igneous
Pumice
Pumice (Volcanic Glass Foam)
Hardness: 6 on the Mohs scale, Color: Light gray, white, yellowish, or tan, Luster: Dull to earthy, Crystal structure: Amorphous (volcanic glass), Cleavage: None (conchoidal fracture), Specific gravity: Less than 1.0 (it floats on water due to high porosity).
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Physical properties
Hardness: 6 on the Mohs scale, Color: Light gray, white, yellowish, or tan, Luster: Dull to earthy, Crystal structure: Amorphous (volcanic glass), Cleavage: None (conchoidal fracture), Specific gravity: Less than 1.0 (it floats on water due to high porosity).
Formation & geological history
Formed from explosive volcanic eruptions where felsic lava containing high amounts of dissolved gases and water is rapidly depressurized and cooled, trapping gas bubbles within the glassy matrix.
Uses & applications
Widely used in lightweight construction aggregates, concrete manufacturing, abrasive materials (such as pumice stones for personal care and stone-washing jeans), and horticulture as a soil conditioner.
Geological facts
Pumice is one of the very few rocks that can float on water. It has been used for thousands of years as an abrasive and exfoliant, dating back to ancient Greece and Rome.
Field identification & locations
Easily identified by its extremely light weight, pale color, and characteristic vesicular (bubbly/sponge-like) texture filled with tiny gas cavities. Found worldwide near active or historic volcanic regions such as the Mediterranean, USA, and New Zealand.
