igneous
Obsidian
Volcanic glass
Hardness: 5-5.5 (Mohs scale), Color: Jet black, Luster: Vitreous/Glassy, Structure: Amorphous (non-crystalline), Fracture: Conchoidal (shell-like curves), Specific Gravity: 2.4
- Hardness
- 5-5
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: Jet black, Luster: Vitreous/Glassy, Structure: Amorphous (non-crystalline), Fracture: Conchoidal (shell-like curves), Specific Gravity: 2.4
Formation & geological history
Formed from extrusive igneous activity when felsic lava (rich in silica) cools extremely rapidly, preventing the growth of mineral crystals. It is common in relatively young volcanic areas.
Uses & applications
Used in gemstone jewelry, ornamental carvings, and historically for surgical scalpels and arrowheads due to its extremely sharp edges. In industry, it is also used to produce perlite.
Geological facts
Because it has no crystal structure, it is considered a mineraloid rather than a true mineral. It was extensively traded in pre-Columbian times for tool making.
Field identification & locations
Identify by its glass-like appearance and smooth, curved fracture surfaces. Found in volcanic regions like the American West (Glass Buttes), Iceland, and Mexico.
