lab Notes, pp.
132–133). But with advancing technology in the laboratory-grown diamond industry, the creation of solid
faceted diamond rings is now a reality.
Recently submitted to the New Yorklaboratory was a 4.04 ct single-crystal
laboratory-grown diamond ring (figure14). The 3.03 mm thick band had an
inner diameter of 16.35–16.40 mm

362

LAB NOTESGEMS & GEMOLOGYFALL 2023

PEARLS
A Traditional Bombay Pearl Bunch

Figure 16. Strong birefringence observed under cross-polarized light (left)
and blue fluorescence observed in the DiamondView (right).

than six months. Creating the ringfrom a single-crystal laboratory-growndiamond involved about 1,131 hours ofprocessing (including pre-grinding) in
the Dutch town of Cuijk, followed by
751 hours of polishing in Belgium.
Infrared absorption analysis revealed it was a type IIa diamond (nodetectable nitrogen), and no hydrogenrelated peaks were detected at 3107 or
3123 cm–1. Photoluminescence spectroscopy showed interesting vacancyrelated defects indicative of amulti-step growth process. A verystrong emission from the silicon vacancy (SiV–) defect was observed with
633 nm laser excitation; this is a common feature used to identify CVDgrown diamond. The conclusion wasthat this ring had not undergone postgrowth treatment; nevertheless, it wasnotable that the ring showed relatively
low nitrogen-related defects such as
NV centers, along with no detectable
468 nm peak or the 596/597 nm doublet. P. Martineau et al. (“Identification of synthetic diamond grownusing chemical vapor deposition(CVD),” Spring 2004 G&G, pp. 2–25)
observed the 596/597 doublet with a
514 nm laser. Also of note, there were
no H3 or 468 nm centers detectedwith 457 nm laser excitation.
Strong birefringence was observed
using cross-polarized light under microscopic analysis, with an unusual radial pattern (figure 16, left) signifying

LAB NOTES

unique growth conditions compared
to typical CVD diamonds available inthe market today. The deep ultraviolet
illumination of the DiamondView (figure 16, right) confirmed these unusual
growth features with a lack of postgrowth fluorescence colors such as
green produced by the H3 center.
The solid laboratory-grown diamond ring was studied by GIA and determined to have VVS2 clarity basedon dark non-diamond carbon pinpoint
inclusions (growth remnants typicalof CVD-grown diamonds) with Good
polish (polishing on the interior surface of the ring precluded Very Good).
Although the ring was a near-perfectcircle (figure 15), symmetry was considered not applicable. The diamond
had an E color specification based on
GIA’s color grading scale. The ring
was laser inscribed “LaboratoryGrown” on a side facet.
The quality and size of this solid
diamond ring (see the video clip at
www.gia.edu/gems-gemology/fall2023-lab-notes-solid-CVD-ring) provide a great example of the advancing
technology in laboratory-grown diamonds and changing trends in the jewelry industry. This is the first time a
GIA laboratory has examined a colorless diamond ring fashioned entirely
from a laboratory-grown diamond.
Paul Johnson, Stephanie Persaud,and Madelyn Dragone

GEMS & GEMOLOGY

During the era when the maharajahs
and maharanis ruled much of India,
natural pearls were in great demand.
In the nineteenth and early twentiethcenturies, many merchants from theMiddle East relocated to Bombay (nowMumbai) to benefit from this demand(R. Carter, Sea of Pearls, Arabian Publishing, London, 2012, pp. 169–175).
Thus, it is no surprise that India has
been a significant center of pearl manufacturing, processing, and trading for
centuries. To showcase their highquality pearls, traders and artisans in
Bombay would sort the pearls, string
them with silk threads, and tie them
together at both ends using decorative
metallic cords of various colors. Thesebunches were in great demand in theheyday of the natural pearl market andwere sold as “Bombay bunches” (M.
Manutchehr-Danai, Dictionary ofGems and Gemology, Springer, Berlinand Heidelberg, 2008, p. 101).
Recently, GIA’s Mumbai laboratory had the opportunity to examine an 80-year-old Bombay bunch
inherited by one of the city’s established pearl families. The bunch consisted of 553 light cream round andnear-round drilled pearls, strung in
nine hanks, each containing four
strands, with the exception of one
hank with seven strands. The hanks
were tied at both ends with white
metal wires, together with silver andblue cords and tassels (figure 17). The
pearls ranged from 3.83 to 5.72 mm,
and the total weight of the bunch
was approximately 80.51 g. The
owner stated that the total weight ofthe pearls was approximately 130
chow (equivalent to 331.8 ct or 66.35
g). Chow is a system of converting
weight into volume (The Pearl Blue
Book, CIBJO, 2020).
The strung pearls were perfectly
matched in color and exhibitedsmooth surfaces with high luster.
When viewed under 40× magnification, they all exhibited typical nacreous overlapping aragonite platelets.
Their internal structures were examined by real-time microradiogra-

