igneous
Obsidian
Obsidian (Volcanic Glass, complex silicate)
Hardness: 5.0 to 6.0; 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
Hardness: 5.0 to 6.0; Color: Jet black; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4
Formation & geological history
Formed as an extrusive igneous rock when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Found in volcanic regions of any geological age, though rarely older than Cretaceous due to recrystallization.
Uses & applications
Used for making scalpel blades (sharper than steel), jewelry/gemstones, ornamental carvings, and historically for arrowheads and tools.
Geological facts
Obsidian breaks with a conchoidal fracture that produces edges thinner than a surgeon's scalpel. It is not technically a mineral because it lacks a crystalline structure.
Field identification & locations
Identify in the field by its glassy texture and curved, shell-like (conchoidal) fracture lines. Commonly found in Oregon, California, and Iceland. Exercise caution as edges are razor-sharp.
