igneous
Pumice
Vesicular Rhyolite (Amorphous glass)
Hardness: 5-6 (but very brittle); Color: Grey to light brown; Luster: Dull to silky; Structure: Vesicular (highly porous/frothy); Specific Gravity: 0.25-1.2 (can float on water)
- Hardness
- 5-6 (but very brittle)
- Color
- Grey to light brown
- Luster
- Dull to silky
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Physical properties
Hardness: 5-6 (but very brittle); Color: Grey to light brown; Luster: Dull to silky; Structure: Vesicular (highly porous/frothy); Specific Gravity: 0.25-1.2 (can float on water)
Formation & geological history
Formed during explosive volcanic eruptions when lava rich in gas is expelled and cools rapidly, trapping gas bubbles in a solidifying glass matrix. Can range from Recent to Tertiary in age.
Uses & applications
Used as an abrasive in cosmetics (exfoliants), toothpastes, and heavy-duty soaps. Also used in construction (lightweight concrete), filtration, and as a soil amendment in horticulture.
Geological facts
Pumice is the only rock that can float on water due to its incredible porosity. Massive rafts of pumice have been known to float in the ocean for years following a volcanic eruption.
Field identification & locations
Identify by its light weight (low density) and the presence of numerous tiny holes or vesicles. Commonly found in volcanic regions such as the Cascades, the Mediterranean, or Iceland.
