Image: James St. John (CC BY 2.0)
amorphouscommonVolcanic Glass (Igneous Rock)
Obsidian
Primarily SiO2 (silica-rich volcanic glass)
A glassy, extrusive igneous rock, typically dark in color, known for its sharp conchoidal fracture. The image displays a vibrant green variety.
Obsidian Physical Properties
Mohs Hardness
5Crystal System
amorphousLuster
vitreousStreak Color
white/colorlessCleavage
noneFracture
conchoidalSpecific Gravity
2.35Colors
black, brown, green, red, gray, iridescentTransparency
opaqueType Locality
MexicoMineral Group
Volcanic Glass (Igneous Rock)Uses
jewelry, cutting tools, decorative objects, surgical scalpelsAssociated Minerals
Rarity
commonGeological Context
Obsidian forms from the rapid cooling of felsic lava, which prevents the formation of mineral crystals, resulting in its characteristic glassy texture. It is an extrusive igneous rock.
