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Obsidian is a naturally occurring glass formed as an extrusive igneous rock. It is produced when acidic lava,extruded from a volcano cools very rapidly, freezing without sufficient time for crystal growth.
Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where cooling of the lava is rapid.
Because of the lack of crystal structure, obsidian blade edges can reach almost molecular thinness, leading to its ancient use as stone age knives and arrowheads, and its modern use as surgical scalpel blades.
Obsidian can be found as lumps of rock of any size up to and including an entire mountainside.

Obsidian has several varieties. Obsidian can contain small bubbles of air that are aligned along layers created as the molten rock was flowing just before being cooled. These bubbles can produce interesting effects such as a golden sheen, known as Sheen Obsidian or a rainbow sheen called Rainbow Obsidian. Inclusions of small, white, radially clustered crystals of cristobalite in the black glass produce a blotchy or snowflake pattern producing Snowflake Obsidian. Small nuggets of obsidian that have been naturally rounded and smoothed by wind and water are called Apache Tears.

Often confused with smoky quartz, obsidian has similar properties to quartz because of a similar chemistry. However, many properties dependant on a crystal structure are altered or absent in obsidian because it lacks any crystal structure of its own. The piezoelectric and optical properties in quartz are thus absent in obsidian. Smoky quartz usually has a splotchy or zoned distribution to its color while Obsidian's color is more uniformly distributed.

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15y ago

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