It is considered a Glass because it has no crystal structure. Pumice varies in density according to the thickness of the solid material between the bubbles; many samples float in Water. Pumice comes in many different colors such as white, yellowish, gray, gray brown, and a dull red.
It is widely used to make lightweight Concrete and as an Abrasive, especially in polishes and Cosmetics exfoliants. When used as an additive for Cement, a fine-grained version of pumice called pozzolan is mixed with lime to form a light-weight, smooth, plaster-like Concrete. This form of concrete was used as far back as Roman times.