Title: Letters: Analysis of Three-Phase Inclusions in Emerald Abstract: In the Summer 2014 issue of Gems & Gemology (pp. 114–132), Sudarat Saeseaw and her colleagues from GIA’s Bangkok laboratory presented a study dealing with three-phase inclusions, absorption spectra, and trace-element analyses for origin determination of emeralds. Examples of three-phase inclusions were presented for samples from Zambia (the Musakashi and Kafubu deposits), the Panjshir Valley in Afghanistan, Davdar in China, and several Colombian localities (Coscuez, Muzo, Peñas Blancas, La Pita, and Chivor).

Unfortunately, the authors did not mention in their literature overview or in their discussion the various other emerald deposits which have supplied samples with three-phase inclusions. These include Nigeria (Henn and Bank, 1991); Capoeirana in Minas Gerais, Brazil (Epstein, 1989); Eastern Himalaya (Niedermayr et al., 2002); the Maria deposit in Mozambique (Vapnik and Moroz, 2002); the Lened emerald prospect in the Northwest Territories of Canada (Marshall et al., 2004); Malipo County in the Yunnan province of China (Huong, 2008); and Eidsvoll in Norway (Rondeau et al., 2008). While some of these occurrences might be of academic interest only, others such as Nigeria, Brazil, and Mozambique have supplied emeralds of gem quality to the market. These localities cannot be ignored in a research paper on origin determination and three-phase inclusions.

Although the chemical data presented in Saeseaw et al.’s table 2 were calibrated using the theoretical Si content of beryl as an internal standard, the laser ablation data show such a wide variation for the main elements that it is impossible to calculate a formula for the samples (compare, for example, the overview of chemical data for emeralds from various sources by Groat et al., 2008). Nevertheless, the authors were able to group their samples into five different categories and to present representative absorption spectra in the UV-Vis-NIR range for one sample from each group. Confusingly, four of the five spectra are labeled “E || c”, but polarized spectra are given for the ordinary ray (ω, equivalent to E ⊥ c) and the extraordinary ray (ε, equivalent to E || c), which is impossible for a primary beam with E || c.

In the spectra of several samples with low iron contents, Saeseaw et al. measured some weak to moderate absorption bands in the near infrared at 810 nm, which were assigned to bivalent iron. In the spectra of samples from Kafubu, Zambia, with higher iron contents, an additional strong absorption band at 620 nm was also assigned to Fe2+. These assignments fail to acknowledge numerous research papers dealing with the role of iron in the beryl structure, which has been established for decades. With regard to the bands mentioned at 810 nm, it has been shown that the intensities of the different iron bands in the near infrared with polarization || or ⊥ c are not directly correlated. Consequently, these absorption bands have been assigned to two different types or coordination states of iron, most likely to Fe2+ in tetrahedral and octahedral sites of the beryl lattice. Concerning the band noted at 620 nm, it has likewise been demonstrated that the intensities of the iron-related absorption bands in the near infrared are not directly correlated with the intensity of this broad band, polarized || c in the visible region around 620 nm (figure 1). Thus the broad absorption from about 600 to 750 nm in the spectra of Kafubu emeralds has been assigned to Fe2+/Fe3+ charge transfer (Schmetzer and Bank, 1981). This indicates that emeralds from Zambia’s Miku-Kafubu mining range contain, in addition to chromium as the dominant color-causing trace element, a distinct aquamarine component (figure 2). The aquamarine component is responsible for a color shift and pleochroism, especially of the color || c from green or bluish green in “ordinary” emeralds to greenish blue or blue in samples with such an aquamarine component. Emeralds from multiple sources show this phenomenon and similar absorption spectra (e.g., Schmetzer, 1988; Henn and Bank, 1991; Henn, 1992; Hänni, 1992; Moroz et al., 1999).

Figure 1. Polarized absorption spectra of emeralds from different sources. Sample A from Chivor, Colombia, represents a typical chromium-vanadium emerald spectrum without distinct iron absorption bands. Sample B from Jos, Nigeria, represents a typical chromium-vanadium emerald spectrum with an Fe2+-related absorption band (3) in the near infrared and two Fe3+ bands in the bluish violet and ultraviolet range (17, 20). Samples C (Ankadilalana, Madagascar), D (Santa Terezinha de Goiás, Brazil), and E (Miku, Zambia) represent the superimposed spectra of chromium-vanadium emeralds with distinct aquamarine components of variable intensities, wherein the aquamarine spectrum consists of two absorption bands in the near infrared (2, 3), iron bands in the bluish violet and ultraviolet (17, 20) regions, and a broad polarized absorption in the red (5). After Schmetzer (1988).

Figure 2. Polarized absorption spectra of emeralds from two different sources and an
aquamarine. Sample A, an emerald from Muzo, Colombia, displays a typical chromium-vanadium emerald spectrum without distinct iron absorption bands. Sample B, an emerald from Miku, Zambia, shows the superimposed spectra of chromium-vanadium emerald with a distinct aquamarine component. Sample C, an aquamarine from Tongafino, Madagascar,
displays a typical aquamarine spectrum with two absorption bands in the near infrared (2, 3), iron bands in the bluish violet and ultraviolet regions (17, 20), and a broad polarized absorption in the red (5). After Schmetzer and Bank (1981).
Another frequently occurring trace element in natural emeralds from various localities is vanadium. According to Saeseaw et al., vanadium absorption bands are observed in natural vanadium-bearing emeralds in the ω spectrum (equivalent to E ⊥ c) at 400 nm and in the ε spectrum (equivalent to E || c) at 654 nm. Natural vanadium-bearing, chromium-free emeralds are rare but have been documented (from Salininha, Brazil, for instance). These also reveal distinct amounts of iron, and the various bands in the absorption spectrum of this type of beryl have been assigned to vanadium and iron (Wood and Nassau, 1968). Nearly iron- and chromium-free samples have been grown synthetically; they are commercially available from Biron in Perth, Australia (Schwarz and Schmetzer, 2001), and from Tairus in Novosibirsk, Russia (Schmetzer et al., 2006; see also the summary of references describing vanadium-related absorption spectra in that paper).

Without going into the details of these spectra or discussing the possible presence of vanadium in valence states other than V3+ (see Hutton et al., 1991), it is evident that the spectrum of trivalent vanadium in beryl consists of two strong absorption bands in the visible range (figure 3). Parts of these absorption bands are split into different maxima or show various shoulders, but both absorption maxima are, in contrast to the spectroscopic characteristics noted by Saeseaw et al., present in both polarization directions, parallel and perpendicular to the c-axis.

Natural beryl from most sources reveals some traces of both vanadium and chromium. The ratio of vanadium to chromium varies considerably, especially in samples from the Colombian emerald deposits (Schwarz, 1992). Because the absorption bands of these two trace elements are found in the same spectral range, vanadium- and chromium-related absorptions are superimposed in the spectra of emeralds containing both trace elements. As a result, the different vanadium and chromium maxima are not shown individually (figure 3).

Figure 3. Polarized absorption spectra of two natural Colombian emeralds and a synthetic vanadium-bearing emerald. Sample A from Colombia shows distinctly higher chromium than vanadium contents, Cr V. Sample B shows almost equal amounts of vanadium and chromium, V ≈ Cr. Sample C, representing a Biron hydrothermally grown emerald, shows distinctly higher vanadium than chromium contents, V >> Cr. After Schwarz and Schmetzer (2001).
The vanadium-chromium ratio in natural emeralds can be approximated from the intensity of the spin-forbidden sharp chromium bands in the 600–700 nm range of the vanadium-chromium spectra. These bands are stronger in samples with distinctly higher chromium than vanadium contents (figure 3A) and become weaker in samples with almost equal chromium and vanadium contents (figure 3B). Furthermore, in samples with distinct vanadium contents, the strong absorption band in the bluish violet range at about 430 nm displays a shoulder in the ultraviolet near 395 nm, observed in both polarization directions, || or ⊥ c (see figures 3B and 3C).

Emeralds from Davdar, China, reveal appreciable amounts of vanadium and chromium (Schwarz and Pardieu, 2009), and they can be distinctly zoned, with a wide variation of vanadium and chromium contents in various growth sectors of the same crystal (Marshall et al., 2012). In Saeseaw et al.’s spectrum for an emerald from Davdar, the sharp chromium lines are distinct and the shoulder in the UV is weak (in the spectrum ⊥ c) or almost invisible (in the spectrum || c), although a vanadium to chromium ratio of about 4:1 is reported for that sample. With such a high ratio, the sharp chromium lines should be noticeably weaker and the vanadium shoulder in the UV should be more intense. Therefore, it would seem desirable to control the chemical analyses obtained by laser ablation, especially for determining the concentration of vanadium and chromium, with other non-destructive methods such as X-ray fluorescence or electron microprobe.

Dr. Karl Schmetzer
Petershausen, Germany
September 3, 2014
Reply
We appreciate the opportunity to answer Dr. Schmetzer’s interesting and informed response to our article. First of all, he has provided several helpful bibliographic references about multiphase inclusions in emeralds from a variety of geographic sources. Nevertheless, the stated purpose of our study was to compare the inclusions in emeralds from the new deposit in Musakashi (Zambia) with those from different sources in our Bangkok reference collection using standard laboratory equipment. In that regard, our article can be considered a preliminary study rather than the final word on the subject.

Dr. Schmetzer goes on to ask about our system of labeling wafers for spectroscopy. In our article, “E ∥ c” means that the wafer plane is parallel to the c-axis, which enables us to collect both ω and ε rays.

Regarding Dr. Schmetzer’s concerns about UV-Vis spectra, we focused our study on inclusions. Nevertheless, we provided some significant spectroscopic and chemical data, as these techniques are very important in emerald origin determination. Dr. Schmetzer’s specific inquiries about UV-Vis spectra and iron and vanadium contributions are beyond the scope of our article. To understand clearly how impurity affects color in beryl, we would have needed to test known samples of beryl doped with different elements. This would have taken our study in an altogether different direction.

Lastly, Dr. Schmetzer points out our inability to correlate the LA-ICP-MS chemical data with the UV-Vis spectra for one emerald from the Davdar deposit. He suggests controlling our LA-ICP-MS data with other techniques. In our opinion, the lack of correlation has more to do with the fact that these different techniques are not analyzing the same thing: UV-Vis spectroscopy is a bulk analysis, while LA-ICP-MS is a spot analysis (40 microns in diameter in this study). As a result, UV-Vis spectroscopy and LA-ICP-MS usually do not provide a perfect correlation when it comes to inhomogeneous natural emeralds with color zoning and inclusions, such as the emerald from Davdar.

Again, we thank Dr. Schmetzer for his comments and assure him that GIA plans to obtain and study more emeralds from different mining areas, to further our lab’s capacity to provide accurate origin determination reports.

Sudarat Saeseaw, Vincent Pardieu, and Supharat Sangsawong
GIA, Bangkok Source: GIA @topic:3


Title: Identification of Natural, Reconstructed, and Imitation Root Amber Abstract: Figure 1. Left to right: Reconstructed root amber (assembled from small fragments and from powders), natural Burmese root amber, and plastic imitation. Photos by Yilei Feng.
Natural root amber is a variety of Burmese amber with a distinct appearance, good luster, and deep color (Y. Wang, Amber Gemology, China University of Geosciences Press, Beijing, 2018, p. 145). Root amber was named for its similarity in color and structure to tree roots. Root amber beads are popular in the Chinese market, and the Guangzhou Gemstone Testing Center receives many of them for identification. Recently we have noticed three different types submitted for identification (figures 1 and 2): natural root amber, reconstructed root amber (assembled from either pressed powders or small fragments), and plastic imitations.

