Background Gypsum, or calcium sulfate dihydrate, (CaSO4 l 2H2O) is the major component of drywall, or gypsum board, core. It is a naturally occurring mineral, deposited largely as a result of the evaporation of water in ancient inland seas, which contained large amounts of dissolved gypsum. For example, the evaporation of a typical 20,000 gallon residential swimming pool filled with seawater wi...