Publish Year: 2023 Title: Blackish Green Omphacite Jade from Guatemala Abstract: Figure 1. Yongchuliao samples collected for testing. The rough sample on the left weighs 30.1 ct, and the carving on the right weighs 12.85 ct. Photos by Shilong Xu.
In recent years, a new kind of Guatemalan jade has entered the Chinese jewelry market, where it is called yongchuliao fei cui (or yongchuliao for short). Prior to the availability of yongchuliao, Chinese consumers had a negative impression of Guatemalan material and preferred Burmese jade. However, the recent emergence of this new high-quality blackish green jade has attracted the attention of Chinese buyers.

Figure 2. Left: Fibrous inclusions observed in the 12.85 ct carved sample; field of view 8.94 mm. Right: The carved sample appeared bright green rather than blackish green under transmitted light. Photos by Shilong Xu.
The authors recently tested a rough stone and a carved pendant of yongchuliao (figure 1). Under reflected light, these samples appeared blackish green with a greasy luster similar to Burmese inky black jade. The rough stone was opaque and had numerous fine white inclusions measuring approximately 300 μm in diameter on its surface. The carved sample was bright green with coarse texture and medium transparency under transmitted light (figure 2). The rough and carved samples had a refractive index of 1.67 and specific gravities of 3.342 and 3.332, respectively. These gemological characteristics are consistent with both jadeite-type jade and omphacite-type jade.
Qualitative analysis using energy-dispersive X-ray fluorescence spectrometry revealed magnesium, aluminum, silicon, calcium, chromium, manganese, and iron, among other elements. It should be noted that the ideal chemical formula of jadeite is NaAlSi2O6 and that of omphacite is (Ca,Na)(Mg,Fe,Al)Si2O6 (S.F. McClure, “The jadeite/omphacite nomenclature question,” GIA Research News, April 12, 2012). Jadeite and omphacite can form a complete solid solution. The occurrence of calcium, magnesium, and other elements implies that the mineral composition of yongchuliao is not pure jadeite.

Figure 3. The mineral species were confirmed by comparison with samples from the RRUFF database. Spectra are offset vertically for clarity. Left: The host mineral and fibrous inclusions of the samples matched with omphacite. Right: The white dotted mineral inclusions in the rough sample matched with titanite. Titanite in the carved sample could also be observed in micro-Raman imaging.
Raman shifts at 681, 514, 411, 378, 340, and 209 cm–1 were consistent with those of omphacite (figure 3). The Raman spectra of fibrous inclusions in the carved sample also matched those of omphacite rather than jadeite. The strongest Raman shift at 681 cm–1 was attributed to the symmetrical Si-O-Si stretching vibration (B. Xing et al., “Locality determination of inky black omphacite jades from Myanmar and Guatemala by nondestructive analysis,” Journal of Raman Spectroscopy, Vol. 53, No. 11, 2022, pp. 2009–2018). Raman spectroscopy was used to compare the samples’ mineral composition against the RRUFF database (B. Lafuente et al., https://rruff.info/about/downloads/HMC1-30.pdf), revealing that yongchuliao material consists almost entirely of omphacite. The fine white inclusions distributed evenly in the rough sample were coincident with titanite (figure 3). In addition, some of the sample was ground into powder for X-ray diffraction analysis to obtain the mineral composition of the whole rock. The results showed an omphacite content of about 98.49% (with a 5% margin of error), and the rest was magnesian calcite. The results from Fourier-transform infrared absorption spectroscopy were consistent with the Raman spectra, identifying the main mineral composition of the samples as omphacite.

Figure 4. In the UV-Vis-NIR spectrum of a piece cut from the rough sample, absorption peaks were observed within the visible range at 437, 637, 657, and 688 nm.
A double-sided polished piece was cut from the rough sample for testing. Its ultraviolet/visible/near-infrared (UV-Vis-NIR) absorption spectrum (figure 4) showed an absorption peak at 437 nm, indicating the presence of Fe3+. Absorption peaks at 637, 657, and 688 nm were also observed and attributed to Cr3+ (G.R. Rossman, “Color in gems: The new technologies,” Summer 1981 G&G, pp. 61–62).
Based on testing, both samples were omphacite-type jade containing titanite inclusions. Since almost all of the yongchuliao we have observed exhibited nearly the same colors and textures as these samples, it is likely that other yongchuliao may also have similar mineral compositions. @topic:9


Publish Year: 2023 Title: Rare Faceted Thomsonite Abstract: Figure 1. A rare 1.04 ct semitransparent thomsonite measuring 7.53 × 6.15 × 4.67 mm. The inset shows the typical appearance of thomsonite. Photos by Adriana Robinson and Scott Lewis (inset).

Figure 2. A fibrous snowflake-like inclusion found within the semitransparent thomsonite. Photomicrograph by Michaela Damba; field of view 3.57 mm.
The Carlsbad laboratory recently examined a colorless semitransparent 1.04 ct oval modified brilliant (figure 1). Standard gemological testing gave a specific gravity (SG) of 2.47 and a refractive index of 1.520–1.538. These properties suggested the stone was a rare faceted thomsonite, which was confirmed by Raman spectroscopy. There are two types of thomsonite: the more common thomsonite-Ca with the chemical formula NaCa2Al5Si5O20 • 6(H2O) and the less common thomsonite-Sr with the chemical formula of Sr1.4Ca0.6NaAl5Si5O20 • 7.1(H2O). X-ray fluorescence was not run on this stone to determine which, for fear of damaging the potentially fragile stone. The SG reading was slightly higher than the expected value of 2.35 (+0.05/–0.10). Multiple surface scratches and abrasions indicated a relatively soft material, consistent with thomsonite’s hardness of 5.0–5.5 on the Mohs scale. This specimen featured a radiating fibrous inclusion resembling a snowflake (figure 2). Although the identity of the inclusion could not be confirmed with Raman spectroscopy, it was likely a member of the zeolite group.
Thomsonite is a rare member of the zeolite group named for Scottish chemist and mineralogist Thomas Thomson (1773–1852). While the source of this specimen is unknown, thomsonite is typically found in Minnesota along Lake Superior. It usually occurs as semitranslucent to opaque rounded crystal aggregates (figure 1, inset) with a fibrous structure. Thomsonite has also been known to appear as part of a rock aggregate (B.M. Laurs et al., “Benitoite from the New Idria District, San Benito, County, California,” Fall 1997 G&G, figure 13) or as rare needle inclusions in Canadian sapphires (Winter 2004 Gem News International, pp. 344–345). Semitransparent and faceted thomsonite is very unusual. To the best of our knowledge, this is the first faceted thomsonite examined by GIA. @topic:1


Publish Year: 2015 Title: Blue Gahnite Inclusions inCat’s-Eye Heliodor Abstract: Figure 1. These four heliodor cabochons display sharp eyes under incandescent fiber-optic illumination. Photo by C.D. Mengason.

	Four golden oval cabochons (figure 1) were submitted to the Carlsbad laboratory by L. Allen Brown (All That Glitters, Methuen, Massachusetts) for scientific examination. Standard gemological testing revealed that the stones were beryl. Under incandescent fiber-optic illumination, the stones showed a very sharp cat’s eye, caused by growth tubes and fine needle-like inclusions oriented parallel to the c-axis. Under magnification, blue crystals with octahedral morphology (figure 2) were the most distinctive internal characteristic.

Figure 2. Diffused fiber-optic illumination reveals well-formed blue octahedral crystals in addition to the hollow tubes that cause the chatoyancy. The black needle-like inclusions may be hematite. Photomicrograph by Nathan Renfro; field of view 1.10 mm.

	Raman microspectroscopy was used to identify the blue octahedral inclusions as gahnite, a zinc-rich end member of the spinel group with the general formula ZnAl2O4. It occurs most commonly as an accessory mineral in granitic pegmatites, usually associated with almandine-spessartine garnet, muscovite, beryl, tourmaline, and nigerite (D.R. Soares, et al., “Chemical composition of gahnite and degree of pegmatitic fractionation in the Borborema Pegmatitic Province, northeastern Brazil,” Anais da Academia Brasileira de Ciências, 2007, Vol. 79, No. 3, pp. 395–404). According to Brown, the stones were purchased in Tucson in 2010 and were represented as being from Brazil. These are the first beryls with gahnite inclusions that GIA has examined to date. Since gahnite is a diagnostic inclusion in sapphires from Sri Lanka (E.J. Gübelin and J.I. Koivula, Photoatlas of Inclusions in Gemstones, Vol. 3, Opinio Verlag, Basel, Switzerland, 2008, p. 290), detailed study of gahnite may also provide some indication of the geographic origin of heliodor. @topic:1


Publish Year: 2013 Title: Stellate Zircon Inclusions in Vivid Purple-Pink Morganite Abstract: Figure 1. Stellate clusters of zircon needles were observed in this purple-pink morganite. Vertical field of view 0.58 mm. Photomicrograph by Nathan Renfro.

              The Carlsbad laboratory recently examined a 4.95 ct vivid purple-pink morganite (figure 1). In addition to its saturated color, the stone was particularly noteworthy because of the inclusions it contained. Microscopic examination revealed numerous stellate inclusions, each with many delicate tapered legs.

Gemological properties revealed an RI of 1.577–1.583 and a hydrostatic SG of 2.73. It did not show fluorescence under either long- or short-wave UV. All of these properties were consistent with beryl, which was further confirmed by FTIR and Raman spectroscopy.

Inclusions in the stone showed an interesting starburst pattern, with thin needles radiating from a central point of nucleation. Viewed with polarized light, the needles exhibited birefringence. A sub-adamantine luster was observed where some of the needles broke the surface (figure 2). Raman spectroscopy identified the inclusions as zircon, consistent with our initial observations. Zircon inclusions are occasionally found in pegmatitic beryl, but they usually occur as prismatic or rounded crystals that cause damage to their host due to zircon’s relative instability (E.J. Gübelin and J.I. Koivula, Photoatlas of Inclusions in Gemstones, ABC Edition, Zurich, 1986, p. 197).