Figure 2. Natural Burmese root amber beads (N-1 through N-3), root amber beads reconstructed from pressed amber powders (M-1 through M-3) and small fragments (M-4 through M-6), and plastic root amber imitations (P-1 through P-3). Photos by Yilei Feng and Zhaoyi Li.
Specific gravity (SG) was measured for three natural Burmese root amber samples (N-1 through N-3), three samples reconstructed from pressed powders (M-1 through M-3), three samples reconstructed from pressed fragments (M-4 through M-6), and three plastic imitations (P-1 through P-3). The SG of most varieties of regular Burmese amber samples is within 1.020–1.050, except for root amber and reddish amber (1.060–1.110). Overall, the natural root amber had higher SG (1.044–1.107) than that of regular Burmese amber and much lower SG than that of the reconstructed root amber from pressed amber powders (1.133–1.137) and the plastic imitations (1.161–1.167). The root amber reconstructed from pressed fragments, meanwhile, had an SG of 1.075–1.077. The variations in SG of the reconstructed amber were due to differences in internal structure and/or gas porosity.

Figure 3. Row 1: Internal features of natural Burmese root amber beads: cellular or porous structures (A), red-brown dots in both transparent and opaque zones (B), and the lamellar flow-like pattern with a natural color transition (C). Row 2: Root amber beads reconstructed from pressed amber powders: a flow-like pattern formed by an accumulation of powders (D and E) and a granular texture (F). Row 3: Root amber beads reconstructed from small fragments of pressed amber: clear and rigid borders of the fragments (G and H) and a small granular texture seen in a larger patch structure (I). Row 4: Plastic root amber imitations showing ribbon-, string-, or ring-like patterns (J–L, respectively). Photomicrographs by Yilei Feng and Zhaoyi Li. Fields of view: 10.6 mm (A), 9.0 mm (B), 5.6 mm (C), 2.80 mm (D), 10.4 mm (E), 7.7 mm (F), 11.3 mm (G), 10.7 mm (H), 9.3 mm (I), 5.6 mm (J), 5.0 mm (K), and 4.9 mm (L).
Most importantly, the internal features of the samples were quite different. There were some cellular or porous structures in the natural Burmese root amber (figure 3A). The typical red-brown dots of Burmese amber could be detected in both transparent and opaque zones (figure 3B). The flow-like pattern of natural Burmese root amber can be lamellar, annular, or flocculent, and there are natural transitions between varying colors (figure 3C). The internal features of the root amber reconstructed from pressed powders displayed an unnatural flow-like pattern similar to the veins of a leaf (figure 3, D–E). Under higher magnification, these samples displayed a granular texture (a sugar- or sand-like pattern with apparent broken particles), confirming that small amber micro-particles had been pressed (figure 3F). There were very clear and rigid borders in the root amber reconstructed from fragments (figure 3, G and H). Some granular texture could still be found in these samples (figure 3I). The flow-like pattern of plastic imitation is mostly ribbon-, string-, or ring-like, with a sense of separation between the brown matrix and the obvious boundaries (figure 3, J–L).

Figure 4. FTIR spectra of natural, reconstructed, and imitation root amber in the mid-infrared range (3500–500 cm–1). Spectra are offset vertically for clarity.
Using Fourier-transform infrared (FTIR) spectroscopy, the plastic imitations were quickly identified in the mid-infrared range (3500–500 cm–1). The extremely strong peak at 1731 cm–1, three peaks of increasing intensity (1240, 1192, and 1148 cm–1), and other peaks suggest that the material is an amino resin (figure 4, blue line). The vibration peaks of functional groups of natural root amber mainly appear at 2928, 2860, 1720, 1458, 1375, 1227, 1141, 1028, and 974 cm–1, consistent with the main FTIR peaks of Burmese amber (figure 4, green line). The obvious “Baltic shoulder” (Y. Wang et al., “Characteristics of hydrothermally treated beeswax amber,” Fall 2019 G&G, pp. 370–387), composed of a broad and weak absorption shoulder at 1265 cm–1 and a sharp peak at 1158 cm–1 as well as an absorption peak near 887 cm–1, appeared in two reconstructed root amber specimens (figure 4, pink and purple lines). It can be inferred that these two reconstructed samples were pressed from rough Baltic amber. Source: GIA @topic:13


Title: Color-Change Glass as a Zultanite Imitation Abstract: Figure 1. These glass imitations of Zultanite are shown in fluorescent (left) and incandescent light (right). The color-change effect is apparent when switching between the two illumination types. Photos by Xiaoyan Yu.
Diaspore, a relatively common mineral with the chemical formula AlO(OH), is found in metamorphic bauxite deposits (A.A. Calagari and A. Abedini, “Geochemical investigations on Permo-Triassic bauxite horizon at Kanisheeteh, east of Bukan, West-Azarbaidjan, Iran,” Journal of Geochemical Exploration, Vol. 94, No. 1, 2007, pp. 1–18), and usually appears as a mineral inclusion in sapphire, ruby, and spinel (V. Pardieu, “Hunting for ‘Jedi’ spinel,” Spring 2014 G&G, pp. 46–57; Spring 2016 GNI, pp. 98–100; Summer 2016 GNI, pp. 209–211). However, gem-quality transparent diaspore is rare and appears to be unique to the Ilbir Mountains area in southwest Turkey (M. Hatipoglu et al., “Gem-quality transparent diaspore (zultanite) in bauxite deposits of the Ilbir Mountains, Menderes Massif, SW Turkey,” Mineralium Deposita, Vol. 45, No. 2, 2010, pp. 201–205). Zultanite is the trade name of diaspore that exhibits a color-change effect; the material appears yellow, pink, or green in different light sources. Zultanite has only been found in the Anatolian Mountains of Turkey (M. Hatipoglu and M. Akgun, “Zultanite, or colour-change diaspore from the Milas (Mugla) region, Turkey,” Australian Gemmologist, Vol. 23, 2009, pp. 558–562).

The Gemological Institute of China University of Geosciences in Beijing recently received two samples, an unmounted 8.44 ct 10 × 12 mm faceted pear-shaped specimen and a ring with an 8 × 10 mm faceted oval, that displayed a color-change effect. The material was reportedly purchased from Turkey as Zultanite, a designation the client wished to confirm. Both samples were yellowish green in  fluorescent light with a color temperature of 5500 K (figure 1, left) and brownish yellow in incandescent light (figure 1, right). The specimens were fairly clean, with no obvious inclusions and no obvious scratches on the surface. Facet junctions were generally smooth, with small chips. A series of absorption lines related to rare earth elements (REE) were observed by a handheld prism spectroscope. These properties, along with electron microprobe analysis, indicated that the two samples were not diaspore or any other natural material, but rather man-made glass. The infrared spectrum of the unmounted specimen, with peaks at 1037, 462, 443, and 430 cm–1, confirmed the material was glass.

LA-ICP-MS data of three points on the loose sample are reported in table 1. The main trace elements were Nd (102,792 average ppmw) and Pr (68,500 average ppmw), both rare earth elements. Other REE included Gd (1473 average ppmw) and Ce (135 average ppmw). Nd and Pr are the chromophores that cause color change in material such as synthetic cubic zirconia (Fall 2015 GNI, pp. 340–341).

TABLE 1. LA-ICP-MS data of glass sample (ppmw).

Element
TG1-01
TG1-02
TG1-03

Ti
65.55
64.02
64.13

V
0.618
0.614
0.621

Cr
0.740
0.832
0.818

Mn
0.882
0.861
0.756

Fe
50.68
49.78
51.31

Co
0.0462
0.0444
0.0444

Ni
0.2291
0.2124
0.2062

Cu
13.14
12.80
13.02

Se
0.75
0.75
0.71

Rb
3.63
3.51
3.50

Sr
68.23
66.01
66.26

Y
2.381
2.29
2.319

Cs
0.028
0.0273
0.028

La
4.78
4.55
4.56

Ce
139.42
133.47
134.65

Pr
69,791.21
67,327.64
68,381.69

Nd
104,391.56
100,985.23
103,001.10

Sm
0.307
0.311
0.301

Eu
0.372
0.356
0.353

Gd
1482.77
1452.45
1480.22

Tb
24.41
23.51
23.85

Dy
8.42
7.98
7.92

Ho
0.658
0.617
0.611

Er
31.30
30.25
31.00

Tm
bdl
bdl
bdl

Yb
0.2224
0.1979
0.2197

Lu
bdl
bdl
bdl

Rare earth elements are displayed in bold text. bdl = below detection limit.

The visible-range absorption spectrum of the loose material (figure 2) showed a typical spectrum of glass with rare earth elements. This spectrum showed bands at 443, 479, 529, and 587 nm. The bands at 443, 479, and 529 nm indicate the presence of Pr3+, which caused the green or yellowish green color. The brownish yellow color is related to the 587 nm absorption peak, which is induced by Nd3+.

Figure 2. The visible absorption spectrum of the unmounted pear-shaped sample shows
four absorption bands at 443, 479, 529, and 587 nm. The peak at 587 nm is associated
with Nd3+, while the bands at 443, 479, and 529 nm are attributed to Pr3+. Source: GIA @topic:2


Title: Quarterly Crystal: Quartz with Axinite Abstract: Figure 1. Two examples of quartz with inclusions of ferroaxinite from the New Melones Dam in Calaveras County, California. The larger specimen measures 65.28 mm tall. Photo by Kevin Schumacher.

In their September-October 1982 Mineralogical Record article, D. Pohl et al. described a discovery of ferroaxinite from New Melones Dam in Calaveras County, California. There was a very brief mention of ferroaxinite inclusions in quartz, but no illustrations of the inclusions were provided. Recent exploration of the Calaveras County locality by one of the authors (JM) led to the discovery of a large pocket that produced some beautiful axinite and quartz specimens (figure 1) containing bladed inclusions of ferroaxinite.

This new mineralized pocket was situated on the edge of a ledge and had a different geological appearance than the surrounding area. Successive layers within the pocket, 6–12 cm in thickness, were composed of metagabbro and crushed coarse rock crystal quartz that contained well-developed single quartz crystals measuring up to 9 cm in length and 6 cm in diameter. These crystals displayed both long and short columnar habits. Also found within them were crushed coarse crystalline axinite and mats of small epidote needles. Cracks in the crystals allowed quartz-forming fluids to seep through and crystallize on the surface of the metagabbro, often surrounding both the epidote matting and a mixed layer consisting of chlorite/axinite/epidote.

The large pocket, measuring approximately 7 feet deep, 4 feet wide, and 6 feet long, produced almost 2,000 pounds of quartz. The specimens ranged from translucent to extremely clear and varied in size from 1 to 18 cm. Some of them contained axinite or chlorite phantoms as well as full and partial inclusions of bladed axinite floater crystals. This huge pocket also produced several spectacular plates of axinite, with individual crystals measuring up to 8 cm long, along with floater crystals of similar dimensions.

