Perlites & Vermiculites
Hydroponics grow medium perlites are derived from volcanic glass created when lava encounters water. When the glasses are superheated, the water vaporizes and causes small granules to puff out like popcorn, creating a very porous surface. Perlites are white, hard, lightweight, highly porous, and pH neutral with air holding capacity which keeps root zones of plant aerated. Vermiculites are similar to perlites derived from superheating the silicates but are soft, tan/brown in color. Perlites hold more air and less water than vermiculites so need to be irrigated more frequently. Both can be used by itself or used in potting soils. However, both floats so they are not the best choice of growing media for the flood and drain system.