igneous
Black Obsidian
Obsidian (Volcanic Glass, SiO2 + impurities)
Hardness: 5.0-6.0 (Mohs); Color: Jet black; Luster: Vitreous/Glassy; Structure: Amorphous (Extilled volcanic glass); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.35-2.6
- Hardness
- 5
- Color
- Jet black
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5.0-6.0 (Mohs); Color: Jet black; Luster: Vitreous/Glassy; Structure: Amorphous (Extilled volcanic glass); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.35-2.6
Formation & geological history
Formed through the rapid cooling of silica-rich felsic lava (rhyolitic) which prevents the growth of crystals. It occurs in geologically young areas where volcanic activity is recent.
Uses & applications
Used primarily in jewelry making for beads and cabochons, ornamental carvings, and historically in surgical blades and stone tools due to its razor-sharp edges.
Geological facts
Obsidian is technically not a mineral because it is a glass and lacks a crystalline structure. It was highly prized by indigenous cultures (like the Aztecs and Maya) for making mirrors and weapons.
Field identification & locations
Identified by its intense jet-black color and smooth, glass-like texture. It can be found near volcanic vents in locations like Mexico, USA (Oregon/California), and Iceland. Collectors look for high polish and lack of surface scratches.