The axinite inclusions themselves displayed the typical bladed habit expected for this mineral. When examined with polarized light, they also showed pronounced pleochroism, from a light brown (figure 2, left) to a more intense pinkish purple (figure 2, right). This represents the first visual record of axinite inclusions in quartz published in the gemological and mineralogical literature.

Figure 2. With plane-polarized light, the axinite inclusions in quartz show very distinct pleochroism. Both of these images were taken with the polarizer rotated at approximately 90 degrees from each other. Photomicrographs by John I. Koivula; field of view 9.0 mm. Source: GIA @topic:2


Title: Libyan Desert Glass Bangle Bracelet Abstract: Figure 1. A 144.67 ct Libyan Desert glass bangle measuring 66.12 × 13.10 mm. Photo by Johnny Leung.
Libyan Desert glass is a light green or yellow natural glass which is composed of almost 98% silica. It is a type of tektite formed by meteorite impact in the desert and the fast quenching of the silica-rich melt produced. It was first reported by Clayton and Spencer in 1934 (F. Fröhlich et al., “Libyan Desert Glass: New field and Fourier transform infrared data,” Meteoritics and Planetary Science, Vol. 48, No. 12, 2013, pp. 2517–2530) and is found in Egypt’s Western Desert. Common inclusions are bubbles, cristobalite, dark brown streaks, and black iron oxides (J.A. Barrat et al., “Geochemistry and origin of Libyan Desert glasses,” Geochimica et Cosmochimica Acta, Vol. 61, No. 9, 1997, pp. 1953–1959).
Recently, GIA’s Hong Kong laboratory examined a transparent light yellow bangle bracelet measuring 66.12 × 13.10 mm and weighing 144.67 ct (figure 1). It had a spot refractive index of 1.44 and revealed weak yellow fluorescence in short-wave UV. The chemical composition, determined by qualitative analysis using energy-dispersive X-ray fluorescence, was nearly pure silica with minor amounts of iron, strontium, potassium, titanium, and zirconium.

Figure 2. Various shapes of gas bubbles were dispersed individually and in clusters in the Libyan Desert glass bangle. The row of gas bubbles in this image resembles peas in a pod. Photomicrograph by Sze Ling Wong; field of view 2.40 mm.

Figure 3. White spherulites in the bangle were identified as cristobalite by Raman analysis. Photomicrograph by Sze Ling Wong; field of view 5.98 mm.
Based on the differences in molecular vibrations detected with Fourier-transform infrared (FTIR) analysis, it was determined that the molecular structure of Libyan Desert glass is significantly different from that of other pure silica glasses. It has a higher ratio of discontinuities and defects in the tetrahedral (SiO4) network (F. Fröhlich et al., 2013). Microscopic observation revealed common inclusions in glass such as numerous gas bubbles (figure 2) and flow structure. This bangle also presented abundant white spherulites identified by Raman spectroscopy as cristobalite (a polymorph of silica). These spherulites were small and individually dispersed throughout the glass (figure 3). The presence of this high-temperature low-pressure silica phase indicates a natural high-temperature formation. From all the gemological, FTIR, and Raman data collected, this bangle was identified as Libyan Desert glass.
Most Libyan Desert glass is tubular in shape, and some are approximately spherical or rod-like (R.A. Weeks et al., “Libyan Desert glass: A review,” Journal of Non-Crystalline Solids, Vol. 67, No. 1-3, 1984, pp. 593–619). Those fragments are usually 2 to 63 mm in size, so it is surprising to examine this material in the form of a bangle bracelet. Source: GIA @topic:2


Title: Appendix 3: Calculation Method for Tourmaline Species Classification Used Here Abstract: The simplified procedure of the method can be described as follows:

Use 29Si as internal standard to calculate raw ppmw.
Convert raw ppmw to atoms per formula or moles.
Calculate Li and B atoms per formula based on stoichiometric chemical formulae.
Convert this formula from atoms to wt.% oxides and ppmw.

The exact procedure of the method is given below:
There are three variables used in this method: Limole, Bmole, and A.
Limole is the Li (in moles) before normalization.
Bmole is the B (in moles) before normalization.
A is the normalization factor, which converts moles of each element into atoms per tourmaline formula unit.
To calculate values of the three unknown variables, three independent equations are required.
Function 1: The numbers of ions in the formula are based on 31 (O, H) per chemical formula.

Assuming stoichiometric amounts, there are three atoms of B per formula unit

. This reduces the number of independent variables to two:

Y is the total of ppm (mole) oxygen to charge balance cations except for Li and B before normalization. Y is measured by LA-ICP-MS. All element (Rppmw) symbols used below represent ppmw of the elements before normalization (this statement holds for all other uses).

Function 2: The summation of cations in Y-, Z-, and T-sites equals 15.

X is the summation of cations per formula in Y-, Z-, and T-sites before normalization. X can be measured by LA-ICP-MS. All element (Rppmw) symbols used below represent ppmw of the elements before normalization.

By solving the following equation set, normalization factor A and values for tourmaline species classification are obtained.

Finally, using A, the raw data for the major elements in ppmw is converted to atoms per formula unit. This is done by dividing the ppmw concentration of each element by its atomic mass and then multiplying by A. The concentration of each element in atoms per formula unit is used for the tourmaline species classification. Source: GIA @topic:12


Title: Letters: Nacken Synthetic Emeralds: Additional Information Abstract: In a recently published study on synthetic emeralds grown by Prof. R. Nacken (K. Schmetzer et al., Winter 2016 G&G, pp. 368–392), three different types of flux-grown crystals and faceted samples were described. The vast majority of the synthetic emeralds, comprising several hundred samples, fell within two groups designated types 1 and 2. Most of these had been obtained either from a parcel donated by Nacken to the Deutsches Museum in Munich or from material that had remained in Nacken’s family and was now in the possession of his grandsons. Upon examination, all crystals and faceted samples of types 1 and 2 were found to contain irregularly shaped seeds of colorless beryl. In contrast, only a few synthetic emeralds of another type, designated type 3, were discovered. These lacked colorless seeds and had come from the collection of the late F.H Pough, who in turn had acquired the crystals from G.O. Wild. Existing documentation shows that Wild possessed a parcel of Nacken synthetic emeralds during the period after 1945 and donated various samples to friends and colleagues for research and related purposes.

	In 1936, the German government decided to affiliate the private Institute for Gemstone Research, located in Idar-Oberstein and directed by G.O. Wild, with the University of Frankfurt. Nacken was named director of the joint entity, with Wild remaining the local leader for activities in Idar-Oberstein. A close collaboration between Wild and Nacken during 1936 and 1937 has long been apparent from known writings, but no direct information about the synthetic emeralds in Wild’s possession has previously been available. Wild’s son, K.E. Wild, had seen the parcel with Nacken synthetic emeralds in the 1950s and 1960s, while working in his father’s office, but no further background about those samples was given to him at the time (K.E. Wild, pers. comms., 2016, 2017).

	A new development, however, serves to unveil further details. A document authored by Nacken and dated May 30, 1937, was recently found in the historical archive of the city of Idar-Oberstein (Stadtarchiv Idar-Oberstein, Department 2b, File I B, No. 94). The four-page summary, written to the head of the local administration for the District of Birkenfeld, reports goals and tasks of the Institute for Gemstone Research. In the section covering scientific research, the following is written (translated from German): “Examination of properties related to crystal growth and synthesis of gemstones. These experiments already resulted in the production of synthetic emeralds.”

	From this short statement, it becomes apparent that growth of synthetic gem materials was one of the specific research topics undertaken or at least planned at the Institute. Equally logical then is the corollary that Wild, being the local representative in Idar-Oberstein, would have had access to the synthetic materials grown in relation to the Institute’s research projects. Although no additional information is provided in Nacken’s report, the timing would support a conclusion that at least some experiments related to the growth of synthetic emeralds were performed in the 1930s, with Nacken attempting to improve the technique by which he had successfully synthesized emeralds in the 1920s. Presumably, he would have tried to avoid larger colorless zones within the synthetic crystals, as such areas are easily observable, especially in faceted samples. Thus, taking into account all known circumstances, current evidence would seem to suggest that Nacken’s type 3 flux-grown synthetic emeralds without colorless seeds were a result of experiments performed in the 1930s, subsequent to the growth of type 1 and type 2 synthetic emeralds with colorless seeds in the 1920s.

Karl Schmetzer
Petershausen, Germany Source: GIA @topic:3


Title: Update on Inclusions in Emeralds from Davdar, China Abstract: Figure 1. Left: A Davdar emerald hosted numerous black mineral inclusions identified by laser Raman microspectrometry as magnetite. Right: The Raman spectrum of the inclusions is shown along with the Raman reference spectrum for magnetite in the RRUFF database. Spectra are offset for clarity. Inset photomicrograph by Di Cui.
We recently had the opportunity to examine emeralds containing unknown solid inclusions and numerous multiphase inclusions reportedly from Davdar, China. Three green transparent rough samples were acquired from the former mine owner Guimin Wong. They weighed 0.55, 0.45, and 0.50 ct, respectively, with a diameter from 4.0 to 5.0 mm, a refractive index of 1.578 ± 0.002–1.584 ± 0.001, and SG ranging from 2.64 to 2.76. They were inert to both long- and short-wave UV radiation. Inclusion features of Davdar emeralds have been reported previously in the literature.
Very few mineral species have been identified as inclusions in this emerald—these include feldspar (plagioclase) (S. Saeseaw et al., “Three-phase inclusions in emerald and their impact on origin determination,” Summer 2014 G&G, pp. 114–132; S. Saeseaw et al., “Geographic origin determination of emerald,” Winter 2019 G&G, pp. 614–646) and to a lesser extent tourmaline, mica, scheelite, and fluorite (D. Marshall, “Geological work,” InColor, Spring 2009, p. 29). Black rounded crystals were observed in some of the Davdar emeralds we studied. Previous studies noted the presence of black minerals as well but did not identify them (S. Saeseaw et al., 2014, 2019). We revealed the black mineral to be magnetite via Raman microspectrometry (figure 1). This is potentially the first time magnetite has been identified in Davdar emeralds, though it has been identified in emeralds from other regions (referenced above). Magnetite as a black iron oxide inclusion is commonly seen in emeralds from Zambian and Brazilian localities and other schist-hosted origins (again, see Saeseaw et al., 2019).
Multiphase inclusions occur commonly in Davdar emeralds with solid phases (mainly halides such as halite assumed by D. Marshall et al., “Conditions for emerald formation at Davdar, China: Fluid inclusion, trace element and stable isotope studies,” Mineralogical Magazine, Vol. 76, No. 1, 2012, pp. 213–226). Since previous studies reported that some birefringent phases did not dissolve during heating (again, see Marshall et al., 2012), we hoped to learn the solid phase identity in fluid inclusions. Comprehensive microscopic and Raman spectroscopic analyses indicated the presence of dolomite and likely calcite daughter inclusions (figures 2 and 3). As the solubility of a carbonate such as calcite seems to show an inverse solubility with respect to temperature (see B. Coto et al., “Effects in the solubility of CaCO3: Experimental study and model description,” Fluid Phase Equilibria, Vol. 324, 2012, pp. 1–7), the first identified dolomite daughter crystals could be attributable to the phases that were insoluble with increasing temperature and added more constraints to fluid inclusions in Davdar emeralds.