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363

Figure 17. A Bombay bunch consisting of nine hanks and 553 high-quality natural pearls ranging from 3.83 to
5.72 mm.

phy. The majority revealed fine
growth arcs and concentric ringed
structures, while others revealed tightor minimal structures, some withsmall faint cores or light organic-richcores (figure 18). It was evident thatthese were natural pearls from Pinctada-species mollusks, as their internal structures were very similar to
those observed in Pinctada radiata
pearls from the Arabian (Persian) Gulf
when compared to GIA’s researchdatabase.

All pearls showed an inert reaction
when exposed to optical X-ray fluorescence analysis. Energy-dispersive Xray fluorescence spectrometry on a
few samples revealed manganesevalues ranging from below detection
limits to 30.7 ppm and strontium
values of 1215 to 1989 ppm, consistent with a saltwater growth environment. Raman analysis using 514 nm
excitation was also carried out on thesurface of selected pearls showing adoublet at 702/705 cm–1 as well as a

Figure 18. Real-time microradiography images of eight pearls from theBombay bunch revealing fine growth arcs and concentric ringed structures typical of those internal structures observed in Pinctada radiata
pearls.

364

LAB NOTESGEMS & GEMOLOGY

peak at 1085 cm–1, indicative of aragonite. Very weak polyenic pigmentrelated peaks at 1130 and 1530 cm–1
were also observed in a few of thepearls, likely associated with theirlight cream coloration (A. Al-Alawi etal., “Saltwater cultured pearls from
Pinctada radiata in Abu Dhabi(United Arab Emirates),” Journal ofGemmology, Vol. 37, No. 2, 2020, pp.
164–179). The photoluminescence
spectra under 514 nm excitation werealso consistent with the Raman results and displayed high fluorescence
together with the aragonite peaks,
typical of most nacreous pearls. When
exposed to long-wave ultraviolet
light, the pearls showed a moderate
blue reaction.
Historically, Bombay bunches
were known to contain high-quality
Pinctada radiata pearls fished fromthe Arabian (Persian) Gulf, commonlyreferred to as “Basra pearls” in the
trade. Records indicate that the proportion of round pearls found in eachnatural pearl harvest today is lessthan 5% (H. Bari and D. Lam, Pearls,
Skira, Milan, 2010, p. 43). Natural
pearls are rare to find, and it can takedecades to match a round pair of similar size, color, and luster. Encountering Bombay bunches in today’s

FALL 2023

Figure 19. A white button-shaped
atypical bead cultured pearl
weighing 8.15 ct and measuring
11.73 × 11.35 × 9.03 mm.

Figure 21. XRF reaction of thepearl, with the sides appearing
brighter than the base and apex.

DiamondView instrument revealed aclear bluish reaction, with the surface
showing a chalky white flame-likestructure extending from the apex
center across the pearl. Raman analysis of the pearl’s surface using a 514
nm excitation showed a doublet at
701/704 cm–1 as well as peaks at 1086
and 1464 cm–1 characteristic of aragonite. The photoluminescence spectra
revealed high fluorescence, with amaximum centered at approximately
620 nm.
Energy-dispersive X-ray fluorescence spectrometry revealed a low
manganese level of 16.9 ppm and ahigher strontium level of 1577 ppm,
indicative of a saltwater environment.
However, when exposed to X-ray fluorescence (XRF) analysis, the pearl exhibited a moderate yellowish green
fluorescence with a higher intensity
toward the sides but a weaker reaction on the base and apex (figure 21).
Saltwater pearls are usually inert
when tested by this method, while
freshwater pearls and saltwater beadcultured pearls with freshwater shell
nuclei tend to fluoresce weak tostrong yellowish green. In the case ofbead cultured pearls, a thinner nacre
usually produces a stronger reaction;
conversely, the thicker the nacre, theweaker the reaction.
Real-time microradiography imaging (RTX) revealed a long, complex
linear feature in the center typicallyassociated with non-bead cultured
pearls (figure 22, left). When viewed
under X-ray computed microtomo-

