Pumice
Mineral NamePumice
Chemical FormulaPrimarily amorphous volcanic glass, typically felsic (rhyolitic to dacitic) in composition, rich in SiO2, Al2O3, K2O, Na2O.
Mohs Hardness5
Crystal Systemamorphous
Streak Colorwhite to very light gray
Cleavagenone
Fractureconchoidal (for the glass), but often uneven/splintery due to vesicles
Specific Gravity0.5
Colorswhite, gray, cream, light brown, yellow
Transparencyopaque
Type LocalitySantorini, Greece
Mineral GroupIgneous rock (volcanic glass)
Usesabrasives, lightweight concrete aggregate, horticulture, cosmetic exfoliants
Associated Mineralsquartz, feldspar, biotite, hornblende
Raritycommon
Description
A light tan-colored, highly porous and frothy volcanic rock, characterized by its numerous gas bubbles (vesicles) which give it a very low density.
Geological Context
Pumice forms during explosive volcanic eruptions when gas-rich, viscous magma rapidly cools and depressurizes, causing dissolved gases to exsolve and create a frothy, glassy texture.
