igneous
Snowflake Obsidian
Volcanic Glass with Spherulite inclusions (Amorphous SiO2 + Cristobalite)
Hardness: 5 to 5.5 Mohs. Color: Black with white or gray patches (flakes). Luster: Vitreous to dull. Structure: Amorphous (non-crystalline glass). Cleavage: None (conchoidal fracture).
- Hardness
- 5 to 5
- Color
- Black with white or gray patches (flakes)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 5 to 5.5 Mohs. Color: Black with white or gray patches (flakes). Luster: Vitreous to dull. Structure: Amorphous (non-crystalline glass). Cleavage: None (conchoidal fracture).
Formation & geological history
Formed when felsic lava cools rapidly with minimal crystal growth. The 'snowflakes' are spherulites, which are radial clusters of needle-shaped cristobalite (a type of quartz) crystals formed during devitrification.
Uses & applications
Primarily used for jewelry (beads, cabochons), ornamental carvings, and metaphysical collecting. Historically used for sharp tools and arrowheads.
Geological facts
Unlike most obsidian, the presence of cristobalite makes this variety less 'sharp' when broken. It is a metastable material that eventually 'devitrifies' or turns into a regular rock over millions of years.
Field identification & locations
Identified by its distinctive white 'snowflake' patterns against a black glassy background. Common locations include Utah (USA), Mexico, and Iceland. Collectors look for high contrast and even distribution of spots.
