igneous
Black Obsidian
Obsidian (Volcanic Glass)
Hardness: 5.0–6.0 on Mohs scale; Color: Jet black to dark grey; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6
- Hardness
- 5
- Color
- Jet black to dark grey
- Luster
- Vitreous/Glassy
Identified More igneous →
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Physical properties
Hardness: 5.0–6.0 on Mohs scale; Color: Jet black to dark grey; 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 felsic lava, which prevents the growth of crystals. It is typically found in volcanic areas near the edges of rhyolitic lava flows or along the borders of dikes and sills. Most specimens are geologically young, as glass eventually devitrifies.
Uses & applications
Historically used for precision cutting tools (scalpels, arrowheads). Modern uses include ornamental jewelry, decorative objects, and metaphysical collecting.
Geological facts
Obsidian breaks with a conchoidal fracture, creating edges that are thinner and sharper than high-quality steel scalpels. It has been traded for thousands of years as a precious material for weapon-making.
Field identification & locations
Identify by its glass-like appearance, lack of grain, and sharp, curved fracture patterns. Commonly found in Iceland, Mexico, lipari Islands, and the western United States.
