igneous
Obsidian
Obsidian (Volcanic Glass)
Hardness: 5-5.5 Mohs scale; Color: typically black but can be green, brown, or gold sheen; Luster: Vitreous (glassy); Crystal structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific gravity: approx. 2.4
- Hardness
- 5-5
- Color
- typically black but can be green, brown, or gold sheen
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5-5.5 Mohs scale; Color: typically black but can be green, brown, or gold sheen; Luster: Vitreous (glassy); Crystal structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific gravity: approx. 2.4
Formation & geological history
Formed through the rapid cooling of silica-rich lava (rhyolitic) which prevents crystal growth. It is relatively young geologically because it eventually weathers and devitrifies.
Uses & applications
Historically used for sharp tools/weapons (scalpels, arrowheads). Modern uses include jewelry, decorative ornaments, and extremely sharp surgical blades.
Geological facts
Because it breaks with a conchoidal fracture, it creates edges thinner and sharper than even the finest steel surgical scalpels. It is technically a mineraloid rather than a mineral because it lacks a crystal structure.
Field identification & locations
Identify by its glass-like appearance, smooth curved (conchoidal) fractures, and sharp edges. Commonly found in areas with recent volcanic activity like the Western USA, Mexico, and Iceland.
