igneous
Pumice
Pumice (volcanic glass)
Hardness: 5-6 (but very brittle); Color: white to light gray; Luster: vitreous to dull; Structure: highly vesicular (porous); Specific Gravity: usually less than 1.0 (floats on water)
- Hardness
- 5-6 (but very brittle)
- Color
- white to light gray
- Luster
- vitreous to dull
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Physical properties
Hardness: 5-6 (but very brittle); Color: white to light gray; Luster: vitreous to dull; Structure: highly vesicular (porous); Specific Gravity: usually less than 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 gas bubbles in a frothy glass structure.
Uses & applications
Used as an abrasive in cleaning products, cosmetic exfoliants, stone-washed jeans, lightweight concrete (pozzolan), and horticulture as a soil amendment.
Geological facts
Pumice is the only rock that can float on water until it becomes waterlogged. Large eruptions can create 'pumice rafts' that drift across oceans for years.
Field identification & locations
Identify in the field by its extremely light weight, frothy appearance, and ability to float. Commonly found in areas of recent or historic explosive volcanism such as Italy, Greece, and the Western USA.
