Pumice /?p?m?s/ is a textural term for a volcanic rock which is a solidified frothy lava. Pumice is typically created when super-heated, highly pressurized rock is violently ejected from a volcano. Alternatively it can be formed when lava and water are mixed. Most pumice is light enough that it floats on water.The unusual foamy configuration of pumice happens because of simultaneous rapid cooling and rapid depressurization. The depressurization creates bubbles by lowering the solubility of gases (including water and CO2) that are dissolved in the lava, causing the gases to rapidly exsolve (like the bubbles of CO2 that appear when a carbonated drink is opened). The simultaneous cooling and depressurization freezes the bubbles in the matrix.
