Igneous
Obsidian
Obsidian (Volcanic Glass)
Hardness: 5-6 (Mohs scale); Color: Typically black, can be green/brown; Luster: Vitreous (glassy); Crystal structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.35-2.6.
- Hardness
- 5-6 (Mohs scale)
- Color
- Typically black, can be green/brown
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Typically black, can be green/brown; Luster: Vitreous (glassy); Crystal structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.35-2.6.
Formation & geological history
Forms from rapid cooling of silica-rich (rhyolitic) lava, which prevents crystal growth. Usually found in geologically young volcanic regions (Quaternary or Tertiary periods).
Uses & applications
Historically used for weapons/tools; modern use includes surgical scalpel blades, jewelry, and ornamental carvings.
Geological facts
Because it is so sharp (down to a molecular level), obsidian scalpels are often thinner and sharper than high-quality steel scalpels. It is technically a mineraloid rather than a mineral.
Field identification & locations
Identify by its distinctive curved, shell-like (conchoidal) fractures and translucent edges. Common in volcanic areas like Iceland, Mexico, and the Western USA (Oregon/California).
