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Mineralogical and gemmological characteristics of garnets associated with xenoliths within trachyte dome, Hisarlıkaya (Ankara), Central Anatolia, Turkey

Garnet-bearing xenoliths are observed within a trachytic dome extrusion in the Hisarlıkaya region (Ankara). These garnets exhibiting greenish-reddish-dark brown colour and ranging in sizes up to 1 cm were examined in terms of mineralogical, geochemical, and gemmological characteristics. Mineralogical studies indicate that these garnets (And88-93 Grs7-12) are linked to solid solution series, which are dominantly andradite with lower content of grossular. According to major, trace, and rare earth element (REE) analysis | Turkish Journal of Earth Sciences Turkish J Earth Sci 2021 30 379-391 http journals.tubitak.gov.tr earth TÜBİTAK Research Article doi 10.3906 yer-2006-14 Mineralogical and gemmological characteristics of garnets associated with xenoliths within trachyte dome Hisarlıkaya Ankara Central Anatolia Turkey 1 2 1 Elif VAROL Sibel TATAR ERKÜL Güllü Deniz DOĞAN KÜLAHCI 1 Department of Geological Engineering Faculty of Engineering Hacettepe University Ankara Turkey 2 Department of Geological Engineering Faculty of Engineering Akdeniz University Antalya Turkey Received 15.06.2020 Accepted Published Online 11.02.2021 Final Version 17.05.2021 Abstract Garnet-bearing xenoliths are observed within a trachytic dome extrusion in the Hisarlıkaya region Ankara . These garnets exhibiting greenish-reddish-dark brown colour and ranging in sizes up to 1 cm were examined in terms of mineralogical geochemical and gemmological characteristics. Mineralogical studies indicate that these garnets And 88-93 Grs 7-12 are linked to solid solution series which are dominantly andradite with lower content of grossular. According to major trace and rare earth element REE analysis the representative garnet crystal shows high CaO Fe2O3 Al2O3 MgO MnO V W and light rare earth elements LREE concentrations. These high concentrations might indicate the mobility of these elements during skarn formation related with contact metamorphism material exchange occurring via hydrothermal fluids site geometry of the crystal ionic radius of cations and charge balance. The Hisarlıkaya garnets display dodecahedron-trapezohedron crystal habits with good translucency glassy transparent features and also optical isotropic character. Their refractive indices are high gt 1.78 and specific gravities range from 3.66 to 3.67 g cm3. These garnets are not suitable for use as gemstones since they cannot be cut or processed considering all the mineralogical properties of garnets. Key words Trachyte xenolith skarn garnet mineralogy