A pumice stone is a rock with highly vesicular rough textured volcanic glass. They are usually light colored and created from hot, highly pressurized rock that has been ejected from a volcano. You can easily clean a pumice stone with a few items generally found around the home. One way as to how you can do this is with dish soap and hot water. You can also simply place the stone inside of a laundry bag or pillow case and place it in the washing machine with your laundry.