Gemmological and mineralogical investigations and genesis of the massive dark green chrysoprase from the Biga-Çanakkale region

While the major commercial chrysoprase deposits in Turkey are present in about five different regions, namely Çanakkale, Eskişehir, Bilecik, Erzurum and Mardin, the most important deposit of gem-quality chrysoprase is located in the Biga?Çanakkale region. Therefore, the present study is focused on the Biga chrysoprase deposit, which is found as fracture fillings covered with a weathering crust in the silicified serpentinites throughout the border of a metamorphic zone. Several previously undocumented characteristics of Biga chrysoprase are described for the first time during this investigation. Some of the Biga chrysoprase samples have been cut and polished into cabochons and slabs as gem objects to show its typical color and quality.Average bulk (XRF) and trace element (ICP-AES) chemical analyses reveal relatively higher concentrations of some trace elements, such as Fe, Cr, Mn, As, Ni, Pb, Sb, and Zn are characteristics for Biga chrysoprase. Some of these elements can be found in any chrysoprase sample from Poland, Kazakhistan, Australia or Tanzania, even though the concentrations of some are unusual.In addition to other well-known analytical methods, Dispersive confocal micro-Raman spectroscopy (DCµRS), was used to characterize and identify in detail the Biga Chrysoprase samples. Accordingly, the strong micro-Raman bands that peaked at 1577, 1430, 1303, 1160, 1082, 549, 501, 460, 394, 352, 259, 206, 139 and 126 cm-1 are characteristics of Biga Chrysoprase.Biga chrysoprase samples also show numerous broad and intensive luminescence bands. Three different luminescence spectra of the Biga chrysoprase [photoluminescence (PL), cathodoluminescence (CL), and thermoluminescence (TL)] were taken into consideration, and evaluated.Finally, gemmological, mineralogical and spectroscopical data provide positive identification of the provenance of Biga chrysoprase. It can be seen that the these data provide a unique fingerprint for this kind of chrysoprase gem material.