igneous
Black tumbled stone, possibly obsidian
Obsidian (volcanic glass), likely; identification uncertain from the image
AI-generated identification · may be incorrectSmall, opaque glossy black piece with a smooth rounded surface and possible conchoidal fracture; obsidian has Mohs hardness about 5–5.5, no crystal structure, and glassy luster. It could also be black tourmaline, hematite, or another dark mineral.
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Physical properties
Small, opaque glossy black piece with a smooth rounded surface and possible conchoidal fracture; obsidian has Mohs hardness about 5–5.5, no crystal structure, and glassy luster. It could also be black tourmaline, hematite, or another dark mineral.
Formation & geological history
Obsidian forms when silica-rich lava cools rapidly, preventing crystallization, typically during Quaternary to older volcanic eruptions. A tumbled specimen has been mechanically polished and rounded.
Uses & applications
Used for ornamental objects, jewelry, cabochons, and historically sharp tools; common polished pieces generally have modest value.
Geological facts
Obsidian is technically volcanic glass rather than a crystalline mineral. Its curved conchoidal edges can be exceptionally sharp when freshly fractured.
Field identification & locations
Commonly found near rhyolitic volcanic fields, especially in the western United States, Mexico, Iceland, and Japan; verify with a close-up, streak, translucency, and fracture examination.
