Mineralogical-Petrographical and Gemological Investigation of Chalcedonies in Nebikoy, Tokat

Abstract

The chalcedony formations observed in the village of Nebikoy and its surroundings in Tokat province are found in Permian-Triassic metamorphic rocks as veins with a thickness a few mm to 10 cm. Chalcedony, which has color of light blue-blue tones, is generally banded and sometimes has a kidney-like structure.In thin sections made from chalcedony, fibrous acicular quartz minerals and microcrystalline quartz minerals were determined in a banded structure. Iron oxide fillings were encountered in the secondary dolomite formations and micro-fractured cracks that cut these minerals in places. Quartz and dolomite associations were detected in XRD analyzes of the chalcedony samples.The main oxides in the chalcedony sample taken from the study area were determined as 94.08% SiO2, 1.45% CaO, 1.06% MgO, 0.37% Al2O3 and 0.31% Fe2O3; In the host rock (metasandstone) sample, it was determined as 37.5% SiO2, 16% CaO, 8% MgO, 6% Al2O3 and 4% Fe2O3. In the chalcedony sample, enrichments were also observed in trace elements of 140.4 ppm As, 36.97 ppm Co, 5.4 ppm Ni and 1.45 ppm Cu; while in the host rock, enrichments were observed in trace elements of 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 and 1.5 ppm Bi.Cabochon cutting studies were carried out from the chalcedony samples taken from the study area to be used in jewelry. Considering the light-dark blue color tone, durability, massive structure and workability observed in an area of approximately 1 km(2), it was determined that the chalcedony in the region can be used as gemstones.