	Figure 2. The needle-like zircons showed a sub-adamantine luster when examined using reflected light. The largest surface-breaking needle measures approximately 10 microns in the longest cross-sectional direction. Photomicrograph by Nathan Renfro.
In addition to the zircon clusters, the stone also contained fluid inclusions, transparent crystals, particulate clouds, and singular needles. The distinctive morphology of the zircon inclusions, coupled with the vivid purple-pink color, create a rather unique gemstone. @topic:3


Publish Year: 2023 Title: Inclusions in Chondrodite Abstract: Figure 1. This 4.63 ct chondrodite contained irregular multiphase and reflective iridescent platelets with a bright orangy yellow color. Photo by Adriana Gudino; courtesy of Bill Vance.
The authors recently examined a 4.63 ct orangy yellow pear modified brilliant (figure 1). The gemological properties as well as infrared and Raman spectroscopy identified the stone as chondrodite.

Figure 2. Platy inclusions were observed throughout the chondrodite. Photomicrograph by Nathan Renfro; field of view 4.11 mm.
Microscopic observation revealed a lively inclusion scene with colorless reflective and iridescent platy inclusions (figure 2). Dark, highly reflective platelets of graphite, which can be associated with low-relief colorless crystals of various minerals (figure 3), were also confirmed by Raman analysis.

Figure 3. Dark, highly reflective platelets of graphite as well as unidentified low-relief colorless inclusions of multiple minerals were also observed in the chondrodite. Photomicrograph by Nathan Renfro; field of view 0.91 mm.
Chondrodite, Mg5(SiO4)2(F,OH)2 is a member of the humite group. This rare mineral occurs primarily in metamorphosed limestones and dolomites (W.L. Roberts et al., Encyclopedia of Minerals, 2nd ed., Van Nostrand Reinhold, New York, 1990, p. 170). If contact metamorphism occurs in an area with sufficient magnesium, chondrodite and other associated magnesium-bearing minerals such as spinel, phlogopite, and tremolite may form.
Chondrodite has been found to originate from Tanzanian localities at Mahenge (Winter 2011 Gem News International, p. 316), Sumbawanga (Winter 2007 Gem News International, pp. 377–379), and Tanga (B. Clark, “Chondrodite reportedly from Tanga, Tanzania,” Journal of Gemmology, Vol. 34, No. 8, p. 655). It has also been identified as an inclusion in a spinel from Mogok, Myanmar (Winter 2021 G&G Micro-World, p. 383). The gemological properties of this stone were consistent with material from Mahenge, but the origin could not be confirmed.
Chondrodite is an uncommon mineral and even more rare as a gemstone. This exceptional example of a bright orangy yellow color, faceted by Bill Vance of Vance Gems, showcases the types of inclusions that can be found in this gemstone. @topic:1


Publish Year: 2016 Title: Garnet Inclusion Illusion Abstract: Figure 1. At first glance, this 42.88 ct quartz double cabochon measuring 28 × 18.5 × 15 mm resembles a beautiful garnet-included quartz gem. Photo by Elise A. Skalwold, from the Si and Ann Frazier Collection.

	A cleverly designed “garnet in quartz” double cabochon represents a new and unexpected challenge for gemologists, collectors, and designers who intend to feature inclusion gemstones in their jewelry lines. This assembled inclusion consists of a fragment of pyralspite-series garnet sandwiched between two quartz cabochons (figure 1). The garnet and quartz were identified with optical and Raman spectroscopy, respectively, at GIA’s Carlsbad laboratory. While the specimen creates the illusion of being natural, clues to its artificial origin include air bubbles and the fragment itself, which shows neither crystal faces nor the rounded appearance of an etched or eroded crystal. Rather, it is a relatively sharp fragment that resides in a pocket filled with glue (figure 2). The subtle glue layer between the cabochons becomes more apparent when viewed under UV light, which causes it to fluoresce chalky white; this fluorescence is stronger under long-wave than short-wave UV.

Figure 2. Gas bubbles can be seen in an otherwise nearly invisible glue layer between the quartz cabochons; these bubbles are abundant in the vicinity of the red garnet fragment. The fragment resides in a hollowed-out pocket and is surrounded with glue. Photomicrograph by Nathan Renfro; field of view 10.28 mm.

	This specimen was purchased at the 2016 Tucson shows from a dealer specializing in inclusion specimens. The cabochon, part a collection of otherwise natural items, was fully disclosed as a man-made novelty. Its appearance in the marketplace represents an emerging trend that gemologists and collectors will see with increasing regularity as the fascination with inclusions grows (see the author’s forthcoming article, “Evolution of the inclusion illusion,” in the Summer 2016 InColor). Careful inspection with a loupe or microscope will in most cases reveal the underlying nature of this inclusion. @topic:3


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Publish Year: - Title: Visit Two of Mogok’s Most Important Mines with GIA Abstract: Dattaw and Baw Mar

	In this video, you’ll visit Mogok’s bustling gem markets and two important working mines: the Dattaw ruby mine and Baw Mar sapphire mine.

	Mogok’s history as a premier gem-producing locale looms large in this new video from GIA’s field gemology department. Join Vincent Pardieu and his team as they explore Mogok’s past and present. You’ll get a glimpse of Mogok’s teeming gem markets and an insider’s look at two of the region’s most important working mine operations: the Dattaw ruby and Baw Mar blue sapphire mines.

	Ashim Roy, the Montepuez ruby mine’s general manager, is here to learn from all that Mogok has to offer. “We hear so much and we read so much about Mogok,” he says. “With over a thousand years of history of ruby mining, my expectation is that when I go back, I should have knowledge of not only the geology or the gemology, but also the mining, the social, the economic…I have a lot of expectations for this visit.”

	Mogok is about 200 km (124 miles) northeast of Mandalay in Myanmar’s north. This most famous of all gem-producing areas is made up of several valleys and their towns. The principal ones are Mogok and Kyatpyin, but gems are also found in the fertile valleys surrounding the villages of Bernardymo, Chaung Gyi, and Kyauk Pya That, along with the Kabaing and Kin valleys. Besides ruby and sapphire, Mogok also produces a wealth of other gems, including spinel, apatite, peridot, tourmaline, scapolite, moonstone, zircon, garnet, iolite, and amethyst.

	From a vantage point high above Mogok, Pardieu points to a hillside on the other side of the valley, where bright white marble tailings are visible from quite a distance. “You have a mine on top of the mountain, this is Dattaw,” he observes, “probably the most famous in all Mogok.”

	The mine is located about 5 km (3 miles) out of town, and the team has to climb a steep path to reach it. “Dattaw is the highest ruby mine in the eastern part of Mogok,” says Pardieu. “It’s also one of the most important, where several very significant rubies were mined.” In fact, this mine has produced some exceptionally large gems, including the infamous 496.5-ct. SLORC ruby (named after the acronym for State Law and Order Restoration Council, the ruling government body at the time of its recovery in 1990).

	Dattaw is a hard rock, tunneling operation in crisp, white calcite marble. There, the team witnesses drilling and preparations for blasting. “Currently, they are drilling and placing the explosives in for the blast,” says Pardieu. “Usually, the blast is at the end of the day…You can see that they are putting a lot of explosives in…They are slow power, so they will break the marble, they will break the calcite, but they will not break the rubies.” Gemologist Wim Vertriest is very taken with the mine’s geology. “The marble is so crystalline!” he exclaims. “There are huge crystals of calcite that give it a very strange appearance—it looks like we’re in some kind of video game!”

	Finally, the team reaches the deepest levels of the mine. “Here we are in the depths of Dattaw, about 200 meters underground,” says Pardieu, “and we are with a team of Burmese miners bringing back some calcite from the depths of the mine, and they will bring that to the surface. At the surface, they will hammer the calcite…to see if there is any ruby inside.” Some of the hammered pieces look as delectable as prime sushi, or perhaps a selection of exotic desserts. In each, a brilliant red ruby crystal sits at the edge of rhombus-shaped, translucent—almost transparent—calcite. They look almost good enough to eat.

	Next, they visit the Baw Lon Gyi mine and village. “What is interesting is the system they have with the Kanase,” explains Pardieu. Kanase are the women who, by tradition, sort through the mine’s tailings in search of gems overlooked by the miners. “You have the people from Baw Lon Gyi village queuing in order to get all the waste of the mine,” continues Pardieu. “Sometimes, hundreds of people are breaking the calcite in order to be able to find the small rubies.” The area resounds with the pounding of hammers as the townspeople methodically break down the calcite. “I think it’s a good way to have the mine also care for people who are not working at the mines, so sustaining the entire community,” attests Vertriest. “And this also gives a market for the small low-quality stones.”

	Some of these smaller gems might well appear at Kyatpyin’s afternoon gem market, which is the group’s next stop. “This is a very interesting market with about one or two thousand people,” says Pardieu, “and it’s a market mainly with blue sapphires.” Asked where the sapphires come from, the merchants respond “Baw Mar.” Since 2008, fine blue sapphires from the Baw Mar area of Mogok have been reaching the market. The mine itself is located in the Kyat Pyin area, west of Mogok. It’s equipped with heavy machinery and combines open-pit mining with tunneling. “This is the largest sapphire mine in all Mogok,” remarks Pardieu, “and it’s the largest primary mine.” The operation—which can produce rough big enough for polished sapphires up to 15 cts.—employs about 300 miners and other workers.

	The team explores Baw Mar’s underground operations, where at the end of timber-lined tunnels, workers extract sapphire crystals from the weathered rock by hand. “It’s about 20 to 30 meters underground,” relates Stanislas Detroyat, “and we are fascinated by what we’re seeing now, because we can see sapphire pockets inside the rock.” As they watch a miner recovering sapphires, Vertriest remarks, “You see this guy, he’s just working with an iron pick and just going for the areas that contain the most sapphire.”

	This is one of the things a field gemologist most wants to see first-hand—recovery of the gems directly from the mine. “So this is great to actually see sapphire in the rock, inside the mine, still in-situ in the matrix!” exclaims Pardieu. “This is the reason why I’m traveling around the world to visit all ruby and sapphire mines to collect all these samples on site at the mine and build the GIA reference collection.”

