igneous
Obsidian
Volcanic glass
Hardness: 5-5.5 (Mohs scale). Color: Black, sometimes with gray or brown. Luster: Vitreous/glassy. Crystal Structure: Amorphous (non-crystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.35-2.60.
- Hardness
- 5-5
- Color
- Black, sometimes with gray or brown
- Luster
- Vitreous/glassy
Identified More igneous →
Explore Obsidian in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5-5.5 (Mohs scale). Color: Black, sometimes with gray or brown. Luster: Vitreous/glassy. Crystal Structure: Amorphous (non-crystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.35-2.60.
Formation & geological history
Formed from the rapid cooling of silica-rich (felsic) lava, which prevents the growth of crystals. Typically found in geologically young volcanic regions (Quaternary age).
Uses & applications
Used in jewelry, scalpels (due to its ability to be sharper than steel), and as a decorative stone in collecting or ornamental carvings.
Geological facts
Obsidian was highly prized by indigenous cultures for making arrowheads and cutting tools because of its razor-sharp edges and predictable conchoidal fracture patterns.
Field identification & locations
Identify by its solid black color, glassy texture, and smooth curved (conchoidal) breaks. Often found in volcanic fields such as in Oregon, California, or Mexico.
