igneous
Obsidian
Volcanic Glass
AI-generated identification · may be incorrectMohs hardness of 5 to 5.5, black or dark brown color, vitreous luster, amorphous crystal structure, conchoidal fracture, specific gravity around 2.4.
Identified More igneous →
Explore Obsidian in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Mohs hardness of 5 to 5.5, black or dark brown color, vitreous luster, amorphous crystal structure, conchoidal fracture, specific gravity around 2.4.
Formation & geological history
Formed from rapidly cooling felsic lava extruded from a volcano, preventing crystal growth; typically associated with recent volcanic activity.
Uses & applications
Used historically for sharp cutting tools and arrowheads, and currently in decorative jewelry and ornamental carvings.
Geological facts
Despite being called a mineraloid, obsidian is a natural glass. It fractures with exceptionally sharp edges sharper than surgical steel.
Field identification & locations
Identified by its intense vitreous luster, dark color, and characteristic conchoidal fracture. Found worldwide near active or recent volcanic regions.
