Perlite is a naturally occurring mineral that is derived from volcanic glass, which forms when a glassy-looking rock called obsidian comes into contact with water. It is a lightweight granular material that is white in color and looks and feels like little bits of polystyrene. Perlite is made by heating the mined raw material to temperatures between 1400° and 1800° F, causing it to expand and pop like popcorn. The resulting product is a much-expanded mineral popcorn, white in color, with a texture that retains water on the surface but retains air in the spaces between. Perlite typically contains 70-75% silicon dioxide, 12-15% aluminum oxide, 3-4% sodium oxide, 3-5% potassium oxide, 0.5-2% iron oxide, 0.2–0.7% magnesium oxide, 0.5–1.5% calcium oxide, and 3–5% loss on ignition (chemical/combined water). Perlite is primarily used in horticulture as a soil amendment or alone as a medium for hydroponics or for starting cuttings. It is also used in lightweight plasters, concrete and mortar, insulation and ceiling tiles, and cosmetics as an absorbent and mechanical exfoliant.