igneous
Pumice
Vesicular volcanic glass, typically rhyolitic to dacitic; mainly silica-rich volcanic glass with feldspar and minor quartz or pyroxene
AI-generated identification · may be incorrectVery light gray to tan, highly porous, and dull to silky; hardness about 5–6 Mohs, with irregular fracture and no cleavage. Low density may allow it to float, though weathering and mineral-filled pores can make it sink.
Identified More igneous →
Explore Pumice in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Very light gray to tan, highly porous, and dull to silky; hardness about 5–6 Mohs, with irregular fracture and no cleavage. Low density may allow it to float, though weathering and mineral-filled pores can make it sink.
Formation & geological history
Forms when gas-rich lava erupts explosively and rapidly cools, trapping abundant bubbles in frothy volcanic glass. It is generally Quaternary to geologically young, although older pumice deposits also occur.
Uses & applications
Used as an abrasive, lightweight aggregate, concrete additive, horticultural soil amendment, and in cosmetics; attractive pieces are collected but are rarely valuable.
Geological facts
The holes are vesicles formed by expanding volcanic gases, not fossils. Pumice commonly occurs with ash and tuff in explosive volcanic deposits.
Field identification & locations
Identify it by its extreme vesicular texture, rough glassy surface, low weight, and lack of visible sedimentary layering; unlike scoria, it is usually pale gray or cream rather than dark red-black. Common near explosive volcanoes, including Italy, Iceland, Japan, New Zealand, Mexico, and the western United States.
