igneous
Pumice
Pumice (Vesicular Rhyolite/Andesite)
Hardness: 5-6 Mohs; Color: White, cream, or light grey; Luster: Dull to pearly; Crystal structure: Amorphous/Glassy; Cleavage: None; Specific gravity: 0.2-0.9 (Floats in water)
- Hardness
- 5-6 Mohs
- Color
- White, cream, or light grey
- Luster
- Dull to pearly
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Physical properties
Hardness: 5-6 Mohs; Color: White, cream, or light grey; Luster: Dull to pearly; Crystal structure: Amorphous/Glassy; Cleavage: None; Specific gravity: 0.2-0.9 (Floats in water)
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected and cools rapidly, trapping gas bubbles (vesicles). Mostly Quaternary to Neogene age.
Uses & applications
Used as an abrasive in soaps (Pumice stones), lightweight concrete aggregate, horticultural soil amendments, and stone-washing denim jeans.
Geological facts
Pumice is the only rock known to float on water for extended periods. Large eruptions can create 'pumice rafts' that drift across oceans for miles.
Field identification & locations
Identified in the field by its extreme lightweight feel and highly porous, frothy texture. Found in areas with history of explosive volcanism such as the Cascades or the Andes.
