igneous
Obsidian with Matrix
Volcanic Glass (SiO2)
Hardness: 5-6 (Mohs); Color: Black with grayish-white matrix; Luster: Vitreous/Glassy; Structure: Amorphous; Cleavage: None (Conchoidal fracture); SG: 2.4
- Hardness
- 5-6 (Mohs)
- Color
- Black with grayish-white matrix
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-6 (Mohs); Color: Black with grayish-white matrix; Luster: Vitreous/Glassy; Structure: Amorphous; Cleavage: None (Conchoidal fracture); SG: 2.4
Formation & geological history
Formed from the rapid cooling of silica-rich lava which inhibits crystal growth. Can be found in volcanic regions of various ages, typically relatively young (Cenozoic) because glass eventually devitrifies.
Uses & applications
Historically used for sharp tools/weapons; currently used for scalpel blades, jewelry, and ornamental carvings.
Geological facts
Obsidian fractures into edges that can be much sharper than high-quality steel scalpels. It is technically a literal glass rather than a true mineral because of its amorphous nature.
Field identification & locations
Identified by its smooth, glassy texture and distinctive shell-like (conchoidal) fracture pattern. Commonly found in volcanic areas like the Western US, Mexico, and Iceland.
