igneous
Snowflake Obsidian
Vitreous volcanic rock with Cristobalite inclusions (mostly SiO2)
Hardness: 5-5.5 | Color: Black with white or gray snowflake-like patches | Luster: Vitreous to dull | Structure: Amorphous (glassy) with radial crystals | Cleavage: Conchoidal fracture | Specific gravity: 2.35-2.6
- Hardness
- 5-5
Identified More igneous →
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Physical properties
Hardness: 5-5.5 | Color: Black with white or gray snowflake-like patches | Luster: Vitreous to dull | Structure: Amorphous (glassy) with radial crystals | Cleavage: Conchoidal fracture | Specific gravity: 2.35-2.6
Formation & geological history
Extrusive igneous rock formed when felsic lava cools rapidly, preventing crystal growth. The 'snowflakes' are formed by the partial devitrification of the glass into spherical crystals of the mineral cristobalite.
Uses & applications
Widely used for tumbled stones, beads, cabochons in jewelry, carvings, and as a popular specimen for rock collectors. Historically used for tools and weapons similarly to standard obsidian.
Geological facts
Unlike most rocks, obsidian is not a mineral but a volcanic glass. The white patches are called spherulites, which are radiating clusters of needle-like crystals of cristobalite.
Field identification & locations
Identified by the distinct white/gray patterns against jet black glass. Commonly found in areas of recent volcanic activity such as Utah, USA, and Iceland. Look for its characteristic conchoidal fracture if broken.
