igneous
Pumice
Pumice (Vesicular Felsic Igneous Rock)
Hardness of 6 on the Mohs scale (for the glass framework), color ranges from white, grey, yellowish, to brown, dull luster, amorphous volcanic glass matrix with vesicular (frothy) texture, poor cleavage, and extremely low specific gravity allowing it to float on water.
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Physical properties
Hardness of 6 on the Mohs scale (for the glass framework), color ranges from white, grey, yellowish, to brown, dull luster, amorphous volcanic glass matrix with vesicular (frothy) texture, poor cleavage, and extremely low specific gravity allowing it to float on water.
Formation & geological history
Formed during explosive volcanic eruptions of felsic or intermediate magma (rich in silica and dissolved gases). As pressure drops rapidly upon eruption, gases bubble out and create a frothy foam that instantly cools and solidifies into glass before the bubbles can escape.
Uses & applications
Used in lightweight concrete, abrasive materials such as pumice stones for personal care and industrial grinding, horticulture as a soil amendment, and as a filtration medium.
Geological facts
Pumice is one of the only natural rocks that can float on water due to the high volume of trapped air bubbles inside its vesicular structure. Large amounts of pumice can form floating mats after underwater volcanic eruptions, sometimes drifting across oceans for months.
Field identification & locations
Easily identified by its extremely light weight, pale color, and abundant vesicular pores. It is commonly found worldwide in regions with past or present explosive volcanic activity, particularly along subduction zones and continental volcanic arcs.
