gems, garnet, andradite, Turkey

In October 2007, Alexandra Woodmansee (Rock Logic, Glencoe, Minnesota) informed GIA of a new demantoid garnet find in eastern Turkey. She acquired both rough and faceted samples, some of which she loaned to GIA for study in time for the 2008 Tucson gem shows. Her supplier, Kerem Özütemiz of Truva Mining Ltd. in Ankara, owns the claim near Erzincan, 700 km east of Ankara, where mining is limited to three months a year (June–August) due to harsh winters. Using pneumatic hammers and hand tools, approximately 300 g of cuttable material was extracted in 2007 and about 120 g in 2008, though much of it was small and included. Mr. Özütemiz has had around 20 stones (0.5–1.2 ct) cut in Germany, along with about 300 carats of melee-sized stones. A gemological examination of 13 stones obtained by Mrs. Woodmansee showed that six were andradite (including demantoid) and seven were grossular (tsavorite). The source of the grossular was unclear, but it may have been mixed in at the cutting factory. The six andradite samples (0.15–0.38 ct) showed colors ranging from orangy brown and brownish yellow to yellow-green and yellowish green, with the latter four identified as demantoid. Refractive index was >1.81, specific gravity ranged from 3.82–3.93 for brown/yellow stones and 4.17–4.43 for green ones. All were inert to UV radiation and exhibited a 440 nm cutoff in the spectroscope. Microscopy revealed radiating curved fibrous needles with fractures (some filled), blocky fingerprints, and cubic growth zoning. These features, aside from high SG, align with known andradite properties. Notably, the demantoid samples exhibited distinctive brown and green cubic color zoning, similar to material from Iran. Electron microprobe analysis at the University of Oklahoma confirmed that the garnets contained 93.4–98.9 mol% andradite component. The demantoid samples were rich in chromium (0.09–1.45 wt.% Cr₂O₃), while the orangy brown andradite had the highest titanium content (0.13 wt.% TiO₂).