Mineralogical-petrographical investigation and gemological properties of chalcedonies of Nebiköy (Tokat)

The chalcedony, which is the subject of the study, is located in Nebiköy and its surroundings within Tokat. It is observed in the Permian-Triassic metamorphic rocks as veins reaching up to 10 cm in thickness. The chalcedony, displays light blue to blue colors, is generally with banding and kidney-like structure at some places. Quartz and dolomite associations were detected in XRD analyzes of chalcedony samples taken from the field. According to XRF analysis, 37.5% SiO2, 16% CaO, 8% MgO, 6% Al2O3, and 4% Fe2O3 were found in the country-rock. In the chalcedony sample, on the other hand, 94.08% SiO2, 1.45% CaO, 1.06% MgO, 0.37% Al2O3, and 0.31% Fe2O3 were found. According to ICP-MS analysis, the host rock contains 53.3 ppm V, 28.9 ppm Ni, 7.5 ppm Co, 4.8 ppm As, 4.6 ppm Cu, 2.4 ppm Mo, 2 ppm Ga, 1.5 ppm Bi elements. On the other hand, it was determined that the chalcedony sample contains 140.4 ppm As, 36.97 ppm Co, 5.4 ppm Ni, 1.45 ppm Cu. The chalcedony samples taken from the field are cut in cabochon to be used in jewelry. Considering the light and dark blue color tone, durability, massive structure and workability observed in an area of approximately 1 km2, it was determined that the chalcedony in the region can be used as a gemstone.