Pumice is also known as ‘pan stone’, which means melted rock in Chinese. Pumice is made of volcanic glass with abundant pores filled with air, like a honeycomb. It has a low density (0.3–0.4/cm3) and can float on water. Pumice generally refers to light-coloured porous acidic volcanic glass rock. Basaltic pumice usually has a higher density, so it does not float on water.