igneous
Black Obsidian
Obsidian (Volcanic Glass, SiO2 + impurities)
Hardness: 5-5.5 (Mohs scale), Color: Jet black, Luster: Vitreous/Glassy, Crystal structure: Amorphous (none), Cleavage: None (conchoidal fracture), Specific gravity: 2.35-2.6
- Hardness
- 5-5
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Physical properties
Hardness: 5-5.5 (Mohs scale), Color: Jet black, Luster: Vitreous/Glassy, Crystal structure: Amorphous (none), 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. It is primarily found in Holocene and Pleistocene volcanic fields as it devitrifies over time.
Uses & applications
Historically used for blades, arrowheads, and scrapers. Modern uses include surgical scalpels, ornamental jewelry, carvings, and metaphysical collecting.
Geological facts
Obsidian is technically a natural glass rather than a true mineral because it lacks a crystalline structure. It can be sharper than high-quality steel scalpels.
Field identification & locations
Identified by its deep black color, lack of grain, and distinctive shell-like (conchoidal) fracture lines. Found in volcanic regions like the American West (Glass Buttes), Mexico, and Iceland.
