igneous
Snowflake Obsidian
Volcanic Glass (spherulitic Obsidian) - SiO2 (with Cristobalite inclusions)
Hardness: 5-5.5 on Mohs scale; Color: Black with white or grey 'snowflake' patterns; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline glass); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6.
- Hardness
- 5-5
- Color
- Black with white or grey 'snowflake' patterns
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-5.5 on Mohs scale; Color: Black with white or grey 'snowflake' patterns; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline glass); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6.
Formation & geological history
Formed when felsic lava cools rapidly with minimal crystal growth. The 'snowflakes' are spherulites composed of radiating needles of cristobalite (a polymorph of silica) that formed as the glass began to devitrify. Found in volcanic areas throughout the Cenozoic era.
Uses & applications
Used primarily in jewelry (cabochons, beads), decorative carvings, and as a popular specimen for collectors. Historically used by indigenous cultures to make sharp tools or points, though it is more brittle than plain obsidian.
Geological facts
The 'snowflakes' are actually internal crystals of cristobalite that grew in a radial pattern within the cooling glass. While obsidian is chemically similar to granite and rhyolite, its lack of crystal structure makes it a mineraloid rather than a true mineral.
Field identification & locations
Identify in the field by its distinct glassy luster, conchoidal (shell-like) fracture, and the presence of white, star-shaped patterns on a black background. It is commonly found in volcanic regions of Utah, Mexico, and Iceland.
