igneous
Black Obsidian
Obsidian / Amorphous volcanic glass (SiO2)
Hardness: 5-5.5 (Mohs scale), Color: Jet black, Luster: Vitreous/Glassy, Crystal Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.4
- Hardness
- 5-5
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Physical properties
Hardness: 5-5.5 (Mohs scale), Color: Jet black, Luster: Vitreous/Glassy, Crystal Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.4
Formation & geological history
Formed from the rapid cooling of silica-rich (felsic) lava that cools so quickly that crystals do not have time to grow. Most specimens found today are from the Quaternary period.
Uses & applications
Historically used for arrowheads and blades. Currently used in jewelry, decorative ornaments, and specialized surgical scalpel blades.
Geological facts
Because it lacks a crystalline structure, obsidian fractures with extremely sharp edges (conchoidal fracture). It is essentially a natural glass.
Field identification & locations
Identify by its glassy texture, deep black color, and sharp, curved fracture patterns. Found in volcanic regions like the American West (Iceland, Mexico, Japan).
