igneous
Obsidian
Obsidian (Volcanic Glass, primarily SiO2)
Hardness: 5.0–6.0; Color: Dark green to black; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4
- Hardness
- 5
- Color
- Dark green to black
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5.0–6.0; Color: Dark green to black; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4
Formation & geological history
Formed from extrusive igneous activity when felsic lava cools rapidly with minimal crystal growth. Specimens can range from prehistoric volcanic eruptions to relatively recent geological events.
Uses & applications
Historically used for making extremely sharp blades/arrowheads. Modern uses include surgical scalpels, ornamental carvings, jewelry, and collector specimens.
Geological facts
Obsidian is technically a glass rather than a true mineral because it lacks a crystalline structure. Ancient civilizations throughout the Americas used it for tools and trade as valuable as gold.
Field identification & locations
Identify by its glass-like appearance and conchoidal (shell-like) fracture patterns with sharp edges. Commonly found in volcanic regions such as the American Northwest, Mexico, and Iceland.
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