Obsidian
Image: Tõnis Saadre (CC BY-SA 4.0)
Mineral NameObsidian
Chemical FormulaSiO2 (amorphous)
Mohs Hardness5.5
Crystal Systemamorphous
Lustervitreous
Streak Colorwhite
Cleavagenone
Fractureconchoidal
Specific Gravity2.35
Colorsblack, white, grey
Transparencytranslucent
Type LocalityWorldwide in areas of recent volcanic activity (e.g., USA, Mexico, Iceland, Japan, Italy)
Mineral GroupMineraloid (volcanic glass)
Usesjewelry, cutting tools, surgical scalpels, collector's specimens
Raritycommon
Description
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.
Geological 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.
