igneous
Black Obsidian
Volcanic Glass (Amorphous Silicon Dioxide, SiO2)
Hardness: 5-5.5; Color: Jet black; Luster: Vitreous (glassy); Crystal Structure: Amorphous (none); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6
- Hardness
- 5-5
- Color
- Jet black
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5-5.5; Color: Jet black; Luster: Vitreous (glassy); Crystal Structure: Amorphous (none); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6
Formation & geological history
Formed from the rapid cooling of silica-rich rhyolitic lava which prevents crystal growth. Common in recently active volcanic areas like the Western USA (Oregon, California), Mexico, and Iceland.
Uses & applications
Used for making scalpel blades (due to its ability to hold an edge thinner than steel), decorative jewelry, gemstones, and meditation tools.
Geological facts
Obsidian fractures with extremely sharp edges, which is why it was used by ancient civilizations for spearheads and knives. It is technically more of a liquid than a solid because it lacks a crystal structure.
Field identification & locations
Identify by its glassy appearance, jet-black color, and characteristic curved, shell-like (conchoidal) fractures. Often found in obsidian flows or as nodules within volcanic ash deposits.
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