igneous
Snowflake Obsidian
Volcanic glass containing Spherulites (SiO2)
Hardness: 5.0-5.5 (Mohs scale); Color: Black with white-to-grayish patches; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline matrix); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.3-2.6
- Hardness
- 5
- Color
- Black with white-to-grayish patches
- Luster
- Vitreous/Glassy
Identified More igneous →
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Physical properties
Hardness: 5.0-5.5 (Mohs scale); Color: Black with white-to-grayish patches; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline matrix); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.3-2.6
Formation & geological history
Formed from rapidly cooling felsic lava where water and impurities were present. The internal crystal 'snowflakes' are spherulites of cristobalite (a silica mineral) that grew during the partial devitrification of the glass.
Uses & applications
Predominantly used for ornamental purposes, including beads, jewelry, cabochons, and decorative carvings. Historically, obsidian was used for making sharp blades and arrowheads.
Geological facts
Despite being an igneous rock, it is often referred to as a mineraloid because it lacks a crystalline structure. The 'snowflakes' result from the chemical process of devitrification, where the glass starts to crystallize over vast periods of time.
Field identification & locations
Identify by its characteristic white radial inclusions on a black glassy surface and smooth, shell-like fracture pattern. Commonly found in volcanic regions such as the United States (Utah and Oregon), Mexico, and Iceland.
