Spectroscopic and geochemical fingerprints for chromophore identification and origin determination of Davdar emeralds from Xinjiang, China.

High quality emeralds were discovered in Davdar County, northwestern China, in 2000. This study provides comprehensive data through standard gemological testing, spectroscopic techniques including FTIR, UV-Vis-NIR and Raman, and LA-ICP-MS elemental analysis. Davdar emeralds exhibit relatively low refractive indices (RI) and specific gravity (SG) values. They contain abundant two- and three-phase inclusions, which contain gas bubble (CO2), liquid and at least two kinds of crystals (colorless cubic crystal and siderite or phlogopite). Calcite and dolomite are common mineral inclusions in Davdar emeralds, and hematite is also observed. Graphite, rutile, talc and gypsum are relatively rare. FTIR spectra indicate that type II H2O absorption generally exceeds that of type I H2O. Raman spectra show that, in color-zoned emeralds, the type II H2O band is stronger than the type I H2O band in the core, whereas the opposite pattern occurs in the rim. Cr and V jointly lead to green color within Davdar emeralds. They contain low alkali metal, high Fe, Mg and Cr, moderate amounts of V, K, Sc and Li, as well as very low Ti, Cs, Ga, Rb and Ni. Davdar emerald can be preliminarily separated by Cs versus Li and Rb versus Cs 2D scatter plots and Fe-Cs-Rb 3D scatter plot.