Igneous
Pumice
Pumicite (Amorphous volcanic glass)
Hardness: 5-6 Mohs. Color: Light gray, tan, or yellowish. Luster: Dull to pearly. Texture: Highly vesicular (honeycombed with air bubbles). Specific Gravity: Often less than 1.0 (floats in water).
- Hardness
- 5-6 Mohs
- Color
- Light gray, tan, or yellowish
- Luster
- Dull to pearly
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Physical properties
Hardness: 5-6 Mohs. Color: Light gray, tan, or yellowish. Luster: Dull to pearly. Texture: Highly vesicular (honeycombed with air bubbles). Specific Gravity: Often less than 1.0 (floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich frothy magma is ejected and cools rapidly, trapping gas bubbles. Common in Quaternary volcanic deposits.
Uses & applications
Used as an abrasive in cosmetics (exfoliants), hygiene (pumice stones), metal polishing, construction (lightweight concrete), and as a soil amendment in horticulture.
Geological facts
Pumice is the only rock known to humans that can float on water until it eventually becomes waterlogged and sinks. Large eruptions can create 'pumice rafts' that drift across oceans for years.
Field identification & locations
Identify by its extremely lightweight feel and visible porous texture. Commonly found in vicinity of volcanoes with silicic lava. To test in the field, see if it floats in a body of water.
