igneous
Obsidian
Obsidian (Volcanic Glass)
Hardness: 5-5.5 (Mohs scale), Color: Black/Dark Brown, Luster: Vitreous/Glassy, Structure: Amorphous (non-crystalline), Fracture: Conchoidal, Specific Gravity: 2.4
- Hardness
- 5-5
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Physical properties
Hardness: 5-5.5 (Mohs scale), Color: Black/Dark Brown, Luster: Vitreous/Glassy, Structure: Amorphous (non-crystalline), Fracture: Conchoidal, Specific Gravity: 2.4
Formation & geological history
Formed when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Found in volcanic regions of recent geological ages (typically Cenozoic).
Uses & applications
Used for making surgical scalpel blades, jewelry, decorative ornaments, and historically for stone tools like arrowheads.
Geological facts
Obsidian is technically a glass, not a mineral, because it lacks a crystalline structure. It is so sharp that its edges can be thinner than a high-quality steel scalpel.
Field identification & locations
Identified by its jet-black color, extremely smooth glassy texture, and bowl-shaped (conchoidal) fractures. Common in Oregon, Arizona, Iceland, and Mexico.