Figure 2. Left: Solid-rich fluid inclusions in Davdar emerald. One of the solid phases was determined to be dolomite. Right: The corresponding spectrum (red) showed peaks from both the host beryl (black) and the reference spectrum for dolomite in the RRUFF database (blue). Photomicrograph by Di Cui.

Figure 3. Two daughter crystals in separate inclusions were identified as likely calcite based on comparison with Raman reference spectra from the RRUFF database. The top and bottom left images show the spectra of the two daughter inclusions (red), the host beryl (black), and the RRUFF calcite reference spectrum (green). The dominant calcite peak at 1087 cm–1 matches with weak peaks in both daughter crystals. The top and bottom right images show the weak 1087 cm–1 peak corresponding to calcite under magnification. Photomicrographs by Di Cui.
As far as we are aware, the carbonate phase could simply refer to the local geologic background and the host rock lithology, which mainly consisted of sandstone and dolomitic limestone. Study of the inclusions showed interesting results due to the genetic environment of the Davdar emerald mine. In addition to the daughter chloride such as halite, the identified dolomite mineral defined the complex multiphase assemblage for the Davdar fluid inclusion population. Source: GIA @topic:3


Title: The Effects of Heat Treatment on Zircon Inclusions in Madagascar Sapphires Abstract: Zircon inclusions in sapphires from Madagascar were studied to investigate the effects of heat treatment on their gemological and spectroscopic features. Progressive decomposition of zircon and chemical reactions between zircon and the host sapphire occurred at temperatures between 1400°C and 1850°C. In unheated sapphires, transparent zircon inclusions displayed euhedral slightly elongated forms and clear interfaces with their corundum host. Most were confined within the host under relatively high pressures (up to 27 kbar), and showed evidence of natural radiation-related damage (metamictization). Subsolidus reactions (i.e., the decomposition of zircon into its component oxides without melting) of some zircon inclusions started at temperatures as low as 1400°C, as evidenced by the formation of baddeleyite (ZrO2) and a SiO2-rich phase. Differences in the degree of preexisting radiation damage are the most likely cause for the decomposition reactions at such relatively low temperatures. Melting of zircon and dissolution of the surrounding sapphire occurred in all samples at 1600°C and above. This resulted in the formation of both baddeleyite and a quenched glass rich in Al2O3 and SiO2. From these data and observations, a systematic sequence of both modification and destruction of zircon inclusions with increasing temperature was compiled. This zircon alteration sequence may be used (1) as a gemological aid in determining whether a zircon-bearing ruby/sapphire has been heated, and (2) to provide an estimate of the heating temperature. Source: GIA @topic:3


Title: Modified Rheinberg Illumination Abstract: Figure 1. In one method of applying Rheinberg-type illumination, glass slides are fitted to the end of two fiber-optic illuminators and painted with red and blue ink (left) to create a filter that is easily positioned by moving the colored portion of the glass slide into the light path (right). Photos by Danny J. Sanchez.

	Lighting control is one of the most important considerations for maximizing the use of the gemological microscope; with greater control over illumination sources, more information may be gathered from observing a specimen. An interesting technique that gives the microscopist another lighting tool is modified Rheinberg illumination, also known as differential color illumination (M. Pluta, Advanced Light Microscopy: Specialized Methods, Vol. 2, PWN-Polish Scientific Publishers, Warsaw, 1989, pp. 113). This method, as modified for gemological microscopy, employs the use of a contrasting color filter between each illumination source and the subject (figure 1) to achieve an “optical staining” effect (figure 2). When viewing crystallographically aligned subjects such as negative crystals or inclusions with well-defined, reflective crystal faces, each illumination source highlights areas that have the same crystallographic orientation (figure 3). This provides dramatic false-color contrast to an otherwise low-contrast subject. This enhanced contrast makes it easier to observe the relationship between areas in an inclusion scene with identical and also differing crystallographic orientations.

Figure 2. This silvery metal sulfide inclusion in fluorite shows angular crystal faces, but the low contrast in the image on the left makes it difficult to resolve the orientation of the faces from different sections of the inclusion. Rheinberg illumination provides stark contrast between differently oriented regions by using two colored illumination sources that reflect their independent color off of crystallographically aligned crystal faces, as seen in the center and right images. This allows the microscopist to easily observe the different orientations of the crystal faces in the metal sulfide inclusion, as evidenced by the dramatic boundary of the two contrasting colors. Photomicrographs by Danny J. Sanchez; field of view 1.66 mm.

Figure 3. With modified Rheinberg illumination to impart contrasting color on some of the crystal faces, the negative crystals in the rock crystal quartz (left) prove to be crystallographically aligned (right). Photomicrographs by Nathan Renfro; field of view 7.34 mm. Source: GIA @topic:1


Title: Violetish Blue Spinel in Yellow Sapphire Abstract: This violetish blue inclusion in a Sri Lankan yellow sapphire was identified as spinel. Photomicrograph by Nathan Renfro; field of view 5.63 mm.

	Spinel as an inclusion in sapphire has been previously documented in blue and yellow sapphires from Sri Lanka (E.J. Gübelin and J.I. Koivula, Photoatlas of Inclusions in Gemstones, Vol. 1, ABC Edition, Zurich, 1986, pp. 353–354). Typically these inclusions are green zinc-rich ghanospinels. Recently the authors examined a transparent light yellow sapphire crystal with a prominent violetish blue octahedral inclusion. Interestingly, microscopic examination showed the violetish blue inclusion to be an intergrowth of at least two gemmy crystals, with the larger one crystallographically aligned with negative crystals that were also present in the host.

	When further examined with polarized light, the violetish blue inclusion appeared to be singly refractive, which meant spinel was a possibility, considering their similar formation environments. The sample was polished down to a plate in order to place the violetish blue inclusion closer to the surface for Raman analysis, which conclusively confirmed that it was spinel. Also present in this sapphire were numerous carbon dioxide–filled negative crystals, fingerprints, and open cracks. The presence of the intact CO2 inclusions and the pristine condition of the spinel inclusion provided clear evidence that the sapphire host had not been subjected to any form of heat treatment. This is the first example of a violetish blue spinel inclusion in sapphire that the authors have examined. Source: GIA @topic:3


Title: Glenn Nord (1928–2019) Abstract: Glenn Nord was captivated by gems since childhood, and this formed the foundation of his education and career. This fascination long benefited GIA, which flourished thanks to the accomplishments of this self-described “GIA man.” His work, first as an instructor, then as president, and finally as a member of the Board of Governors, secured the Institute’s place as the world leader in gemological education and research.

After completing military service, Nord enrolled at GIA using his GI Bill benefits, earning his Graduate Gemologist (GG) diploma in 1959. He was invited by then-president Richard Liddicoat to join the faculty in 1961. He became a tireless advocate for GIA’s traveling classes, introducing the Institute’s first corporate training courses with the Zale Corp. in the 1960s. In 1970, Nord taught GIA’s first international gemology courses, in Ramat Gan, Israel. He resigned in 1974 for health-related reasons, but returned nine years later to serve as GIA president.

Nord’s term as president (1983–1986) restored financial stability in the wake of a global recession. It also brought an era of increased student enrollment, revitalized curriculum, and expanded global development. His lasting contributions to the Institute include the establishment of student financial aid services and the founding of the highly successful Gemfest, free educational seminars now held regularly in Asia and Europe.

A longtime member of the Board of Governors, Nord was named Governor Emeritus, and received the Richard T. Liddicoat Distinguished Achievement Award, the Institute’s highest honor. More than five decades after his graduation, GIA and the public it serves continue to reap the benefits of Glenn Nord’s leadership and dedication.

Glenn Nord passed away on June 9, 2019. Source: GIA @topic:10


Title: Dyed Quartzite Imitation of Ruby-in-Zoisite Abstract: Figure 1. Green to dark green and pinkish purple to dark purple dye concentrations were observed in the fissures and structure of this quartzite, which resembled ruby-in-zoisite. Photo by HyeJin Jang-Green; field of view 9.61 mm.

The New York laboratory recently received a bracelet composed of translucent multicolored beads that closely resembled ruby-in-zoisite. Standard gemological testing of one of the round beads (measuring 8.33 × 8.17 mm) revealed an refractive index (RI) of 1.55 for both the purple and green areas (instead of approximately 1.76 or 1.69 for ruby and zoisite, respectively) and very weak red to inert fluorescence in long-wave and short-wave ultraviolet light, respectively. Microscopic observation revealed fissures and a translucent aggregated/grainy structure, both of which contained green to dark green and pinkish purple to dark purple dye concentrations (figure 1).

Although most of the translucent green and purple aggregate material we encounter for identification is ruby-in-zoisite, the gemological features of this bead were inconsistent with our expectations. Raman spectra were collected to confirm the identity. Spectra from both the purple and green areas matched quartz (figure 2). Since the material was an aggregate, we concluded that it was dyed quartzite.

Figure 2. Raman spectra collected from the sample’s purple and green areas indicated quartz rather than ruby and zoisite. Spectra are offset for clarity.
The Lab Notes section has documented many cases of dyed quartzite imitating jadeite, ruby, lapis lazuli, and sugilite (Spring 1986, pp. 49–50; Summer 1991, pp. 122–123; Summer 1995, pp. 125–126; Summer 1998, pp. 131–132; Spring 2001, pp. 62–63; and Fall 2003, pp. 219–220). But this is the first example we have seen of quartzite being used to imitate ruby-in-zoisite. This dyed quartzite provides an intriguing example for consumers to be aware of when purchasing ruby-in-zoisite. Source: GIA @topic:12


Title: Blue Spinel Crystals in the MgAl2O4-CoAl2O4 Series, Part I: Flux Growth and Chemical Characterization Abstract: Synthetic CoAl2O4 spinel, a high-temperature oxide (melting point of 1955°C), is the most stable compound of a family of spinel-structured oxides obtained from CO3O4 at progressive increase of Al contents. High-quality spinel single crystals with compositions closely corresponding to the solid-solution series spinel sensu stricto (MgAl2O4)-cobalt spinel (CoAl2O4) were produced by flux growth method, with Na2B4O7 as the flux. Low cooling rates and linear temperature profiles were applied in the thermal interval 1200–800°C, followed by rapid cooling. Thermal runs were performed in a reducing atmosphere. Selected crystals were investigated by SEM/EDS X-ray mapping to check for compositional homogeneity and by electron-microprobe analysis to obtain the chemical formula.

								Crystals were found to be chemically homogeneous and entirely representing the MgAl2O4-CoAl2O4 solid-solution series, with the latter component ranging from 7% to 100%. The saturation of the vivid blue color increased with total cobalt content, but no shift in color hue was observed along the series. The unit-cell parameter a increased from 8.084 to 8.105 Å along the solid-solution series. The observed linear increase of the a parameter was seemingly due to the higher CoAl2O4 component. This was a premature and misleading conclusion, however, because structural changes in spinel may depend on both chemical composition and inversion parameter, which in turn is a function of thermal history. The composition of crystal products does not correspond to the composition of the starting oxide mixture: cobalt enriched in the crystals. A tentative explanation of this behavior is suggested by considering possible ionic potential as well crystal field stabilization effects.

