igneous
Pumice
Pumice (Vesicular Felsic Glass)
Hardness: 5-6 Mohs (though fragile), Color: light gray to tray-white, Luster: dull to silky, Crystal Structure: amorphous glass (non-crystalline), Specific Gravity: 0.25-0.9 (floats on water), highly vesicular.
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Physical properties
Hardness: 5-6 Mohs (though fragile), Color: light gray to tray-white, Luster: dull to silky, Crystal Structure: amorphous glass (non-crystalline), Specific Gravity: 0.25-0.9 (floats on water), highly vesicular.
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, silica-rich lava is violently ejected. The rapid cooling and depressurization freeze gas bubbles in the petrifying lava. Generally found in Quaternary to modern volcanic deposits.
Uses & applications
Used as a lightweight aggregate in concrete, as an abrasive in polishing compounds, stone-washing textiles (jeans), and in cosmetic products (exfoliating skin).
Geological facts
Pumice is the only rock that consistently floats on water due to its air-filled pores. Large eruptions can create 'pumice rafts' that can travel across oceans for years.
Field identification & locations
Identify by its extremely lightweight feel and sponge-like, porous texture with glass-sharp edges. Found in areas with history of explosive volcanism like the Andes, Cascades, or Mediterranean.
