igneous
Polished snowflake obsidian
Obsidian, volcanic glass (SiO₂-rich rhyolitic composition) with cristobalite spherulites
AI-generated identification · may be incorrectHardness about 5–5.5 Mohs; black, opaque, and glassy with pale gray-white snowflake patterns; conchoidal fracture and no cleavage. The visible pattern comes from devitrified cristobalite/feldspar-rich inclusions, and the piece is polished and shaped.
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Physical properties
Hardness about 5–5.5 Mohs; black, opaque, and glassy with pale gray-white snowflake patterns; conchoidal fracture and no cleavage. The visible pattern comes from devitrified cristobalite/feldspar-rich inclusions, and the piece is polished and shaped.
Formation & geological history
Forms when silica-rich lava cools rapidly, preventing normal crystal growth; the snowflake texture develops as the glass partially devitrifies. It can form in relatively young volcanic flows, commonly Quaternary to older Cenozoic deposits.
Uses & applications
Used for cabochons, beads, carvings, worry stones, and decorative objects; historically fashioned into sharp tools. This small polished specimen has modest collector value.
Geological facts
Despite its patterned appearance, obsidian is technically volcanic glass rather than a fully crystalline rock. The contrasting “snowflakes” are usually radial spherulitic aggregates.
Field identification & locations
Identify by its uniform glassy black body, sharp conchoidal fracture, and pale rosettes or patches; common sources include Mexico, especially Jalisco and Querétaro, and the western United States. Avoid strong impacts because edges can be razor sharp.
