igneous
Snowflake Obsidian
Obsidian with Cristobalite inclusions (70-75% SiO2)
Hardness: 5-6 (Mohs scale); Color: Black with white or gray radial patterns; Luster: Vitreous/Glassy; Structure: Amorphous (glass) with spherulitic crystals; Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6
- Hardness
- 5-6 (Mohs scale)
- Color
- Black with white or gray radial patterns
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Black with white or gray radial patterns; Luster: Vitreous/Glassy; Structure: Amorphous (glass) with spherulitic crystals; Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6
Formation & geological history
Formed when felsic lava cools rapidly, preventing large crystal growth. The 'snowflakes' are spherulites of cristobalite (a type of quartz) that formed through devitrification of the glass over time.
Uses & applications
Used primarily for jewelry (cabochons, beads), decorative carvings, metaphysical stones, and collectible specimens. Historically used for sharp tools and arrowheads.
Geological facts
Unlike most rocks, obsidian is actually a natural volcanic glass. The white patches are not stains but are actual crystals that 'grew' inside the glass as it aged. Old obsidian is rare because it eventually devitrifies or hydrates into perlite.
Field identification & locations
Identify by its glassy texture, shell-like (conchoidal) fractures, and distinctive white 'snowflake' spots. Commonly found in volcanic regions like Utah (USA), Mexico, and Iceland.
