igneous
Obsidian (likely mahogany or snowflake obsidian)
Volcanic glass; chiefly amorphous SiO₂-rich rhyolitic composition
AI-generated identification · may be incorrectTypically black to dark brown, with vitreous luster and conchoidal fracture; hardness about 5–5.5 Mohs, no cleavage, and glassy/amorphous structure. The specimen appears naturally fractured or roughly shaped, with possible brown-red mahogany patches.
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Physical properties
Typically black to dark brown, with vitreous luster and conchoidal fracture; hardness about 5–5.5 Mohs, no cleavage, and glassy/amorphous structure. The specimen appears naturally fractured or roughly shaped, with possible brown-red mahogany patches.
Formation & geological history
Forms when silica-rich lava cools so rapidly that crystals cannot develop, usually in Quaternary to Cenozoic volcanic flows and domes. Common sources include Mexico, the western United States, Armenia, and Iceland.
Uses & applications
Used historically for exceptionally sharp tools and arrowheads; today it is popular for carvings, cabochons, jewelry, ornaments, and lapidary pieces. It has limited construction use.
Geological facts
Fresh edges can be razor sharp, sharper than many steel blades at microscopic scale. Obsidian may hydrate over time, and its glassy texture distinguishes it from crystalline basalt.
Field identification & locations
Identify by its smooth glassy surface, curved shell-like fracture, lack of visible grains, and light-to-dark translucent edges. Common forms include black, mahogany, snowflake, rainbow, and sheen obsidian.
