Gypsum: Wikis


Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.


From Wikipedia, the free encyclopedia


Desert rose, 10 cm long
Category Sulfate mineral
Chemical formula Calcium sulfate CaSO4 · 2 H2O
Color Colorless to white; with impurities may be yellow, tan, blue, pink, brown, reddish brown or gray
Crystal habit Massive, flat. Elongated and generally prismatic crystals
Crystal system Monoclinic 2/m - Prismatic
Twinning Very common on {110}
Cleavage Perfect on {010}, distinct on {100}
Fracture Conchoidal on {100}, splintery parallel to [001]
Mohs scale hardness 1.5-2
Luster Vitreous to silky, pearly, or waxy
Streak White
Diaphaneity transparent to translucent
Specific gravity 2.31 - 2.33
Optical properties 2V = 58° Biaxial (+)
Refractive index nα = 1.519 - 1.521 nβ = 1.522 - 1.523 nγ = 1.529 - 1.530
Birefringence δ = 0.010
Pleochroism None
Fusibility 5
Solubility hot, dilute HCl
References [1][2]
Major varieties
Satin spar Pearly, fibrous masses
Selenite Transparent and bladed crystals
Alabaster Fine-grained, slightly colored

Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4 · 2 H2O.[3]


Crystal varieties

Gypsum from New South Wales, Australia

Gypsum occurs in nature as flattened and often twinned crystals and transparent cleavable masses called selenite. It may also occur in a silky, fibrous form, in which case it is commonly called satin spar. Finally it may also be granular or quite compact. In hand-sized samples, it can be anywhere from transparent to opaque. A very fine-grained white or lightly-tinted variety of gypsum is called alabaster, which is prized for ornamental work of various sorts. In arid areas, gypsum can occur in a flower-like form typically opaque with embedded sand grains called desert rose. Up to the size of 11m long, gypsum forms some of the largest crystals found in nature, in the form of selenite.[4]


Gypsum var. selenite from Andamooka Ranges - Lake Torrens area, South Australia

Gypsum is a common mineral, with thick and extensive evaporite beds in association with sedimentary rocks. Deposits are known to occur in strata from as early as the Permian age.[5] Gypsum is deposited in lake and sea water, as well as in hot springs, from volcanic vapors, and sulfate solutions in veins. Hydrothermal anhydrite in veins is commonly hydrated to gypsum by groundwater in near surface exposures. It is often associated with the minerals halite and sulfur.

Fibrous Gypsum from Brazil

The word gypsum is derived from the Greek word γύψος, "chalk" or "plaster"[6]. Because the gypsum from the quarries of the Montmartre district of Paris has long furnished burnt gypsum used for various purposes, this material has been called plaster of Paris. It is also used in foot creams, shampoos and many other hair products.

Gypsum is moderately water-soluble (~2.0 – 2.5 g/L at 25 °C)[7] and, in contrast to most other salts, it exhibits a retrograde solubility, becoming less soluble at higher temperatures. As for anhydrite, its solubility in saline solutions and in brines is also strongly dependent on NaCl concentration [7]. Because gypsum dissolves over time in water, gypsum is rarely found in the form of sand. However, the unique conditions of the White Sands National Monument in the US state of New Mexico have created a 710 km² (275 square mile) expanse of white gypsum sand, enough to supply the construction industry with drywall for 1,000 years.[8 ] Commercial exploitation of the area, strongly opposed by area residents, was permanently prevented in 1933 when president Herbert Hoover declared the gypsum dunes a protected national monument.

Commercial quantities of gypsum are found in the cities of Araripina and Grajaú, Brazil, Pakistan, Jamaica, Iran (world's second largest producer[9]), Thailand, Spain (the main producer in Europe), Germany, Italy, England, Ireland, in British Columbia, Manitoba, Ontario, Nova Scotia and Newfoundland in Canada,[10] and in New York, Michigan, Indiana[10],Texas(in the Palo Duro Canyon),Iowa, Kansas, Oklahoma, Arizona, New Mexico, Colorado, Utah and Nevada in the United States. There is also a large open pit quarry located at Plaster City, California in Imperial County, and in East Kutai, Kalimantan.

