igneous
Snowflake Obsidian
Volcanic glass containing Spherulitic Cristobalite (SiO2)
Hardness: 5–5.5 Mohs; Color: Black with white-to-gray 'snowflake' patches; Luster: Vitreous (glassy); Structure: Amorphous (glassy) with dendritic mineral inclusions; Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6.
- Hardness
- 5–5
- Color
- Black with white-to-gray 'snowflake' patches
- Luster
- Vitreous (glassy)
Identified More igneous →
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Physical properties
Hardness: 5–5.5 Mohs; Color: Black with white-to-gray 'snowflake' patches; Luster: Vitreous (glassy); Structure: Amorphous (glassy) with dendritic mineral inclusions; Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6.
Formation & geological history
Formed when rhyolitic lava cools rapidly, preventing significant crystal growth of the bulk material. The white 'snowflake' patches are christobalite inclusions (a form of silica) that grew through devitrication of the glass over time.
Uses & applications
Primarily used for jewelry (beads, cabochons), ornamental carvings, and 'metaphysical' meditation stones. Historically, obsidian was used for making sharp tools like arrowheads and surgical blades.
Geological facts
Despite being an igneous rock, it contains no large crystal structures and is technically considered mineraloid. The 'snowflakes' are actually radial clusters of needle-like crystals called spherulites.
Field identification & locations
Identify in the field by its distinct glass-like feel, sharp conchoidal edges when broken, and the unique white stellate patterns against a dark matrix. Common in volcanic regions of Iceland, Mexico, and the United States (Utah/Oregon).
