One of nature's most spectacular and largest mineral deposits lies in the desert country of south central New Mexico. White Sands is 225 square miles of dazzling white gypsum sand that has been blown into dunes up to 50 ft in height. In another spectacular deposit is at the Cave of Swords, in Chihuahua, Mexico, numerous transparent, sword like selenite gypsum crystals reach lengths of 6 ft. or more.
Gypsum takes its name from the Greek gypso, meaning "chalk", "plastic", or "cement". Uses of Gypsum: Is an important economic mineral since the time of ancient Egyptian civilization. The Romans discovered that heating Gypsum to 600 degrees made a plaster that sets hard when mixed with water. This plaster was used for building, and is still widely used today.
It is colorless or white, but impurities tint it light brown, gray, yellow, green and orange. It often occurs in well-developed crystals. Single crystal can be blocky with a slanted parallelogram outline, tabular, bladed, or in a long thin shape like a ram's horn. twinned crystals are common, and frequently form characteristic "swallowtails" or "fishtails". Gypsum is also found in a parallel, fibrous variety with a silky luster, called satin spar. The massive fine-grained variety is called alabaster. Rosette-shaped crystals are call desert rose, and are common and less dense than the barite "sand crystals" that they resemble. Gypsum occurs in extensive beds formed by the evaporation of ocean brine, along with other minerals similarly formed in particular, anhydrite and halite and has low solubility and is the first mineral to separate from evaporated sea water.
Gypsum also occurs as an alteration product of sulfides in ore deposits; as disseminated crystals and rosette-shaped aggregates in sedimentary deposits, including sands and clays; and as deposits around volcanic fumaroles.
Group : Sulfates
Crystal System : Monoclinic
Color: Colorless, White, Light Brown, Yellow, Pink
Hardness : 2
Cleavage : Perfect
Luster : Sub vitreous to Pearly
Streak : White
Gravity : 2.3
Transparency : Transparent to Translucent
Form/Habit: Prismatic to Tubular
Wikipedia and Smithsonian Rock and Gem Book