Image: James St. John (CC BY 2.0)
amorphouscommonVolcanic Glass
Obsidian
SiO2 (amorphous)
A dark green, glassy volcanic rock, exhibiting a characteristic conchoidal fracture on fresh surfaces and a duller, weathered texture in other areas.
Obsidian Physical Properties
Mohs Hardness
5.5Crystal System
amorphousLuster
vitreousStreak Color
whiteCleavage
noneFracture
conchoidalSpecific Gravity
2.4Colors
green, black, brown, red, grayTransparency
translucentType Locality
MexicoMineral Group
Volcanic GlassUses
jewelry, tools, collector's itemAssociated Minerals
rhyolite, pumice, quartz, feldsparRarity
commonGeological Context
Obsidian is an extrusive igneous rock formed by the rapid cooling of viscous, silica-rich lava, which prevents the formation of crystalline structures, resulting in a natural glass.
