Pumice

Pumice is a highly vesicular volcanic rock formed when gas-rich lava cools rapidly. Its abundant cavities make it unusually lightweight and abrasive.

Vesicle (geology): A cavity in volcanic rock formed by gas bubbles in molten rock. Abundant vesicles are the cavities that give pumice its porous texture.
Porosity: The fraction of a material’s volume occupied by pores or voids. Pumice’s high porosity accounts for its low bulk density.
Pumice concrete: Lightweight concrete made with pumice as a porous aggregate. Pumice replaces denser aggregate to reduce concrete’s weight and improve insulation.
Hunga Tonga–Hunga Haʻapai eruption: The 2022 eruption of a submarine volcano in Tonga that generated a major ash plume and tsunami. The eruption produced pumice rafts that drifted across the Pacific Ocean.
Volcanic glass: Amorphous solid formed when molten rock cools too quickly to crystallize. Pumice’s glassy material records the rapid cooling of gas-rich lava.
Bulk density: A material’s mass divided by its total volume, including internal pores. Pumice’s many cavities reduce its bulk density below that of water in some specimens.
Pumice stone: A piece of pumice used as an abrasive for smoothing or cleaning surfaces. Its rough, porous surface removes dead skin and cleans hard materials.
Pumice raft: A floating mass of pumice fragments formed during a volcanic eruption. The cavities in pumice can keep fragments afloat, allowing rafts to travel far from their source.
Magma degassing: The release of dissolved gases from magma as pressure falls or magma cools. Gas escaping from rising magma expands into the bubbles preserved in pumice.
Silicate minerals: Minerals built from silicon–oxygen structures, the dominant mineral group in Earth’s crust. Pumice’s composition is largely silicate glass, whose chemistry varies with the magma.

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