Perlite A natural glass similar to granite composition, broken into small pieces in pearly appearance, formed by the sudden cooling of magma or dense lava. Perlite is also called pearl stone. The gray and greenish ones are Famous, but there are also various shades of brown, red and blue. Their luster is pearly or oily like. Perlite was not of commercial importance until the 1950s. But after 1950 it gained a lot of importance. If the crushed perlite is heated rapidly to the softening temperature of about 800-1000°C, the 3-4% water in it evaporates and explodes the perlite. The volume of blasted perlite becomes 20 times the volume before it was blasted. Thus, a material with a very low density is obtained. It is also used in the plant soil mixture, increasing the moisture of the soil.