Investigations on minero-petrographic, spectroscopic and gemological properties of pyroxene crystals in pegmatite gabbro

Abstract

The ultramafic-mafic rocks in southwestern part of Turkey, are called as the Yeşilova ophiolite was firstly described by Sarp [1]. The Yeşilova ophiolite represents an ophiolite suite with missing row character and is comprised tectonites, followed upwards by ultramafic-mafic cumulates, gabbroic rocks, plagiogranite and basalt from the bottom to the top. The pegmatite gabbro is very minor lithology within the olivine gabbro and/or tectonite and formed in lenticular shaped or thin dike. They are greenish grey in color and have medium to coarse grained (2->5 mm) crystal size. Microscopically, pegmatite gabbros have sub-ophitic to ophitic texture and contain plagioclase, pyroxene, chlorite, epidotite, and ilmenite. This mineral composition is also supported by X-Ray Diffractometer. In addition, pyroxenes are diopside in composition, and has chiefly seven Raman peaks. The strong peaks are at 1011-1012; 662-666, and 322-325 cm-1. Four intense peaks are seen at 509-510; 389-393; 253, and 136 cm-1. In terms of EPMA results, pyroxenes vary from Wo41.72-49.63En44.99-49.83Fs5.39-8.53 in composition. They plot on the diopside region on the Wollastonite-Enstatite-Ferrosillite triangular diagram. According to pyroxene geothermobarometry by Putrika [2], crystallization of diopside took place at temperature of 1445.59 °C and pressure of 14.36 kbar. Some non-destructive gemological tests (specific gravity, refractive index, color, UV properties) were carried out on the polished pyroxene samples. The pyroxenes have specific gravity range from 2.87 and 3.01. R.I values of pyroxene have varying from 1.665 to 1.728. Diopside is light green, translucent, and has dull luster on the crystal surface. It characteristically displays an iridescent optical effect. Moreover, diopside showed purple fluorescence under UV rays but did not show phosphorescence. All mineralogic, spectroscopic, geochemical and gemological results indicate that there may be economic values of diopside crystals in pegmatite gabbro in case of single crystals with sufficient reserve. © SGEM2019.