igneous
Black obsidian (likely)
Volcanic glass, chiefly silica-rich rhyolitic composition (SiO₂-rich); exact identification cannot be confirmed from the image
AI-generated identification · may be incorrectGlossy black with a glassy luster and irregular, sharp conchoidal fractures; typically Mohs 5–5.5, amorphous (no crystal structure), and without cleavage. The specimen’s shiny surface and fracture pattern are consistent with obsidian.
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Physical properties
Glossy black with a glassy luster and irregular, sharp conchoidal fractures; typically Mohs 5–5.5, amorphous (no crystal structure), and without cleavage. The specimen’s shiny surface and fracture pattern are consistent with obsidian.
Formation & geological history
Forms when silica-rich lava cools so quickly that crystals do not grow; obsidian is geologically young and commonly found around volcanic flows and domes.
Uses & applications
Used for ornaments, jewelry, and collectible specimens; historically, carefully worked obsidian was used for cutting tools and blades.
Geological facts
Obsidian is natural volcanic glass, not a crystalline mineral, and its edges can be exceptionally sharp.
Field identification & locations
Look for a glassy sheen, black color, and curved, shell-like fracture surfaces; it occurs in volcanic regions such as Iceland, Mexico, and the western United States.
