Perlite is an amorphous siliceous volcanic glass that contains between 2 and 5 percent water. Light gray to black in color, perlite is found worldwide and is most often mined using openpit methods. When perlite ore is rapidly heated to about 900 °C, the contained water converts to steam and the ore expands up to 20 times its original volume. The resulting material, which is lightweight and bright ...
