igneous
Obsidian
Obsidian (Volcanic Glass)
Hardness: 5-5.5 Mohs; Color: Black, sometimes dark green or brown; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6.
- Hardness
- 5-5
- Color
- Black, sometimes dark green or brown
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-5.5 Mohs; Color: Black, sometimes dark green or brown; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6.
Formation & geological history
Formed by the rapid cooling of silica-rich (felsic) lava, which prevents the formation of mineral crystals. Usually found in geologically young volcanic areas (Pliocene to Holocene).
Uses & applications
Historically used for arrowheads and knives due to sharp edges. Today used in scalpel blades, jewelry, and as a semi-precious gemstone.
Geological facts
Obsidian is biologically inert and can be fashioned into blades far sharper than high-quality steel scalpels. It is technically a glass rather than a mineral because it lacks a crystalline structure.
Field identification & locations
Identify by its smooth, glassy texture and razor-sharp conchoidal (shell-like) fracture edges. Commonly found in volcanic regions of Oregon, California, and Iceland.
