igneous
Pumice
Pumice (Vesicular volcanic glass)
Hardness: 5-6 (Mohs), Color: Light gray, cream, or pale yellow, Luster: Dull to pearly, Structure: Vesicular (highly porous/frothy), Specific Gravity: 0.25-0.90 (floats on water)
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Physical properties
Hardness: 5-6 (Mohs), Color: Light gray, cream, or pale yellow, Luster: Dull to pearly, Structure: Vesicular (highly porous/frothy), Specific Gravity: 0.25-0.90 (floats on water)
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich molten rock (magma) is ejected into the air; rapid cooling and depressurization create bubbles (vesicles). Found in volcanic regions.
Uses & applications
Used as an abrasive in soaps (Lava soap), foot stones for exfoliation, lightweight concrete aggregate, pencil erasers, and stone-washed denim production.
Geological facts
Pumice is the only rock that can float on water due to its air-filled pores. After a major eruption, 'pumice rafts' can float on the ocean for years and support migrations of sea life.
Field identification & locations
Identify by its extremely lightweight feel and sponge-like appearance. It is typically found near volcanoes or on beaches after traveling via ocean currents.
