igneous
Polished black stone, likely obsidian
Volcanic glass; predominantly silica-rich rhyolitic glass (SiO₂), identification uncertain from the image
AI-generated identification · may be incorrectBlack, glossy to vitreous luster with irregular conchoidal-looking surfaces; hardness about 5–5.5 Mohs, no cleavage, amorphous rather than crystalline, and typically specific gravity 2.35–2.60.
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Physical properties
Black, glossy to vitreous luster with irregular conchoidal-looking surfaces; hardness about 5–5.5 Mohs, no cleavage, amorphous rather than crystalline, and typically specific gravity 2.35–2.60.
Formation & geological history
Obsidian forms when silica-rich lava cools so rapidly that crystals cannot grow, usually in volcanic settings during the Quaternary and older Cenozoic eruptions.
Uses & applications
Used for ornamental objects, cabochons, beads, carvings, and historically extremely sharp tools; common polished pieces generally have modest market value.
Geological facts
The specimen appears small, dark, and polished, but the photo cannot exclude black glass, slag, or another dark stone; a sharp conchoidal edge and lack of bubbles favor obsidian.
Field identification & locations
Commonly found in volcanic regions such as Mexico, the western United States, Iceland, Armenia, and Japan; inspect edges, bubbles, flow bands, and hardness, while avoiding destructive tests.
