Image: Tõnis Saadre (CC BY-SA 4.0)
amorphouscommonMineraloid (volcanic glass)
Obsidian
SiO2 (amorphous)
A dark, glassy volcanic rock characterized by its amorphous structure and sharp, conchoidal fracture. This specimen is Snowflake Obsidian, featuring distinctive white or greyish spherulitic inclusions against a black background.
Obsidian Physical Properties
Mohs Hardness
5.5Crystal System
amorphousLuster
vitreousStreak Color
whiteCleavage
noneFracture
conchoidalSpecific Gravity
2.35Colors
black, white, greyTransparency
translucentType Locality
Worldwide in areas of recent volcanic activity (e.g., USA, Mexico, Iceland, Japan, Italy)Mineral Group
Mineraloid (volcanic glass)Uses
jewelry, cutting tools, surgical scalpels, collector's specimensAssociated Minerals
Rarity
commonGeological Context
Obsidian forms from the rapid cooling of felsic lava, typically rhyolitic, preventing the formation of a crystalline structure. Snowflake obsidian develops its characteristic pattern due to the partial crystallization of cristobalite or feldspar spherulites within the glass during cooling.
