Pumice is a volcanic rock whose variably sized holes are formed by escaping bubbles. The fast cooling and depressurization of the lava/water combination traps the bubbles as they move through the material, leaving permanent voids in the hardened rock. Pumice is a relatively soft, light stone that has been used to make lightweight concrete since antiquity. A finer grain of the rock called pozzolan is mixed with lime to create a workable substance similar to plaster. The Romans used this form of concrete for the Pantheon’s dome and many aqueducts. Pumice stones’ abrasive qualities make them useful for pencil erasers, exfoliants and making stone-washed jeans. Ancient Greek and Roman citizens also used pumice stones to remove unwanted hair.
I don’t know that I’d recommend trading in your shaving implements for a rock, but maybe the next time your teenager begs for new jeans that are strategically “worn,” you can hand them a pumice stone instead… hey, it’s worth a try.