igneous
Pumice
Pumice (a highly vesicular amorphous volcanic glass)
Hardness: 5-6 (Mohs scale), Color: light gray to pale green/tan, Luster: vitreous to silky, Crystal structure: amorphous (none), Cleavage: none, Specific gravity: 0.25-1.2 (often floats in water), Porosity: highly vesicular.
Identified More igneous →
Explore Pumice in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5-6 (Mohs scale), Color: light gray to pale green/tan, Luster: vitreous to silky, Crystal structure: amorphous (none), Cleavage: none, Specific gravity: 0.25-1.2 (often floats in water), Porosity: highly vesicular.
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization cause gases to expand rapidly, creating a frothy, glass-like foam that solidifies. Can be found in volcanic regions of all ages, commonly Holocene.
Uses & applications
Used as an abrasive in soaps, pencil erasers, and stone-washed jeans. Also used in lightweight concrete, horticulture (soil aeration), and beauty products like pumice stones for skincare.
Geological facts
Pumice is the only rock that can reliably float on water for long periods. After massive volcanic eruptions, giant 'pumice rafts' can form in the ocean, drifting for thousands of miles and occasionally reaching heights of several feet thick.
Field identification & locations
Identify by its unusually light weight (low density) and frothy, sponge-like texture with numerous small holes (vesicles). It is commonly found near volcanic activity, especially near rhyolitic or dacitic vents.
