igneous
Pumice
Pumice (a frothy volcanic glass)
Hardness: 5-6 Mohs. Color: white, cream, or light grey. Luster: dull to pearly. Structure: vesicular (highly porous). Specific Gravity: less than 1.0 (it floats).
- 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. Structure: vesicular (highly porous). Specific Gravity: less than 1.0 (it floats).
Formation & geological history
Formed during explosive volcanic eruptions when pressurized lava is ejected and quickly cools, trapping gas bubbles within the rock.
Uses & applications
Used as an abrasive in liquid soaps and dental pastes, in construction for lightweight concrete, and as a cosmetic stone for exfoliating skin.
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large rafts of pumice have been known to float for miles in the ocean after eruptions.
Field identification & locations
Identify by its extremely lightweight feel and visible sponge-like holes (vesicles). Found in areas with past or present explosive volcanic activity like various islands or the Pacific Northwest.
