A light, porous type of pyroclastic igneous rock, formed during explosive volcanic eruptions when liquid lava is ejected into water or air as a froth containing masses of gas bubbles. As the lava solidifies, the bubbles are frozen into the rock.
User Defined Definitions
"a light glass formed on the surface of some lavas; used as an abrasive"
"rub with pumice, in order to clean or to smoothen"