igneous
Black Obsidian
Obsidian (Volcanic Glass)
Hardness: 5-5.5 (Mohs scale), Color: Jet black to dark gray, Luster: Vitreous/Glassy, Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.35-2.6
- Hardness
- 5-5
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Physical properties
Hardness: 5-5.5 (Mohs scale), Color: Jet black to dark gray, Luster: Vitreous/Glassy, Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.35-2.6
Formation & geological history
Formed through the rapid cooling of silica-rich felsic lava, which prevents crystal growth. Usually found in geologically young volcanic areas due to its eventual devitrification into quartz and feldspar.
Uses & applications
Used in ornamental jewelry, decorative items, and historically for surgical-grade scalpel blades and weapons (arrowheads/knives) due to its extremely sharp edges.
Geological facts
Unlike minerals, obsidian is a 'mineraloid' because it lacks an internal crystal structure. It breaks with a distinctive conchoidal fracture, creating edges thinner and sharper than even high-quality steel.
Field identification & locations
Commonly found in volcanic regions such as the United States (Oregon, California), Mexico, and Iceland. Identified by its glossy black appearance, lack of grain, and glass-like shell-shaped break patterns.
