Feature Gems & Gemology, Summer 2008, Volume 44, No. 2

Coated Tanzanite

Examination of 23 tanzanites coated by an apparently new technique revealed that the smaller stones (4–5 mm) could be identified as coated based on a combination of the unusually intense color and microscopic examination, which revealed surface iridescence as well as wear on facet junctions (small areas where the coating was abraded away). The two larger (3+ ct) stones did not show iridescence or wear, only small clues with high magnification, and therefore were much more difficult to identify. EDXRF and LA-ICP-MS analyses showed the presence of Co, Zn, Sn, and Pb in the coating.