Crystals of gypsum up to 11 meters long have been found in the caves of the Naica Mine of Chihuahua, Mexico. The crystals thrived in the cave's extremely rare and stable natural environment. Temperatures stayed at 58 °C, and the cave was filled with mineral-rich water that drove the crystals' growth. The largest of those crystals weighs 55 tons and is around 500,000 years old.[11][12]

Gypsum is also formed as a by-product of sulfide oxidation, amongst others by pyrite oxidation, when the sulfuric acid generated reacts with calcium carbonate. Its presence indicates oxidizing conditions. Under reducing conditions, the sulfates it contains can be reduced back to sulfide by sulfate reducing bacteria (SRB).

Synthetic gypsum is recovered via flue gas desulfurization at some coal-fired electric power plants. It can be used interchangeably with natural gypsum in some applications.

Gypsum also precipitates onto brackish water membranes, a phenomenon known as mineral salt scaling, such as during brackish water desalination of water with high concentrations of calcium and sulfate. Scaling decreases membrane life and productivity. This is one of the main obstacles in brackish water membrane desalination processes, such as reverse osmosis or nanofiltration. Other forms of scaling such as calcite scaling, depending on the water source, can also be important considerations in distillation as well as in heat exchangers where either the salt solubility or salt concentration can change rapidly.

Orbital pictures from the Mars Reconnaissance Orbiter (MRO) indicate the existence of gypsum dunes in the northern polar region of Mars.[13]

Uses of gypsum

Gypsum is used in a wide variety of applications:

Cones of gypsum which formed on the sea floor during the Messinian salinity crisis
  • Gypsum Board[14] primarily used as a finish for walls and ceilings; known in construction slang as Drywall.
  • Plaster ingredient.
  • Fertilizer and soil conditioner. In the late eighteenth and early nineteenth century, Nova Scotia gypsum, often referred to as plaster, was a highly sought fertilizer for wheat fields in the United States. It is also used in ameliorating sodic soils.[15]
  • A binder in fast-dry tennis court clay.
  • Plaster of Paris (surgical splints; casting moulds; modeling).
  • A wood substitute in the ancient world; for example, when wood became scarce due to deforestation on Bronze Age Crete, gypsum was employed in building construction at locations where wood was previously used.[16]
  • A tofu (soy bean curd) coagulant, making it ultimately a major source of dietary calcium, especially in Asian cultures which traditionally use few dairy products.
  • Adding hardness to water used for homebrewing.[17]
  • Blackboard chalk.
  • A component of Portland cement used to prevent flash setting of concrete.
  • Soil/water potential monitoring (soil moisture tension).
  • A common ingredient in making mead.
  • A medicinal agent in traditional Chinese medicine called Shi Gao.

