Pumice is a type of igneous rock that forms during explosive volcanic eruptions. It is composed of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. The rock is extremely porous and has a foamy appearance due to the presence of gas bubbles that were trapped in the rock during the rapid cooling of a gas-rich frothy magma. Pumice is commonly pale in color, ranging from white, cream, blue or grey, to green-brown or black. It is usually classed as rhyolite, which is a volcanic rock high in silica content and low in iron and magnesium. Pumice is very light in weight, with a specific gravity of less than one, giving the rock an ability to float on water.
In summary, pumice is an igneous rock that is composed of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is extremely porous, has a foamy appearance, and is usually pale in color. Pumice is classed as rhyolite and is very light in weight, with a specific gravity of less than one.
