Icy quartz and gondites of the Borussian ophiolite belt (Western Sayan Mountains)

Background. Icy quartz and gondites of the Borussian ophiolite belt (Western Sayan Mountains) are promising as jewelry and ornamental raw materials and industrial stone materials for various purposes; however, these deposits have been poorly studied. Aim. To investigate the structural and material composition of icy quartz and gondites of the Borussian ophiolite belt and to determine their applicability in jewelry production and as industrial stone materials. Materials and methods. Samples of icy quartz and gondites from the Western Sayan Mountains were provided by TomGDK LLC. The structure and mineral composition of rocks were determined by optical methods in polished thin sections. The chemical composition of samples was determined by X-ray fluorescence analysis (XFA). Individual minerals were studied by scanning electron microscopy using a Jeol JSM-6390LV microscope equipped with an INCA Energy 450 X-Max 80 energy dispersive attachment. The mineral composition of microquartzite and gondite was assessed by X-ray analysis performed at the Common Use Center “Geoanalyst” of the Institute of Geology and Geochemistry of the Ural Branch of the Russian Academy of Sciences (Ekaterinburg). Results. Icy quartz is a massive, fine-grained quartzite of almost monomineral composition with minor admixtures of chlorite, fluorapatite, and calcite. The best varieties transmit light to a depth of 10 cm or greater. Gondites are represented by the same microquartzites of a coarse-banded texture; they are characterized by abundant inclusions of almandine-spessartine. These exhibit signs of shear deformations and recrystallization, which caused the formation of banding and small folds of drawing. The ornamental and mechanical properties render icy quartz and gondite suitable for jewelry, glyptic, and souvenir production. The purest (free from mineral impurities) icy quartz is similar in its characteristics to such an expensive abrasive material as Arkansas stone. Conclusions. Due to their decorative qualities and mechanical properties, icy quartz, gondites, and black microquartzites of the Borussian ophiolite belt can be used for jewelry, glyptic, and souvenir production. Icy quartz, free from mineral impurities, can be used as an abrasive material, such as Arkansas stone.