Pumice, called the “featherweight of rocks,” is another form of solid lava.
It looks like brown-gray bits of soapsuds frozen together. Pumice is light enough to float on water because it is chock full of holes, evidence of gas bubbles.
You probably experience the benefit of volcanoes every day without even knowing it. Every time you brush your teeth, you may be putting volcanic rock in your mouth.
Pumice—the highly porous, feather-light volcanic rock—is also a mild abrasive often used in toothpaste and scouring powders. You can find pieces of pumice for sale in most health and beauty stores as it is helpful in scrubbing away calluses.