igneous
Obsidian
Obsidian (Volcanic Glass)
Hardness: 5-5.5 (Mohs scale); Color: Black, sometimes with white inclusions; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.352-2.55
- Hardness
- 5-5
- Color
- Black, sometimes with white inclusions
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Black, sometimes with white inclusions; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.352-2.55
Formation & geological history
Formed from extrusive igneous activity when felsic lava cools rapidly with minimal crystal growth. Found in volcanic regions of all ages, though mostly young as it eventually devitrifies into crystalline rock.
Uses & applications
Used historically for sharp tools and weapons (scalpels, arrowheads). Currently used in jewelry, ornamental carvings, and specialized surgical blades.
Geological facts
Obsidian fractures with edges so sharp that they can be thinner than a standard steel scalpel blade, allowing for specialized surgical use. It is technically a 'mineraloid' rather than a true mineral because it lacks a crystalline structure.
Field identification & locations
Identify by its intense black color and characteristic conchoidal fracture which leaves very sharp, curved edges. Commonly found in volcanic areas like the Cascades in the US, Iceland, and Mexico.