	This GIA Field Expedition (FE75) took place in 2015. Besides Pardieu, the participants were video cameraman Didier Barriere-Doleac and expedition members Stanislas Detroyat, Wim Vertriest, Ashim Roy, Victoria Raynaud, Lauriane Pinsault, and Floriane Duret. @topic:9


Publish Year: 2023 Title: Heliodor with a Large Schorl Inclusion Abstract: Morphological features of the tourmaline crystal included in the heliodor are visible; striations and triangular growth marks are present. A band of fluid inclusions is visible near the tip of the schorl tourmaline. Photomicrograph by Rhiana Elizabeth Henry; field of view 2.90 mm. Gift of Mark Mauthner, GIA Museum no. 37772.
An 8.33 ct long rectangular heliodor, the yellow variety of beryl (ideally Be3Al2Si6O18), was examined by the author. It was reportedly from the Zelatoya Vada mine in Murgab, Tajikistan; however, it was likely from Pakistan (J.S. White, “Let’s get it right: Tajikistan heliodor,” Rocks and Minerals, Vol. 80, No. 4, 2005, pp. 285–286). The heliodor had a large schorl tourmaline inclusion prominently under the table facet (see above) and a small schorl tourmaline near one corner. A thin band of fine fluid inclusions ran parallel to the length of the stone adjacent to the tourmaline. The stone was clearly cut to highlight the interesting inclusion rather than hide or remove it; aside from the two tourmaline inclusions and the thin band of fluids, the beryl had high clarity.
Both the heliodor and the tourmaline were analyzed by Raman spectroscopy and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) to better understand the structure and chemistry of the minerals. Analyses were conducted on the girdle of the heliodor and on the back end of the tourmaline inclusion where it intersected a pavilion facet. The heliodor had low-moderate water bound in its structural channels, as determined qualitatively by Raman spectroscopy, which is expected for heliodor with low sodium content (R.E. Henry et al., “Crystal-chemical observations and the relation between sodium and H2O in different beryl varieties,” Canadian Mineralogist, Vol. 60, No. 4, 2022, pp. 625–675). The heliodor fit well within the expected chemistry; it had low overall cation substitutions, with minor or trace iron, magnesium, lithium, sodium, and cesium content. The tourmaline was confirmed to be schorl dominant due to its predominant sodium and iron content; however, due to high vacancy at the X structural site, the tourmaline had a high foitite component (D.J. Henry et al., “Nomenclature of the tourmaline-supergroup minerals,” American Mineralogist, Vol. 96, 2011, pp. 895–913).
After data collection for research, this stone will be used in the GIA GemKids program as an educational piece for young students at the Carlsbad campus. It will represent the heliodor variety of beryl, showing fascinating inclusions as well as evidence of LA-ICP-MS laser pits on the girdle of the stone (not shown in the photomicrograph). @topic:1


Publish Year: 2015 Title: Pink and Reddish Purple Cobaltocalcite Abstract: Figure 1. The pink and reddish purple cobaltocalcite specimens (246.3 and 361.0 g, respectively) are shown with some of the wafers cut from them.

Cobaltocalcite is a pink to purple variety of calcite. The mineral is popular as a collector’s item because of its striking purplish pink color, which is caused, as the name suggests, by the presence of cobalt. Cobalt occurs in calcite in octahedral coordination as Co2+ (E. Fritsch and G.R. Rossman, “An update on color in gems. Part 1: Introduction and colors caused by dispersed metal ions,” Fall 1987 G&G, pp.126–139).

Recently, GIA’s laboratory in Bangkok examined the botryoidal purplish pink and rough reddish purple cobaltocalcite specimens shown in figure 1. Gemological properties were obtained from both, and we also prepared several polished wafers for advanced testing.

Standard gemological testing of these translucent stones revealed strong double refraction with an RI of 1.49–1.66 (as expected for a carbonate material) and an SG of approximately 2.70. The reddish purple cobaltocalcite exhibited a very weak purplish pink reaction to long-wave UV radiation and an inert reaction to short-wave UV. The purplish pink stone had a moderate orangy pink reaction to long-wave UV and weak pink to short-wave. Magnification revealed white particulate flakes of a fibrous nature forming bands in the reddish purple specimen, while the purplish pink one contained pronounced irregular fibrous inclusions forming a mosaic pattern in areas (figure 2).

Figure 2. Left: The reddish purple cobaltocalcite showed a banded structure formed by white particles with a fibrous appearance. Field of view 4.1 mm. Right: Irregular bands of fibrous inclusions in the pink stone formed a mosaic pattern. Fiber-optic illumination, field of view 4.1 mm. Photomicrographs by Jonathan Muyal.
The UV-Vis-NIR spectrum of the reddish purple cobaltocalcite wafer (figure 3) showed a dominant absorption band at 543 nm and a small peak at 431 nm. The pink wafer only showed a weak absorption feature at 543 nm. Color calculations (see box A in R. Lu, “Color origin of lavender jadeite: An alternative approach,” Winter 2012 G&G, pp. 273–283) were consistent with the respective reddish purple and purplish pink color of the two specimens (figure 3, inset).

Figure 3. UV-Vis-NIR spectra in the 300–1000 nm region showed broad absorption bands at approximately 431 and 543 nm in the reddish purple cobaltocalcite, and a weak broad band at 543 nm in the pink stone. Inset: The reddish purple and pink stones’ CIE L*a*b* color coordinates (71, 47, 24 and 96, 3, 4, respectively) are reproduced from their UV-visible spectra.
Elemental analysis was performed using laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS). Besides the main constituent calcium, both the reddish purple and the purplish pink cobaltocalcites showed significant amounts of Co at 5673 and 730 ppmw, respectively. The reddish purple sample’s higher concentration is consistent with a higher Co level produces a more saturated color. The concentration of Co is consistent with the intensity of the 543 nm absorption bands in the visible region of both samples. The purplish pink cobaltocalcite also showed 8719 ppmw of Mn. Manganese can cause pink to purple color in appropriate concentrations, so its contribution to the purplish pink color in this material may require further analysis. @topic:3


Publish Year: 2023 Title: Synthetic Color-Change Wakefieldite Abstract: Figure 1. Faceted and rough synthetic wakefieldite in LED lighting with 6400K color temperature. The faceted stone is 5.04 ct. Photo by Adriana Gudino; courtesy of Arya Akhavan.
Author AA, a gemstone cutter and collector of rare synthetic gems, recently submitted one rough and one faceted stone to GIA for scientific examination. The material, sourced from RG Crystals in Bangkok, was stated to be Czochralski-pulled, neodymium-doped yttrium orthovanadate, which is commonly used in laser applications. It can also form naturally as the mineral wakefieldite-(Y), with an ideal chemical formula of YVO4. His first observation was a striking color change from pink or purple to a blue or even green color under various lighting conditions and viewing angles. The finished gemstone (figures 1 and 2) displayed strong fire due to the material’s very high dispersion.

Figure 2. The color change of the faceted synthetic wakefieldite, observed between daylight (left) and cool fluorescent light F10 (right). Photos by Aaron Palke; courtesy of Arya Akhavan.
Wakefieldite is a rare tetragonal mineral belonging to the xenotime mineral family with an ideal general formula of (REE)VO4, where REE = Y, La, Ce, and Nd among other rare earth elements. Its general physical and optical properties include a hardness of 5, specific gravity of 4.25, uniaxial + optic sign with refractive indices of nω = 2.000 and nε = 2.140, birefringence of 0.140, and dispersion of 0.084. With prominent, perfect cleavage and relatively low hardness, the material is difficult to polish. Natural wakefieldite occurs as very small, non-gem crystals unsuitable for faceting; Czochralski-pulled materials represent the only examples of faceted wakefieldite. In fact, this was the first faceted synthetic wakefieldite seen in a GIA laboratory. Chemistry and visible absorption spectra were collected to quantitatively study the striking color-change behavior.

Figure 3. The visible absorption spectra of neodymium-doped YVO4 are shown with the relative power distribution curves of CIE illuminants F10 and D65 and an Eiko warm white fluorescent bulb with color temperature of 2800K.
A polished wafer with 10.6 mm thickness was analyzed. Laser ablation–inductively coupled plasma–mass spectrometry revealed the material was composed of mostly yttrium and vanadium, with 2.2% neodymium by weight (0.03 per formula unit). Since Y3+ does not produce color on its own, the color must be derived from the addition of Nd3+ ions substituting for Y3+ ions in the crystal lattice. Figure 3 shows polarized absorption spectra in the visible range collected with an ultraviolet/visible/near-infrared spectrometer for both the ordinary ray (o-ray) and extraordinary ray (e-ray). The expected color was calculated from the absorption spectra based on the formula described by Z. Sun et al. (“Quantitative definition of strength of chromophores in gemstones and the impact on color change in pyralspite garnets,” Color Research and Application, Vol. 47, No. 5, 2022, pp. 1134–1154).

Figure 4. Color panels of the 10.59 mm wafer in six different lighting conditions were calculated for both the o-ray and e-ray. In the top row, A and D65 are CIE standard illuminants for incandescent light and daylight. Eiko is a fluorescent bulb with color temperature of 2800K, while F10 is a CIE standard narrowband fluorescent illuminant. Warm (2700K) and cool (6700K) LEDs represent the illuminants in the GIA standard viewing box.
As shown in figure 4, the material exhibited a general pink to purple to violet color in most illuminants except the Eiko warm fluorescent light and the o-ray of CIE standard illuminant F10, which represents a typical cool fluorescent light. In fact, the color-change behavior noticed by author AA could be replicated when comparing illuminant F10 to any of the other illuminants such as daylight or incandescent light. Switching between warm incandescent light and actual cool daylight did not produce a dramatic change of color. The emission spectrum of F10 fluorescent light is mainly composed of sharp peaks at 435, 545, and 610 nm (figure 3). Therefore, the color of the synthetic wakefieldite crystal under illuminant F10 is only determined by the small absorption features at ~435, 541, and 610 nm of the Nd3+ ions. Broadband emitters such as incandescent light and actual daylight (D65 in figure 3), on the other hand, do not have these sharp emission features, so the color was determined by the transmission windows in the spectrum (440–460, 490–500, 550–570, and 620–670 nm), which remain constant when switching between these illuminants. This was confirmed by observation of the stone in outdoor conditions, which produced the same pinkish purple color seen in incandescent light. The use of warm fluorescent light (Eiko fluorescent light in figures 3 and 4) with color temperature of 2800K also reproduced the greenish blue to blue color seen in cool fluorescent light (F10). It is also worth noting that the absorption features of Nd3+ ions at 541 and 610 nm were strongly dependent on the polarization of the light, resulting in a strong pleochroism (grayish purple for the o-ray and green-blue for the e-ray), only observed under F10 illuminant (figure 4).
The color panels under two LED illuminants in GIA’s standard viewing box were also calculated in figure 4. The two LED lights, warm and cool, closely imitate the CIE standard illuminants A and D65. The two sets of color panels (A = LED warm pair and D65 = LED cool pair) are extremely close to each other based on their L, C, and H (lightness, chroma, and hue) color coordinates. This study also illustrates the consistent results of GIA’s standard viewing box in grading gemstone color. @topic:1


Publish Year: 2023 Title: Arrow-Patterned Negative Crystals in Sapphire Abstract: Negative crystals arrayed in an arrow-like pattern. Photomicrograph by Suwasan Wongchacree; field of view 1.07 mm.
Negative crystals are a common inclusion in corundum and often rupture upon exposure to moderate heat treatment. The author recently analyzed a sapphire containing a series of negative crystals arranged in an arrow-like pattern (see above). Careful examination revealed a partially healed fissure intersecting one of the negative crystals, indicating the stone had been subjected to heat treatment.
Fortunately, this spectacular pattern of negative crystals endured the heat treatment process, decorating the internal micro-world of this sapphire. @topic:3


Publish Year: 2017 Title: Emerald with Mobile Inclusion Abstract: This 9.02 g rough emerald contains a prominent eye-visible mobile inclusion. Photo by Robison McMurtry.

