igneous
Pumice
Pumice (Vesicular volcanic glass)
Hardness: 5-6 (but fragile due to vesicles); Color: light gray, tan, or cream; Luster: dull to pearly; Structure: highly vesicular (porous) glass; Specific Gravity: typically <1.0 (floats on water).
- Hardness
- 5-6 (but fragile due to vesicles)
- Color
- light gray, tan, or cream
- Luster
- dull to pearly
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Physical properties
Hardness: 5-6 (but fragile due to vesicles); Color: light gray, tan, or cream; Luster: dull to pearly; Structure: highly vesicular (porous) glass; Specific Gravity: typically <1.0 (floats on water).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is violently ejected and cools rapidly, trapping air bubbles in the solidifying glass.
Uses & applications
Used as an abrasive in cleaning products and cosmetics (exfoliants), a lightweight aggregate in concrete/cinder blocks, and in horticulture to aerate soil.
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large rafts of floating pumice can travel across oceans for years after an eruption.
Field identification & locations
Identify in the field by its extremely lightweight feel, porous appearance, and ability to float. Commonly found in areas with active or dormant explosive volcanism.
