igneous
Black Obsidian
Obsidian (Volcanic Glass)
Hardness: 5-5.5 (Mohs scale); Color: Jet black; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6
- Hardness
- 5-5
- Color
- Jet black
- 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 (Mohs scale); Color: Jet black; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6
Formation & geological history
Formed from rapid cooling of silica-rich (felsic) lava, preventing crystal growth. Usually found in geologically recent volcanic regions such as the Cascades or Rift Valleys.
Uses & applications
Used primarily in jewelry (beads, cabochons), ornamental carvings, and historical cutting tools. In modern medicine, it is sometimes used for ultra-sharp surgical scalpel blades.
Geological facts
Obsidian is technically an igneous rock but behaves like a mineral. It was highly prized in pre-Columbian Mesoamerica for creating weapons (Macuahuitl) due to its ability to break into edges thinner than steel.
Field identification & locations
Identify by its characteristic glassy luster and conchoidal (shell-like) fracture patterns. Frequently found in volcanic fields. Collectors look for high-gloss, uniform color and no visible air bubbles.
