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Lab Notes Editors Thomas M Lab Notes Editors Thomas M. Moses | Shane F. McClure Faceted CHIOLITE Like their namesakes, they are some- Recently, the GIA lab in Carlsbad re- times found together, though chio- ceived a colorless 1.04 ct gemstone of lites are rarer. a material that was new to the lab This gem has a very low hardness (figure 1). The measured refractive (3.5–4 on the Mohs scale) and perfect index was 1.342–1.349 with a bire- cleavage. The stones are usually small fringence of 0.007 and an optic char- and nondescript. Nevertheless, chio- acter of uniaxial negative. The lite has joined the ranks of minerals specific gravity, measured hydrostat- cut by faceters who wish to try their ically, was 3.01. These properties hand at everything clean enough to were consistent with the mineral chi- cut, and a cut stone would make quite a specimen for a gem collection. olite, which was confirmed by Figure 1. This 1.04 ct colorless Chiolite occurs in some granite Raman spectroscopy (see figure 2 and octagonal cut was identified as pegmatites and is associated with ral- http://rruff.info/R050412). chiolite. Chiolite is a very rare transparent stonite, pachnolite, elpasolite, cryolite, to translucent colorless or snow- thomsenolite, cryolithionite, fluorite, white mineral with a vitreous luster, comes from Greek for “ice stone,” phenakite, and topaz (see mindat.org perfect cleavage in one direction, and while chiolite means “snow stone.” and rruff.info). a white streak. It crystallizes in the tetragonal system and is composed of Figure 2. Raman spectroscopy confirmed the colorless stone’s identity as sodium and aluminum, with the for- mula Na Al F (the presence of these chiolite. 5 3 14 elements was confirmed with EDXRF). The principal source of gem- RAMAN SPECTRUM quality material is Ivigtut, Green- 14000 land, where it occurs in association with cryolite. Other gem-quality sources include Miass in the Ilmen 12000 Mountains region of Russia, where it is found in a cryolite pegmatite, and the Morefield pegmatite mine in Vir- 10000 ginia (see AZoMining.com). The min- eral was first discovered at Miass in 1846. The name is very similar to COUNTS COUNTS 8000 cryolite, a related mineral. Cryolite 6000 Editors’ note: All items were written by staff members of GIA laboratories. 4000 GEMS & GEMOLOGY, Vol. 55, No. 3, pp. 416–425. 100 200 300 400 500 600 700 800 900 © 2019 Gemological Institute of America RAMAN SHIFT (cm–1) 416 LAB NOTES G EMS & GEMOLOGY F ALL 2019 tering micro-inclusions consistent with those that have been reported to be graphite (B. Rondeau et al., “Three historical ‘asteriated’ hydrogen-rich diamonds: Growth history and sector- dependent impurity incorporation,” Diamond and Related Materials, Vol. 13, No. 9, 2004, pp. 1658–1673) that correlate strongly with the presence of hydrogen (W. Wang and W. Mayer- son, “Symmetrical clouds in dia- mond—the hydrogen connection,” Journal of Gemmology, Vol. 28, No. 3, 2002, pp. 143–152). Also observed was brown radiation staining in a Figure 3. This 3.70 ct brownish greenish yellow faceted octahedron con- shallow feather, indicating that the tained a remarkable stellate hydrogen cloud (left) that showed strong yel- stone had been exposed to natural lowish green fluorescence under long-wave UV light (right). alpha radiation (figure 5). While the cutting style was un- conventional, it served to showcase Chiolite is difficult to cut, ex- ing star-like clouds are sometimes re- the remarkable inclusion scene con- tremely rare, and has little commer- ferred to as “asteriated” in the trade tained within the diamond. This is cial appeal. It is solely a curiosity in (T. Hainschwang et al., “The Rhode- one of the most interesting diamonds the gem world. sian Star: An exceptional asteriated of this type examined at GIA’s Carls- bad laboratory. Forozan Zandi diamond,” Journal of Gemmology, Vol. 34, No. 4, 2014, pp. 306–315). Maryam Mastery Salimi and While GIA occasionally encounters Nathan Renfro asteriated diamonds, this one was Faceted DIAMOND Octahedron striking due to the well-defined na- with a Remarkable Stellate Cloud ture of the star and the strong yellow- GROSSULAR GARNET Crystals in Inclusion ish green color it exhibited under Demantoid Garnet A 3.70 ct faceted Fancy brownish long-wave UV (figure 3, right). Demantoid, the green variety of an- greenish yellow diamond (figure 3, Gemological examination re- dradite garnet, is a rare gemstone. It left) was recently submitted to the vealed a type Ia diamond, showing