Quebrada Rupasca, Los Andes Department, Salta, Argentina
Quebrada Rupasca, Los Andes Department, Province of Salta, Elevation: 4,458 m. above sea level, with the other known Obsidian deposits of the region: Ramadas, Tocomar and Quirón.
The District of Rupasca, is located 50 Km South of San Antonio de los Cobres on a volcanic complex located to the West of the Hill Acay and is accessed by a road, currently little traveled. There are quarries tub, Betina, Cristina, Argentina, Delfina, Yanina, Carolina and Martina. These deposits are associated with fronts of cast domicas that descend towards the quebrada Rupasca westward from unrecognized emission centers at present. The beads, observable in the front of the lava flows located in the quebrada Rupasca have different characteristics, among the variety of grey color and silky appearance, texture, solid and pearlitic structure.
Since Obsidian is metastable at the surface of the Earth (over time, the glass becomes crystals,fine-grained minerals), Obsidian have not been found more older than Cenozoic (70 million years ago). This deterioration the Obsidian accelerates in the presence of water.
The Obsidian has low water content when it is fresh,typically less than 1%, but is hydrating progressively when are exposed to groundwater or meteoric. Thus, as time goes on, the Obsidian is aging and becoming a structure pearlitic, causing the decomposition of the rock in small spheres and fragments of mm size of cracks of irregular contraction. Starting at the cracks and tiny bubbles(the small spheres) starts the devitrification. First microscopic crystals are formed by Quartz,cristobalite and feldspar and may be a orderly growth of crystals in radial fibres (spherulites) form.
Obsidian characterized by the spherulites are called Perlite, you already have the appearance of a Pearl to microscopically observe few increases.
1 entry listed.
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Locality Updated: Wheal Coates, St Agnes, St Agnes District, Cornwall, England, UKFrom David Ifold, 19th Jun 2013 22:44:10