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Gypsum

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Gypsum, common sulfate mineral of superb industrial significance, composed of hydrated calcium sulfate (CaSO4 ·2H2O). In properly-developed crystals the mineral normally has been called selenite. The fibrous large variety has a silky lustre and is known as satin spar; it is translucent and opalescent and is valued for ornaments and jewellery. The fine-grained big variety called alabaster is carved and polished for statuary and decorative use when natural and translucent. Gypsite is the earthy pulverulent variety.

Gypsum is found in a number of forms and is of great economic importance. It is colorless or white but can be tinted light brown, gray, yellow, green, or orange due to the presence of impurities. Single, well-developed crystals can be blocky with a slanted parallelogram outline, tabular, or bladed. Twinned crystals are common and frequently form characteristic “fishtails.” Numerous transparent, swordlike selenite gypsum crystals 61 ⁄2 ft (2 m) or more long can be found at the Cave of Swords, Chihuahua, Mexico, one of the world’s most spectacular mineral deposits. Gypsum occurs in extensive beds formed by the evaporation of ocean brine. It also occurs as an alteration product of sulfides in ore deposits and as volcanic deposits.

Name: From the Greek name for the mineral, but more especially for the calcined mineral.

Association: Halite, celestine, calcite, aragonite, anhydrite, dolomite, sulfur.

Composition: Hydrous calcium sulfate, CaS04-2H20. CaO = 32.5 percent, S03 = 46.6 percent, H 20 = 20.9 percent.

Diagnostic Features: Characterized by its softness and its three directions of unequal cleavage. Its solubility in acid and the presence of much water distinguish it from anhydrite.

Crystallography. Monoclinic; prismatic. Crystals are of prismatic habit; tabular parallel to clinopinacoid; diamondshaped, with edges beveled by prism and pyramid faces. Other forms rare. Twins common with the orthopinacoid the twin plane often resulting in swallowtail twins. Cleavable massive; foliated; granular massive. Satin spar is a fibrous gypsum with silky luster. Alabaster is the fine-grained massive variety. Selenite is a variety which yields broad colorless and transparent cleavage folia

Chemical Properties

Chemical Classification Sulfate minerals
Chemical Composition CaSO4·2H2O

Gypsum Physical Properties

Color Colorless to white; may be yellow, tan, blue, pink, brown, reddish brown or gray due to impurities
Streak White
Luster Vitreous to silky, pearly, or waxy
Diaphaneity Transparent to translucent       
Mohs Hardness 2
Specific Gravity 2.31–2.33
Diagnostic Properties Transparent and bladed crystals Alabaster      Fine-grained, slightly colored
Crystal System Monoclinic

Gypsum Optical Properties

Gypsum is under the microscope
Crystal Habit Massive, flat. Elongated and generally prismatic crystals
Cleavage Perfect
Twinning Very common on
Optic Sign Biaxial (+)
Birefringence 0.010
Relief Low

Occurrence of Gypsum

Gypsum is a not unusual mineral, with thick and good sized evaporite beds in affiliation with sedimentary rocks. Deposits are recognized to occur in strata from as a long way lower back as the Archaean eon. It is deposited from lake and sea water, as well as in hot springs, from volcanic vapors, and sulfate answers in veins. Hydrothermal anhydrite in veins is commonly hydrated to gypsum by means of groundwater in near-floor exposures. It is regularly associated with the minerals halite and sulfur. It is the most not unusual sulfate mineral. Pure this rock is white, however other materials discovered as impurities might also deliver a huge range of colors to local deposits. Because it dissolves through the years in water, it is hardly ever discovered inside the form of sand. However, the particular conditions of the White Sands National Monument inside the US nation of New Mexico have created a 710 km2 (270 sq.Mi) expanse of white gypsum sand, sufficient to supply the construction enterprise with drywall for 1,000 years. Commercial exploitation of the area, strongly antagonistic by vicinity residents, was completely avoided in 1933 whilst president Herbert Hoover declared the gypsum dunes a blanketed countrywide monument.

It is also formed as a spinoff of sulfide oxidation, among others by pyrite oxidation, while the sulfuric acid generated reacts with calcium carbonate. Its presence suggests oxidizing conditions. Under reducing conditions, the sulfates it contains can be reduced back to sulfide via sulfate-reducing bacteria. Electric strength stations burning coal with flue gas desulfurization produce large portions of its as a byproduct from the scrubbers.

Gypsum Uses Area

  • It is used in construction as drywall, wallboard, sheetrock or plasterboard.
  • concrete blocks in building construction.
  • Plaster ingredients
  • A binder in fast-dry tennis court clay
  • A tofu (soy bean curd) coagulant, making it ultimately a major source of dietary calcium
  • Soil/water potential monitoring (soil moisture)
  • A common ingredient in making mead
  • In foot creams, shampoos and many other hair products
  • Used in mushroom cultivation to stop grains from clumping together

Distribution

The most common sulfate mineral. Localities listed here have provided especially fine or large specimens.

  • From Italy, on Sicily, as at Racalmuto, Girgenti, and Cianciana.
  • In Germany, in several mines in the Eisleben–Mansfeld–Sangershausen district, Saxony-Anhalt, and from near K¨onigslutter, Lower Saxony.
  • At Bex, Valais, Switzerland.
  • In Austria, from Aussee, Styria, and Hall, Tirol.
  • At Zaragoza, Zaragoza Province, Spain.
  • From Montmartre, Paris, France.
  • In Poland, large crystals from Tarnobrzeg.
  • At Meskerabad, near Teheran, Iran.
  • From Cloncurry, Queensland, Australia.
  • In Mexico, huge crystals in a cave complex in the Naica Pb–Ag mine, and also in the San Antonio mine, Santa Eulalia, Chihuahua.
  • Large crystals in the El Teniente mine, 67 km west of Rancagua, O’Higgins Province, Chile.
  • In the USA, large crystals at South Wash and elsewhere in Wayne Co., Utah; from Great Salt Plains, Alfalfa Co., Oklahoma; exceptional speleothems in Lechuguilla Cave, Carlsbad Caverns National Park, New Mexico.

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Dana, J. D. (1864). Manual of Mineralogy… Wiley.
  • Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
  • Geosciences | Smith College. [online] Available at: https://www.smith.edu/academics/geosciences [Accessed 15 Mar. 2019].
Cite this article as: Geology Science. (2019). Gypsum. [online] Available at: http://geologyscience.com/minerals/gypsum/ [8th December 2019 ]
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