Multiphase inclusions are key indicators when identifying emeralds and determining their origin. Gemologists look for the jagged three-phase inclusions in stones of Colombian origin or blocky two-phase inclusions in Brazilian or Zambian emerald. These multiphase inclusions typically require higher magnification and considerable maneuvering of the emerald to get a precise view.

Recently, the Carlsbad laboratory received a 9.02 g rough emerald from Lucas Fassari (Costa Mesa, California). The rough had an eye-visible mobile inclusion (see above) consisting of a CO2 gas bubble and salt crystals suspended in a fluid. The emerald was identified using a handheld spectroscope and optical properties. It was determined to be of Colombian origin by its jagged three-phase inclusions and crystals that had characteristics of pyrite and calcite. The mobile inclusion was quite large in relation to the rough emerald, which measured 28.76 × 14.82 × 12.83 mm, including its calcite and shale matrix. The CO2 bubble measured approximately 4 × 3 mm.

Mobile inclusions of this size are captivating to observe, and to see one in an emerald adds more allure to the piece. Cutting this specimen into a faceted gemstone would lose what makes this rough emerald unique. @topic:3


Publish Year: - Title: Ruby Description Abstract: Ruby and sapphire are varieties of the mineral corundum. - Courtesy Hamilton Jewelers

Ruby is one variety of the corundum mineral species, which also includes sapphire. Ruby is highly regarded and can command high per-carat prices. It is arguably one of the most important gems in the colored stone market.
In its purest form, the mineral corundum is colorless. Trace elements that become part of the mineral’s crystal structure cause variations in its color. Chromium is the trace element that causes ruby’s red, which ranges from an orangy red to a purplish red.

The strength of ruby’s red depends on how much chromium is present—the more chromium, the stronger the red color. Chromium can also cause fluorescence, which adds to the intensity of the red color.

The most renowned rubies, like those from Myanmar, the Himalayas, and northern Vietnam, typically form in marble. They’re found in layers that are distributed irregularly within the surrounding marble. Marble forms as part of the metamorphic (rock-altering) process, when heat and pressure from mountain formation act on existing limestone deposits.

Rubies found in marble deposits often have a vibrant red glow.
Marble has low iron content, so the rubies that originate in marble (called “marble-hosted” by gemologists) lack iron. Because of this, many have an intense red color.

In addition, rubies found in marble typically fluoresce red under ultraviolet light—even the ultraviolet light in sunlight. Fluorescence can make a ruby’s color even more intense and increase its value.

In other locations, rubies can be found in basalt rocks. Rubies from these sources can have higher iron content, which can make the rubies darker and less intense in color. Higher iron content in the chemical makeup of a ruby can also mask the red fluorescence, eliminating that extra glow of red color seen in marble-hosted rubies. @topic:3


Publish Year: 2017 Title: Sapphires from Northern Ethiopia Abstract: Figure 1. Rough sapphires from a new deposit near Chila, Ethiopia. Photo by Simon Bruce-Lockhart.

Since February 2017, rumors of a newly discovered sapphire deposit in northern Ethiopia have been circulating in the trade. In June, one of the authors (SB-L) visited the mining area, located in the country’s Tigray region. The city of Aksum (or Axum), about 35 km south of the Eritrean border, is used as a base for gem merchants. Mining and trading is concentrated around the town of Chila, about 25 km northwest of Aksum. Based on the literature, the alkali basalt field that produces the sapphire stretches into Eritrea, although no sapphires from that area have reached the market. Several sites are active, and about 5,000 miners were working the deposits. All of the deposits are secondary in nature and have yielded rounded crystals. The majority of the rough (figure 1) weighs 2–3 grams, but crystals over 50 g have been reported; the larger ones are usually cracked. Heat treatment experiments are being conducted in Chanthaburi (Thailand) and Beruwala (Sri Lanka) to see how the material reacts. It is estimated that 5–10% of the sapphires do not require heat treatment.

At the end of April, the first parcels started to arrive in Bangkok, and GIA was able to study selected samples donated by author SB-L. The color of the crystals ranged from dark to light blue, and many contained fine rutile particles. Some stones had a trapiche-like pattern. The stones occasionally exhibited a green or yellow color, sometimes combined with blue in bicolor sapphires. All of the sapphires studied by GIA showed strong blue-green pleochroism. The main inclusions were intersecting twinning planes (figure 2), along with crystals, fingerprints, tubules, and bands of rutile particles (figure 3).

Figure 2. An Ethiopian sapphire wafer with two polished windows perpendicular to the c-axis under crossed polarizers shows two sets of twinning planes. Photo by Victoria Raynaud; field of view 13.4 mm.

Figure 3. Left: An unidentified crystal surrounded by a fingerprint. Many particles and fine wispy fingerprints can be seen throughout the stone in darkfield lighting. Center: Intersection tubules associated with different types of fingerprints, shown here in fiber-optic lighting, were always found in the twinning planes of the Ethiopian sapphires. Right: Bands of particles seen with fiber-optic lighting. Photomicrographs by Victoria Raynaud; fields of view 1.20 mm (left), 3.60 mm (center), and 1.44 mm (right).
TKTrace-element analysis using laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) was performed on two samples. On each stone we measured 12 spots: six in a clean area and six in a particle-rich area. The clean areas from both stones showed very similar chemical composition, and the same was observed for the particle-rich areas. The compositional ranges of both stones, presented in table 1, clearly show that the chemical concentrations are different between the clean and particle- rich areas. None of the areas contained enough natural Be or Cr to detect with LA-ICP-MS. All samples showed a high Fe concentration. While Ti content was higher than Mg concentration in both areas, the particle-rich areas showed elevated levels of titanium (table 1). The UV-Vis-NIR spectrum shows a broadband around 860 nm, which is typical of basalt-related sapphires (figure 4).

TABLE 1. Chemical composition (ppma) of Ethiopiansapphire, obtained by LA-ICP-MSa.

24Mg
47Ti
51V
57Fe
69Ga

Clean area
8–9
10–12
0.7–1.0
1362–1450
58–66

Particle-rich area
11–14
15–43
0.6–0.8
1365–1588
57–64

aIn total, 12 spots in clean areas and 12 in particle-rich areas were analyzed. Be and Cr were both below detection limit (0.2 and 0.4 ppma, respectively).

Figure 4. UV-Vis-NIR spectrum of the o-ray of a greenish blue Ethiopian sapphire.
Optical path length 1.13 mm.
Starting in May, many Sri Lankan dealers have traveled to Ethiopia to buy this material, causing steep price increases in local gem markets. All of the mining around Chila is artisanal, but large volumes of sapphire have been mined in a short time span. Time, and the results of the heat treatments, will show the viability of this deposit.

View Gallery @topic:9


Publish Year: 2015 Title: New Production of Brazilian Emerald from Minas Gerais Abstract: Figure 1.  This exceptional 9.22 ct emerald is from Belmont’s underground mine. Photo by Robert Weldon/GIA; courtesy of the Belmont mine.

At the GJX show, Marcello Ribeiro (Belmont Mine, Itabira, Brazil) showed us production from Belmont’s underground mine, including one especially fine 9.22 ct stone (figure 1). As a GIA team visited Belmont in April 2014, it was interesting to see the gems from this relatively new part of the mining operation for sale at the show.

Originally the site of a cattle ranch, Belmont yielded its first emeralds in 1978 (H.A. Hänni et al., “The emeralds of the Belmont Mine, Minas Gerais, Brazil,” Journal of Gemmology, Vol. 20, Nos. 7–8, 1987, pp. 446–457). Since then, the mine has expanded to include both open-pit and underground operations with a highly sophisticated recovery plant. Mining is supported by a comprehensive geological survey program. To date, more than 15 km (9.3 miles) of 3.8 cm (1.5 inch) diameter cores have been drilled. Geological surveys indicated that a 300-meter-thick schist layer—with emerald potential—underlies much of the property, including the recovery plant. Core sampling defined the extent and depth of the emerald ore body and proved the viability of an underground mine at Belmont. Sampling the underlying rocks also helped plan the mine’s mechanical structure by showing which layers would be capable of supporting underground tunnels.

The underground mine is accessed via a 666-meter ramp that allows removal of up to 30 to 40 truckloads of ore per day using large commercial trucks (figure 2). At the time of our visit, approximately 10 to 15 truckloads per day (about 200 tonnes) were being taken to the recovery plant. The underground workings deliver a ratio of one tonne of ore to one tonne of waste. Each tonne of ore yields about two grams of rough emerald. On average, those two grams of rough produce two carats of faceted emeralds. By contrast, the ratio for the current open pit is only one tonne of ore per 11 tonnes mined. The rest is overburden or waste. There is clearly the capacity for many more years of productive mining at Belmont.

Figure 2. A full-size truck navigates the tunnels of Belmont’s underground mine. From the outset, the operators determined this would be a high-capacity, ramp-style mine. Photo by Duncan Pay/GIA; courtesy of the Belmont mine.
During the same April 2014 trip, GIA field gemologists visited the Montebello mine, near Nova Era. At this year’s GJX show, Sergio Martins (Stone World, São Paulo) showed us new production from that mine (figure 3). These gems were in the 2–4 ct range, bright with strong color and good luster.

Figure 3. This array of gems in the 2–4 ct range from the Montebello mine shows the bright, vivid appearance of high-quality emeralds from Nova Era. Photo by Robert Weldon/GIA; courtesy of the Montebello mine.
The Montebello mine is adjacent to the independent miners’ village of Capoeirana, about 6 km (3.7 miles) from Nova Era. Capoeirana is about 26.5 km (16.5 miles) east of Itabira. Unlike the larger mechanized operation at Belmont, the area around Capoeirana hosts a variety of small-scale mining activities by these independent miners, known as garimpeiros. The Montebello mine is perhaps the largest, employing 15 of them.

