igneous
Snowflake Obsidian
Spherulitic Volcanic Glass (primarily SiO2 with Cristobalite inclusions)
Hardness: 5-5.5 on Mohs scale; Color: Black with white or gray flower-like 'snowflakes'; Luster: Vitreous (glassy); Crystal Structure: Amorphous (glass); Cleavage: Conchoidal fracture; Specific Gravity: 2.3 - 2.6.
- Hardness
- 5-5
- Color
- Black with white or gray flower-like 'snowflakes'
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5-5.5 on Mohs scale; Color: Black with white or gray flower-like 'snowflakes'; Luster: Vitreous (glassy); Crystal Structure: Amorphous (glass); Cleavage: Conchoidal fracture; Specific Gravity: 2.3 - 2.6.
Formation & geological history
Formed through the rapid cooling of felsic lava. As the glass begins to devitrify over geological time, needle-like crystals of cristobalite form radiating patterns known as spherulites, which create the white 'snowflake' appearance.
Uses & applications
Commonly used for lapidary work, jewelry (beads and cabochons), small carvings, and as a popular teaching specimen for geology students.
Geological facts
Unlike minerals, obsidian is a 'mineraloid' because it lacks a crystalline structure. The 'snowflakes' are actually internal crystals of cristobalite, a type of quartz that grows as the glass cools or ages.
Field identification & locations
Identify by its glass-like texture and prominent white splotches on a jet-black background. It is commonly found in areas of recent volcanic activity such as Utah, USA, and parts of Mexico. Collectors should look for sharp conchoidal edges on unpolished pieces.
