igneous
Pumice
Vesicular Rhyolite / Glassy Igneous Rock
Hardness: 5-6 (Mohs scale), but feels soft/crumbly; Color: light gray to cream/tan; Luster: dull to pearly; Crystal structure: Amorphous/Vitreous (volcanic glass); Highly vesicular (porous) with a frothy appearance; Specific gravity: < 1.0 (floats on water).
- Hardness
- 5-6 (Mohs scale), but feels soft/crumbly
- Color
- light gray to cream/tan
- Luster
- dull to pearly
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Physical properties
Hardness: 5-6 (Mohs scale), but feels soft/crumbly; Color: light gray to cream/tan; Luster: dull to pearly; Crystal structure: Amorphous/Vitreous (volcanic glass); Highly vesicular (porous) with a frothy appearance; Specific gravity: < 1.0 (floats on water).
Formation & geological history
Formed through explosive volcanic eruptions. It is created when super-heated, highly pressurized molten rock is violently ejected from a volcano, cooling so rapidly that gas bubbles are trapped in a glassy matrix. Most common in young Cenozoic volcanic regions.
Uses & applications
Used in construction as lightweight aggregate/concrete, in personal care as an exfoliant (pumice stones), for stone-washing denim jeans, as an abrasive in polishing and erasers, and in horticulture for aeration.
Geological facts
Pumice is the only rock known to float on water due to its incredible porosity. After large undersea volcanic eruptions, 'pumice rafts' can form, which are floating islands of stone that can travel thousands of miles across the ocean.
Field identification & locations
Identify in the field by its light weight (low density), light color, and surface full of tiny bubbles. It is commonly found in areas of explosive silicic volcanism, such as Italy, Turkey, Greece, and the Western United States.
