igneous
Snowflake Obsidian
Volcanic glass with Cristobalite inclusions (70–75% SiO2)
Hardness: 5–5.5 (Mohs scale); Color: Black with white or grayish radiating patches; Luster: Vitreous (glassy); Crystal structure: Amorphous (glassy) with internal radiating mineral inclusions; Cleavage: None (conchoidal fracture); Specific gravity: 2.35–2.40.
- Hardness
- 5–5
- Color
- Black with white or grayish radiating patches
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5–5.5 (Mohs scale); Color: Black with white or grayish radiating patches; Luster: Vitreous (glassy); Crystal structure: Amorphous (glassy) with internal radiating mineral inclusions; Cleavage: None (conchoidal fracture); Specific gravity: 2.35–2.40.
Formation & geological history
Formed when felsic lava cools rapidly, preventing crystal growth. The 'snowflakes' are spherulites of the mineral cristobalite, which form during the devitrification (slow crystallization) of the glass over time, typically in Pliocene or Pleistocene volcanic deposits.
Uses & applications
Primarily used in jewelry (pendants, beads, cabochons), lapidary arts, and ornamental carvings. Historically, obsidian was used to make sharp blades and arrowheads.
Geological facts
Because the inclusions are made of cristobalite, they often resemble snowflakes or flowers. While obsidian is a glass, it is metastable and will eventually turn into a fine-grained crystalline rock over millions of years.
Field identification & locations
Identify in the field by its distinctive glassy black base and white, bloom-like spots. It is commonly found in areas of recent volcanic activity such as Utah (USA), Mexico, and Iceland. Collectors should look for balanced patterns and high-polish finishes.
