igneous
Snowflake Obsidian
Spherulitic Obsidian (Amorphous volcanic glass with Phenocrysts of Cristobalite)
Hardness: 5-5.5 (Mohs scale); Color: Black with white or gray flower-like patches; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline) containing radial clusters of Cristobalite; Specific Gravity: 2.35-2.6
- Hardness
- 5-5
- Color
- Black with white or gray flower-like patches
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Black with white or gray flower-like patches; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline) containing radial clusters of Cristobalite; Specific Gravity: 2.35-2.6
Formation & geological history
Formed when silica-rich lava cools too rapidly for crystal growth to occur, creating glass. The white 'snowflakes' are spherulites of cristobalite, which form during the devitrification process of the volcanic glass.
Uses & applications
Primarily used for lapidary work, jewelry (beads, cabochons), ornamental carvings, and 'healing' stone markets. Historically used by indigenous peoples for tools and arrowheads.
Geological facts
Despite being an 'amorphous' glass, the 'snowflakes' are an example of the glass beginning to crystallize over geological time. It is technically metastable and will eventually turn entirely into mineral crystals.
Field identification & locations
Identify by its distinct black glassy base and white, radial star-shaped inclusions. It is commonly found in areas of recent volcanic activity, such as the Western United States (Utah, Oregon), Mexico, and Iceland.