Emeralds were first discovered near here in 1988 (D. Epstein, “The Capoeirana emerald deposit near Nova Era, Minas Gerais, Brazil,” Fall 1989 G&G, pp. 150–158; www.gia.edu/gems-gemology/fall-1989-brazil-emeralds-epstein). The exploration that led to a mining boom in nearby Capoeirana was triggered by the discovery of emerald at Belmont. Production has dwindled in Nova Era, due in part to the 2008 global economic recession and the greater depths—often more than 100 meters—required to reach the emerald mineralization (A. Lucas, “Brazil’s emerald industry,” Spring 2012 G&G, pp. 73–77; www.gia.edu/gems-gemology/spring-2012-brazil-emerald-lucas). Emerald mineralization in the surrounding area appears to start in Nova Era and finish at the Belmont mine. Between them is another—currently unworked—mine, called Piteiras, which Martins used to operate. Mining stopped there due to ownership disputes that the parties hope will be resolved shortly.

At Montebello, the main elevator shaft descends 130 meters. At the time of GIA’s visit, miners had sunk a new vertical shaft about 40 meters below the level of the existing main shaft (figure 4). It follows a new vein that dips steeply underground. Neighbors in an adjacent mine have already found a productive vein at about that level. When the miners sunk their shaft, they located a seven-meter-thick seam of soft black schist underlain by granite. Emeralds occur in the boundary where the quartz meets the schist. The dark color of the schist and the presence of quartz are good indicators for emeralds and pale beryl crystals. From this new 40-meter shaft, they are driving a new horizontal tunnel out into the schist. The miners plan to expand the shaft and install a second elevator. The miners added that Montebello’s stones appear to increase in size and color with depth.

Figure 4. At Montebello, the miners have sunk a new shaft to follow a promising vein of emerald-bearing schist to deeper levels in the mine. The base of the new shaft is 170 meters below the surface. Photo by Andy Lucas/GIA; courtesy of the Montebello mine. @topic:9


Publish Year: 2018 Title: Unusual Orange Pyrope-Spessartine-Grossular Garnet Abstract: Figure 1. The unique composition of this 7.97 ct orange pear-shaped garnet was revealed as pyrope-spessartine-grossular. Photo by Robison McMurtry.

GIA’s New York laboratory recently examined an orange pear-shaped faceted stone (figure 1). Standard gemological testing revealed a refractive index of 1.771 and a hydrostatic specific gravity of 3.89. The fluorescence reaction was inert to long-wave and short-wave UV light. The stone did not show any pleochroism when viewed with a dichroscope. Using a handheld spectroscope, absorption bands located at 410 and 430 nm in the blue and violet sections were clearly observed. All of these gemological properties are consistent with pyrope-spessartine garnet based on the classification system from Stockton and Manson (“A proposed new classification for gem-quality garnets,” Winter 1985 G&G, pp. 205–218).

Besides standard gemological testing, all garnets submitted to GIA laboratories are routinely analyzed by energy-dispersive X-ray fluorescence (EDXRF) spectroscopy (see column 4 of the supplementary table below). EDXRF results showed that the stone was predominantly composed of 15.37 mol.% pyrope, 53.70 mol.% spessartine, and—surprisingly—25.39 mol.% grossular. Unlike normal pyrope-spessartine garnet submitted to GIA that contains a small amount of grossular (less than 10 mol.%), this garnet had a much higher grossular component that had never been reported before in gem-quality garnets, to our knowledge. (Note that “malaia/malaya” is a trade name for yellowish, reddish, or pinkish orange pyrope-spessartine garnets that can potentially contain 2–94% spessartine, 0–83% pyrope, 2–78% almandine, 0–24% grossular, and 0–4% andradite. The garnet we examined falls into this concentration range.)

To validate the accuracy of the chemistry, we performed laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) analysis using a Thermo Fisher iCAP Qc ICP-MS coupled with a New Wave Research UP-213 laser ablation unit to obtain an additional set of chemical composition. USGS glass standard GSD-1G and GSE-1G were used as external standards. 29Si was used as internal standard. The LA-ICP-MS results showed good agreement with the EDXRF results (see columns 1–3 of the supplementary table above).

Figure 2. (Pyrope + grossular)-spessartine-almandine ternary diagram with data points based on molecular percentages for pyralspite garnet (modified after Stockton and Manson, 1985). The orange spot is the average of three sets of LA-ICP-MS data (table 1, columns 1-3). Refractive index and spectral boundaries are used to distinguish among the six proposed garnet species labeled in the diagram.
Garnets are a group of isometric nesosilicates with the general chemical formula X3Y2Z3O12. Natural rock-forming silicate garnets are commonly divided into the pyralspite (pyrope, almandine, and spessartine) and ugrandite (uvarovite, grossular, and andradite) groups. In pyralspite, Al3+ occupies the Y-site and the X-site may contain Mg2+, Fe2+, or Mn2+; these garnets are composed predominantly of pyrope (Mg3Al2Si3O12), almandine (Fe2+3Al2Si3O12), and spessartine (Mn3Al2Si3O12) end members. Stockton and Manson (1985) presented a ternary plot (figure 2) to gemologically classify the pyralspite garnet species, and this showed the correlation among refractive index, visible spectroscopic observation, and chemistry. They determined that pyrope-spessartine should have a refractive index between 1.740 and 1.780 along with clear 410 and 430 nm absorption bands. We concluded that the orange pear-shaped garnet should be classified gemologically as pyrope-spessartine garnet.

To understand why this garnet with a high grossular component still shows the same gemological properties of normal pyrope-spessartine, we plotted the orange garnet chemistry in this ternary plot by combining pyrope with a grossular component. The orange spot representing the orange garnet appeared in the pyrope-spessartine region, because the refractive index of pure pyrope (1.714) is close to and functions almost the same as the RI of pure grossular (1.734) in contributing to the combined refractive index. Since there is not a specific gemological species name for this orange garnet with higher grossular than pyrope component, the authors suggest that the stone be called pyrope-spessartine-grossular. This case demonstrates that sophisticated chemical analysis of garnet should be practiced routinely in gemological laboratories to make sure unique garnets are not misidentified. @topic:1


Publish Year: 2014 Title: Challenges in Orienting Alexandrite: The Usambara and Other Optical Effects in Synthetic HOC-Grown Russian Alexandrite Abstract: K. Schmetzer, H.-J. Bernhardt, W. A. Balmer, and T. Hainschwang. “Synthetic alexandrites grown by the HOC method in Russia: Internal features related to the growth technique and colorimetric investigation,” Journal of Gemmology, Vol. 33, No. 5–6, 2013, pp. 113–129. Photo courtesy of Karl Schmetzer.

Dr. Schmetzer and his coauthors contribute another gemological description of a unique source of synthetic alexandrite, the chromium-bearing variety of chrysoberyl. These crystals, grown in Russia since the late 1980s and similar in color to natural alexandrites from the Hematita deposit in Minas Gerais, Brazil, were formed using a direct melt gradient technique. This alexandrite crystal growth process, developed by Dr. Vladimir Gurov, uses the horizontally oriented crystallization (HOC) method. The crystals have all been grown along the b-axis in molybdenum crucibles that contain both the melt and the solidified portion.

These crystals, which range up to 450 g, are used both for laser applications and gem-quality synthetics. Since 1994, they have been produced for the gem market in a joint venture with the Tairus company in Novosibirsk. Among their distinguishing inclusions are curved growth striae (similar to Czochralski-grown material and sometimes accompanied by bubbles), elongated and irregularly shaped flat cavities (figure 1), some rare occurrences of tiny birefringent crystals, and the occasional appearance of irregularly oriented fibers and fissures. Of note is the very uniform distribution of the chromophores Cr3+ and V3+ within the material. The amount of Fe3+ found in this material is extremely low.

Figure 1. The illustration demonstrates the three optical effects studied in the article: Pleochroism, the alexandrite effect, and the Usambara effect. Represented are two oriented cubes of HOC synthetic alexandrite with edge lengths of 3mm and 8mm viewed in unpolarized daylight and incandescent light down the a-, b- and c-axes. With identical lighting and edge length, pleochroism is clearly seen. The alexandrite effect is illustrated by comparing same size cubes along the same axis but under different lighting. Comparing the two different cubes under the same lighting and orientation, the Usambara effect is observed. Photos and artwork by Karl Schmetzer.
Of particular interest in this latest study of synthetic alexandrite, made possible by rare access to uniformly doped material, was the investigation of color related to various optical effects: the alexandrite effect (color change between daylight and incandescent light), the Usambara effect (variable coloration according to the path length of light), and pleochroism (coloration in views parallel to the three crystallographic axes). To accomplish this, the authors used a series of crystallographically oriented cubes with edges ranging from 2 to 10 mm. A particularly notable finding is that, similar to chromium-containing tourmaline, larger crystals display more redness (and less greenness) in all three directions of view. The Usambara effect, the variation of color with material thickness (assuming uniform lighting conditions), was first reported in 1997 (A. Halvorsen and B.B. Jensen, “A new colour-change effect,” Journal of Gemmology, Vol. 25, No. 5, pp. 325–330) and further described by Kurt Nassau in 2001 (The Physics and Chemistry of Color: The Fifteen Causes of Color, 2nd ed., Wiley, New York, pp. 94–96). Essentially, a material can have a variable transmittance in different areas, depending on the thickness of the material.

Additional color variations are described for the individual crystal orientations between daylight and incandescent light (figure 2). The subsequent discussion shows why it is difficult to ideally orient the table facet of an alexandrite with variable chromium concentrations and thicknesses. Also, there truly is no single orientation that maximizes the purest green and displays the most dramatic color change from daylight to incandescent light. This presents a formidable challenge to the gem cutter. Further research to investigate the impact of chromophore concentration (particularly Cr3+) on alexandrite’s color properties would be useful in fully describing this unique gem’s unusual range of appearances. @topic:3


Publish Year: 2018 Title: Lepidocrocite in Boulder Opal Abstract: Figure 1. This boulder opal contains a layer of needle-like lepidocrocite inclusions along the interface between the opal and the ironstone matrix. Photomicrograph by Nathan Renfro; field of view 0.96 mm.

