Obsidian

Natural volcanic glass, formed when silica-rich lava cools so fast that crystals have no time to grow.

Obsidian specimen — Photo: Ji-Elle It feels nice and warm It feels like a love storm, CC BY-SA 3.0, via Wikimedia Commons

How to identify obsidian

Shiny, glass-like and usually black.
Curved, shell-shaped (conchoidal) fractures with razor-sharp edges.
Thin edges are translucent brown or gray.
May show white 'snowflakes' or a gold/rainbow sheen.

Often confused with

Coal
Coal is far lighter, softer and leaves black marks on your fingers.
Compare side by side
Basalt
Basalt is dull and grainy, never glassy.
Compare side by side

Where it's found

Glass Buttes, Oregon
Yellowstone, Wyoming
Lipari, Italy
Armenia

Uses

Stone tools, arrowheads, and even some surgical scalpels.

Rock tumbling

Can be tumbled with care. It's glass — chips easily; go gentle.

Did you know?

A fractured obsidian edge can be sharper than a steel razor blade.

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