igneous
Snowflake Obsidian
Spherulitic Volcanic Glass (primarily SiO2)
Hardness: 5-5.5 (Mohs scale), Color: Black with white or gray patches, Luster: Vitreous (glassy), Structure: Amorphous with radiator-shaped crystal inclusions (spherulites), Cleavage: None/Conchoidal fracture, Specific Gravity: 2.35-2.60.
- Hardness
- 5-5
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Physical properties
Hardness: 5-5.5 (Mohs scale), Color: Black with white or gray patches, Luster: Vitreous (glassy), Structure: Amorphous with radiator-shaped crystal inclusions (spherulites), Cleavage: None/Conchoidal fracture, Specific Gravity: 2.35-2.60.
Formation & geological history
Formed when felsic lava cools rapidly with minimal crystal growth. The 'snowflakes' are inclusions of the mineral Cristobalite (a polymorph of silica) that form through partial devitrification of the glass over time.
Uses & applications
Predominantly used for jewelry, lapidary work (cabochons and beads), ornamental carvings, and by collectors. Historically used for making sharp tools and arrowheads.
Geological facts
Obsidian is technically a mineraloid rather than a mineral because it is volcanic glass and lacks a crystalline structure; the 'snowflakes' represent the transition from glass back into crystalline quartz.
Field identification & locations
Identified by its distinctive white 'snowflake' patches against a jet-black glassy groundmass. Common in volcanic regions such as Utah and California in the USA, Mexico, and Iceland.