GIA’s Mumbai laboratory recently received an atypical bead cultured pearl
with a unique surface appearance.
The white button-shaped pearl
weighed 8.15 ct and measured 11.73 ×
11.35 × 9.03 mm (figure 19).
Viewed under 40× magnification,
the surface exhibited typical fine nacreous overlapping aragonite platelets,
but a distinct pattern similar to theflame structures observed in someporcelaneous pearls was also noted(Summer 2021 Lab Notes, pp. 152–
153). These flame-like features wereformed due to the presence of relatively opaque, frosty white rounded
depressions on the pearl’s surface. Although rounded, they seemed to beoriented longitudinally and weremore tapered toward the base andapex and broader along the sides of thepearl (figure 20). Also observed on thesurface were small white spots withslightly elongated comet tails thatflowed tangentially to the circumference of the button. The base and apexof the pearl lacked the whitish subsurface opaque features that produced
the flame structure effect, and these
two areas appeared more translucent
than the other parts of the pearl.
Under long-wave ultraviolet radiation, the pearl showed a strong yellowish green reaction, and a similar
but weaker reaction was noted undershort-wave ultraviolet radiation. The
deep-UV (<230 nm) radiation of the

Figure 20. Rounded depressions
forming the flame-like structure.
Field of view 0.4 mm.

Figure 22. Left: RTX image of the pearl’s internal structure with a large
linear feature. Right: μ-CT image showing a freshwater-type linear featurein the center and a faint boundary (arrow).

market is a rarity, and it was a great
opportunity for GIA Mumbai to examine such an interesting and memorable pearl submission.
Pfokreni Nipuni, Abeer Al-Alawi,
and Roxane Bhot Jain

Flame-Like Surface Structure in a
Nacreous Atypical Bead Cultured
Pearl

LAB NOTESGEMS & GEMOLOGYFALL 2023

365graphy (μ-CT), the linear feature
looked very similar to those often observed in freshwater non-bead cultured pearls. A faint boundary was
also seen around the central linear feature (figure 22, right) and other growthrings. All these observations, together
with the XRF reaction of the pearl andthe saltwater chemistry, were indicative of an atypical bead cultured
saltwater pearl with a freshwater pearl
used as its nucleus (P. Kessrapong and
K. Lawanwong, “Atypical bead cultured Pinctada maxima pearls nucleated with freshwater non-bead
cultured pearls,” GIA Research News,
April 6, 2020). The nacre thickness
overlying the freshwater non-bead cultured pearl nucleus ranged from approximately 1.09 to 1.90 mm. The
thicker nacre was positioned near thebase and apex and the thinner nacre
toward the sides. This aligned with
the XRF reaction observed, as athinner saltwater nacre will allow
more fluorescence from the freshwater pearl nucleus to pass throughthe nacre layers, while thicker nacremasks the reaction.
Over the years, GIA has encountered similar atypical bead cultured
pearls with sizeable freshwater nonbead cultured pearls used as a nucleus(Spring 2023 Lab Notes, pp. 74–76).
However, the presence of flame-likestructures seen on nacreous pearls is
a very rare phenomenon. This combination of interesting culturing alongwith the unique surface features
make this pearl noteworthy.
Prasad Mane, Nishka Vaz, andAbeer Al-Alawi

Pearls in Traditional
Indian Nose Rings
The beauty of Indian jewelry lies in
the artisanship involved in creating
intricate, unique designs. One example is the classic Indian nose ring(known as the nath). It is typically
cashew shaped, with a chain to connect it to a hairpiece or earring. The
nath exemplifies traditional Maharashtrian jewelry and is usuallycrafted in yellow gold. Made famous

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Figure 23. Two traditional Indian-style pearl nose rings (nath) set with colored gemstones and pearls measuring approximately 6.63 × 6.09 mm to8.42 mm (left) and 5.38 mm to 8.02 × 7.61 mm (right).