The term “boulder opal” is used to describe gem-quality opal that fills in the pore spaces and cracks of its ironstone host. When cut, some of that ironstone matrix is included in the finished stone, often to add structural support to delicately thin veins of opal (R.W. Wise, “Queensland boulder opal,” Spring 1993 G&G, pp. 4–15). The authors recently examined a boulder opal, presumed to be from Australia, that showcased some interesting inclusions along the interface between the opal and ironstone matrix. Microscopic observation revealed a carpet of minute needle-like inclusions radiating outward from the ironstone into the surface opal layer (see above). Where some of the inclusions broke the surface, they showed a submetallic luster in reflected light. In order to identify these unusual inclusions, we used Raman spectroscopy to analyze some of the surface-reaching needles. Raman spectroscopy and comparison with the reference spectra from the RRUFF mineral database showed that these inclusions were the iron hydroxide mineral lepidocrocite. Energy-dispersive X-ray fluorescence (EDXRF) testing revealed only the presence of iron, which was consistent with the Raman results. This is the first time the authors have encountered a lepidocrocite inclusion in boulder opal. @topic:13


Publish Year: 2021 Title: Cat’s-Eye Opal Abstract: Figure 1. This 3.79 ct gray transparent opal shows dominant blue play-of-color with a distinct chatoyancy. Photo by Shunsuke Nagai.

Precious opal characteristically shows a spectacular play-of-color effect and may also display cat’s-eye or star phenomena produced by the internal structure (e.g., Winter 1990 Gem News, p. 304; Spring 2003 Lab Notes, pp. 43–44; Summer 2014 Lab Notes, pp. 152–153). Chatoyancy and asterism in opal are quite rare, however, because opal is a hydrated silica and has no repeating crystal lattice (J.V. Sanders, “The structure of star opals,” Acta Crystallographica, Vol. A32, 1976, pp. 334–338). The keys to creating and maximizing chatoyancy in opal is careful arrangement of the play-of-color patches, orienting the “brushstrokes” (stripe structure caused by misalignment of the tiny silica spheres producing play-of-color), and good cutting.
Recently, GIA’s Tokyo laboratory had an opportunity to examine a transparent double cabochon measuring 12.65 × 10.06 × 5.70 mm and weighing 3.79 ct. It showed blue to green play-of-color against a gray background as well as a distinct chatoyancy (figure 1). Standard gemological testing gave a specific gravity of 2.13 and a spot RI reading at 1.45, suggesting that the stone was opal. The brushstroke pattern within play-of-color patches and the strong bluish white fluorescence and phosphorescence after exposure to ultraviolet light were consistent with a natural origin. Advanced testing using Fourier-transform infrared spectroscopy (FTIR) also indicated that this was natural opal with no evidence of polymer impregnation and/or sugar treatment (G. Brown, “Treated Andamooka matrix opal,” Summer 1991 G&G, pp. 100–106). This opal had no synthetic features such as “snake skin” and “columnar structure” in any direction. There was no evidence that this stone was assembled.

Figure 2. Chatoyant effect caused by light reflecting off parallel brushstroke patterns within play-of-color patches. A: This opal contained several large play-of-color patches with parallel brushstrokes. B: A close-up of the brushstroke pattern seen in the white square in (A). Field of view 13.3 mm (A) and 5.60 mm (B). Photos by Makoto Miura.
In microscopic observation, this opal contained several large blue to green play-of-color patches with parallel brushstroke patterns. The brushstrokes in each patch were mostly perpendicular to the length of the stone and parallel to each other, and the light reflection from the pattern created a distinct chatoyant effect (figure 2). Because the opal was composed of large blue dominant play-of-color patches, the parallel brushstrokes and the high-dome cabochon shape produced a distinct chatoyancy against the gray background. This was a striking example of cat’s-eye precious opal. @topic:13


Publish Year: 2017 Title: Pink Sapphire Filled with Bismuth-Based Glass Abstract: Figure 1. This 2.77 ct light pink sapphire cabochon was treated with a bismuth-based glass filling. Photo by Nuttapol Kitdee.

	Recently, GIA’s Bangkok laboratory received a 2.77 ct light pink sapphire (figure 1) for an identification report. The sample was a semi-transparent cabochon with natural inclusion features: silk needles and particles, twinned planes, and thin films. Also observed throughout the stone were numerous gas bubbles of various shapes and sizes that were trapped along surface-reaching fractures and cavities (figure 2). These indicate the presence of glass filling. However, no flash effect was evident in the filled fractures. The stone’s refractive index of 1.76 and UV fluorescence reaction (medium red to long-wave and weak red to short-wave) were consistent with corundum. Its specific gravity of 3.87 was lower than that of corundum and possibly a result of the filler. Due to the sapphire’s very light color, its visible-range absorption spectrum was difficult to observe.

	Figure 2. With the aid of fiber-optic illumination, magnification revealed these trapped gas bubbles of various shapes and sizes in the light pink sapphire. Photo by Charuwan Khowpong; field of view 2.00 mm.

	Qualitative chemical analysis using energy-dispersive X-ray fluorescence (EDXRF) spectroscopy showed the presence of bismuth in addition to the expected Al, Cr, Fe, and Ga. No lead was detected in the sample, even with the aid of the thick palladium filter. The chemical composition of the filler indicated that the stone had undergone fracture filling using bismuth-based glass (“Ruby treatments – revisited, with Mozambique’s perspective,” Lab Information Circular, Gem Testing Laboratory, Vol. 63, December 2011). Due to the large difference in refractive indices between the bismuth-based glass filled area and the surrounding corundum, this treatment was easier to visually detect than lead-glass filling (figure 3).

	Figure 3. Under reflected illumination, the pink sapphire’s large cavity filling was readily visible with the unaided eye. Photo by Charuwan Khowpong; field of view 2.70 mm.

	Fracture filling with lead glass and non-lead glass has been widely used in low-grade ruby (S.F. McClure et al., “Identification and durability of lead glass–filled rubies,” Spring 2006 G&G, pp. 22–34). Pink sapphires such as this 2.77 ct stone are less commonly encountered in the laboratory for examination and identification. @topic:3


Publish Year: 2024 Title: An Exceptional Cat’s-Eye Emerald Abstract: Double cabochon cat’s-eye emerald weighing 5.11 ct and measuring 10.77 × 8.95 × 7.39 mm, from Goiás State, Brazil. Photo by Robert Weldon; courtesy of Douglas M. Liebman Estate Jeweler.
Those in the gem trade often recall a memorable experience, gemstone, or business connection. A Brazilian cat’s-eye emerald (see above) presented at the AGTA show by estate dealer Doug Liebman (Scottsdale, Arizona) conjured all three.
Liebman shared the story of how in 1983, early in his career, he forged a long-term relationship with Albert Sabbagh, cofounder of Ben Sabbagh Bros. in Brazil. Liebman’s early buying trips to Brazil revealed a wide variety of gemstone offers at all price points, including the magnificent cat’s-eye emerald.
Emeralds have been mined sporadically and in small quantities in the Brazilian state of Goiás for more than 100 years. In 1981, the deposits were found to produce emerald of a desirable quality. This prompted more steady mining, which has been continuous ever since. The emeralds occur in a talc schist as stubby crystals usually less than 1 cm long. Their color ranges from pale to dark green, often with a bluish overtone. The best faceted stones are rarely over one carat.
Last year, at GJX 2023, Liebman visited the Ben Sabbagh Bros. booth and spoke with Albert’s sons Samuel and Clement. They showed him a cat’s-eye emerald from Goiás that had been part of their late father’s private collection. Liebman recalled the emerald from his early days with Sabbagh. While impressed by the stone, he left the booth without buying.
After some reflection, Liebman returned to GJX first thing the next morning. He said yes to the emerald before they even told him the price.
The 5.11 ct cat’s-eye emerald is extraordinary for its color, clarity, legacy, and allure, with no additional light source needed to display the centerline cat’s-eye effect. What goes around often does come back around, at the right time, in the right place: Tucson, Arizona. @topic:3


Publish Year: 2022 Title: Unusual “Horsetail” and Columnar Inclusions in Demantoid Abstract: Figure 1. Fibers of serpentine were observed throughout this demantoid garnet in an unusual randomly curved pattern. Photomicrograph by Shunsuke Nagai; field of view 2.00 mm.
Demantoid, a gem variety of andradite garnet, sometimes contains “horsetail” inclusions, a type of fibrous inclusion commonly seen in demantoid from Russia (e.g., W.R. Phillips and A.S. Talantsev, “Russian demantoid, czar of the garnet family,” Summer 1996 G&G, pp. 100–111). Recent studies have shown that these horsetail inclusions from Russian demantoid are in fact hollow tubes partially filled with serpentine (e.g., A.Y. Kissin et al., “‘Horsetail’ inclusions in the Ural demantoids: Growth formations,” Minerals, Vol. 11, No. 8, 2021, article no. 825).
Recently, the authors had an opportunity to examine a unique yellowish green demantoid weighing 0.73 ct. Horsetail inclusions often occur in a radial form, but these were quite unusual, showing random spiral- or coil-like structures throughout the stone (figure 1). Raman spectroscopic analysis identified these inclusions as serpentine. While their formation remains an open question, horsetail inclusions may suggest complicated geological conditions such as decompression (again, see Kissin et al., 2021).

Figure 2. Columnar two-phase negative crystals containing mobile gas bubbles were another unique feature seen in the demantoid garnet. Photomicrographs by Makoto Miura; field of view 1.06 mm.
Also of interest in this stone were two-phase columnar negative crystals containing mobile gas bubbles (figure 2). Based on analysis of the OH stretching region of Raman spectra (e.g., M.C. Caumon et al., “Fused-silica capillary capsules (FSCCs) as reference synthetic aqueous fluid inclusions to determine chlorinity by Raman spectroscopy,” European Journal of Mineralogy, Vol. 25, No. 5, 2013, pp. 755–763; Winter 2015 Gem News International, pp. 446–448), these inclusions were determined to be mainly composed of saline solutions, possibly a mix of water and small amounts of sodium chloride, although the composition of the gas phase was not detected.
Fluid inclusions in demantoid garnet have previously been reported (again, see Winter 2015 GNI, pp. 446–448). However, the columnar shape of the two-phase inclusions seen here is quite unusual considering the cubic crystal system of the host andradite garnet. These two-phase inclusions could be related to the formation of hollow canals within the host demantoid in the presence of water, although we are not yet able to determine how these negative crystals formed in this peculiar shape. @topic:1


Publish Year: 2022 Title: A “Cobalt Blue” Gahnospinel Abstract: Figure 1. This 1.01 ct gahnospinel had an intense “cobalt blue” color. Photo by Lhapsin Nillapat.
GIA’s Bangkok laboratory recently examined an intense blue 1.01 ct transparent oval mixed cut (figure 1). Standard gemological testing revealed a refractive index of 1.742 and a hydrostatic specific gravity of 3.96. The stone was inert to long-wave and short-wave UV light. Microscopic observation revealed dense intersecting needles, iridescent thin films, particulate clouds, and flaky whitish inclusions. Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) was used to obtain oxide weight percentages (wt.% oxides) of aluminum, iron, magnesium, and zinc to calculate the chemical formula of the stone. It was determined to be (Mg0.64Fe2+0.02Zn0.34)Al2O4. All of these properties were consistent with gahnospinel, which is a zinc-rich variety of the spinel group. Its chemical properties result from zinc substituting for magnesium in a solid solution series with end members gahnite (ZnAl2O4) and spinel (MgAl2O4).

