igneous
Black Obsidian
Obsidian (Amorphous Silicon Dioxide)
Hardness: 5-5.5; Color: Deep black; Luster: Vitreous/glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6
- Hardness
- 5-5
- Color
- Deep black
- Luster
- Vitreous/glassy
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Physical properties
Hardness: 5-5.5; Color: Deep black; Luster: Vitreous/glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6
Formation & geological history
Formed through the rapid cooling of rhyolitic lava, preventing crystal growth. It is relatively young geologically as glass decays naturally over time, mostly found from the Tertiary and Quaternary periods.
Uses & applications
Used for making scalpel blades, jewelry (cabochons), ornamental carvings, and historically for stone tools like arrowheads.
Geological facts
Obsidian is technically a 'mineraloid' rather than a mineral because it lacks a crystal structure. It breaks with extremely sharp edges, sometimes down to nearly molecular thickness.
Field identification & locations
Identify by its glassy texture, smooth jet-black appearance, and curved conchoidal fractures. Commonly found in volcanic regions like Iceland, Mexico, and the Western United States.
