igneous
Pumice
Pumice (Silicic volcanic glass with vesicular texture)
Hardness: 5-6 (Mohs scale, though fragile/brittle); Color: Light tan, cream, gray, or off-white; Luster: Dull to earthy; Texture: Highly vesicular with microscopic pores; Specific Gravity: Very low (0.25 to 0.9, often floats on water)
- Hardness
- 5-6 (Mohs scale, though fragile/brittle)
- Color
- Light tan, cream, gray, or off-white
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-6 (Mohs scale, though fragile/brittle); Color: Light tan, cream, gray, or off-white; Luster: Dull to earthy; Texture: Highly vesicular with microscopic pores; Specific Gravity: Very low (0.25 to 0.9, often floats on water)
Formation & geological history
Formed during explosive volcanic eruptions when highly gas-charged felsic magma (rich in silica) cools rapidly, trapping expanding gas bubbles inside a frothy matrix of glass.
Uses & applications
Used as an abrasive in soaps, stones for exfoliating skin, lightweight concrete aggregate, stonewashing denim, and soil conditioning in horticulture.
Geological facts
Pumice is so light and porous due to trapped gas bubbles that it is one of the few rocks capable of floating on water until it eventually becomes waterlogged.
Field identification & locations
Identified by its extremely low weight, porous sponge-like texture, light color, and ability to float on water. Commonly found in volcanic regions worldwide, especially around subduction zone volcanoes and island arcs.
