Perlite is volcanic grit, which is originally inorganic. The rock is purified and broken into various gradations. The Perlite is then processed in special ovens at 950 °C. This expands the Perlite to about 20 times its original volume. This expansion makes the Perlite lightweight and porous in structure. Perlite is used in potting soil mixtures to boost aeration of the mixture. It also contributes to quick water absorption and water distribution within a mixture. Perlite also reduces the amount of shrinking in a mixture, contributing to a stable structure.