Pumice, << PUM ihs, >> is a grayish-white natural glass with many tiny holes. It is a valuable scouring, scrubbing, and polishing material in both powdered form and as pumice stone. Pumice forms when lava from a volcano flows onto the earth’s surface or erupts violently into the air. The hot, gas-filled lava then cools quickly to form glass. Many tiny holes remain after the volcanic gases escape from the cooling lava.
