igneous
Obsidian
Obsidian (Volcanic Glass)
Hardness: 5-5.5 (Mohs scale); Color: Typically black but can be green, brown, or red; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.4
- Hardness
- 5-5
- Color
- Typically black but can be green, brown, or red
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Typically black but can be green, brown, or red; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.4
Formation & geological history
Formed from extrusive igneous activity when felsic lava cools rapidly with minimal crystal growth. Common in areas of geologically recent volcanic activity.
Uses & applications
Historically used for cutting tools, arrowheads, and mirrors. Currently used in surgery for ultra-sharp scalpels, jewelry (beads, pendants), and ornamental carvings.
Geological facts
Because it has no crystal structure, its edges can reach almost molecular thinness, making it sharper than even high-quality steel scalpels. It is technically a mineraloid rather than a mineral.
Field identification & locations
Identify in the field by its distinct glassy luster and razor-sharp conchoidal fractures. Commonly found in Western USA, Mexico, Iceland, and Japan.
