igneous
Polished obsidian (likely snowflake obsidian)
Volcanic glass, chiefly rhyolitic; snowflake patterns are cristobalite/spherulites in obsidian
AI-generated identification · may be incorrectBlack, glossy, glassy luster with pale gray-white patches; hardness about 5–5.5 Mohs, amorphous (no crystal structure), and conchoidal fracture. The image shows a polished, irregular piece; its exact variety is not certain from the photo.
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Physical properties
Black, glossy, glassy luster with pale gray-white patches; hardness about 5–5.5 Mohs, amorphous (no crystal structure), and conchoidal fracture. The image shows a polished, irregular piece; its exact variety is not certain from the photo.
Formation & geological history
Forms when silica-rich lava cools rapidly, preventing crystals from growing. Snowflake patterns develop as small mineral spherulites during devitrification; formation ages vary by volcanic deposit.
Uses & applications
Used for carvings, ornaments, jewelry, and historically for sharp cutting tools; obsidian is also collected as a decorative volcanic glass.
Geological facts
Obsidian can break into exceptionally sharp edges, but is brittle and not a true crystalline mineral.
Field identification & locations
Identify by its glassy shine, dark color, and curved, shell-like fracture; snowflake obsidian has distinctive pale spots. Occurs near volcanic areas, including the western United States, Mexico, and Iceland.