Abstracted by Guy Lalous Source: GIA @topic:3


Title: The Special Color Effect in “Chameleon” Amber Abstract: Figure 1. A good-quality 88.25 ct “chameleon” amber with a red bodycolor displaying a vivid green fluorescence color that appears to float on the surface. Photo by Yan Li.

Figure 2. A and B: A 78.51 ct chameleon amber exposed to white light against white and black backgrounds. C and D: A 12.50 ct brownish reference sample exposed to similar lighting and backgrounds. Photos by Jinfeng Yang.
One special variety of Burmese amber is “chameleon” amber, named for the bluish green color that appears to float on its surface (figure 1). This material is found in the famous Tengchong market in Yunnan Province, China’s largest Burmese amber market. Its bodycolor ranges from golden brown to brownish red or even red (figure 2A). When exposed to sunlight or strong white light against a black background, its surface shows a uniform green color (figure 2B). Chameleon amber is rare and expensive compared to regular Burmese golden or brownish amber, especially with the severe reduction of exports from Myanmar.
Until recently, few studies have been conducted on chameleon amber. X. Jiang et al. speculated that the green surface color might be caused by the superposition of its bodycolor and the fluorescence of amber (“Gemmological and spectroscopic characteristics of different varieties of amber from the Hukawng Valley, Myanmar,” Journal of Gemmology, Vol. 37, No. 2, 2020, pp. 144–162). C.C. Shuai et al. proposed that the “light retention” effect was related to elevated sulfur and calcium contents (“The spectrum characteristic research of color change effect and ‘light tarry effect’ amber from Burma,” Spectroscopy and Spectral Analysis, Vol. 40, 2020, pp. 1174–1178). Z. Shi et al. reported that the effect might be due to unique internal aromatic hydrocarbon structures (“Spectral characteristics of unique species of Burmese amber,” Minerals, Vol. 13, No. 2, 2023, article no. 151).

Figure 3. A and B: A 71.05 ct Burmese chameleon amber and its bluish white fluorescence under long-wave UV light. C and D: 16 mm brownish Burmese amber beads (12.60 ct on the left, 12.16 ct on the right) and their bluish purple fluorescence under long-wave UV. Photos by Jinfeng Yang.
For this study, three Burmese chameleon amber specimens were acquired from the Tengchong market (see figures 1, 2A, and 3A). All three displayed a translucent brownish red bodycolor, with a few bubbles and flow lines within them. The bluish green floating color was observed when the specimens were rotated. This phenomenon is most obvious with a black background. Standard gemological properties and Fourier-transform infrared spectroscopy data were consistent with those of regular Burmese amber. While the bluish green floating color might be related to fluorescence, no such effect is seen on other types of fluorescing Burmese amber (e.g., brownish amber). To further explore this, brownish Burmese amber beads with bodycolor similar to that of chameleon amber were selected as a reference (figures 2C and 3C). Their bodycolor was not as vivid as chameleon amber, and it did not display the bluish green floating fluorescence. Observation under a UV lamp showed that the chameleon amber in figure 3A produced strong bluish white fluorescence (figure 3B) in long-wave UV (365 nm), while the brownish amber beads in figure 3C showed a weak bluish purple fluorescence (figure 3D).

Figure 4. 3D fluorescence spectra of Burmese chameleon amber (A) and brownish amber (B).
The samples were then examined with 3D fluorescence spectroscopy (figure 4) under the excitation of a continuous-wavelength excitation light source. The fluorescence intensity of brownish amber was clearly much lower than that of chameleon amber. In addition, two peaks (455 and 384 nm) were absent in the excitation spectrum of brownish amber. A high degree of similarity was exhibited in the samples’ emission spectra, with all the peaks positioned at approximately 434, 464, 469, and 497 nm. However, the biggest difference was in the fluorescence intensity, which was easily observed in chameleon amber.
The 3D fluorescence spectra of chameleon amber exhibited several fluorescence centers, mainly at 434, 464, 469, and 497 nm generated by excitation wavelengths of 386, 406, 436, and 457 nm. The fluorescence color could be calculated by the fluorescence centers, and the results showed that the spectral color was blue under 386 nm excitation and bluish green under 436 nm excitation. We believe that the bluish green floating color under sunlight is caused by the bluish green fluorescence center at 469 nm under 436 nm excitation. This is much more consistent with observations in daylight. Due to the low fluorescence intensity of brownish amber, its blue fluorescence color is very weak, and most light penetrates it without producing any special optical effect. The difference in fluorescence intensity between the 469 and 434 nm fluorescence centers corresponds with the relative spectral power distribution of the light source. Under the excitation of a xenon lamp, the fluorescence center at 434 nm is more intense than the light-emitting center at 469 nm. However, amber is usually observed in daylight. The optimal excitation wavelengths for the emission centers at 434 and 469 nm are 386 nm and 436 nm, respectively. From the relative spectral power distribution of the two light sources, it can be seen that the spectral density of the xenon lamp at 386 nm is greater than 436 nm, while the D65 daylight-equivalent source is the opposite. Against a dark background and under daylight, the fluorescence of chameleon amber should be dominated by the bluish green fluorescence emitted at 436 nm.
The fluorescence center at 469 nm is very common in Baltic, Dominican, Mexican, and Burmese amber. This fluorescence center in chameleon amber is unique for its high intensity and separation from other fluorescence colors. Only if the fluorescence intensity is high enough will it show as the dominant fluorescence color. The optimal excitation wavelength (436 nm) corresponding to the 469 nm fluorescence center is far removed from the optimal excitation wavelength of other strong fluorescence centers; therefore, the fluorescence color is not a mixture of multiple colors. Many varieties of amber can also produce strong fluorescence at 469 nm, but often mixed with other fluorescence colors of similar intensity. For example, the fluorescence peaks of 448 and 474 nm in Dominican blue amber always appear together, and their strong fluorescence peaks can be seen with exposure to the same excitation wavelength. In most cases, the fluorescence intensity of the former is slightly greater, which leads to the fluorescence of the blue amber being mainly blue, without a green modifier. Some Dominican blue amber with uneven fluorescence distribution can also show a mosaic pattern (X. Chenxing et al., “Characterisation of patchy blue and green colouration in Dominican blue amber,” Journal of Gemmology, Vol. 37, No. 7, 2021, pp. 700–713). The fluorescence distribution of the chameleon amber tested in this study was uniform, with high intensity and good separation, producing a high-quality bluish green floating fluorescence effect. Source: GIA @topic:13


Title: Spectroscopic Characteristics of Low-Temperature Heated Blue to Violet Spinel Abstract: Figure 1. Color-calibrated photos of blue to violet spinels before heating (left) and after heating at 1000°C for four hours (right). There are three groups of spinel samples in this study: violet (top row), iron-dominated blue (middle row), and cobalt-dominated blue (bottom row). Photos by Sasithorn Engniwat.
Although spinel is rarely treated, there have been some heated spinels available in the trade. The effect of heat treatment on pink to red spinel has been previously reported (e.g., S. Saeseaw et al., “Distinguishing heated spinels from unheated natural spinels and from synthetic spinels,” 2009, GIA Research News, https://www.gia.edu/gia-news-research-NR32209A; A. Peretti et al., “Heat-treatment of spinel,” in World of Magnificent Spinels: Provenance and Identification, GRS Gemresearch Swisslab, 2015, pp. 269–278). Chromium-bearing spinel with pink to red color generally becomes darker after heat treatment, and the clarity of spinel containing particulate clouds can be significantly enhanced by heating between approximately 950° and 1150°C (S. Saeseaw et al., 2009).
In addition to the most popular pink to red spinel, another important and desirable variety is blue spinel, especially with a vibrant cobalt blue color. The dominant chromophores in blue to violet spinel includes Fe2+ and Fe3+ at both tetrahedrally (T) and octahedrally (M) coordinated sites of spinel structure as well as Co2+ at the T site (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). Previous works have revealed the application of cobalt diffusion treatment to enhance blue color in spinel (e.g., S. Saeseaw et al. “GIA lab reports on a new cobalt diffusion treatment of natural spinel,” GIA Research News, 2015, https://www.gia.edu/gia-news-research/cobalt-diffusion-natural-spinel-report). A study on the heat treatment of blue spinel without external chemical diffusion is lacking in the literature, to our knowledge.
To understand the change of chromophores in blue to violet spinel caused by heat treatment, this preliminary study involved exploratory heat treatment of samples from various localities: Madagascar, Myanmar, Tanzania, and Vietnam. The samples were separated into three groups: violet, iron-dominated blue, and cobalt-dominated blue spinel (figure 1, left).

Figure 2. Representative UV-Vis-NIR spectra of unheated spinels for the three color groups. They have relatively similar absorption spectra with different intensities and some band positions, depending on Fe and Co contents. A series of Fe absorption bands in the spectrum consists of Fe2+ at T site (TFe2+) bands at approximately 371, 385, 400, 558, 580, and 780 nm; Fe2+ at M site (MFe2+) band at around 920 nm; Fe3+ at M site (MFe3+) band at 457 nm; MFe2+- MFe3+ intervalence charge transfer (IVCT) band at about 655 nm; and Co2+ at T site (TCo2+) bands at approximately 558, 580, and 625 nm (Andreozzi et al., 2019; D’Ippolito et al., 2015). Fe and Co concentrations reported in the figure were analyzed by LA-ICP-MS.
UV-Vis-NIR spectrum of representatives in each group show relatively similar absorption spectra (figure 2), consisting of a strong UV-edge absorption at approximately below 330 nm; multiple absorption bands between 350 and 1100 nm of Fe2+, Fe3+ at T and M sites; and multiple bands between 500 and 670 nm of Co2+ at the T site (Andreozzi et al., 2019; D’Ippolito et al., 2015). With a very similar absorption pattern between violet and blue iron-dominated spinels, the difference in color appearance is associated with different intensity of absorption bands which is more intense in iron-dominated blue spinel due to higher Fe concentrations (Andreozzi et al., 2019). The spinel samples were heated at 600°, 700°, 800°, 900°, and 1000°C in air and held for four hours at each heating temperature. Progressively heating from 600° to 1000°C showed that violet color changed little in this temperature range, whereas blue spinel became more grayish after heating at approximately 800°–900°C (figure 1, right). Heat treatment could affect the color appearance of iron-dominated blue spinel colored much more than cobalt-dominated blue spinel.

