igneous
Snowflake Obsidian
Vitreous volcanic silicate (SiO2 with Cristobalite inclusions)
Hardness: 5-5.5 (Mohs scale); Color: Black with white or gray patches; Luster: Vitreous/Glassy; Structure: Amorphous; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.3-2.6.
- Hardness
- 5-5
- Color
- Black with white or gray patches
- Luster
- Vitreous/Glassy
Identified More igneous →
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Black with white or gray patches; Luster: Vitreous/Glassy; Structure: Amorphous; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.3-2.6.
Formation & geological history
Formed when felsic lava cools very rapidly, preventing crystal growth. The 'snowflakes' are spherulitic inclusions of cristobalite (a polymorph of quartz) that formed during the cooling process.
Uses & applications
Used primarily in jewelry (beads, cabochons), ornamental carvings, and decorative stones. Historically used for making sharp tools like arrowheads and knives.
Geological facts
Unlike most rocks, obsidian is technically a volcanic glass because it lacks a crystalline structure. The white patches are internal 'devitrification' where the glass has begun to turn into mineral crystals.
Field identification & locations
Identified by its distinctive white 'snowflake' patches against a smooth, black glassy background. Commonly found in volcanic regions such as the United States (Utah, Oregon), Mexico, and Iceland.
