Igneous
Snowflake Obsidian
Volcanic glass with Cristobalite inclusions (70–75% SiO2)
Hardness: 5-5.5 (Mohs scale); Color: Black with white or gray 'snowflake' patches; 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 gray 'snowflake' patches
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Black with white or gray 'snowflake' patches; 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, preventing significant crystal growth. The 'snowflakes' are spherulites of the mineral cristobalite, which form through partial devitrification of the glass. Most deposits are relatively young (Cenozoic) because glass eventually crystallizes or erodes.
Uses & applications
Used primarily in jewelry (cabochons, beads), decorative carvings, and as a popular specimen for rock collectors. Historically, obsidian was used for making sharp cutting tools like arrowheads and knives.
Geological facts
Unlike pure obsidian, Snowflake Obsidian is considered a 'dirty' glass because of its inclusions. The white patches are actually radiating fibers of a polymorph of quartz called cristobalite. It is often associated with themes of purity and balance in metaphysical circles.
Field identification & locations
Identify in the field by its distinct conchoidal (curved, shell-like) fracture and the presence of white, star-shaped patterns against a jet-black background. Common locations include Utah (USA), Mexico, and Iceland. Collectors should look for high contrast between the glass and the cristobalite.