a typically possesses high dispersion Carlsbad laboratory for color origin typical cape series in the visible spec- and diamond-like luster, which is and identification service. The dia- trum. Hydrogen bands in the infrared often partly masked by the green and mond was remarkable in that it con- spectrum and the UV-Vis-NIR spec- yellow-green bodycolors. Variations tained an eye-visible stellate cloud trum were consistent with the ob- inclusion consisting of six legs that served “hydrogen cloud” inclusions each radiated to a point on the pol- (figure 4). These clouds in diamonds ished octahedron. Diamonds contain- consist of a high density of light scat- Figure 5. An irregularly shaped dark brown radiation stain on the diamond’s surface-reaching Figure 4. The six-ray star pattern is composed of microscopic particles inclusion clearly shows that it commonly referred to as “hydrogen clouds” (left) that fluoresce strong was exposed to natural alpha ra- green to long-wave UV (right). Field of view 6.27 mm. diation. Field of view 3.51 mm. LAB NOTES G EMS & GEMOLOGY F ALL 2019 417 TABLE 1. LA-ICP-MS results on three areas of the demantoid sample: the host material (spot 1), the outer area of the inclusion (spot 2), and the inner area of the inclusion (spot 3). Concentration (ppmw) of Mg Al Si Ca Ti V Cr Mn Fe different elements Spot 1 449 414 185000 275000 17.7 nda nd 328 186000 Spot 2 162 32200 205000 296000 338 4.66 nd 723 152000 Spot 3 127 85100 192000 271000 3570 10.4 nd 13000 57600 Detection limits (ppmw) 0.17 0.92 221 36 0.65 0.06 0.80 0.15 5.03 Wt.% oxides, converted MgO Al O SiO CaO TiO V O Cr O MnO FeO from LA-ICP-MS 2 3 2 2 2 5 2 3 Spot 1 0.1 0.1 39.6 38.5 0.0 nd nd 0.0 23.9 Spot 2 0.0 6.1 43.9 41.4 0.1 0.0 nd 0.1 19.6 Spot 3 0.0 16.1 41.1 37.9 0.6 0.0 nd 1.7 7.4 Normalized to 12 oxygen Mg Al Si Ca Ti V Cr Mn Fe O atoms Spot 1 0.01 0.01 3.38 3.52 0.00 nd nd 0.00 1.71 12.0 Spot 2 0.00 0.54 3.30 3.34 0.00 0.00 nd 0.01 1.23 12.0 Spot 3 0.00 1.42 3.09 3.05 0.03 0.00 nd 0.11 0.47 12.0 and refers to elemental concentrations below the detection limits of LA-ICP-MS. in the color of demantoid garnet are spectra of the two areas of the crystals ical analysis is better suited to sepa- generally caused by traces of were similar to that of the host, rate the species of garnet. chromium (Cr3+), ferric iron (Fe3+), matching with andradite garnet. Gar- In this case, laser ablation–induc- Fe2+-Ti4+ intervalence charge transfer, net species typically possess similar tively coupled plasma–mass spec- and Fe2+-Fe3+ interactions (G. Giu- physical properties and crystal forms, trometry (LA-ICP-MS) was used to liani et al., “Gem andradite garnet but differ in chemical composition. compare the chemical composition of deposits demantoid variety,” In- For example, andradite is a calcium- the demantoid against that of the sur- Color, No. 36, Summer 2017, pp. 28– iron garnet with the formula face-reaching inclusions. Spot 1 was 39). Ca Fe (SiO ) , whereas grossular is a on the host material, spot 2 on the 3 2 4 3 Recently, GIA’s Bangkok labora- calcium-aluminum garnet with the outer area of the crystal inclusion, and tory received a 4.47 ct yellowish green formula Ca Al (SiO ) . Those two gar- spot 3 on the inner area of the crystal 3 2 4 3 gemstone for identification. Standard net species are in the same isomor- (figure 8). gemological testing, including a re- phous series and therefore have the Surprisingly, the three spot areas fractive index over the limits of the same general chemical formula, but exhibited different chemical compo- refractometer and a specific gravity of differ only in containing Fe or Al. Due sitions, especially between the host 3.86, and Raman spectroscopy identi- to their similar Raman spectra, chem- demantoid area and the inner area of fied it as demantoid garnet. Micro- scopic examination revealed strong internal graining, fingerprints, and Figure 6. A cluster of transparent Figure 7. Some of the transparent particles mixed with short needles. octahedral crystals observed in a octahedral crystals reached the Interestingly, it also exhibited trans- yellowish green demantoid gar- surface of the demantoid. Field of parent octahedral crystals at the net. Field of view 1.2 mm. view 2.0 mm. crown (figure 6). Some of them reached the surface and had a different luster from the host material. Close examination showed that the crystals contained two different luster areas, which also distinguished them from the host demantoid (figures 7 and 8).
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