gems, chrysoprase, chalchedony, quartz, Turkey, Biga–Çanakkale

The commercial quantities of gem-quality dark green chrysoprase are found as fracture fillings covered with a weathering crust in the silicified serpentinites throughout the border of a metamorphic zone in the Biga–Çanakkale region of Turkey. However, green-stained opaque quartz materials are also present in the same deposit, but these materials are common and in low demand compared to chrysoprase in terms of gemmological importance. Thus, it is necessary to distinguish these two similar materials from each other non-destructively. In addition, all chrysoprase roughs in this deposit also have alpha-quartz and moganite inclusions. Accordingly, dispersive (visible) confocal micro-Raman spectroscopy (DCμRS) allows us to distinguish clearly the chalcedonic-quartz silica phase (fibrous quartz (chalcedony)) from the crystalline-quartz silica phase (fine-grained alpha-quartz) in the case of both quartz inclusions in the chrysoprase material and the green-stained quartz material in the same deposit. This study characterizes the Biga chrysoprase (Turkey) in terms of silica building phases, chemical content, and individual Raman bands, using several destructive and non-destructive analytical techniques. The Raman spectra show that the most characteristic intensive and the widest Raman bands peaked at about 498 and 460 cm⁻¹ can be inferred to ν₂ doubly symmetric bending modes of [SiO₄/M] centers. The “M” includes some cationic substitutions of Si by Fe, Cr, Mn, As, Ni, Pb, Sb, and Zn, and K and Na as well. The second characteristic Raman band peaked at about 206 cm⁻¹ can be inferred to a single translational libration mode. The last readable Raman bands peaked at about 139 and 126 cm⁻¹ can be inferred to doubly translational libration modes as well. In addition, the weaker Raman bands peaked at about 1577, 1430, 1303, 1160, 1082, 549, 394, 352, and 259 cm⁻¹ are also present. As a result, the dispersive confocal micro-Raman spectrum of chrysoprase is directly related to its silica building phases and trace element implications.