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Colorless Selenite Crystal

The Mineral gypsum

Gypsum has many interesting properties, including its very unique crystal habits. Many Gypsum crystals are found perfectly intact without distortions or parts broken off. Such crystals are found in a clay beds as floater crystals, where they fully form without being attached to a matrix. Gypsum crystals are known for their flexibility, and slim crystals can be slightly bent. (Though trying to bend good crystals is not recommended, as their flexibility is weak, and if flexed too much they will break.)

Gypsum has the same chemical composition as the mineral Anhydrite, but contains water in its structure, which Anhydrite lacks. Many Anhydrite specimens absorb water, transforming into the more common Gypsum. Some Gypsum specimens show evidence of this, containing growths of crumpling layers that testify to their expansion from the addition of water.

In a small number of Gypsum specimens, water gets trapped inside a crystal in a hollow channel while the crystal forms. When such a crystal is rotated, a water "bubble" moves around inside it toward the lowest point in the channel. Such specimens are considered a mineralogical oddity, and are very desirable to collectors. These are called "enhydros".

Gypsum sometimes forms in sandy areas, and crystals may trap sand inside when forming, causing a specimen to become brown or gray and opaque. These sand inclusions sometimes form hourglass formations in a crystal. They are also present in the well-known "Desert Rose", which is rosette shaped Gypsum with sand inclusions. (The term "Desert Rose" also applies to rosette shaped Barite with sand inclusions, and the two should not be confused.)

Gypsum specimens should only be cleaned with water. Soaps and detergents should be avoided, as they can enter cracks and crevices of a crystal and ruin its luster.
Chemical Formula CaSO4 · 2H2O
Composition Hydrous calcium sulfate
Color Colorless, white, gray, brown, beige, orange, pink, yellow, light red, green
Streak White
Hardness 2
Crystal System Monoclinic
3D Crystal Atlas
(Click for animated model) 
Crystal Forms
and Aggregates
Commonly as tabular crystals, sometimes perfect with no imperfections. Also prismatic, acicular, bladed, and as dense bundles of fragile acicular crystals. Other forms are as fibrous veins, scaly, grainy, lenticular, rosette, massive, and as parallel, cactus-like growths. Crystals and fibrous masses may be curved, sometimes severely, forming formations that are sometimes called "Rams Horns". Crystals frequently twin, forming perfect fishtail twins or swallowtail twins. Crystals can be enormous in size. In fact, the largest crystals ever found on earth were of Gypsum.
Transparency Transparent to opaque
Specific Gravity 2.3 - 2.4
Luster Vitreous to pearly
Cleavage 1,1 - micaceous ; 2,2
Fracture Uneven
Tenacity Sectile and slightly flexible
Other ID Marks Often fluorescent light yellow in shortwave ultraviolet light, and occasionally also phosphorescent.
In Group Sulfates; Hydrous Sulfates
Striking Features Crystal habits, low hardness, flexibility, and sectility
Environment In enormous deposits and beds in sedimentary rock, specifically limestone. Also in clay sedimentary deposits, and in dry caves. Occasionally in igneous traprock and in the oxidation zone of sulfide deposits.
Rock Type Igneous, Sedimentary
Popularity (1-4) 1
Prevalence (1-3) 1
Demand (1-3) 1


 -  Massive, fine grained variety of Gypsum. Occasionally may also refer to a translucent, banded type of Aragonite in the form of Travertine or Tufa.
 -  Rosette shaped Barite or rosette shaped Gypsum with sand inclusions.
 -  Rosette shaped Gypsum found in caverns with spreading fibers.
 -  Rock composed primarily of the mineral Gypsum, but also contain impurities such as Calcite, Anhydrite, Halite, Dolomite, Limonite, and clay.
 -  Curved Gypsum with a shape similar to a ram's horn.
 -  Gypsum with inclusions of sand, causing the specimen to be brown or grayish in color and opaque.
 -  Fibrous variety of Gypsum. May occasionally also describe a fibrous form of Calcite or Aragonite.
 -  Transparent and colorless (or very lightly colored) variety of Gypsum that forms in distinct crystals.

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 fibrous Satin 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.

Gypsum is a very common mineral; only a select few of the best and most classic are mentioned here. The finest European localities are Lubin, Poland; Kapnick, Maramures Co., Romania; and the Sulfur mines of Agrigento Province, Sicily, Italy. Desert Roses and Sand Gypsum come from several places in the Sahara Desert in Algeria and Morocco. Excellent Gypsum specimens have come from China at Liupanshui, Guizhou Province. Fragile, acicular bunches occur in Whyalla, South Australia; and green, grass-like mats in Mt. Gunson, Pernatty Lagoon, South Australia. (It is debatable whether these green crystals are natural or are formed from acid runoff from mining operations.)

Exceptional, bright orange crystals of Gypsum come from the salt mine of Las Salinas de Paracas, Pisco, Peru. Mexico boasts the most notable and finest localities of this mineral. Besides for the abundance of specimens that have come from Naica, in Chihuahua, several famous caves have been discovered in these mines bearing the worlds largest known crystals. In 2001, a cave called "Cave of the Crystals" was discovered where gigantic, elongated clear crystals were found. The largest was measured to be 37.4 feet long! (Make sure to view the link to National Geographic link in the "Additional Resources" section below.)

Other important Mexican Gypsum localities are Saltillo, in Coahuila, which provides much of the Gypsum Desert Rose available on the mineral market. These specimens can be identified by their whitish edges. Santa Eulalia, in Chihuahua has produced outstanding Selenite. In Canada, excellent yellow crystals come from the Red River Floodway in Winnipeg, Manitoba. A huge industrial deposit mined for sheet rock is in Windsor, Nova Scotia.

In the U.S., Desert Roses are plentiful in the Great Salt Plains, near Jet, Alfalfa Co., Oklahoma. Some excellent hourglass Sand Gypsum has also come from there. Desert Roses are also plentiful in the Mojave Desert in California. Stand-alone, perfect Selenite crystals come from Ellsworth, Mahoning Co., Ohio. Curved Gypsum crystals and Gypsum Flowers exist in the Mammoth Caves of Kentucky, and large crystals of Selenite have come from Hanksville, Wayne Co., Utah. Curved fibrous masses come from Terlingua, Brewster Co., Texas; and nice clear crystals are found in New York at Lockport, Niagara Co.; and at Kerhonkson, Ulster Co.

Halite, Dolomite, Barite, Anhydrite, Sulfur

Brucite - Harder.
Calcite - Harder, not flexible and not sectile.
Barite - Distinguished from Gypsum Desert Rose in that it is harder (3 - 3½) and much heavier (4.3 - 4.6).

gypsum PHOTOS
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