Pumice is a very light, porous igneous rock that is formed during volcanic eruptions. It is made up of very tiny crystals, since they cool so quickly above ground. The texture of pumice is rough and has many hollows and cavities. It sort of looks like froth or foam that has hardened. In fact, it forms from frothy lava that has lots of gas bubbles trapped in it, and all those little holes used to have gas trapped in them. Because pumice has all those holes and gas pockets it is very light and can actually float in water! Sometimes a volcano erupts underwater and the pumice that is produced often floats away.