igneous
Snowflake Obsidian
Vitreous Volcanic Glass (Siliceous Obsidian with Cristobalite inclusions)
Hardness: 5-5.5 (Mohs scale); Color: Black with white or gray cloud-like patches; Luster: Vitreous (glassy); Crystal structure: Amorphous (non-crystalline glass); Cleavage: None (conchoidal fracture); Specific gravity: 2.35-2.6
- Hardness
- 5-5
- Color
- Black with white or gray cloud-like patches
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Black with white or gray cloud-like patches; Luster: Vitreous (glassy); Crystal structure: Amorphous (non-crystalline glass); Cleavage: None (conchoidal fracture); Specific gravity: 2.35-2.6
Formation & geological history
Formed through the rapid cooling of felsic (silica-rich) lava. Over time, the glass begins to devitrify, where minerals like cristobalite grow into radial, needle-like crystals (spherulites) that appear as 'snowflakes.'
Uses & applications
Used primarily in lapidary arts for jewelry, beads, cabochons, and decorative carvings. Historically, obsidian was used for making sharp blades and arrowheads.
Geological facts
The white 'snowflakes' are actually internal clusters of cristobalite, a type of quartz. While obsidian is chemically similar to granite, its lack of crystal growth due to rapid cooling makes it a glass rather than a mineral.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture and smooth glassy texture interrupted by white spots. Commonly found in volcanic regions like Utah and California (USA), Iceland, and Mexico.
