igneous
Pumice
Pumice (Felsic volcanic glass)
Hardness of 6 on the Mohs scale, colors range from white, grey, yellowish, to brown, dull to earthy luster, vesicular texture (filled with gas bubble cavities), amorphous crystal structure (volcanic glass), and extremely low specific gravity allowing it to float on water.
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Physical properties
Hardness of 6 on the Mohs scale, colors range from white, grey, yellowish, to brown, dull to earthy luster, vesicular texture (filled with gas bubble cavities), amorphous crystal structure (volcanic glass), and extremely low specific gravity allowing it to float on water.
Formation & geological history
Formed from explosive volcanic eruptions where felsic lava containing high amounts of dissolved gases is ejected rapidly into the atmosphere, cooling so quickly that crystals do not have time to form while gas bubbles are trapped inside.
Uses & applications
Widely used in lightweight concrete, landscaping, abrasive soaps, personal care for skin exfoliation, and as a horticulture soil additive.
Geological facts
Pumice is one of the very few rocks that can float on water due to its high porosity and trapped air vesicles. Major deposits are found globally near active and past volcanic regions.
Field identification & locations
Easily identified by its extremely light weight, pale color, and abundant small holes (vesicles). Commonly found in regions with historical explosive felsic volcanism such as the Mediterranean, parts of western North America, and New Zealand.
