igneous
Black Obsidian
Obsidian (Volcanic Glass)
Mohs hardness: 5-5.5. Color: Jet black to dark grey. Luster: Vitreous/glassy. Crystal structure: Amorphous (non-crystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.35-2.6.
- Hardness
- 5-5
- Color
- Jet black to dark grey
- Luster
- Vitreous/glassy
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Physical properties
Mohs hardness: 5-5.5. Color: Jet black to dark grey. Luster: Vitreous/glassy. Crystal structure: Amorphous (non-crystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.35-2.6.
Formation & geological history
Formed when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Found in areas of recent volcanic activity, dating from the Cenozoic era.
Uses & applications
Used for making surgical scalpels, arrowheads, ornamental jewelry, and crystal healing specimens.
Geological facts
Obsidian can be sharper than high-quality steel scalpels because it lacks a crystalline structure, allowing it to fracture down to nearly molecular thickness.
Field identification & locations
Identify by its smooth, glassy texture and distinctive shell-like (conchoidal) fractures. Found in volcanic regions like Iceland, Mexico, and the Western USA.
