igneous
Obsidian
Obsidian (Volcanic Glass)
Hardness: 5-5.5 (Mohs); Color: Jet black to smoky; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4
- Hardness
- 5-5
- Color
- Jet black to smoky
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-5.5 (Mohs); Color: Jet black to smoky; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4
Formation & geological history
Formed when highly silica-rich lava cools extremely rapidly, preventing the growth of mineral crystals. Typically found at the edges of rhyolitic lava flows or along volcanic cooling margins.
Uses & applications
Used historically for sharp-edged tools (arrowheads, knives), currently used in surgical scalpel blades, jewelry, and as a semi-precious collector's gemstone.
Geological facts
This specific specimen is an artifact, likely a projectile point (arrowhead) made through flintknapping. Obsidian is so sharp that its edge can be thinner than a single molecule.
Field identification & locations
Identify by its characteristic glassy texture, shell-like (conchoidal) fractures, and sharp edges. Common in volcanic regions such as Oregon, Mexico, and Iceland.
