Pumice Stone

Pumice is a light and porous type of pyroclastic igneous rock. It is formed from the lava that is full of gas. During the explosive volcanic eruptions, the liquid lava is ejected in the air. As the lava hurtles through the air, it cools and the gases escape from the rock, leaving it full of holes. 

Any type of igneous rock can form pumice rock, provide suitable eruptive conditions it get. It can be andesite, basalt, dacite or rhyolite. When larger amounts of gas are present in the rock, the resultant is a finger-grained variety of pumice, which is known as pumicite.

Pumice stone is popular for washing denims and also in making lightweight concrete and is used as abrasive, particularly in polishes and cosmetics exfoliants. When pumice is used as an additive for cement, its fine-grained version knowns as pozzolan is mixed with lime to form a light-weight, smooth, plaster-like concrete. This type of concrete has been in use since Roman times.