igneous
Pumice
Pumice (a highly vesicular volcanic glass)
Hardness: 5-6 (Mohs scale), Color: light grey to cream-colored, Luster: dull to vitreous, Structure: highly vesicular (porous) and amorphous (glassy), Cleavage: none, Specific Gravity: 0.25 to 0.7 (floats on water)
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Physical properties
Hardness: 5-6 (Mohs scale), Color: light grey to cream-colored, Luster: dull to vitreous, Structure: highly vesicular (porous) and amorphous (glassy), Cleavage: none, Specific Gravity: 0.25 to 0.7 (floats on water)
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization trap gas bubbles, creating a frothy rock. Found worldwide in regions of previous or active volcanism.
Uses & applications
Used as an abrasive in cleaning products, cosmetic exfoliants (pumice stones), lightweight aggregate in concrete/cinder blocks, and in the production of stone-washed jeans.
Geological facts
Pumice is the only rock that can float on water until it becomes waterlogged. During massive eruptions, huge blankets of pumice called 'pumice rafts' can float on the ocean for years, sometimes carrying small organisms across oceans.
Field identification & locations
Identify by its extremely lightweight feel, light color, and the presence of numerous tiny holes (vesicles). It is commonly found near volcanic arcs and subduction zones like the Ring of Fire or Iceland.
