igneous
Obsidian
Volcanic Glass (Mainly SiO2)
Hardness: 5-5.5; Color: Black, deep grey; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4
- Hardness
- 5-5
- Color
- Black, deep grey
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-5.5; Color: Black, deep grey; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4
Formation & geological history
Extrusive igneous rock formed when felsic lava cools extremely rapidly, preventing crystal growth. Common in Cenozoic volcanic regions.
Uses & applications
Ancient tools/weapons (arrowheads), modern surgical scalpels, jewelry, ornamental carvings, and spiritual collection.
Geological facts
Obsidian fractures with extremely sharp edges, often thinner than steel blades. Ancient peoples used it for trade and tool-making for thousands of years.
Field identification & locations
Identify by its glassy texture and shell-like (conchoidal) fractures. Found in volcanic areas like the American West, Mexico, Iceland, and Italy.
