pumice

Pumice is a light-colored, highly vesicular volcanic rock formed when silica-rich magma erupts explosively and depressurizes rapidly. The rapid cooling traps a large number of gas bubbles, producing a frothy glassy texture. Because of its low density, fresh pumice can float on water, though weathering and compaction usually cause it to sink over time.

Geologically, pumice is a volcanic glass with high silica content, typically of rhyolitic to andesitic composition. It is usually pale and porous, with colors ranging from white to gray; some specimens may appear pink, brown, or green due to mineral impurities or oxidation. The surface is rough and highly abrasive.

Common uses include abrasive products for polishing and cleaning, as well as consumer pumice stones used for foot care. It also serves as a lightweight aggregate in cement and concrete, a filtration medium in water treatment, and a soil conditioner to improve drainage and aeration in horticulture.

Formation and occurrence: pumice forms during explosive eruptions at convergent plate boundaries where magma is gas-rich. It has been quarried worldwide, with notable deposits in the Mediterranean region (including the Aeolian islands and the area around Mount Vesuvius), as well as in Italy, Greece, Iceland, the Pacific Northwest, and parts of Asia, New Zealand, and Africa.