igneous
Pumice
Pumice (volcanic glass foam)
Hardness of 6 on the Mohs scale, color ranges from white, yellowish, grey, to brown, dull to earthy luster, amorphous crystal structure (volcanic glass), specific gravity less than 1.0 (floats on water) due to high vesicularity.
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Physical properties
Hardness of 6 on the Mohs scale, color ranges from white, yellowish, grey, to brown, dull to earthy luster, amorphous crystal structure (volcanic glass), specific gravity less than 1.0 (floats on water) due to high vesicularity.
Formation & geological history
Formed from explosive volcanic eruptions where gas-rich felsic lava cools rapidly, causing gases to bubble out and become trapped in the solidifying glass.
Uses & applications
Used in lightweight concrete, landscaping, abrasive soaps, personal care (exfoliating pumice stones), and horticulture.
Geological facts
Pumice is one of the very few rocks that can float on water due to its trapped air bubbles. Some massive pumice rafts can drift across oceans for months after major underwater or island volcanic eruptions.
Field identification & locations
Easily identified by its extremely low density, light weight, vesicular (foamy) texture with many tiny pores, and pale color. Found globally near active or historical volcanic regions, particularly along subduction zones.