during the Peshwa rule, the nath has
been crafted using diamonds, pearls,
rubies, and emeralds. Today, the nathis worn mainly for weddings or special occasions, while everyday noseadornments take the form of smaller,
simpler studs or rings made from goldor silver. Recently, GIA’s Mumbai laboratory received two traditional noserings for pearl identification.
Each was set with 17 drilled
pearls, near-drop and button, ranging
from light cream to cream in color.
They were skillfully strung together
with yellow metal wire and set withcolored gemstones of various shapes
and cutting styles. The pearls in thelarger nose ring (figure 23, left) ranged
from approximately 6.63 × 6.09 mm
to 8.42 mm, and the item weighed atotal of 13.96 g. Those in the smaller
nose ring (figure 23, right) ranged from
5.38 mm to 8.02 × 7.61 mm, and thispiece weighed 9.05 g overall. Whenviewed under 40× magnification, thepearl surfaces in both pieces showed
typical nacreous overlapping aragonite platelets and a medium to highsurface luster. Energy-dispersive X-ray
fluorescence (EDXRF) spectrometry
revealed manganese levels below the
instrument’s detection level and astrontium content averaging 950
ppm. In addition, the pearls were inert
to X-ray fluorescence, indicative ofsaltwater origin. They showed a moderate greenish yellow reaction underlong-wave ultraviolet light and aweaker reaction of similar color undershort-wave UV. Real-time microradiography imaging revealed internal
structures similar to those observedin natural pearl studies for various
Pinctada-species mollusks (K. Scarratt et al., “Natural pearls from Australian Pinctada maxima,” WinterGEMS & GEMOLOGYFALL 2023

Figure 24. Real-time microradiography of the internal structures observedin the larger nose ring consisting of organic-rich acicular structures andgrowth arcs (left) and a “collapsed core” near the drill hole area surrounded by growth arcs (right).

of 950 ppm) and manganese (mostly
below detection limits) consistent
with that mollusk species and below
those expected from P. maxima pearls(A. Homkrajae et al., “Internal structures of known Pinctada maxima
pearls: Natural pearls from wild marine mollusks,” Spring 2021 G&G,
pp. 2–21).
The combinations of natural
pearls made these two pieces very attractive. It is no easy task to create
traditional nose ornaments withpearls of such size. These two uniquepearl jewelry items provide an excellent example of Indian heritage.
Lubna Sahani, Abeer Al-Alawi, andRoxane Bhot Jain

2012 G&G, pp. 236–261; N. Nilpetploy et al., “The gemological characteristics of Pipi pearls reportedly from
Pinctada maculata,” Winter 2018
G&G, pp. 418–427). The radiopaqueareas visible on the microradiographsof both items correspond to the yellow metal fittings and wire, since
they are denser and prevent X-rays
from passing through.
Five pearls from the larger nath revealed an organic-rich internal structure with varying patchy light anddark gray contrasting areas, alongwith an acicular structure radiatingfrom their centers that occupied almost half of the internal structure(figure 24, left). Two pearls showed“collapsed cores” close to the drill
holes (figure 24, right); the bulk of thecores, if any, were removed as a resultof drilling. The remaining ten pearls
displayed fine concentric rings andgrowth arcs, all proving their natural
origin.
Microradiography of the pearls inthe smaller nath revealed similar internal structures. While the majorityof those pearls showed fine concentricrings and growth arcs, three of them(marked with arrows in figure 25) also
possessed organic-rich and acicularcores that occupied varying degrees of
their structure. The internal structures observed in both items contained classic natural pearl structures
similar to those observed in known
Pinctada radiata pearls in GIA’s research database. The EDXRF results
were also within the range expected
for Pinctada radiata samples, withthe lower levels of strontium (average

RUBY“Nebula” Inclusion in Ruby
Beryllium-Diffused to Heal Fractures
Recently the Carlsbad laboratory received a 4.12 ct purple-red stonemeasuring approximately 11.50 ×
7.70 × 4.72 mm (figure 26) for identification services. It featured unusualveil-like reddish color zoning wafting
throughout a purple bodycolor. The
refractive index measured 1.760–
1.770, identifying the stone as a ruby.

Figure 26. An unusual ruby withcoloring reminiscent of a nebula
found in the depths of outer space.

Figure 25. The majority of the pearls in the smaller nose ring showed faintgrowth arcs and concentric ringed structures, while three of them showedorganic-rich acicular cores (marked with arrows) typical of natural pearls.

LAB NOTESGEMS & GEMOLOGYFALL 2023

367

Figure 27. Fingerprints resulting from flux-assisted heating of a berylliumrich flux. Field of view 7.19 mm.

