PETROCHEMISTRY AND TEXTURES OF ARMENIAN OBSIDIAN

The acid volcanic glass deposits in Armenia were characterized using p etrochemical and glass-chemical methods. This paper aims to help inter pret the extrusion mechanism of such lava flows, 50 to 250 m thick, wi th respect to the chemical composition of the matrix glass, crystallin e inclusions and volatile content. The microstructure of the Armenian obsidian indicates that the lava flow and the formation of magnetite w hiskers are two independent processes. Crystallization of Fe-Mn-pyroxe ne and euhedral magnetite probably occurred in the melt during the ext rusion period. During a second heating process, the pyroxene decompose d simultaneously with an oxidation process and magnetite formed. The f orm of the whiskers indicates that viscosity during the melt must have been lower than 10(-4) Pas. This therefore would mean that the solidi fied melt was reheated up to at least 1000 degrees C.