igneous
Pumice
Pumice (a highly vesicular amorphous silicate)
Hardness: 5-6 (though brittle); Color: Light gray to white; Luster: Dull to pearly; Crystal structure: Amorphous (glassy); Cleavage: None; Density: Low (can float in water)
- Hardness
- 5-6 (though brittle)
- Color
- Light gray to white
- Luster
- Dull to pearly
Identified More igneous →
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Physical properties
Hardness: 5-6 (though brittle); Color: Light gray to white; Luster: Dull to pearly; Crystal structure: Amorphous (glassy); Cleavage: None; Density: Low (can float in water)
Formation & geological history
Formed during explosive volcanic eruptions when pressurized, gas-rich lava is ejected and quickly cools, trapping gas bubbles within a glassy matrix.
Uses & applications
Used as an abrasive in polishing, skin exfoliation (pumice stones), lightweight aggregate in concrete, and in horticulture to improve soil aeration.
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large eruptions can create 'pumice rafts' that drift for thousands of miles.
Field identification & locations
Identify in the field by its frothy, 'swiss cheese' appearance and its extreme lightweight. It is commonly found near volcanic arcs and subduction zones.
