Pumice

pumis, a form of lava through which gas or steam has escaped during the process of cooling, leaving it full of air holes. Three-fourths of typical pumice by weight consists of fine sand converted into minute powdery particles of glass, mixed with alumina, iron, lime, soda, etc. It varies in color from brown to a whitish gray. Although twice as heavy as water, it is so full of air holes that it floats until it becomes watersoaked. Powdered pumice is used to polish marble, glass, and ivory surfaces. It also serves as the gritty ingredient of many tooth-powders. It is used by the painter in polishing wood and metal. A piece of pumice stone in the lavatory is useful to scour stains from the hands. The pumice of commerce is obtained largely from the Lipari Islands, north of Sicily. Pumice of excellent quality is to be had also from Mexico and Iceland. See Volcano