igneous
Obsidian
Volcanic Glass (Amorphous Silicon Dioxide)
Hardness: 5 to 5.5 on the Mohs scale, Color: Typically pitch black, dark brown, or green, Luster: Vitreous (glassy), Crystal Structure: Amorphous (non-crystalline), Cleavage: Conchoidal fracture, Specific Gravity: 2.35 to 2.60
- Hardness
- 5 to 5
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Physical properties
Hardness: 5 to 5.5 on the Mohs scale, Color: Typically pitch black, dark brown, or green, Luster: Vitreous (glassy), Crystal Structure: Amorphous (non-crystalline), Cleavage: Conchoidal fracture, Specific Gravity: 2.35 to 2.60
Formation & geological history
Formed as an extrusive igneous rock when felsic lava extruded from a volcano cools rapidly with minimal crystal growth.
Uses & applications
Used in historical cutting tools, surgical scalpels, decorative objects, and jewelry.
Geological facts
Obsidian fractures with extremely sharp edges, often making blades thinner and sharper than high-quality steel surgical scalpels.
Field identification & locations
Easily identified by its glass-like appearance, dark color, and characteristic conchoidal fracture. Found in regions with recent volcanic activity.
