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.
Marilyn M. Lindstrom, Ph.D., Planetary Scientist, National Aeronautics and Space Administration, Johnson Space Center. How to cite this article.