Figure 3. UV-Vis-NIR spectra comparisons of cobalt blue (top), blue and violet spinels (bottom) in figure 2, before heating (solid line) and after heating at 1000°C for four hours (dashed line). Broader absorption bands, with less prominent bands below 650 nm and more prominent bands at around 920 nm, were observed.
After heat treatment (figure 3), the spectra displayed generally broader absorption bands, with less prominent bands below 650 nm and more prominent bands at around 920 nm. The broadening of the chromium emission peak in photoluminescence spectroscopy (PL) is an effective criterion for detecting heat treatment in spinel (e.g., Saeseaw et al., 2009; Peretti et al., 2015). PL spectra of the treated samples in this study were also analyzed and showed that the Cr emission peak of the material broadened after heating at 800°–900°C. The change in color and spectroscopic data after heat treatment resulted from a direct spinel transforming to a partially inverse spinel (R. Widmer et al., “Effects of heat treatment on red gemstone spinel: Single-crystal X-ray, Raman, and photoluminescence study,” Physics and Chemistry of Minerals, Vol. 42, 2015, pp. 251–260) as well as the changes of valence and site distribution of Fe chromophores in the spinel structure. The less desirable blue color of the treated spinel in this preliminary study, regardless of any improvement in clarity, suggests that the heat treatment of the blue to violet spinels was likely unintentional. In addition, as demand for gray colored spinels has increased in the trade over the past few years (Spring 2019 GNI, p.130), some concerns about heat treatment in gray spinels should be raised. Source: GIA @topic:3


Title: Chalcedony Beads Coated With Titanium Nitride Abstract: Figure 1. The beads in this necklace, ranging in diameter from 12.0 to 12.5 mm, have a submetallic luster and a gray tinge with goldish reflection. Small vugs lined with sparkling crystals are clearly visible in most of the beads. Photos by Raffaella Navone.

Recently, RAG Gemological Laboratory in Turin received a necklace of unusual metallic appearance (figure 1). The beads showed irregular surfaces that were actually small geodes with shiny and well-shaped crystals. The cavities in the beads (figure 2) were reminiscent of the small quartz-lined holes that are often formed in agates and chalcedony. The necklace consisted of 29 beads ranging from 12.0 to 12.5 mm in diameter, with a total weight of 84 g.

Figure 2. SEM imaging shows the small, well-shaped quartz crystals within the
cavities. The crystal in the lower middle clearly displays the classic “flute”
termination typical of quartz. Image by Emanuele Costa; field of view 1 mm.
Some loose opaque beads provided by the necklace’s owner allowed us to measure the material’s density. The value of 2.60 g/cm3 was in agreement with chalcedony. Refractive index was not measurable on the beads due to their rough surface. No fluorescence reaction was observed under long- or short-wave UV. A sawed bead revealed that the inner part consisted of light gray chalcedony without zonation (figure 3). Observation of the area near the drill holes showed discoloration and the true color of the underlying material. The coating on these grayish gold chalcedony beads in this necklace had an unusual composition. The unusual color and reflectivity of the external surface, clearly not inherent to chalcedony, warranted investigation.

Figure 3. This sawed cross-section clearly demonstrates the homogeneity and light gray color of the chalcedony that constitutes most of the bead. Photo by Emanuele Costa.
The chemical composition of the bead was confirmed by energy-dispersive spectroscopy (EDS) using a Cambridge Stereoscan 360 scanning electron microscope equipped with an Oxford Inca Energy 200 EDS and a Pentafet detector for the determination of elements from boron to uranium. The results showed homogeneous composition on the sample surface, with titanium, oxygen, and silicon as major elements. No known compound of Ti and Si could explain the nature of the bead’s surface or the goldish gray metallic tinge.

Low-acceleration voltage conditions in EDS analysis (4kV) allowed us to enhance the X-ray emission yield of lighter elements and reduce the penetration depth of the electron beam at around 100 nm into the bead’s surface. The EDS spectra at low acceleration voltage showed the presence of nitrogen and titanium, suggesting a coating of titanium nitride (TiN) on the beads. At low potential the electron beam could pass through the thin layer of TiN, so the oxygen and silicon peaks from the underlying silica were still visible in the spectra. We calculated the thickness of the coating by acquiring several EDS spectra at different acceleration voltages (from 4 to 10 kV). The presence of the silicon peak even at 4 kV suggests that the electron beam could penetrate the layer and generate the signal through the TiN coat. The Casino software package evaluated the corresponding excitation depth of the electron beam using a Monte Carlo simulation. The calculated maximum thickness in our samples was less than 200 nm.

TiN is a very difficult material to analyze due to the presence of nitrogen, which is not always revealed with standard gemological techniques. To confirm the presence of a TiN film coating, we performed micro-Raman investigations. Spectra were obtained using a micro/macro Horiba LabRAM HR 800 (UV-Vis-IR) equipped with an Olympus microscope. The backscattered Raman signal was collected with a 50× objective and the 632.8 nm line of a He-Ne laser. The spectra were collected with multiple and repeated acquisitions to improve the signal-to-noise ratio, but even with these precautions the quality of the spectra is very poor due to the low intensity of Raman response from TiN. The Raman spectrum was recorded from 100 to 1200 cm–1. Spectral manipulation such as baseline adjustment, smoothing, and normalization were performed using LabSpec 5 software. Band component analysis using the Fityk software package enabled the type of fitting function to be selected and specific parameters to be fixed or varied accordingly.

The Raman spectrum of a deposited TiN film is shown in figure 4. The Raman spectrum of the TiN layer can be fitted with Gaussian-Lorentzian peaks at 260, 330, 418, and 584 cm–1. The spectrum is the same as those of TiN films reported, also with very poor quality, in the literature (Y.H. Cheng et al., “Substrate bias dependence of Raman spectra for TiN films deposited by filtered cathodic vacuum arc,” Journal of Applied Physics, Vol. 92, 2002, pp. 1845–1849). Slight variations in peak position, shape, and relative intensity can be influenced by thickness (C.C. Chen et al., “Raman spectra of titanium nitride thin films,” Chinese Journal of Physics, Vol. 32, No. 2, 1994, pp. 205–210), treatment time, and deposition temperature of TiN films (R.R.M. de Sousa et al., “Cathodic cage plasma deposition of TiN and TiO2 thin films on silicon substrates,” Journal of Vacuum Science & Technology A, Vacuum, Surfaces and Films, Vol. 33, No. 4, p. 041502), as well as substrate bias.

Figure 4. Raman spectrum of the TiN film in the 100–800 cm–1 region. The Raman
bands are related to transverse acoustic (at 260 cm–1), longitudinal acoustic
(330 cm–1), second-order acoustic (418 cm–1), and transverse optical (584 cm–1)
modes of TiN, respectively (Cheng et al., 2002). The poor quality of the spectrum,
despite a long collection time and enhanced sensitivity, is due to the faint response
of the TiN to Raman investigation (as well as to the extreme thinness of the coating);
it is comparable to the reported spectra available in the literature.
The TiN films also contained a small quantity of crystalline phase of TiO2 (i.e., brookite) that was identified in the bead coating using Raman spectroscopy. There was a close match between the collected spectrum and that of brookite available in the RRUFF database (R050363). The association of TiN and TiO2 films is well known and widely studied (de Sousa et al., 2015).

TiN deposition is widely used for the coating of small mechanical parts or tools, giving them a higher resistance to corrosion and scratching. Therefore, TiN films are essential for applications such as wear-resistant coatings, diffusion barriers, and optical coatings. The coating typically produces a golden hue, but other colors are also possible. Even though TiN films are common in industrial applications, this may be the first time such a coating has been reported in gemology. Source: GIA @topic:13


Title: Internal World of Aquamarine from Xinjiang Abstract: Figure 1. Hematite inclusions extend from the center of an aquamarine sample from Xinjiang, China. Photomicrograph by Yubing Chen; field of view 3.64 mm.
The authors recently examined a batch of aquamarine samples from the Xinjiang autonomous territory of China. Microscopic observation revealed rich and colorful features.
The aquamarines contained yellow-brown to black-brown inclusions. Microscopic observation and further Raman analysis confirmed that these dot-like, flaky, and dendritic yellow-brown to black-brown inclusions were hematite. Interestingly, when observed with a microscope using LED white light illumination, the hematite inclusions appeared to extend from the center to the periphery, and the overall hexagonal shape resembled a rose floating on a calm sea (figure 1).

Figure 2. Thin-film liquid inclusions and visible internal tubes parallel to the c-axis with spectral interference colors were observed in the aquamarine samples. Photomicrograph by Yubing Chen; field of view 0.70 mm.

Figure 3. Disk-shaped fissures in the aquamarine were caused by solid inclusions in the middle with tubular fissures extending inward. Photomicrograph by Yubing Chen; field of view 1.50 mm.
Colors generated by interference phenomena are very common in gemstones. A number of thin-film liquid inclusions were seen in the aquamarines, along with the spectral interference color phenomenon parallel to the c-axis (figure 2). Many disk-shaped inclusions (figure 3) were also found. Stress fractures were caused by solid inclusions in the middle to the surrounding areas, and tubular fractures extended in the direction perpendicular to the disk-shaped fractures. The disks were filled with thin films of liquid, and the interference phenomenon could be seen under the microscope using oblique fiber-optic illumination. The entire disk-shaped inclusion resembled a jellyfish floating in the sea. Source: GIA @topic:3


Title: Plastic Imitations of Emerald Abstract: Figure 1. An imitation emerald in the form of a chess knight measuring approximately 35.05 mm in height. Photo by Kristin Reinheimer.

Figure 2. A closer look at the knight’s head (left, in daylight) reveals the material’s aggregate structure when viewed under long-wave ultraviolet light (right). Photos by Emily Jones.
GIA’s New York laboratory recently examined two imitations, each submitted for an emerald identification report, that might have been convincing to the untrained eye. One was a chess piece weighing 46.55 ct (figure 1). At a glance, the knight appeared to be carved emerald with remnants of metallic yellow “matrix” still intact. However, the low heft and relatively warm feel of the piece suggested otherwise. Microscopic examination revealed an aggregate structure composed of jagged blocks, clearly illustrated under long-wave ultraviolet light due to its marked whitish fluorescence, typical of plastic (figure 2). The presence of gas bubbles and bluish dye concentrations indicated that the material was in fact an assemblage. The lack of a polished surface prevented a refractive index reading. Infrared and Raman spectroscopy were used to identify the main component as plastic; no beryl was detected. The metallic yellow crystal fragments were identified as pyrite, consistent with matrix associated with natural emeralds, notably those from Colombia.

Figure 3. An assemblage of plastic and various minerals imitating rough emerald in matrix, measuring approximately 51.79 mm in height. Photo by Michele Wong.

Figure 4. Gas bubbles and bluish green dye concentrations indicate that this “crystal” is in fact a manufactured product. Photomicrograph by Abadie Ludlam; field of view 8.23 mm.
The second imitation emerald (figure 3) was in the form of an elongated hexagonal “rough” emerald crystal embedded in a “matrix” of white and metallic yellow crystals, with a total weight of 179.71 ct. It too appeared natural to the unaided eye, but microscopic examination quickly distinguished the specimen as an imitation. The “emerald” portion of the rough contained large gas bubbles as well as bluish green dye concentrations (figure 4), an overall blotchy color appearance, and parallel surface striations. This material was identified as plastic using Raman and infrared spectroscopy. The surface striations were presumably created in the mold or carved to resemble the texture of a rough emerald crystal. Raman spectroscopy revealed that the smaller crystals mixed into the plastic were quartz and beryl. The white portion of the “matrix” was identified as calcite and the metallic crystals as pyrite, making this piece another convincing imitation of Colombian emerald.
The natural materials incorporated into these mostly plastic manufactured products might lead some astray upon first inspection. These two pieces demonstrate the need for a deeper inspection of all materials, regardless of how genuine they may seem on the surface. Source: GIA @topic:3


Title: Volcano-Shaped Internal Feature in Trapiche-Like Sapphire Abstract: Figure 1. Each of these trapiche-like sapphires from Changle, Shandong Province, has a brown-black hexagonal core in the center and six white radiating arms. Three of the four sample slices weigh ~3.1 ct with a thickness of ~2.1 mm; the sample slice on the bottom right weighs ~0.7 ct with a thickness of ~1 mm. Photos by Suqin Xia.
Trapiche-like sapphires with hexagonal color zoning have been found in the Changle area of Shandong Province, China. Samples examined by the authors possessed a brown-black hexagonal core and a distinct six-rayed pattern (figure 1). The six rays or fibrous arms were oriented perpendicular to the sides of the core and the hexagonal growth structure. Graphite was randomly distributed in the dark core region in this sapphire, identified by Raman spectroscopy.

