igneous
Snowflake Obsidian
Volcanic glass (SiO2) with Cristobalite (SiO2) inclusions
Hardness: 5-5.5 | Color: Black with white-to-gray splotches | Luster: Vitreous to dull | Structure: Amorphous (non-crystalline glass) | Cleavage: Conchoidal fracture
- Hardness
- 5-5
Identified More igneous →
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Physical properties
Hardness: 5-5.5 | Color: Black with white-to-gray splotches | Luster: Vitreous to dull | Structure: Amorphous (non-crystalline glass) | Cleavage: Conchoidal fracture
Formation & geological history
Formed through the rapid cooling of silica-rich (felsic) lava, which prevents large crystals from growing. The 'snowflakes' are spherulites of white cristobalite crystals that formed during subsequent devitrification.
Uses & applications
Predominantly used for ornamental purposes including semi-precious jewelry (beads, cabochons), carvings, and as decorative tumbling stones. Historically, obsidian was used for tools and surgical blades.
Geological facts
Despite being an igneous rock, it contains no large crystals and is technically a mineraloid. The white patterns are essentially a form of internal 'growing' of crystals within the glass over thousands of years.
Field identification & locations
Identify by its glass-like texture and characteristic white radiating patterns on a black base. Found in areas with geologically recent volcanic activity like the USA (Utah, Oregon), Mexico, and Iceland.
