igneous
Obsidian (Black Obsidian)
Obsidian (Volcanic Glass)
Hardness: 5–5.5 Mohs; Color: Jet black; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4
- Hardness
- 5–5
- Color
- Jet black
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5–5.5 Mohs; Color: Jet black; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4
Formation & geological history
Formed from rapid cooling of felsic (silica-rich) lava, preventing crystal growth. Usually found in geologically recent volcanic fields (often less than 20 million years old because it eventually devitrifies).
Uses & applications
Used for making ultra-sharp surgical scalpels, decorative jewelry (cabochons), and ornamental carved objects. Historically used for arrowheads and daggers.
Geological facts
Obsidian fractures with extremely sharp edges—thinner than a steel scalpel—which allows for cleaner incisions and faster healing in certain medical procedures. It is technically a 'mineraloid' rather than a mineral because it lacks a crystalline structure.
Field identification & locations
Identify by its glassy texture and distinctive shell-like (conchoidal) fracture pattern when chipped. Found globally in volcanic regions like Iceland, Mexico, and the Western United States (Oregon, California).
