![]() It can be found in Argentina, Armenia, Azerbaijan, Australia, Canada, Chile, Georgia, El Salvador, Greece, Guatemala, Iceland, Italy, Japan, Kenya, Mexico, New Zealand, Papua New Guinea, Peru, Scotland, Turkey, and the United States. Obsidian older than a few million years is rare because the glassy rock is rapidly destroyed or altered by weathering, heat, or other processes. It is confined to areas of geologically recent volcanic activity. Obsidian is found in many locations worldwide. Other types with dark bands or mottling in gray, green, or yellow are also known. Though obsidian is typically jet-black in color, the presence of hematite (iron oxide) produces red and brown varieties, and the inclusion of tiny gas bubbles may create a golden sheen. Obsidian has a glassy lustre and is slightly harder than window glass. Obsidian is extremely rich in silica (about 65 to 80 percent), is low in water, and has a chemical composition similar to rhyolite. ![]() It is an amorphous material known as a “mineraloid.” The result is a volcanic glass with a smooth uniform texture that breaks with a conchoidal fracture. In the past, it was used to manufacture cutting and piercing tools, and it has been used experimentally as surgical scalpel blades. Obsidian is hard, brittle, and amorphous it, therefore, fractures with sharp edges. ![]() The inhibition of atomic diffusion through this highly viscous lava explains the lack of crystal growth. It is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition (high silica content) causes a high viscosity, which, upon rapid cooling, results in a natural glass-forming from the lava. It is produced when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Obsidian is an igneous rock occurring as a natural glass formed by the rapid cooling of viscous lava from volcanoes.
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