igneous
Pumice (likely weathered/water-worn)
Vesicular volcanic glass
Hardness: 5-6 Mohs (though fragile), Color: light gray to cream, Luster: Vitreous to dull, Crystal structure: Amorphous (glassy), highly vesicular (porous) texture, floats in water
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Physical properties
Hardness: 5-6 Mohs (though fragile), Color: light gray to cream, Luster: Vitreous to dull, Crystal structure: Amorphous (glassy), highly vesicular (porous) texture, floats in water
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized gas is trapped in rapidly cooling lava. These specimens appear to be rounded cobbles, likely shaped by water transport (river or beach action).
Uses & applications
Used as an abrasive in cleaning products, cosmetic exfoliants (pumice stones), lightweight concrete aggregate, and horticulture (soil aeration).
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged. Large eruptions can create 'pumice rafts' that float across oceans for thousands of miles.
Field identification & locations
Identify in the field by its extremely light weight relative to size (low density) and the presence of numerous small holes (vesicles). It is commonly found near volcanic arcs and on beaches after eruptions.
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