igneous
Tumbled dark stone, possibly obsidian or basalt
Uncertain from the photograph; likely volcanic glass (obsidian, SiO₂) or fine-grained basalt
AI-generated identification · may be incorrectSmall, rounded and polished; black to dark brown with a glossy luster. Obsidian has Mohs hardness ~5–5.5 and conchoidal fracture; basalt is ~6 and typically duller, dense, and opaque.
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Physical properties
Small, rounded and polished; black to dark brown with a glossy luster. Obsidian has Mohs hardness ~5–5.5 and conchoidal fracture; basalt is ~6 and typically duller, dense, and opaque.
Formation & geological history
Obsidian forms when silica-rich lava cools rapidly; basalt forms from rapidly cooled mafic lava. Most specimens are geologically young, commonly Cenozoic, though volcanic rocks occur throughout Earth history.
Uses & applications
Used as a tumbled specimen, carving material, and occasionally jewelry; basalt is widely used as crushed aggregate, paving stone, and building material. Obsidian is also valued for ornamental objects and historically for sharp tools.
Geological facts
The image shows a polished object but lacks enough detail for confident species identification. A strong glassy sheen and sharp conchoidal chips favor obsidian; a granular texture and greater density favor basalt.
Field identification & locations
Common sources include volcanic regions such as Mexico, the western United States, Iceland, Italy, and Hawaii. Check streak, texture, translucence at thin edges, and hardness; avoid destructive testing on a polished piece.
