igneous
Black Obsidian
Obsidian (Volcanic Glass), primarily SiO2 (Silicon Dioxide) with impurities
Hardness: 5–5.5 (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
- 5–5
- Color
- Jet black to dark grey
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5–5.5 (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 silica-rich (felsic) lava from volcanic eruptions, preventing crystal growth. Most specimens found today are from the Quaternary period (less than 2.6 million years old).
Uses & applications
Used historically for sharp tools and weapons (arrowheads/knives); currently used for jewelry, decorative carvings, scalpel blades in specialized surgery, and metaphysical collecting.
Geological facts
Obsidians are technically 'frozen liquids' rather than true minerals because they lack a crystal structure. Ancient civilizations like the Aztecs and Mayans used polished obsidian as mirrors and currency.
Field identification & locations
Identify by its distinctive shell-like (conchoidal) fracture and sharp edges. Commonly found in volcanic regions such as the American West (Oregon, California), Mexico, Iceland, and Japan.
