igneous
Polished black stone, likely obsidian
Obsidian — natural volcanic glass, compositionally silica-rich (typically rhyolitic)
AI-generated identification · may be incorrectSmooth, glossy dark brown-black surface with curved, glassy fracture; hardness about 5–5.5 Mohs. The photo does not show enough detail to confirm the identification; polished basalt or another dark stone is also possible.
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Physical properties
Smooth, glossy dark brown-black surface with curved, glassy fracture; hardness about 5–5.5 Mohs. The photo does not show enough detail to confirm the identification; polished basalt or another dark stone is also possible.
Formation & geological history
Obsidian forms when silica-rich lava cools rapidly, preventing crystals from growing; it is generally Quaternary or younger and occurs near volcanic centers.
Uses & applications
Used for decorative carvings, jewelry, and collectibles; historically shaped into sharp tools and blades.
Geological facts
Obsidian is technically a volcanic glass rather than a crystalline mineral, and can display conchoidal fracture.
Field identification & locations
A glassy luster and sharp, curved fracture edges support obsidian identification; common sources include volcanic regions of the western United States, Mexico, and Iceland. This rounded, polished piece cannot be identified confidently from appearance alone.