Microscopic examination indicated that the reddish color zoning
was associated with altered fingerprints that resembled a cosmic nebula
due to a flux-rich residue (figure 27).
These fingerprints appeared to be consistent with fractures that had been
healed using a flux-assisted heatingprocess in a high-heat environment.
Due to the indications of highheat, laser ablation–inductively coupled plasma–mass spectrometry (LAICP-MS) chemical analysis was
performed to check for the presence ofberyllium diffusion. Initially, LA-ICPMS conducted on two spots revealed
beryllium concentrations of <0.019
ppma and 60.87 ppma. This significant discrepancy prompted additional
LA-ICP-MS testing in three spots, revealing beryllium concentrations of<0.19 ppma, 1780 ppma, and <0.19
ppma. Microscopic observation of thetesting spots showed areas of high beryllium on or near the reddish colorzones, while areas of very low beryllium were associated with testingareas on the purple areas of the stone.
Therefore, it was concluded that aberyllium-rich flux was used to heal
the fractures naturally present in thestone. The ruby was likely heated inthis flux at temperatures high enoughto allow the beryllium to seep fromthe flux into the stone, but not long

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LAB NOTES

enough for the beryllium to infiltrate
its entirety.
Michaela Damba

Translucent Ruby Filled with
Zinc Glass
Recently the Carlsbad laboratory received an 8.57 ct translucent purplish
red heart-shaped mixed-cut stone for
identification service (figure 28). Stan-

dard gemological testing revealed a refractive index of 1.760–1.769, and aruby spectrum was obtained with ahandheld spectroscope. The stone
showed a medium to strong red fluorescence to long-wave UV radiation
and a very weak red fluorescence toshort-wave UV radiation. During microscopic analysis, several fracturescontaining a whitish filler and air
pockets were seen using fiber-optic
lighting (figure 29). Using reflected
light, fractures with a lower luster
than the host corundum were also observed, which confirmed the presenceof a filling material.
The stone did not show the blue
flash effect typically observed inrubies filled with lead glass (S.F.
McClure et al., “Identification anddurability of lead glass–filled rubies,”
Spring 2006 G&G, pp. 22–36). Although the filler improved the durability, it did not appear to improvethe clarity.
Glass filling treatment has beenused on heavily fractured rubies to increase their clarity and durability
since the early 1980s, and cavity filling was noted and described as early
as 1984. The original filler was silica
glass, which was easily visible since
its refractive index (~1.5) is significantly lower than corundum (R.E.

Figure 28. An 8.57 ct heart-shaped fracture-filled ruby treated with a zincglass filling.

GEMS & GEMOLOGYFALL 2023

Figure 29. A fracture with whitish filler (left) and trapped air pockets (right). Fields of view 1.58 mm (left) and2.90 mm (right).

Kane, “Natural rubies with glassfilled cavities,” Winter 1984 G&G,
pp. 187–199). In early 2004, gemologists discovered a new type of glassfiller with high lead content and amuch better clarity enhancement due
to its higher reflective index (~1.70)(GAAJ Research Laboratory, “Leadglass impregnated ruby,” March 15,2004). Since then, lead glass fillers
have become the most popular filler
for rubies, although other glass types
such as bismuth and cobalt have also
been used (T. Leelawatanasuk et al.,“Cobalt-doped glass-filled sapphire:
An update,” Australian Gemmologist, Vol. 25, No. 1, 2013, pp. 14–20;
Spring 2020 Lab Notes, p. 139).
In the heart-shaped ruby submitted
to the laboratory, energy-dispersive X-

ray fluorescence spectroscopy did notdetect lead or bismuth but did show
chromium, iron, and zinc. Additional
chemical analysis was performed withlaser ablation–inductively coupledplasma–mass spectrometry on two
spots of one larger fracture with a substantial amount of filler in order toquantitatively measure the elementsin the glass filler. The averages of thetwo analysis spots were 28750 ppmw
silicon, 1091 ppmw zinc, and 108
ppmw lead.
Chemical results and gemologicalproperties revealed that this glassfiller was not the lead or bismuth
glass the authors first suspected, butrather a silica-based glass doped withzinc. While this type of filler had visual properties similar to those ofother glass fillers in corundum, it did
not show a flash effect. This is thefirst time the authors have encountered a ruby filled with zinc glass.
Shiva Sohrabi and Amy Cooper

PHOTO CREDITS
Adriana Robinson—1, 26, 28; Matthew Hardman—2, 3; Evelina Goldort—4; Diego Sanchez—5; Barbara Whalen—6; Elina
Myagkaya—8–10; Sally Eaton-Magaña—13(right); Towfiq Ahmed—14, 15; Paul Johnson—
16 (left); Madelyn Dragone—16 (right); Gaurav
Bera—17, 19, 23; Nishka Vaz—20; Nathan
Renfro—27; Shiva Sohrabi—29

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

gia.edu/gems-gemology

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