igneous
Black Obsidian
Volcanic Glass (SiO2 + impurities)
Hardness: 5-5.5 (Mohs scale), Color: Jet black, Luster: Vitreous/glassy, Crystal structure: Amorphous, 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, Cleavage: None (conchoidal fracture), Specific Gravity: 2.4
Formation & geological history
Formed through the rapid cooling of silica-rich rhyolitic lava, preventing crystal growth. Found in geologically young volcanic areas (Quaternary age).
Uses & applications
Used in ornamental jewelry, scalpel blades for surgery, and historical tool-making (arrowheads). High value for crystal collecting and decorative carvings.
Geological facts
Obsidian fractures with extremely sharp edges, often down to molecular thickness. It was a vital trade commodity for ancient civilizations like the Aztecs and Mayans.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture and sharp edges. Commonly found in volcanic regions like the American West (Glass Buttes), Mexico, and Iceland.
