igneous
Obsidian (likely snowflake-free black variety)
Volcanic glass; primarily SiO₂-rich rhyolitic composition
AI-generated identification · may be incorrectBlack to brown, vitreous luster, conchoidal fracture, no visible crystals, and Mohs hardness about 5–5.5; typically lightweight with sharp glassy edges. The specimen appears naturally fractured or roughly knapped, not metallic.
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Physical properties
Black to brown, vitreous luster, conchoidal fracture, no visible crystals, and Mohs hardness about 5–5.5; typically lightweight with sharp glassy edges. The specimen appears naturally fractured or roughly knapped, not metallic.
Formation & geological history
Forms when silica-rich lava cools rapidly, preventing crystal growth; most examples are Quaternary to recent, generally younger than several million years. Common in volcanic regions and lava flows.
Uses & applications
Used historically for razor-sharp tools and arrowheads, and today for carvings, jewelry, decorative objects, and archaeological study. Small rough fragments commonly sell for $2–$15.
Geological facts
Obsidian is technically a mineraloid rather than a true mineral because it lacks an ordered crystal lattice. Its conchoidal fracture can produce edges sharper than many steel blades.
Field identification & locations
Identify it by its uniformly glassy appearance, curved fracture surfaces, sharp edges, and lack of cleavage; unlike slag, it usually lacks abundant bubbles or metallic textures. Common sources include Arizona, Oregon, California, Mexico, Iceland, Italy, and Armenia.
