igneous
Obsidian
Volcanic glass
Hardness: 5-6 (Mohs); Color: Black, deep brown, or grey; Luster: Vitreous/glassy; Crystal structure: Amorphous; Cleavage: None (conchoidal fracture); Specific gravity: 2.35-2.6
- Hardness
- 5-6 (Mohs)
- Color
- Black, deep brown, or grey
- Luster
- Vitreous/glassy
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5-6 (Mohs); Color: Black, deep brown, or grey; Luster: Vitreous/glassy; Crystal structure: Amorphous; Cleavage: None (conchoidal fracture); Specific gravity: 2.35-2.6
Formation & geological history
Formed from rapid cooling of felsic lava, preventing crystal growth. It is typically found in tertiary or quaternary volcanic regions globally.
Uses & applications
Used in ornamental jewelry, scalpel blades for high-precision surgery, decorative items, and historical weapon/tool making.
Geological facts
Obsidian has been used since prehistoric times for sharp tools. Some of the sharpest blades in existence are made of obsidian, with an edge only molecules thick.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture and sharp edges. Common in areas of recent volcanic activity like the American West, Iceland, and Mexico.
