igneous
Snowflake Obsidian
Spherulitic Obsidian (SiO2 + impurities)
Hardness: 5-5.5 (Mohs); Color: Black with grayish-white snowflake-like patches; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline) glass with phenocrysts; Fracture: Conchoidal; Specific Gravity: 2.3-2.6
- Hardness
- 5-5
- Color
- Black with grayish-white snowflake-like patches
- Luster
- Vitreous/Glassy
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5-5.5 (Mohs); Color: Black with grayish-white snowflake-like patches; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline) glass with phenocrysts; Fracture: Conchoidal; Specific Gravity: 2.3-2.6
Formation & geological history
Formed when silica-rich lava cools rapidly, preventing crystal growth. The 'snowflakes' are inclusions of the mineral cristobalite (a type of quartz) that grew in radial patterns within the glass after cooling.
Uses & applications
Primarily used for decorative purposes, including jewelry (beads, cabochons), carvings, and ornamental gemstones. Historically used for sharp tools and arrowheads, though snowflake variety is more brittle.
Geological facts
The white 'snowflakes' are actually crystals of cristobalite. While most obsidian is completely amorphous, snowflake obsidian shows the early stages of devitrification, where the glass begins to turn back into solid crystal over millions of years.
Field identification & locations
Identify in the field by its distinct glassy texture and white radial splotches against a dark black background. Found commonly in areas of past volcanic activity, particularly in Utah (USA), Mexico, and Iceland.
