igneous
Obsidian flake
Volcanic glass; primarily silica-rich rhyolitic composition (approximately SiO₂)
AI-generated identification · may be incorrectDark gray, translucent to opaque, with vitreous luster and conchoidal fracture; it has no crystal structure or cleavage and is about 5–5.5 on the Mohs scale. The sharp, curved edges and glassy surface are characteristic.
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Physical properties
Dark gray, translucent to opaque, with vitreous luster and conchoidal fracture; it has no crystal structure or cleavage and is about 5–5.5 on the Mohs scale. The sharp, curved edges and glassy surface are characteristic.
Formation & geological history
Obsidian forms when silica-rich lava cools so rapidly that crystals cannot grow, usually in volcanic flows and domes. Most specimens are Quaternary to Cenozoic, though obsidian occurs in older volcanic terrains as well.
Uses & applications
Used historically for cutting tools and arrowheads because it fractures into extremely sharp edges; today it is collected, used ornamentally, and occasionally fashioned into jewelry or surgical blades.
Geological facts
The specimen appears to be a worked or naturally fractured flake, possibly gray or “snowflake”-free obsidian rather than a crystalline mineral. Its sharpness can exceed that of many steel blades at a microscopic edge.
Field identification & locations
Identify it by its glassy luster, lack of visible grains, conchoidal fracture, and sharp margins; test cautiously because edges can cut skin. Common sources include Mexico, the western United States, Iceland, Armenia, and Japan.
