igneous
Black Obsidian
Volcanic Glass (SiO2 + impurities)
Mohs Hardness: 5.0–5.5; Color: Jet black; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4
- Hardness
- 5
- Color
- Jet black
- Luster
- Vitreous/Glassy
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Physical properties
Mohs Hardness: 5.0–5.5; Color: Jet black; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4
Formation & geological history
Formed when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. It is found in geologically recent volcanic areas, typically from the Cenozoic era.
Uses & applications
Used for making jewelry, ornamental beads, and surgical scalpel blades due to its ability to produce an edge thinner than steel. Also highly valued in gemstone collecting and spiritual practices.
Geological facts
Obsidian fractures with very sharp edges (conchoidal fracture). In ancient times, it was prized for making arrowheads and spear tips because it is sharper than diamond on a molecular level.
Field identification & locations
Identify by its deep black color, glossy surface, and distinctive curved chip marks (conchoidal fracture). Found in volcanic regions like the American West (Oregon, California), Mexico, and Iceland.
