igneous
Obsidian (worked into an arrowhead profile)
Obsidian (volcanic glass), primarily SiO2 (Silicon Dioxide)
Hardness: 5–6 Mohs; Color: Jet black to dark translucent; Luster: Vitreous/glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.4
- Hardness
- 5–6 Mohs
- Color
- Jet black to dark translucent
- Luster
- Vitreous/glassy
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Physical properties
Hardness: 5–6 Mohs; Color: Jet black to dark translucent; Luster: Vitreous/glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.4
Formation & geological history
Formed through the rapid cooling of felsic (silica-rich) lava, preventing crystal growth. Usually associated with geologically recent volcanic activity (Cenozoic era) due to its tendency to devitrify over time.
Uses & applications
Historically used for cutting tools and weapons (arrowheads/knives); modern use in surgical scalpels, jewelry (cabochons), and ornamental decorative items.
Geological facts
Obsidian edges can be sharpened to nearly molecular thickness, making them sharper than high-quality steel scalpels. This specific specimen has been 'knapped' or flaked manually into a projectile point shape.
Field identification & locations
Identify in the field by its distinct glass-like sheen and sharp, curved fracture lines. Commonly found in volcanic regions such as the American West (Oregon, California), Mexico, and Iceland. Look for edges that are translucent when held to light.