Figure 2. The UV-Vis spectrum of the gahnospinel showed a series of absorption bands at approximately 550, 593, and 622 due largely to Co2+ with additional minor contributions from Fe2+ and Fe3+ absorption bands at approximately 456, 550, and 593 nm.
Interestingly, gahnospinel is usually found with a more muted dark blue to dark greenish blue color, but this intense blue specimen contained cobalt as the primary coloring agent, similar to “cobalt blue” gem spinel. Ultraviolet/visible (UV-Vis) spectroscopy showed significant amounts of absorption attributable to cobalt at approximately 550, 593, and 622 nm (figure 2), with additional contribution from iron at approximately 456, 550, and 593 nm (G.B. Andreozzi et al., “Color mechanism in spinel: A multi-analytical investigation of natural crystals with a wide range of coloration,” Physics and Chemistry of Minerals, Vol. 46, 2019, pp. 343–360; V. D’Ippolito et al., “Color mechanism in spinel: Cobalt and iron interplay for the blue color,” Physics and Chemistry of Minerals, Vol. 42, 2015, pp. 431–439). The significant amount of cobalt (198–224 ppmw) from LA-ICP-MS data and the reddish Chelsea filter reaction provided strong evidence that the intense blue color was induced by cobalt. While blue cobalt spinel and gahnite have been previously reported (see J.E. Shigley and C.M. Stockton, “‘Cobalt-blue’ gem spinels,” Spring 1984 G&G, pp. 34–41; T. Stephan et al., “On the colour mechanism of blue gahnite from Nigeria,” Journal of Gems & Gemmology, Vol. 38, No. 2, 2022, pp. 183–193), to our knowledge this is the first report of blue gahnospinel predominantly colored by cobalt. @topic:3


Publish Year: 2014 Title: Using Conventional Equipment to Separate Natural from Synthetic Ametrine Abstract: Payette F. “A simple approach to separate natural from synthetic ametrine,” The Australian Gemmologist, Vol. 25, No. 4, 2013, pp. 132–141. Photo courtesy of Francine Payette.

              Ametrine is a bicolored quartz variety that contains both amethyst and citrine zones in the same crystal. The only significant source of natural ametrine is eastern Bolivia’s Anahi mine, where it occurs in veins in a dolomitic limestone. The amethyst-citrine bicoloration results from quartz precipitation at very specific geochemical conditions, temperatures, and growth rates. The color of iron-bearing quartz depends on the valence state of the iron. The citrine color in Bolivian ametrine appears to come from the incorporation of very small aggregates of Fe3+. The amethyst color develops in two steps. First, individual Fe3+ ions replace Si4+ ions in the quartz structure. To develop the amethyst color, the crystal must be exposed to ionizing radiation to oxidize the iron in the 4+ state.

Beginning in 1994, Russian gem-quality synthetic ametrine entered the market. Synthetic ametrine can be identified by employing a combination of techniques, such as visible inspection of twinning and color zoning, EDXRF chemical analysis, and IR spectra. In this article, Payette explains the possibilities for separating natural from synthetic ametrine with conventional gem lab equipment.

Quartz is a uniaxial mineral with two unique refractive indeces along its three crystallographic axes. The unique axis is the optic axis. The amethyst-citrine color boundary in natural ametrine is oriented roughly parallel to the optic axis; in synthetic stones, the boundary is oriented at an oblique angle to the optic axis. The gemologist needs only to find the direction of the optic axis to determine whether an ametrine is natural or synthetic. The optic axis in a uniaxial gemstone can be found with a polariscope that has a conoscope lens and, on occasion, with a refractometer.

The conoscope is a polariscope accessory tool. It is a strongly converging, strain-free glass sphere. When a gemstone is positioned between two crossed polarizers, interference colors that are centered in the specimen will be witnessed with the conoscope when the optic axis is exactly perpendicular to the polarizers.

	Polariscope with a conoscope lens. The optic axis perpendicular to the polarizers.  Illustration courtesy of Francine Payette.
In this study, three types of natural and two types of synthetic ametrine were identified using a polariscope with a conoscope lens. Of the three natural stones, one was cut with its table perpendicular to the optic axis, one with its table parallel to the optic axis, and one with its table randomly oriented relative to the optic axis. One synthetic specimen was cut with its table parallel to the optic axis and the other with its table randomly oriented relative to the optic axis.

When a facet perpendicular to the optic axis of a uniaxial gemstone is measured with the refractometer, two constant readings will be observed while rotating the gem. If the facet measured is cut parallel to the optic axis, then the variable shadow will touch the constant shadow at one position during the rotation of the gem. This information enabled the identification of two of the natural samples and one of the synthetic ametrine samples with the refractometer alone. The direction of the optic axis could not be obtained by refractometer readings for the natural and synthetic ametrine samples cut with their table at random orientation to the optic axis, as those readings were not conclusive.

Separating synthetic ametrine from its natural counterpart using conventional gem lab equipment is possible, provided that the gemologist has a good understanding of the morphology and optical mineralogy of both natural and synthetic material. @topic:1


Publish Year: 2019 Title: A Special Type of Trapiche Quartz Abstract: Figure 1. This 22.18 g hexagonal quartz piece was unusual for its texture under transmitted light. Small crystals are seen on the side. Photo by Xiaodi Wang.

Recently, the National Gem and Gold-Silver Jewelry Testing Center at Zhengzhou examined a light yellow hexagonal piece of quartz (figure 1) weighing 22.18 g and measuring approximately 42.4 × 34.5 × 10.3 mm, which the buyer said was purchased from the Inner Mongolia autonomous region of northern China. Standard gemological testing gave a spot refractive index of 1.54 and a hydrostatic specific gravity of approximately 2.65. The sample was inert to both long-wave and short-wave UV.
This special sample was made up of three incomplete trapiche quartz. All growth reached prism faces in both of the tabular crystals, as well as those faces on the secondary growth crystals. The sample exhibited the tabular prismatic habit characteristic of the species, but with six-spoke trapiche structure that was clearly visible in both reflected and transmitted light.
The infrared reflectance spectra (figure 2) of the translucent star lines and other areas both indicated quartz, with characteristic peaks at 1197, 1100, 799, 693, 551, and 482 cm–1. Raman spectra of the star lines and other areas (e.g., figure 3) were obtained using 785 and 532 nm laser excitation, respectively. Peaks at about 466, 205, 353, and 396 cm–1 further confirmed quartz. This phenomenon may be caused by different growth rates and growth conditions. The origin of the special structure observed here is uncertain, but it is strong evidence of nature’s ability to produce rarities.

Figure 2. Major mineral composition at the star lines (a) and the area between the star lines (b) was quartz, with characteristic peaks at 1197, 1100, 799, 693, 551, and 482 cm–1. The spectra are offset for clarity.

Figure 3. The sample’s Raman spectrum further confirmed quartz, with characteristic peaks at 466, 205, 353, and 396 cm–1. @topic:3


Publish Year: 2015 Title: A New Natural-Color Bluish Green Chalcedony Abstract: Figure 1. This bluish green chalcedony, colored by chromium and nickel, is marketed under the trade name “Aquaprase.” Photo by Kevin Schumacher.

A new type of chalcedony (figure 1) was recently submitted to GIA’s Carlsbad laboratory by Yianni Melas of Greece. According to Melas, this material originated in Africa (figure 2), although a more precise location has not been made available. The translucent material displayed a vibrant bluish green color and is currently marketed under the trade name “Aquaprase.” Although chalcedony varieties such as chrysoprase and Gem Silica are well known and occur in yellowish green and greenish blue colors, the color of this material was distinctly different from any African chalcedony examined by GIA to date.

Figure 2. A large piece of chalcedony rough recovered from the mining area. Photo by Yianni Melas.
From a gemological perspective, it was important to conclusively determine that this material was naturally colored and not artificially dyed. Since the quartz crystals present in this material were colorless rather than brown, we ruled irradiation out as a possible treatment. Microscopic examination of rough and cut stones in conjunction with chemical analysis and visible spectroscopy were used to characterize this chalcedony. Standard gemological testing revealed an RI range from 1.531 to 1.539, with no observable birefringence. The SG, measured hydrostatically, ranged from 2.55 to 2.57. A handheld spectroscope revealed faint, narrow lines in the red end of the spectrum, rather than the broadband absorption one would expect if the material had been dyed with an organic pigment. All of these features were consistent with natural-color chalcedony.

Microscopic examination revealed a granular aggregate structure with a few areas showing subtle banding and faint green concentrations of color between some of the coarser quartz grains, which appeared to be a greenish mineral phase located along the grain boundaries. A waxy luster was observed on fractured areas, consistent with an aggregate material. Some areas contained small cavities that were filled with colorless drusy quartz crystals (figure 3, left and center). Dark brown and black inclusions of various metal oxides were also observed scattered throughout most of the samples examined, along with some areas of whitish cloudy inclusions that were not identified (figure 3, right).

Figure 3. The Aquaprase samples contained minute pockets of colorless drusy quartz (left and center) and irregular brown and black metal oxide inclusions (right). Photomicrographs by Nathan Renfro; field of view 2.83 mm (left), 4.76 mm (center), and 4.62 mm (right).
Raman analysis confirmed the material was quartz. EDXRF was used to analyze the trace-element metals that might be responsible for the bluish green color. All seven finished gemstones tested showed the presence of chromium and nickel. Interestingly, iron, vanadium, and copper were also detected in one of the cut samples, but these elements might not be related to the color, as other bluish green samples did not contain them. Visible spectroscopy (figure 4) revealed broad absorption bands centered at approximately 420 and 600 nm, with a large transmission window at approximately 500 nm producing the bluish green color. Sharp absorption peaks at 646, 676, and 679 nm were presumably related to chromium (http://www.gia.edu/gia-news-research-nr7809).