See also


  1. ^ Handbook of Mineralogy
  2. ^ Mindat
  3. ^ Cornelis Klein and Cornelius S. Hurlbut, Jr., 1985, Manual of Mineralogy, John Wiley, 20th ed., pp. 352-353, ISBN 0-471-80580-7
  4. ^ Juan Manuel García-Ruiz, Roberto Villasuso, Carlos Ayora, Angels Canals, and Fermín Otálora (2007). "Formation of natural gypsum megacrystals in Naica, Mexico". Geology 35 (4): 327–330. doi:10.1130/G23393A.1.  
  5. ^ Barry F. Beck, Felicity M. Pearson, P.E. LaMoreaux & Associates, National Groundwater Association (U.S.), Karst Geohazards: Engineering and Environmental Problems in Karst Terrane, 1995, Taylor & Francis, 581 pages ISBN 9054105356
  6. ^ "Compact Oxford English Dictionary: gypsum".  
  7. ^ a b Bock, E. (1961). "On the solubility of anhydrous calcium sulphate and of gypsum in concentrated solutions of sodium chloride at 25 °C, 30 °C, 40 °C, and 50 °C". Canadian Journal of Chemistry 39 (9): 1746–1751.  
  8. ^ Abarr, James (1999-02-07). "Sea of Sand". The Albuquerque Journal. Retrieved 2007-01-27.  
  9. ^
  10. ^ a b "Mines, Mills and Concentrators in Canada". Natural Resources Canada. 2005-10-24. Retrieved 2007-01-27.  
  11. ^ "World's largest crystal discovered in Mexican cave". The Telegraph. Retrieved 2009-06-06.  
  12. ^ [1] Electric Caverns - picture from Peñoles Mine - article also includes a link to a picture of a spectacular gypsum flower at Lechuguilla Cave
  13. ^
  14. ^ *Complimentary list of MasterFormat 2004 Edition Numbers and Titles (large PDF document)
  15. ^ Oster and Frenkel. 1980. The Chemistry of the Reclamation of Sodic Soils with Gypsum and Lime. SSSAJ. 44:41-45
  16. ^ C. Michael Hogan, Knossos fieldnotes, Modern Antiquarian (2007)
  17. ^ "Water Chemistry Adjustment for Extract Brewing". How To Brew by John Palmer. Retrieved 2008-12-15.  

External links


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

GYPSUM, a common mineral consisting of hydrous calcium sulphate, named from the Gr. 71APos, a word used by Theophrastus to denote not only the raw mineral but also the product of its calcination, which was employed in ancient times, as it still is, as a plaster. When crystallized, gypsum is often called selenite, the QEX77PLT713 of Dioscorides, so named from oeXirri, "the moon," probably in allusion to the soft moon-like reflection of light from some of its faces, or, according to a legend, because it is found at night when the moon is on the increase. The granular, marble-like gypsum is termed alabaster.

Gypsum crystallizes in the monoclinic system, the habit of the crystals being usually either prismatic or tabular; in the latter case the broad planes are parallel to the faces of the clinopinacoid. The crystals may become lenticular by curvature of certain faces. In the characteristic type represented in fig. I, f represents the prism, 1 the hemi-pyramid and P the clinopinacoid. Twins are common, as in fig. 2, forming in some cases arrow-headed and swallowtailed crystals. Cleavage is perfect parallel to the clinopinacoid, yielding thin plates, often diamond-shaped, with pearly lustre; these flakes are usually flexible, but may be brittle, as in the gypsum of Montmartre. Two other cleavages are recognized, but they are imperfect. Crystals of gypsum, when occurring in clay, may enclose much muddy matter; in other cases a large proportion of sand may be mechanically entangled in the crystals without serious disturbance of form; whilst certain crystals occasionally enclose cavities with liquid and an air-bubble. Gypsum not infrequently becomes fibrous. This variety occurs in veins, often running through gypseous marls, with the fibres disposed at right angles to the direction of the vein. Such gypsum when cut and polished has a pearly opalescence, or satiny sheen, whence it is called satin-spar.

Gypsum is so soft as to be scratched even by the finger-nail (H 1.5 to 2). Its specific gravity is about 2.3. The mineral is slightly soluble in water, one part of gypsum being soluble, according to G. K. Cameron, in 372 parts of pure water at 26° C. Waters percolating through gypseous strata, like the Keuper marls, dissolve the calcium sulphate and thus become permanently hard or "selenitic." Such water has special value for brewing pale ale, and the water used by the Burton breweries is of this character; hence the artificial dissolving of gypsum in water for brewing purposes is known as "burtonization." Deposits of gypsum are formed in boilers using selenitic water.

