igneous
Obsidian
Volcanic glass (SiO2 + impurities)
Hardness: 5-5.5; Color: Deep black to dark green brown; Luster: Vitreous/glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (creates sharp edges)
- Hardness
- 5-5
- Color
- Deep black to dark green brown
- Luster
- Vitreous/glassy
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Physical properties
Hardness: 5-5.5; Color: Deep black to dark green brown; Luster: Vitreous/glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (creates sharp edges)
Formation & geological history
Formed when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Common in areas with geologically recent volcanic activity.
Uses & applications
Historically used for arrowheads and cutting tools. Today used for scalpel blades, jewelry, and ornamental carvings.
Geological facts
Obsidian fractures with an edge that is thinner and sharper than a surgeon's steel scalpel. Because it is a glass and not a mineral, it is considered a mineraloid.
Field identification & locations
Identify by its smooth, glassy texture and distinctive shell-like (conchoidal) fractures. Found in volcanic regions like the American West, Mexico, and Iceland.
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