igneous
Obsidian
Volcanic Glass (Primary composition: SiO2 - Silicon Dioxide)
Hardness: 5-5.5 (Mohs scale); Color: Jet black to dark grey; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6
- Hardness
- 5-5
- Color
- Jet black to dark grey
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Jet black to dark grey; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6
Formation & geological history
Formed from rapid cooling of felsic lava, preventing crystal growth. Usually found in volcanic regions from the Holocene to Pliocene epochs, as it devitrifies over millions of years into more stable minerals.
Uses & applications
Used in jewelry as tumbled stones or cabochons, manufacturing high-precision surgical scalpels, and historical tool-making (arrowheads). Also popular in metaphysical/collecting circles.
Geological facts
Obsidian is often called 'nature's glass.' Because it creates an edge thinner and sharper than a steel scalpel, it is still used in specialized medical procedures to reduce scarring.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture and extremely smooth, glassy surface. Commonly found in Oregon (USA), Mexico, and Iceland. If held to light, thin edges may appear translucent or smoky.