Pure gypsum is colourless or white, but it is often tinted, especially in the alabaster variety, grey, yellow or pink. Gypsum crystallizes with two molecules of water, equal to about 21% by FIG. FIG. 2.

weight, and consequently has the formula CaSO 4.2H 2 O. By exposure to strong heat all the water may be expelled, and the substance then has the composition of anhydrite. When the calcination, however, is conducted at such a temperature that only about 75% of the water is lost, it yields a white pulverulent substance, known as "plaster of Paris," which may readily be caused to recombine with water, forming a hard cement. The gypsum quarries of Montmartre, in the north of Paris, were worked in Tertiary strata, rich in fossils. Gypsum is largely quarried in England for conversion into plaster of Paris, whence it is sometimes known as "plaster stone," and since much is sent to the Staffordshire potteries for making moulds it is also termed "potter's stone." The chief workings are in the Keuper marls near Newark in Nottinghamshire, Fauld in Staffordshire and Chellaston in Derbyshire. It is also worked in Permian beds in Cumberland and Westmorland, and in Purbeck strata near Battle in Sussex.

Gypsum frequently occurs in association with rock-salt, having been deposited in shallow basins of salt water. Much of the calcium in sea-water exists as sulphate; and on evaporation of a drop of sea-water under the microscope this sulphate is deposited as acicular crystals of gypsum. In salt-lagoons the deposition of the gypsum is probably effected in most cases by means of micro-organisms. Waters containing sulphuretted hydrogen, on exposure to the air in the presence of limestone, may yield gypsum by the formation of sulphuric acid and its interaction with the calcium carbonate. In volcanic districts gypsum is produced by the action of sulphuric acid, resulting from the oxidation of sulphurous vapours, on lime-bearing minerals, like labradorite and augite, in the volcanic rocks: hence gypsum is common around solfataras. Again, by the oxidation of iron-pyrites and the action of the resulting sulphuric acid on limestone or on shells, gypsum may be formed; whence its origin in most clays. Gypsum is also formed in some cases by the hydration of anhydrite, the change being accompanied by an increase of volume to the extent of about 60%. Conversely gypsum may, under certain conditions, be dehydrated or reduced to anhydrite.

Some of the largest known crystals of selenite have been found in southern Utah, where they occur in huge geodes, or crystallined cavities, in deposits from the old salt-lakes. Fine crystals, sometimes curiously bent, occur in the Permian rocks of Friedrichroda, near Gotha, where there is a grotto called the Marienglashohle, close to Rheinhardsbrunn. Many of the best localities for selenite are in the New Red Sandstone formation (Trias and Permian), notably the salt.-mines of Hall and Hallein, near Salzburg, and of Bex in Switzerland. Excellent crystals, usually of a brownish colour arranged in groups, are often found in the brine-chambers and the launders used in salt-works. Selenite also occurs in fine crystals in the sulphur-bearing marls of Girgenti and other Sicilian localities; whilst in Britain very bold crystals are yielded by the Kimeridge clay of Shotover Hill near Oxford. Twisted crystals and rosettes of gypsum found in the Mammoth Cave, Kentucky, have been called "oulopholites" (015Xo, "woolly"; gwXEbs, "cave").

In addition to the use of gypsum in cement-making, the mineral finds application as an agricultural agent in dressing land, and it has also been used in the manufacture of porcelain and glass. Formerly it was employed, in the form of thin cleavage-plates, for glazing windows, and seems to have been, with mica, called lapis specularis. It is still known in Germany as Marienglas and Fraueneis. Delicate cleavage-plates of gypsum are used in microscopic petrography for the determination of certain optical constants in the rock-forming minerals. (F. W. R.*)

<< Gyp

Gyroscope And Gyrostat >>


Up to date as of January 15, 2010
(Redirected to gypsum article)

Definition from Wiktionary, a free dictionary



Wikipedia has an article on:








gypsum (plural gypsums)

  1. A mineral consisting of the hydrated calcium sulphate. When calcined, it forms plaster of Paris.

Derived terms

  • gypsum board panels




gypsum (plural gypsi)

  1. gypsum; a plaster figure

Simple English


Gypusm is a common mineral, calcium sulfate. Gypsum has been used as a building material for a long time, possibly since the neolithic. Today, it is an ingredient of plaster. It can also be used as a fertilizer.


Got something to say? Make a comment.
Your name
Your email address