igneous
Pumice
Highly vesicular volcanic glass, commonly rhyolitic or andesitic in composition
AI-generated identification · may be incorrectVery light, porous, pale gray to white, with a dull to glassy luster and no visible crystal structure; Mohs hardness about 5–6, typically low density and rough texture.
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Physical properties
Very light, porous, pale gray to white, with a dull to glassy luster and no visible crystal structure; Mohs hardness about 5–6, typically low density and rough texture.
Formation & geological history
Forms when gas-rich volcanic magma erupts explosively and rapidly cools, trapping bubbles in the glass. Most specimens are geologically young, from Quaternary volcanic eruptions, though older pumice also occurs.
Uses & applications
Used as an abrasive, exfoliant, lightweight aggregate, concrete additive, horticultural substrate, and decorative stone; generally inexpensive as a specimen.
Geological facts
Pumice can float on water when its interconnected pores are sealed enough to retain air. It differs from scoria because pumice is usually lighter colored and more silica-rich.
Field identification & locations
Identify it by its exceptionally low weight, abundant holes, pale color, and ability to scratch softer materials; common near explosive volcanic fields and as floating marine pumice.
