igneous
Obsidian
Volcanic Glass (Amorphous SiO2)
Hardness: 5-5.5 (Mohs); Color: Black; Luster: Vitreous; Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6
- Hardness
- 5-5
- Color
- Black
- Luster
- Vitreous
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Physical properties
Hardness: 5-5.5 (Mohs); Color: Black; Luster: Vitreous; Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6
Formation & geological history
Formed by the rapid cooling of silica-rich (rhyolitic) lava, preventing the growth of mineral crystals. Typically found in geologically young volcanic regions.
Uses & applications
Historically used for making sharp weapons and tools; currently used in jewelry, decorative ornaments, and specialized surgical scalpel blades.
Geological facts
Because it lacks a crystalline structure, obsidian is not technically a mineral but a mineraloid. It breaks with extremely sharp edges, often down to a few nanometers thick.
Field identification & locations
Identified by its jet-black color, glassy texture, and distinct shell-like (conchoidal) fracture patterns. Found in volcanic areas like Iceland, Mexico, and the Western USA.
