Preliminary Study on Erciş Obsidians Regarding Mineralogical- Petrographical and Geochemical Proporties

Erciş Obsidyenlerinin Mineralojik-Petrografik, Jeokimyasal Özellikleri ve Süs Taşı Olarak Değerlendirilmesi Üzerinde Ön Çalışma

Abstract

Erciş/Van obsidians with economical value are located in 20 km Northern of Van in Norteast of Anatolian plate.Volcanic rocks situated in the region are made up of such as stratigraphic sequence ; (i) paleozoic aged metamorphic series(chlorite-muscovite, quartz schist, fillat) and above them (ii) basalt(iii) obsidian, , (iv) perlite, and (v) tuffaceous rocks. Basaltsin study area and in Eastern Anatolia like the other volcanic rocks in the world, their genesis is subalkaline which correspondto oceanic crust tholeitic basalt. Tuffacious rocks show geochemically the products of magmatic differentiation of andesiticand rhiolitic in type of magma. Perlites and obsidians in point of geochemically are similar to rhyolites like chemical composition.Perlites can be esily differentiated from rhyolites by their high K2O, Rb and Nb values. Obsidians having high SiO2 valuesare distinguished from both perlites and rhyolites clearly. Perlites and obsidians which are giving outcrop in Erciş and surroundingarea display geochemical values with Sarıkamış obsidians and perlites regarding occurrence mode. Obsidians havebeen formed by addition of water into volcanic glass through hydration process during the cooling of magma. Length of obsidianzone 1250 m, wideness 250 m, and thickness 8 m were determined with respect to 1/25 000 scaled geological map duringthe investigation of study area. According to reserve calculations, the amount of obsidian was found as 5 850 000 tones. Obsidiansin Van Erciş Ulupamir village to the near the study area are semi-valued gemstones. During the evaluation of Erciş obsidiansas a gemstone; color of the rock, luster, transmission of the light, crystallographic property, appearance, reflection of thelight, hardness, density, streak color, occurrence and identification of the rock in the field were taken into consideration as mainparameters. Mentioned gemstones were produced from mine deposits by companies and carried to workshops to be processedto manufacture germ materials by exporting the products and employing the people contribute to significant amount economicalinput to the national income

Özet

Ekonomik önemi olan Erciş/Van yöresi obsidyenleri Anadolu plakasının kuzeydoğusunda Van ilinin 20 km kuzeyinde