igneous
Pumice
Pumice (Felsic vesicular volcanic glass)
Hardness: 5-6 (Mohs scale), Color: Light gray, tan, cream, or off-white, Luster: Dull to earthy, Structure: Amorphous/glassy with vesicular texture, Specific Gravity: <1.0 (often floats on water due to trapped gas bubbles)
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Physical properties
Hardness: 5-6 (Mohs scale), Color: Light gray, tan, cream, or off-white, Luster: Dull to earthy, Structure: Amorphous/glassy with vesicular texture, Specific Gravity: <1.0 (often floats on water due to trapped gas bubbles)
Formation & geological history
Formed during explosive volcanic eruptions when highly gas-charged, felsic (silica-rich) lava cools very rapidly, trapping gas bubbles (vesicles) before they can escape.
Uses & applications
Used widely as a lightweight aggregate in concrete, as an abrasive in industrial cleansers, polishing compounds, cosmetic skin exfoliation (pumice stones), and in landscaping.
Geological facts
Pumice is the only rock that can routinely float on water for extended periods until it becomes waterlogged. Mass rafts of floating pumice created during underwater volcanic eruptions can drift across entire oceans for years.
Field identification & locations
Identified by its distinctive porous, sponge-like texture, exceptionally light weight, and off-white to light gray coloration. Frequently found in volcanic belts, volcanic beaches, and active geothermal zones.
