igneous
Obsidian
Volcanic Glass (SiO2 with impurities)
Hardness: 5-5.5 Mohs. Color: Jet black to dark grey. Luster: Vitreous/glassy. Fracture: Distinctive conchoidal fracture. Structure: Amorphous (non-crystalline).
- Hardness
- 5-5
- Color
- Jet black to dark grey
- Luster
- Vitreous/glassy
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Physical properties
Hardness: 5-5.5 Mohs. Color: Jet black to dark grey. Luster: Vitreous/glassy. Fracture: Distinctive conchoidal fracture. Structure: Amorphous (non-crystalline).
Formation & geological history
Formed as extrusive igneous rock when felsic lava extruded from a volcano cools rapidly with minimal crystal growth.
Uses & applications
Historically used for arrowheads and blades; currently used in jewelry, ornamental carvings, and specialized surgical scalpel blades.
Geological facts
Obsidian fractures with extremely sharp edges—much sharper than high-quality surgical steel scalpels—making it useful in specialized modern surgeries.
Field identification & locations
Identified by its shiny glassy appearance, deep black color, smooth curved conchoidal fractures, and lack of visible mineral grains.
