igneous
Snowflake Obsidian
Vitreous volcanic silicate rock (SiO2) with Spherulite inclusions
Hardness: 5-5.5 (Mohs scale); Color: Black with white or gray patches; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline) glass with phenocrysts; Cleavage: None (Conchoidal fracture); Gravity: 2.3-2.6.
- Hardness
- 5-5
- Color
- Black with white or gray patches
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Black with white or gray patches; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline) glass with phenocrysts; Cleavage: None (Conchoidal fracture); Gravity: 2.3-2.6.
Formation & geological history
Formed when felsic lava cools rapidly with minimal crystal growth, though the white 'snowflakes' are inclusions of cristobalite (a polymorph of quartz) produced through devitrification (partial crystallization).
Uses & applications
Commonly used in lapidary work for cabochons, beads, jewelry, and small carvings. Historically used for making sharp tools like scrapers and arrowheads.
Geological facts
The white patterns that look like snowflakes are known as spherulites. Unlike true obsidian which is entirely glass, this variety has begun the chemical process of turning back into a rock through crystallization.
Field identification & locations
Identify by its characteristic glassy black base and mottled white patterns. Often found in volcanic regions of Utah, Iceland, Mexico, and Italy. Collectors look for high contrast between the 'snow' and the 'glass'.
