igneous
Pumice
Pumice (volcanic glass foam)
Hardness of 6 on the Mohs scale, color ranges from white, yellowish, grey, to brown-green, vitreous to dull luster, amorphous crystal structure (volcanic glass), specific gravity less than 1.0 (floats on water) due to extreme vesicularity.
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Physical properties
Hardness of 6 on the Mohs scale, color ranges from white, yellowish, grey, to brown-green, vitreous to dull luster, amorphous crystal structure (volcanic glass), specific gravity less than 1.0 (floats on water) due to extreme vesicularity.
Formation & geological history
Formed from explosive volcanic eruptions where gas-rich, felsic to intermediate lava rapidly cools and depressurizes, trapping gas bubbles within the glass matrix. Often associated with rhyolitic eruptions.
Uses & applications
Used in lightweight concrete, abrasives (such as pumice stones for skin care, scouring soaps, and polishing), horticulture as a soil amendment, and filtration media.
Geological facts
Pumice is one of the only rocks that can float on water because of its low density caused by the interconnected gas bubble network. It has been used since antiquity for personal grooming and construction.
Field identification & locations
Easily identified by its extremely light weight, frothy vesicular texture, abrasive feel, and ability to float on water. Found globally near regions of past or active explosive volcanism.
