Feature Gems & Gemology, Summer 2011, Volume 47, No. 2

Research on Gem Feldspar from the Shigatse Region of Tibet

The existence of a natural red andesine deposit in China/Tibet has been the subject of controversy since 2006. In late September 2010, an international group traveled to the Shigatse region of Tibe tand visited two reported andesine occurrences, at Zha Lin village and the Yu Lin Gu alluvial fan. These sites are located ~3 km from the previously investigated Bainang andesine mining area near Nai Sa village. The Zha Lin deposit appeared genuine, but the group could not confirm the authenticity of the Yu Lin Gu occurrence, and no primary andesine-bearing source rocks were found in either area. Some of the samples had glassy surface residues that are difficult to explain naturally, while initial argon isotopic measurements of a few Zha Lin and Yu Lin Gu andesines (without glassy residues) showed that they had not been heated. Laboratory studies of the Tibetan samples—and a comparison to known-treated red andesine from Inner Mongolia—showed that it may be possible to separate these feldspars using a combination of several advanced destructive techniques, but this methodology is not practical for gem testing laboratories. More detailed investigations will be needed to establish feasible identification criteria for natural-color andesine from Tibet.