igneous
Black Obsidian
Obsidian (Volcanic Glass)
Hardness: 5–6 (Mohs); Color: Jet black to dark grey; Luster: Vitreous/glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (creates sharp edges); Specific Gravity: 2.4
- Hardness
- 5–6 (Mohs)
- Color
- Jet black to dark grey
- Luster
- Vitreous/glassy
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Physical properties
Hardness: 5–6 (Mohs); Color: Jet black to dark grey; Luster: Vitreous/glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (creates sharp edges); Specific Gravity: 2.4
Formation & geological history
Formed through the rapid cooling of silica-rich felsic lava, which prevents crystal growth. It typically originates in extrusive volcanic environments from the Pliocene to Holocene epochs.
Uses & applications
Used for making surgical scalpel blades, jewelry (cabochons and beads), ornamental carvings, and historically for stone tools like arrowheads.
Geological facts
Because it lacks a crystal structure, obsidian edges can be thinned down to nearly molecular levels, producing edges much sharper than high-quality steel scalpels.
Field identification & locations
Identify in the field by its smooth, glassy appearance and distinctive shell-like (conchoidal) fracture patterns. Frequently found in volcanic areas such as the western United States, Mexico, Iceland, and Italy.
