igneous
Black Obsidian
Volcanic Glass (SiO2)
Hardness: 5-5.5 (Mohs scale); Color: Jet black to dark green; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4
- Hardness
- 5-5
- Color
- Jet black to dark green
- Luster
- Vitreous/Glassy
Identified More igneous →
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Jet black to dark green; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4
Formation & geological history
Obsidian forms when silica-rich lava cools extremely rapidly, preventing the growth of mineral crystals. It is common in extrusive igneous environments from the Cenozoic era.
Uses & applications
Historically used for arrowheads and knives. Today it is used in scalpel blades for precision surgery, jewelry (beads/cabochons), and as decorative/healing stones.
Geological facts
Obsidian fractures into edges that are thinner than can be achieved with steel blades, sometimes reaching molecular thinness. It is often called 'Dragon Glass' in popular culture.
Field identification & locations
Identify by its smooth, glassy texture and characteristic shell-like (conchoidal) fracture patterns. It is frequently found in volcanic regions like Mexico, Iceland, and the Western USA.
