igneous
Black polished stone (possibly obsidian)
Obsidian (volcanic glass; composition typically rhyolitic)
AI-generated identification · may be incorrectSmall, dark gray-black, smooth polished piece with a glassy luster; obsidian has no crystal structure or cleavage and Mohs hardness around 5–5.5. The image lacks enough detail to distinguish it confidently from other dark stones.
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Physical properties
Small, dark gray-black, smooth polished piece with a glassy luster; obsidian has no crystal structure or cleavage and Mohs hardness around 5–5.5. The image lacks enough detail to distinguish it confidently from other dark stones.
Formation & geological history
Obsidian forms when silica-rich lava cools rapidly, preventing crystals from growing; it is geologically young and occurs near volcanic flows and domes.
Uses & applications
Used for jewelry, ornaments, and collectibles; historically, sharp flakes were fashioned into cutting tools.
Geological facts
Obsidian breaks with a distinctive curved, shell-like fracture and can form exceptionally sharp edges.
Field identification & locations
A glassy surface and conchoidal fracture support identification; common sources include volcanic regions such as Iceland, Mexico, and the western United States. A small polished piece like this may sell for about $2–$15 USD.