Figure 2. Inclusions along the white arms of trapiche-like sapphire. A: Thin-film inclusions display colorful interference colors under reflected light. B: Triangle-shaped fissures, which are perpendicular to the crystallographic c-axis, resemble overlapping hills, including a volcano just right of center. These fissures show spectral interference colors under reflected light. C: In transmitted light, the pattern of inclusions resembles a Chinese landscape painting with a volcano in it. Photomicrographs by Xiaojing Lai; fields of view 0.30 mm (A) and 0.15 mm (B and C).
Through further microscopic observation, we found that these fibrous arms were composed of thin-film fluid inclusions and fine fissures generally parallel to their elongation direction (figure 2). Many of these inclusions were two-phase, containing both gas and liquid, and a few were gas-liquid-solid three-phase. Interestingly, the fissures were triangular, scalloped, striped, or irregular in shape and about 10 to 40 μm in size, with spectral interference colors (figure 2A). With overhead lighting, the internal features presented a dramatic scene reminiscent of a post-eruption volcano surrounded by overlapping hills and rivers (figure 2B). In transmitted light, however, the same features resembled a Chinese landscape painting, and the previous “rivers” looked more like clouds surrounding the volcano and hills (figure 2C). The internal features found in this sapphire are interesting to gemologists both scientifically and artistically. Source: GIA @topic:3


Title: Inclusion-Rich Black Topaz from the Thomas Mountains, Utah Abstract: Figure 1. The black appearance of a topaz was due to these small dark mineral inclusions. Photomicrograph by Jonathan Muyal; field of view 1.44 mm.

Topaz is an important gemstone that occurs in various colors. The authors had the opportunity to examine some unusual black topaz crystals and crystal fragments whose appearance was the result of numerous small dark mineral inclusions (figures 1 and 2). The topaz originated from an undisclosed locality in the Thomas Mountains in Juab County, Utah. They were provided by Shaun Rasmussen and Krisann Morrill (SK Star Claims, Provo, Utah), who discovered the occurrence. Careful microscopic examination revealed the presence of several inclusion minerals (figure 3, top). Among these were thin, translucent brownish plates of annite/phlogopite mica; transparent colorless, spherical crystals of fluorite; and opaque black octahedral crystals of magnetite. These minerals, which are well-known inclusions in topaz, were confirmed by Raman microspectrometry.

Figure 2. A black topaz crystal specimen from the Thomas Mountains in Utah (24.8 × 17.92 × 12.29 mm). Photo by Kevin Schumacher.

Figure 3. Top: Inclusions seen in this photomicrograph include black magnetite, colorless fluorite, and brown annite/phlogopite. Bottom: Clusters of tabular wolframoixiolite crystals along with fluorite and mica inclusions. Photomicrographs by Jonathan Muyal; fields of view 0.288 mm (top) and 0.36 mm (bottom).
The most abundant inclusions—and apparently the principal cause of the black appearance—were numerous opaque flattened or stubby crystals of wolframoixiolite (figure 3, bottom), a rare complex oxide mineral with the ideal formula (Nb,W,Ta,Fe,Mn,Nb)2O4 (N. Ray, “Mineralogy and geochemistry of unusual localized W-Nb included black topaz from the Thomas Mountain Range, UT,” unpublished and undated manuscript, provided by SK Star Claims to the authors). Quantitative chemical analysis by LA-ICP-MS revealed a composition of 1.66 wt.% CaO, 2.28 wt.% TiO2, 5.52 wt.% MnO, 19.93 wt.% Fe2O3, 1.94 wt.% ZrO2, 24.66 wt.% Nb2O5, 1.17 wt.% MoO3, 1.17 wt.% Ta2O5, 40.15 wt.% WO3, and 1.53 wt.% other elements. This gave a calculated chemical formula of (Ca0.074, Ti0.071, Mn0.193, Fe3+0.620, Zr0.039, Nb0.461, Mo0.020, Ta0.013, W0.430, others0.026)1.948O4, which is consistent with the chemistry of this uncommon mineral.
The presence of both magnetite and wolframoixiolite inclusions in the topaz resulted in a slight magnetic behavior. The corroded and sometimes altered appearance of both dark inclusion phases suggests that they represent protogenetic inclusions that formed during an earlier stage of mineral crystallization in the growth environment and were subsequently incorporated within the topaz. In spite of their abundance, these different inclusion minerals did not create any optical phenomena.
We thank those who provided these samples, which represent the first black-appearing topaz we have examined. Source: GIA @topic:2


Title: Mexican Demantoid from New Deposits Abstract: Figure 1. Demantoid was recently discovered in Veracruz State, Mexico. The photo on the left shows an association of topazolite + demantoid. Demantoid crystals are seen in the photo on the right. Photos by Mikhail Ostrooumov.

	Gemologists have recognized three andradite varieties: melanite (black), topazolite (yellow-brown), and demantoid. Demantoid, the yellowish green to green variety, is the most important to the jeweler-gemologist. The traditional demantoid garnet sources are Russia (Ural Mountains) and Italy (Val Malenco and Sondrio). More than 20 years ago, small garnet crystals of pale yellowish green color were found in the Sonora andradite occurrence near the Mexican city of Hermosillo (Fall 1994 GNI, p. 194). This garnet has been classified as demantoid without any detailed gemological and mineralogical analysis.

	It is very interesting to note that in some deposits of metamorphic skarns (e.g., Kamchatka, Russia; Val Malenco, Italy; and Arizona, USA), the demantoid crystals are associated with topazolite (E.P. Kievlenko, Geology of Gems, Ocean Pictures, Littleton, Colorado, 2003). In late 2014, our investigations showed that the same mineralogical association (figure 1, left) is characteristic for the Las Vigas Mexican topazolite source (Fall 2014 GNI, pp. 246–247). These green to yellow-green garnet crystals, measuring 1.5–5.5 mm, are also hosted by the Las Vigas skarn deposits (Cerro de la Concordia, in Las Vigas de Ramirez municipality and the Piedra Parada mine in Tatatila municipality). These deposits are located in Veracruz State, about 50 km southeast of the town of Valle de Veracruz. Studying crystals from these two new Mexican deposits with different analytical techniques, the mineral was identified as demantoid garnet (figure 1, right).

	Three samples of rough demantoid (measuring 4.0–5.5 mm in the longest dimension) were characterized for this report, and the following gemological properties were determined: color—green; polariscope reaction—isotropic and weakly anisotropic; weak strain birefringence; RI—nα = 1.888–1.889; very strong dispersion, at 0.055 (visual indicator identification); hydrostatic SG—3.82–3.88; fluorescence—inert to both long- and short-wave UV radiation.

	The garnet composition was determined by means of electron microprobe analysis (EPMA), using a total of 15 analysis points. Standard conditions of 20 kV, 20 mA, and 1 µm beam size were used with a JEOL JSM-35c microprobe. The analyses showed little compositional heterogeneity or zonation. The structural formula was calculated on the basis of 12 oxygen atoms, yielding an average approximate composition of (Ca2.96 Fe2+0.08)3.04 Fe3+2.05 Si2.94O12. This structural formula has an abundance at the X-site and Y-site cations but is close to electroneutrality due to the sum of the positive and negative charges (Wc = +23.99; Wa = –24.00). The EPMA-WDS data showed that these green garnets were almost pure andradite (And 95.60 mol.%). No chromium was detected in the chemical composition of the studied crystals.

	Infrared transmission spectra were measured with a Bruker Tensor 27 FTIR spectrometer, scanning from 4000 to 400 cm–1 and using the KBr pellet method. The pellets were prepared by mixing approximately 3 mg of the sample with 300 mg KBr. OPUS software was used for the spectroscopic interpretation of the infrared spectra. Raman (figure 2, left), mid-infrared (figure 2, right) and X-ray analysis confirmed that the crystals belonged to the demantoid variety (http://rruff.info). The mid-IR spectra showed the presence of hydroxyl groups. The infrared spectra consisted of a prominent band at 3420 cm–1, with a secondary band at about 3610 cm–1 due to the fundamental OH stretching vibration of water molecules, as well as the water bending vibration at approximately 1650 cm–1.

	Figure 2. Raman (left) and infrared (right) spectra of the samples confirm their demantoid garnet identity.

	UV-Vis-NIR spectroscopy showed absorption bands at 403, 444, 574, 617, 854, and 1170 nm, which can be assigned to spin-forbidden crystal-field transition of Fe3+, substituted on the octahedral Al3+ site of the garnet structure. Our EPMA analyses of garnet generally indicated the presence of some divalent iron. The spectra showed absorption bands in the 900–1000 nm and 1150–1250 nm ranges, which are assigned to Fe2+, and corresponding absorption features were observed at about 860 and 1170 nm. The simultaneous presence of both Fe3+ and Fe2+ means that intervalence charge transfer is possible (in accordance with A.S. Marfunin, Advanced Mineralogy, Vol. 2, Springer-Verlag, Berlin, 1995, pp. 113–114), and the 574 nm band is therefore assigned to an Fe2+→Fe3+ intervalence charge transfer band. The typical absorption bands of Cr3+ in the visible region between 630 and 690 nm are absent, consistent with the EPMA results. Our investigations have also shown that some demantoid garnets from Russia do not show any chromium absorption, and their color is due to the presence of Fe3+ alone.

	The color measuring system of the International Commission of Illumination (ICI) has been found useful for describing the color characteristics of minerals (K. Langer et al., “Optical absorption spectroscopy,” in A.S. Marfunin, Ed., Advanced Mineralogy, Vol. 2, Springer-Verlag, Berlin, 1995, pp. 119–122). The color of a mineral is assigned to a point in the x-y coordinates of the ICI color chart. Special computer programs are used to calculate the color parameters (x-y coordinates, λ—dominant wavelength, P—saturation or purity, Y—lightness) of a mineral directly from the measured optical absorption spectrum. The dominant wavelength λ, or hue, is the human eye’s psycho-sensory interpretation of wavelengths that are identified by the x-y coordinates of the ICI color chart. Preliminary colorimetric calculations showed that the colors of the Mexican demantoid have low saturation (P=20%) and lightness (Y=17%). Therefore, they are darker than pure green demantoid from other deposits (e.g., Bobrovka River in the Ural Mountains). The dominant wavelength of Mexican demantoid (λ=560 nm) is a slightly yellowish green. This combination of colorimetric parameters defines a color different from that of chromium-bearing demantoid. Measurements on the demantoid from the Urals showed higher values of saturation (P=44–50) and lightness (Y=20–37%) and a purer green hue, with λ=530–545 nm (M. Ostrooumov, “Colorimetry of minerals,” Priroda, No. 6, 1987, pp. 43–53, in Russian). Such demantoids are more attractive to the gem trade.

