igneous
Snowflake Obsidian
Obsidian with Cristobalite inclusions (70–75% SiO2)
Hardness: 5–5.5 (Mohs); Color: Black with white or grayish ‘snowflake’ patterns; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline) glass with crystalline inclusions; Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6.
- Hardness
- 5–5
- Color
- Black with white or grayish ‘snowflake’ patterns
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5–5.5 (Mohs); Color: Black with white or grayish ‘snowflake’ patterns; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline) glass with crystalline inclusions; Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6.
Formation & geological history
Formed from felsic lava that cools rapidly, preventing large crystal growth. The ‘snowflakes’ are spherulites of cristobalite (a type of quartz) formed by partial devitrification of the glass over time. Most specimens are from the Neogene or Quaternary periods.
Uses & applications
Used primarily in jewelry (beads, cabochons), ornamental carvings, and as a popular specimen for rock collectors and metaphysical practitioners.
Geological facts
Geologically, obsidian is unstable and slowly 'decrystallizes' into quartz. Because of this process, very old obsidian (older than the Cretaceous) is extremely rare. It was historically used to make sharp tools and arrowheads.
Field identification & locations
Identify by its glassy texture and distinctive white radial patterns against a dark background. Commonly found in areas of recent volcanic activity such as Utah (USA), Mexico, and Iceland. In the field, look for volcanic glass with conchoidal (shell-like) fractures.
