igneous
Snowflake Obsidian
Volcanic Glass with Spherulite Inclusions (70-75% SiO2)
Hardness: 5-5.5 (Mohs); Color: Black with white or gray 'snowflake' patches; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline matrix); Cleavage: None/Conchoidal fracture; SG: 2.35-2.60
- Hardness
- 5-5
- Color
- Black with white or gray 'snowflake' patches
- Luster
- Vitreous/Glassy
Identified More igneous →
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Physical properties
Hardness: 5-5.5 (Mohs); Color: Black with white or gray 'snowflake' patches; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline matrix); Cleavage: None/Conchoidal fracture; SG: 2.35-2.60
Formation & geological history
Formed through the rapid cooling of silica-rich rhyolitic lava. The 'snowflakes' are spherulites of cristobalite (a silica polymorph) that grew as the glass cooled or underwent devitritication.
Uses & applications
Used primarily for ornamental carvings, jewelry (cabochons and beads), and as a popular specimen for metaphysical or lapidary collectors.
Geological facts
Unlike crystalline rocks, obsidian is technically a mineraloid. The 'snowflake' pattern is actually a form of partial crystallization known as devitrification, where crystals grow in a radial pattern within the glass.
Field identification & locations
Identify by its glassy texture, sharp conchoidal (shell-like) fractures, and distinct radial white clusters. Commonly found in volcanic regions such as Utah and California (USA), Iceland, and Mexico.
