Template:POTD/2010-02-12
Gypsum, a common mineral composed of calcium sulfate dihydrate, in its crystallised selenite form. In addition to selenite, it may also occur in a silky, fibrous form called "satin spar", and a very fine-grained white variety is called alabaster. In arid areas, it can also occur in a flower-like form called desert rose. In the form of selenite, gypsum forms some of the largest crystals found in nature, up to 11 m (36 ft) long.Photo credit: Noodle snacks