I just did a google search and it is a form of gypsum. "Gypsum is an industrially important mineral. It is the primary ingredient of plaster-of-Paris, which is finely ground Gypsum, and it is used in the production of cement. It is also the main component of sheet rock. It is used as a flux for creating earthenware, and can be used as a fertilizer. The variety Alabaster is is carved for ornamental use, such as artistic sculptures and pottery. It is porous and is therefore easily dyed. The fibrousSatin Spar variety is sometimes cut into cabochons for collectors because of its strong cat's eye effect. Fine Gypsum specimens are very popular among mineral collectors, especially the varieties Selenite and Desert Rose."
Also for people who believe that crystals have "powers" it is known as a healing stone.