igneous
Black Obsidian
Extrusive Volcanic Glass (primarily SiO2)
AI-generated identification · may be incorrectHardness: 5-5.5; Color: Jet black, sometimes with green or brown undertones; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6
- Hardness
- 5-5
- Color
- Jet black, sometimes with green or brown undertones
- Luster
- Vitreous (glassy)
Identified More igneous →
Explore Black Obsidian in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5-5.5; Color: Jet black, sometimes with green or brown undertones; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6
Formation & geological history
Formed from the rapid cooling of silica-rich rhyolitic lava, which prevents crystal growth. This specimen is post-processed through tumbling and polishing.
Uses & applications
Used in jewelry, decorative ornaments, and historically for making sharp cutting tools, arrowheads, and surgical scalpels.
Geological facts
Obsidian is technically a supercooled liquid rather than a true mineral because it lacks a crystalline structure. It was highly prized by ancient cultures for its razor-sharp edges.
Field identification & locations
Identified by its intense black color, glassy sheen, and characteristic shell-like (conchoidal) fracture pattern. Found in volcanic regions like the American West, Mexico, and Iceland.
