igneous
Pumice
Pumice (Vesicular volcanic glass)
Hardness: 5-6 Mohs (though fragile), Color: Light gray/white/cream, Luster: Dull/pearly/silky, Crystal Structure: Amorphous/Vitreous (glassy), Cleavage: None, Specific Gravity: 0.2-0.9 (low density, floats on water)
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Physical properties
Hardness: 5-6 Mohs (though fragile), Color: Light gray/white/cream, Luster: Dull/pearly/silky, Crystal Structure: Amorphous/Vitreous (glassy), Cleavage: None, Specific Gravity: 0.2-0.9 (low density, floats on water)
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is violently ejected and cools rapidly, trapping gas bubbles as vesicles. Found in volcanic regions worldwide.
Uses & applications
Used as an abrasive in cleaning supplies, exfoliating stones in personal care, lightweight aggregate in concrete, horticultural soil additives, and historically for polishing documents.
Geological facts
Pumice is the only rock that can float on water due to its highly vesicular (bubbly) structure. Large rafts of floating pumice can travel across oceans for years after an undersea eruption.
Field identification & locations
Identify in the field by its extremely light weight, frothy texture, and ability to float in a puddle or stream. Commonly found near stratovolcanos or calderas.