	Thus, electron microprobe (EPMA-WDS) chemical analyses, various spectroscopic techniques, X-ray diffraction, and standard gemological testing have confirmed the discovery of demantoid in the Las Vigas skarn deposits of Veracruz State. The discovery could represent an interesting mineralogical and gemological opportunity. Although the full range and economic potential of this demantoid has not been determined, it may well have features that distinguish it from other important deposits worldwide. Source: GIA @topic:2


Title: Book Review: Minerals of Georgia: Their Properties and Occurrences Abstract: By Robert B. Cook and Julian C. Gray, softcover, 326 pp. illus., publ. by the University of Georgia Press, Athens, Georgia, 2016, $32.95.

	This book is an updated version of Dr. Cook’s original volume, published in 1978. It has a revised format as minerals are listed alphabetically rather than by chemical class, with allowances given to mineral groups such as garnet and tourmaline.

	The description of the geology is not overly technical but still gives the big picture. The distinction is made between crystalline and sedimentary regions. The state has five distinct geologic provinces. The Piedmont and Blue Ridge provinces of northern Georgia are underlain almost exclusively by metamorphic and igneous rocks. The Coastal Plain, which covers the southern half of the state, mostly consists of unconsolidated sediments and some limestones. In the northwest corner of the state, the Cumberland Plateau contains relatively undeformed Paleozoic sediments while the Ridge and Valley regions consist of folded sedimentary rocks.

	In-depth sections focus on the state’s remarkable finds of rutile and amethyst. Georgia’s amethyst is considered the nation’s finest. The Charlies Creek material is quite distinctive, as it occurs in short single crystals or groups of only two or three distinctly color-zoned crystals. In either instance, amethyst is found in the rhombohedral zones of the pyramidal terminations. The prismatic sections are often colorless. Jacksons Crossroads in Wilkes County has produced the finest amethyst in the United States. Spectacular specimens have found their way into important private collections, while faceted material with deep purple color is entering the gem market. Benny Ray specimens are quite different from those found at Charlies Creek or Jacksons Crossroads, occurring in irregular narrow pockets in massive milky vein quartz.

	Graves Mountain is famous for its rutile specimens and fine lazulite. The rutile crystals are unsurpassed in terms of crystal perfection, twinning, size, and luster. Fifty–one mineral species are reported from this locale.

	The highlight of the book is the chapter with alphabetical descriptions of Georgia’s mineral species. Every mineral is fully documented: chemical formula, classification, crystallographic information, habit, physical properties, and occurrences listed alphabetically by county.

	The volume is successful in presenting the most accurate, up-to-date information available on the subject. It is the ultimate bible of Georgia’s mineralogy. The work is well written and illustrated, with more than 150 color photographs. It is suited for collectors, mineralogists, and treasure hunters. It contains handy appendix sections, complete with a County Index, a Locality Index with mineral occurrences, and a Mineral Index. I highly recommend it. Source: GIA @topic:1


Title: Amber with Mite Inclusion Abstract: Figure 1. A mite with exceptionally long front legs (2.1 mm), as seen using shadowed transmitted and fiber-optic illumination (left), was found in this small 13.15-mm-long fragment of amber (right). Images by Nathan Renfro.

              A most unusual mite (figure 1, left) was discovered as an inclusion in an approximately 30-million-year-old double-polished plate of amber from the Dominican Republic (figure 1, right). The specimen was acquired from the private collection of William W. Pinch of Pittsford, New York. The plate itself weighed 0.77 ct and measured 13.15 × 7.59 × 2.76 mm, while the mite’s body was 0.34 mm in length.

What made this mite unusual was that the longest front leg measured approximately 2.10 mm, disproportionately long in relation to the rest of its body. This type of mite, of the genus Podocinum, might be awkward-looking, but its morphology has survived millions of years virtually unchanged, an indication that it was just as efficient a predator then as its living counterpart today. Podocinum is a very slow-moving mite that lives in loose soil, feeding on springtails (Collembola). As it travels about, the mite uses its extremely long front legs to explore the soil around it and quickly snare any springtail that happens to come too close.

A literature search failed to turn up any other example of a Podocinum mite as an inclusion in amber, making this an even more interesting specimen. So while a small polished piece of amber itself might have virtually no commercial or scientific value, the addition of a well-preserved microscopic organism completely changes the value factor of the specimen. Source: GIA @topic:14


Title: Appendix 5: Simplified Tourmaline Species Classification for LA-ICP-MS Data Abstract: Abbreviations used below:
TSi: T-site Si atoms per formula.
YZR2+: Y+Z-site total divalent cation.
Vac: Vacancy
Decide which primary group the tourmaline belongs to:
If Na+K(+Rb+Cs) is greater than both Ca(+Pb) and the X-site vacancy (X□apfu), the tourmaline belongs to the alkali primary group. If Ca(+Pb) is greater than both Na+K(+Rb+Cs) and X□apfu, the tourmaline belongs to the calcic primary group. If X□apfu is greater than both Na+K(+Rb+Cs) and Ca(+Pb), the tourmaline belongs to the vacant primary group (Henry et al., 2011).
Alkali-group tourmaline – classify alkali subgroups 1 and 2.
If TSi is greater than 4.5 and YZR2+/(2Li+ YZR2+) is greater than 0.5, the tourmaline belongs to alkali subgroup 1.
If TSi is greater than 4.5 and YZR2+/(2Li + YZR2+) is less than or equal to 0.5, the tourmaline belongs to alkali subgroup 2.
Otherwise the tourmaline belongs to alkali subgroups 3, 4, or 5, which are not considered here.
Alkali subgroup 1
If Al3+ is the dominant trivalent cation on the Z-site and Mg2+ is the dominant divalent cation on the Y-site, the tourmaline is dravite.
If V3+ is the dominant trivalent cation on the Z-site and Mg2+ is the dominant divalent cation on the Y-site, the tourmaline is vanadium-dravite, now redefined as oxy-vanadium-dravite (Bosi et al., 2013).
If Cr3+ is the dominant trivalent cation on the Z-site and Mg2+ is the dominant divalent cation on the Y-site, the tourmaline is chromium-dravite.
If Al3+ is the dominant trivalent cation on the Z-site and Fe2+ is the dominant divalent cation on the Y-site, the tourmaline is schorl.
Alkali subgroup 2
If the tourmaline belongs to alkali subgroup 2, it is elbaite.
Calcic-group tourmaline – classify calcic subgroups 1 and 2.
If TSi is greater than 4.5 and YZR2+/(1.5Li+ YZR2+) is greater than 0.5, the tourmaline belongs to calcic subgroup 1.
If TSi is greater than 4.5 and YZR2+/(1.5Li+ YZR2+) is less than or equal to 0.5, the tourmaline belongs to calcic subgroup 2.
Calcic subgroup 1
If Al3+ is the dominant Z-site cation and Mg2+ is the dominant Y-site cation, the tourmaline is uvite.
If Al3+ is the dominant Z-site cation and Fe2+ is the dominant Y-site cation, the tourmaline is feruvite.
Calcic subgroup 2
If the tourmaline belongs to calcic subgroup 2, it is liddicoatite.
Vacant-group tourmaline – classify vacant subgroups 1 and 2.
If TSi is greater than 4.5 and YZR2+/(2Li+ YZR2+) is greater than 0.5, the tourmaline belongs to vacant subgroup 1.
If TSi is greater than 4.5 and YZR2+/(2Li+ YZR2+) is less than or equal to 0.5, the tourmaline belongs to vacant subgroup 2.
Vacant subgroup 1
If Al3+ is the dominant Z-site cation, and Fe2+ is the dominant Y-site cation, the tourmaline is foitite.
If Al3+ is the dominant Z-site cation and Mg2+ is the dominant Y-site cation, the tourmaline is magnesio-foitite.
Vacant subgroup 2
If the tourmaline belongs to vacant subgroup 2, it is rossmanite. Source: GIA @topic:12


Title: Synthetic Sapphire with Diffusion-Induced Color and Star Abstract: Figure 1. This 24.58 ct star cabochon was a colorless synthetic sapphire whose color and star had been induced by diffusion treatment. Photo by Sutas Singbamroong.

The Dubai Central Laboratory recently examined an asteriated blue oval cabochon that weighed 24.58 ct and measured 17.37 × 14.61 × 9.59 mm. The client submitted the sample for an identification report and origin determination.

The cabochon appeared to be completely transparent, evenly colored, and clean. Fiber-optic lighting revealed two sharp, six-rayed white stars with long, straight arms of equal length. The stars seemed to float over the dome surface with internal reflection from the base, very similar to those typically seen in synthetic star sapphires (figure 1).

Standard gemological testing established the following properties: spot RI—1.76; pleochroism—distinct light green and bluish violet (viewed parallel to the girdle); hydrostatic SG—3.98; and fluorescence—inert to both long- and short-wave UV radiation. No characteristic absorption spectrum was seen with a desk-model spectroscope; a faint absorption band was observed at about 560 nm. These properties were consistent with sapphire, though the sample did not show the Fe line at 450 nm commonly seen in natural blue sapphire. Observation of the cabochon immersed in water with diffused transmitted light revealed shallow coloration and a colorless circular area of repolishing (figure 2). This suggested that the specimen owed its color to a diffusion process. The melted appearance of the cabochon’s base confirmed that it had been subjected to the heat required for diffusion treatment. Microscopic examination showed only a few small melted fingerprint-like inclusions near the surface, and very fine oriented needle-like inclusions confined to a shallow layer below the surface (figure 3). No curved color banding or angular color zoning was present. Higher magnification indicated that the oriented needles were approximately 5–25 microns long. Further examination with immersion in methylene iodide between crossed polarizers, viewing parallel to the optic axis direction, uncovered the distinct Plato lines strongly indicative of Verneuil synthetic origin.

Figure 2. Immersed in water and viewed with diffused transmitted light, the star cabochon
showed shallow coloration with a colorless circular area of repolishing. This feature, along
with the melted appearance of the base, indicated that the color and asterism had been
produced by a diffusion process. Photo by Sutas Singbamroong.

Figure 3. Very fine oriented needle-like inclusions causing the star were confined to a
shallow layer below the surface. Photomicrograph by Sutas Singbamroong, magnified 25×.
EDXRF chemical analysis revealed traces of Ti, Fe, and V; no Ga, Cr, or other trace elements were detected. Unoriented UV-Vis-NIR absorption spectroscopy showed two broad bands, one centered at about 330 nm due to Fe3+ ions, and one with maxima at about 565 nm due to Fe2+-Ti4+ intervalence charge transfer (figure 4). No Fe3+-related sharp bands at approximately 375, 390, and 450 nm were seen.

Figure 4. An unoriented UV-Vis-NIR spectrum of the diffusion-induced star synthetic
sapphire exhibited two broad bands centered at about 330 and 565 nm, the latter of which
is typically responsible for sapphire color.
This combination of properties and features indicated that colorless synthetic sapphire was used as a starting material, and both the color and the asterism were produced by a diffusion process. Source: GIA @topic:3