Pine Country Gem & Mineral Society

Deep in the Heart of the Piney Woods of East Texas


May, 2014


Jody Dorman, member PCGMS


Gypsum One of natures most spectaulular


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.  Selenite, from the Greek word selene, meaning "the moon", is the name for transparent crystals of gypsum, but is often incorrectly used for gypsum in general.

Gypsum takes its name from the Creek gypso, meaning "chalk", "plastic", or "cement".  Uses of Gypsum: Is an important economic mineral since the time of ancient Egyptian civilization, gypsum was mined to the west of Alexandria, near Suez, in the AI Fayyum, and near the Red Sea coast.  It was used for motor and plaster in the Giza necropolis and it was used elsewhere to plaster walls, cover bodies, make statues and masks, as an adhesive, and as a filler in pigments.  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.  Gypsum is also used to help clear up muddy ponds.  Gypsum is widespread calcium sulfate hydrate that is found in a number of forms, and is of great economic importance.  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.  Gypsum occurs widely throughout the world, but the US, Canada, Austrailia, Spain, France, Italy and England are among the leading commercial producers of gypsum.



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