Igneous
Obsidian
Obsidian
Hardness: 5-5.5. Color: commonly black, but can be brown, gray, or banded. Luster: vitreous (glassy). Crystal structure: amorphous (volcanic glass). Cleavage: none; exhibits conchoidal fracture.
- Hardness
- 5-5
- Color
- commonly black, but can be brown, gray, or banded
- Luster
- vitreous (glassy)
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Physical properties
Hardness: 5-5.5. Color: commonly black, but can be brown, gray, or banded. Luster: vitreous (glassy). Crystal structure: amorphous (volcanic glass). Cleavage: none; exhibits conchoidal fracture.
Formation & geological history
Forms from the rapid cooling of silica-rich lava, preventing crystal formation. Often geologically young as older obsidian typically devitrifies over time.
Uses & applications
Historically used for cutting tools, arrowheads, and weapons due to its sharp edges. Used in jewelry, ornamental objects, and sometimes as surgical scalpel blades.
Geological facts
Obsidian has been used since prehistoric times. It can have extremely sharp edges, sharper than high-quality steel scalpels.
Field identification & locations
Identified by its deep black color, glassy luster, and conchoidal fracture. Found in areas of recent volcanic activity, such as the western United States, Mexico, and parts of Europe.
