igneous
Pumice
Pumice (a highly vesicular volcanic glass)
Hardness: 5-6 (Mohs scale), Color: light grey to cream-white, Luster: dull to vitreous, Crystal Structure: amorphous (non-crystalline), Cleavage: none, Specific Gravity: 0.25 to 0.7 (extremely low, often floats in water)
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Physical properties
Hardness: 5-6 (Mohs scale), Color: light grey to cream-white, Luster: dull to vitreous, Crystal Structure: amorphous (non-crystalline), Cleavage: none, Specific Gravity: 0.25 to 0.7 (extremely low, often floats in water)
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich molten rock (lava) is ejected into the air; the rapid cooling and depressurization trap gas bubbles, creating a vesicular texture.
Uses & applications
Used as an abrasive in polishing compounds, stone-washing blue jeans, personal care (exfoliating pumice stones), and as a lightweight aggregate in concrete and landscaping.
Geological facts
Pumice is the only rock that can reliably float on water for long periods due to its high porosity; large rafts of pumice have been known to float in the ocean for years after a volcanic eruption.
Field identification & locations
Identify in the field by its extreme lightness, sandpaper-like texture, and plethora of small holes (vesicles). It is commonly found near volcanic sites such as Italy, Turkey, Greece, and the Western United States.