Figure 4. The visible spectrum for the Aquaprase (bluish green trace) showed two broad
absorption bands at 420 and 600 nm in addition to sharper peaks at 646, 676, and
679 nm. This absorption pattern is clearly different from that of chrysoprase (yellowish
green trace) and Gem Silica (greenish blue trace).
This new type of African chalcedony is easily recognized by its unique composition and absorption spectrum, which is significantly different from the chrysoprase and Gem Silica varieties. The attractive bluish green color of Aquaprase, which may be caused by chromium and nickel, should prove to be a popular and welcome addition to the gem trade. @topic:1


Publish Year: 2016 Title: Red Cordierite from Madagascar Abstract: Figure 1. These three gems, weighing (from left) 4.17, 1.28, and 1.28 ct, were fashioned from the same piece of cordierite rough; red is a new color for this gem. The specimen originated from a recently explored deposit in southeast Madagascar. Photo by Benjamin Rondeau.

	At the Mineral Expo show in Paris in early December 2015, we procured a large piece of dark red cobbed rough presented as cordierite. This would be the first documented occurrence of red cordierite. The slightly fractured 3 cm rough offered a magnificent deep red color when examined using transmitted light from a Maglite illuminator. The identity of the rough as cordierite was confirmed using Fourier-transform Raman (FTR) spectrometry. The spectrum obtained showed excellent agreement with a reference spectrum for cordierite from Madagascar in the RRUFF database (http://rruff.info).

	Author TP confirmed that the piece we examined was from the Iakora district, Fianarantsoa province, in southeast Madagascar. Cordierite has long been known in this general area (A. Lacroix, Minéralogie de Madagascar, A. Challamel, Paris, 1922). There is no mechanized mining. According to a miner’s sketch obtained locally by one of the authors, red cordierite occurs in a “vein” (probably a layer) associated with orange and blue cordierite, parallel to other layers containing kornerupine or blue spinel. The cordierite vein is about 1.50 m thick and wide and is apparently contained in a kornerupine layer. Cordierite is usually found in a metamorphic environment, but the layered appearance, with each band containing specific minerals in thicknesses of about 1 m, is reminiscent of metasomatic deposits. The association of cordierite with kornerupine and spinel is already known; blue gem-quality cordierite is found in such a metasomatic reaction zone in Kenya (C. Simonet, pers. comm., 2015).

	To determine the material’s gemological properties, three stones were fashioned by Jacques Le Quéré (Auray, France): a 2.69 ct modified rectangle; a 1.28 ct flat cabochon, cut to obtain a lighter color; and a 4.17 ct parallelepiped, faceted based on the optical directions to best show its trichroism (figure 1). The RIs, measured with a Rayner LED sodium-equivalent lamp, ranged from 1.527 to 1.541 (nx = 1.528–1.530, ny = 1.532–1.533, and nz = 1.538–1.540). Interestingly, this crystal presented a biaxial positive character, whereas gem cordierite is typically biaxial negative.

	The trichroism was very strong, as expected with cordierite. With a standard dichroscope, the colors ranged from deep red to orange to grayish brown with a hint of blue or purple (figure 2), this last color becoming black at a thickness of about 1 cm (figure 3). Hydrostatic SG measured 2.548–2.554. These properties are consistent with cordierite, though SG was at the lower end of the range.

Figure 2. Pleochroism of the oval cabochon observed in polarized light in the two orthogonal directions. On this thinner sample (about 3 mm thick), the desaturated grayish brown color with a hint of blue or purple is best observed. The stone measures 9.85 × 6.75 mm. Photos by Emmanuel Fritsch.

Figure 3. Trichroism of the 9.45 × 6.95 × 5.28 mm cordierite parallelepiped observed in polarized light in the three orthogonal directions to represent the three “extreme” colors of the material’s pleochroism: deep red, black (both seen with a thickness of 9.45 mm), and orange (seen with a thickness of 6.95 mm). Photos by Emmanuel Fritsch.

	As the rough was sawed, we noticed that the vivid red transparent color of the thick crystal turned to orange with reduced thickness. This is the definition of dichromatism, also known in gemology as the Usambara effect, a variation of hue that is affected by the optical path length.

	The UV-visible absorption spectrum was measured on a Unicam UV4. When the material was a few millimeters to a centimeter thick, in the direction where red is observed there is an extremely strong absorption in the violet and blue areas; this band leads to the red color. The absorption decreases abruptly from about 550 to 685 nm, with only a weak broad band from about 710 to 800 nm. This leaves a steep transmission window in the red, which is consistent with the color observed. The shape of the absorption and a rapid decrease in the orange-yellow also explains the Usambara effect. Through a few millimeters, the perceived color is orange; through a centimeter or more, it is deep red. @topic:1


Publish Year: 2022 Title: Rare Blue Apatite Inclusion in Smoky Quartz Abstract: Figure 1. A hexagonal apatite inclusion in smoky quartz. Photomicrograph by Nattapat Karava; field of view 6.3 mm.
A natural smoky quartz with an obvious mineral inclusion at the center of the stone (figure 1) was recently observed by the author. Raman analysis confirmed that this mineral was apatite. The apatite had very light blue color and a hexagonal twinned morphology. Under cross-polarized light, the inclusion showed interference colors, confirming its doubly refractive nature (figure 2).

Figure 2. A hexagonal apatite inclusion with interference colors in smoky quartz, viewed in cross-polarized illumination. Photomicrograph by Nattapat Karava; field of view 6.3 mm.
Apatite is a phosphate mineral with the chemical formula of Ca5(PO4)3(Cl/F/OH). Generally, smoky quartz and apatite can occur under the same geologic conditions, including pegmatitic hydrothermal environments. Apatite is commonly a protogenetic inclusion, but it can occasionally result from a later stage and be considered a syngenetic inclusion in quartz. The rounded shape of this apatite example suggests a protogenetic inclusion, one that would be a welcome sight for any gemologist examining stones in a microscope. @topic:1


Publish Year: 2023 Title: Rare Faceted Brucite Abstract: A rare and very fragile 3.09 ct brucite. Photo by Annie Haynes.
Gem-quality transparent blue brucite is a very rare, very soft and heat-sensitive magnesium hydroxide (Mg(OH)2) with a Mohs hardness of approximately 2.5–3.0 and perfect cleavage. Brucite was named in 1824 in honor of the first person to describe the species: Archibald Bruce, an American mineralogist, physician, and editor of the American Mineralogical Journal.
Recently the Carlsbad laboratory received for identification services a transparent greenish blue stone weighing 3.09 ct and measuring 9.74 × 9.71 × 5.98 mm (see above). Microscopic observation revealed numerous scratches and abrasions on the surface, as well as strong doubling, some needles, and a large fracture. Standard gemological testing yielded a specific gravity of 2.37. Refractive index was not measured for fear of damaging this soft and fragile stone. A uniaxial optic character was observed with a polariscope and optic figure sphere. Raman spectroscopy confirmed the gem’s identity as brucite. Worldwide, this was the second brucite examined by GIA. @topic:1


Publish Year: 2023 Title: Star Aquamarine Abstract: Figure 1. A 13.37 ct grayish blue aquamarine displaying asterism. Photo by Towfiq Ahmed.
The Carlsbad laboratory recently received a grayish blue aquamarine for an identification report. The unique 13.37 ct oval double cabochon displayed a six-rayed star (figure 1). Standard gemological testing revealed a spot refractive index of 1.570 and a hydrostatic specific gravity of 2.68. Raman analysis confirmed that the stone was beryl.

Figure 2. Negative crystals, film-like inclusions, and ilmenite were observed under magnification in the star aquamarine. Photomicrograph by Jessa Rizzo; field of view 3.57 mm.
Under magnification (figure 2), the stone displayed planes of negative crystals, film-like inclusions, ilmenite, and reflective particles that resulted in a six-rayed star. Asterism in aquamarine is due to three sets of elongated channel-like or thin-film inclusions oriented in three different directions perpendicular to the c-axis (e.g., Spring 2004 Gem News International, p. 104; K. Schmetzer et al., “Asterism in beryl, aquamarine, and emerald—an update,” Journal of Gemmology, Vol. 29, No. 2, 2004, pp. 66–71). Of all the aquamarines examined at GIA laboratories, this was one of the first to display asterism. @topic:3


Publish Year: 2022 Title: Flux-Grown Synthetic Beryl Overgrowth Abstract: Figure 1. Doubly terminated flux synthetic beryl crystal, measuring 32.45 × 30.36 × 25.29 mm. Photo by Annie L. Haynes.
Most of the synthetic beryl currently on the market has been created by a hydrothermal process. Hydrothermally grown crystals have obviously different crystal forms compared to their natural counterparts. Hydrothermal synthetics are often easily identified by their typical zigzag- or chevron-patterned graining and color zoning. Flux-grown synthetics, though less common, are able to form more natural-looking crystals. However, despite having natural forms, flux synthetics contain many unusual inclusions that clearly distinguish them from their natural counterparts. Copper platelets that form within the crystal either from contamination or intentionally introducing metal in the growth material are obvious indications of synthetic origin. Flux fingerprints are another easily observed type of inclusion unique to flux synthetic crystals.

Figure 2. A suite of columbite rods, copper crystals, and a large air bubble seen within a film of blue flux liquid. Photomicrograph by Jamie Price; field of view 7.19 mm.
Weighing 211.78 ct, the hexagonal doubly terminated crystal in figure 1 looks like a natural beryl crystal at first glance. Eye-visible well-formed copper platelets and wispy flux fingerprints indicate that the stone did not form naturally. A closer look revealed reddish clouds of well-formed minute copper platelets and copper crystals. Euhedral red rod-like crystals of columbite were scattered throughout, similar to those in a natural sample. Partially healed tension cracks with white secondary flux particles were also present. A few areas throughout the crystal had unique thin angular and jagged films containing blue flux liquid and gas bubbles (figure 2). Areas with higher clarity reveal the boundary between the natural aquamarine seed crystal and the flux overgrowth. This stone is a product of synthetic flux beryl overgrowth on a natural aquamarine seed crystal produced in a Russian synthetic gem facility. @topic:3