Pumice

Physical Properties

Vesicular (pitted with gas bubbles), highly porous, very low density (often floats on water), Mohs hardness of 5-6, light gray to cream color, dull luster, vitreous texture, no cleavage.

Formation & Geological History

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization cause gas bubbles to be trapped as the rock solidifies quickly into glass.

Uses & Applications

Used as an abrasive in cleaning and personal care (pumice stones), lightweight aggregate in concrete/cinder blocks, a soil conditioner in horticulture, and for stone-washing denim.

Geological Facts

Pumice is the only rock that can float on water due to its air-filled vesicles. Large eruptions can create 'pumice rafts' that drift across oceans for years.

Field Identification & Locations

Identify by its unusually light weight and sponge-like appearance. It is commonly found in areas of recent volcanic activity such as Iceland, Italy, Greece, and the Western United States.

Identified on: 4/26/2026

Mode: Standard