igneous
Black Obsidian
Volcanic Glass (Amorphous Silicon Dioxide, SiO2)
AI-generated identification · may be incorrectHardness: 5-5.5 (Mohs scale); Color: Jet black to dark grey; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4
- Hardness
- 5-5
- Color
- Jet black to dark grey
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Jet black to dark grey; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4
Formation & geological history
Formed through the rapid cooling of silica-rich (felsic) lava, preventing the formation of a crystalline structure. Usually found at the margins of rhyolitic lava flows.
Uses & applications
Historically used for cutting tools and arrowheads; currently used in jewelry, ornamental carvings, and high-quality surgical scalpels.
Geological facts
Obsidian fractures with extremely sharp edges—down to nearly molecular thinness—making it sharper than steel. Some varieties like 'Snowflake' or 'Silver Sheen' have inclusions that create unique visual effects.
Field identification & locations
Identify by its glass-like appearance, smooth conchoidal (curved) fracture surfaces, and sharp edges. Common in volcanic regions such as Iceland, Mexico, and the Western United States.
