Pumice is a type of stone that comes from cooled lava that has a high amount of both gas and water in it. Pumice is a type of volcanic rock, and due to its high gas content, it can float on top of water. Lava typically exits the volcano, begins to froth up as it cools and then hardens further as it cools.
Pumice is a useful material in a variety of consumer and commercial applications. It can be used as an abrasive for filing or cleaning. It is also widely used to make certain types of light-weight concrete due to its strength and low density.