igneous
Tumbled snowflake obsidian
Obsidian (volcanic glass), commonly with cristobalite spherulites
AI-generated identification · may be incorrectBlack, glassy to waxy luster with irregular white-gray snowflake patches; hardness about 5–5.5 Mohs, amorphous rather than crystalline, no cleavage, and conchoidal fracture. The rounded shape indicates tumbling/polishing.
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Physical properties
Black, glassy to waxy luster with irregular white-gray snowflake patches; hardness about 5–5.5 Mohs, amorphous rather than crystalline, no cleavage, and conchoidal fracture. The rounded shape indicates tumbling/polishing.
Formation & geological history
Rapid cooling of silica-rich rhyolitic lava formed this volcanic glass, with white cristobalite or feldspar spherulites crystallizing during cooling. It is generally Quaternary to geologically young, commonly associated with volcanic flows.
Uses & applications
Used for ornamental stones, cabochons, beads, carvings, and lapidary specimens; historically, sharp obsidian flakes served as cutting tools. It has minor decorative architectural use.
Geological facts
The “snowflake” pattern is caused by devitrification—localized crystallization within otherwise glassy lava—not actual snow or fossil material.
Field identification & locations
Identify by its black glassy body, pale snowflake-like spherulites, conchoidal fracture, and lack of visible grain; common sources include Oregon, Utah, California, Mexico, and Armenia. A strong glassy luster and sharp fracture distinguish it from black-and-white granite.
