a = 5.679(5), b = 15.202(14) c = 6.522(6) Å; β = 118.43°; Z = 4
Identification
Color
Colorless (in transmitted light) to white; often tinged other hues due to impurities; may be yellow, tan, blue, pink, dark brown, reddish brown or gray
The wordgypsum is derived from theGreek wordγύψος (gypsos), "plaster".[10] Because thequarries of theMontmartre district of Paris have long furnished burnt gypsum (calcined gypsum) used for various purposes, this dehydrated gypsum became known asplaster of Paris. Upon adding water, after a few dozen minutes, plaster of Paris becomes regular gypsum (dihydrate) again, causing the material to harden or "set" in ways that are useful for casting and construction.[11]
Gypsum was known in Old English asspærstān, "spear stone", referring to its crystalline projections. Thus, the wordspar in mineralogy, by comparison to gypsum, refers to any non-ore mineral or crystal that forms in spearlike projections. In the mid-18th century, the German clergyman and agriculturalistJohann Friderich Mayer investigated and publicized gypsum's use as a fertilizer.[12] Gypsum may act as a source of sulfur for plant growth, and in the early 19th century, it was regarded as an almost miraculous fertilizer. American farmers were so anxious to acquire it that a lively smuggling trade with Nova Scotia evolved, resulting in the so-called"Plaster War" of 1820.[13][14]
Gypsum crystals are soft enough to bend under pressure of the hand. Sample on display at Musée cantonal de géologie de Lausanne.
Gypsum is moderately water-soluble (~2.0–2.5 g/L at 25 °C)[15] and, in contrast to most other salts, it exhibitsretrograde solubility, becoming less soluble at higher temperatures. When gypsum is heated in air it loses water and converts first to calcium sulfate hemihydrate (bassanite, often simply called "plaster") and, if heated further, to anhydrouscalcium sulfate (anhydrite). As with anhydrite, the solubility of gypsum in saline solutions and inbrines is also strongly dependent onsodium chloride (common table salt) concentration.[15]
The structure of gypsum consists of layers of calcium (Ca2+) and sulfate (SO2−4) ions tightly bound together. These layers are bonded by sheets ofanion water molecules via weakerhydrogen bonding, which gives the crystal perfect cleavage along the sheets (in the {010} plane).[4][16]
Gypsum occurs in nature as flattened and oftentwinnedcrystals, and transparent, cleavable masses called selenite. In the form of selenite, gypsum forms some of the largest crystals found in nature, up to 12 m (39 ft) long.[17] Selenite contains no significantselenium; rather, both substances were named for the ancient Greek word for theMoon.
Selenite may also occur in a silky, fibrous form, in which case it is commonly called "satin spar".
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, calledalabaster, 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 calleddesert rose.
Gypsum is a common mineral, with thick and extensiveevaporite beds in association withsedimentary rocks. Deposits are known to occur instrata from as far back as theArchaeaneon.[18] Gypsum is deposited from lake and sea water, as well as inhot springs, fromvolcanic vapors, and sulfate solutions inveins.Hydrothermalanhydrite in veins is commonly hydrated to gypsum by groundwater in near-surface exposures. It is often associated with the mineralshalite andsulfur. Gypsum is the most common sulfate mineral.[19] Pure gypsum is white, but other substances found as impurities may give a wide range of colors to local deposits.
Because gypsum dissolves over time in water, gypsum is rarely found in the form of sand. However, the unique conditions of theWhite Sands National Park in the US state ofNew Mexico have created a 710 km2 (270 sq mi) expanse of white gypsum sand, enough to supply the US construction industry withdrywall for 1,000 years.[20]Commercial exploitation of the area, strongly opposed by area residents, was permanently prevented in 1933 when PresidentHerbert Hoover declared the gypsumdunes a protectednational monument.
Gypsum is also formed as a by-product ofsulfideoxidation, amongst others bypyriteoxidation, when thesulfuric acid generated reacts withcalcium carbonate. Its presence indicates oxidizing conditions. Under reducing conditions, the sulfates it contains can be reduced back to sulfide bysulfate-reducing bacteria. This can lead to accumulation of elemental sulfur in oil-bearing formations,[21] such as salt domes,[22] where it can be mined using theFrasch process[23] Electric power stations burning coal withflue gas desulfurization produce large quantities of gypsum as a byproduct from the scrubbers.
Commercial quantities of gypsum are found in the cities ofAraripina andGrajaú in Brazil; in Pakistan, Jamaica, Iran (world's second largest producer), Thailand, Spain (the main producer in Europe), Germany, Italy, England, Ireland, Canada[27] and the United States. Large open pit quarries are located in many places includingFort Dodge, Iowa, which sits on one of the largest deposits of gypsum in the world,[28] andPlaster City, California, United States, and EastKutai,Kalimantan, Indonesia. Several small mines also exist in places such asKalannie inWestern Australia, where gypsum is sold to private buyers for additions of calcium and sulfur as well as reduction of aluminium toxicities onsoil for agricultural purposes.[29][30]
Crystals of gypsum up to 11 m (36 ft) long have been found in the caves of theNaica Mine ofChihuahua, Mexico. The crystals thrived in the cave's extremely rare and stable natural environment. Temperatures stayed at 58 °C (136 °F), and the cave was filled with mineral-rich water that drove the crystals' growth. The largest of those crystals weighs 55 tonnes (61 short tons) and is around 500,000 years old.[31]
Flue gas desulfurization gypsum (FGDG) is recovered at some coal-fired power plants. The main contaminants are Mg, K, Cl, F, B, Al, Fe, Si, and Se. They come both from the limestone used in desulfurization and from the coal burned. This product is pure enough to replace natural gypsum in a wide variety of fields including drywalls, water treatment, and cement set retarder. Improvements in flue gas desulfurization have greatly reduced the amount of toxic elements present.[32]
Gypsum precipitates onto brackish watermembranes, a phenomenon known as mineral saltscaling, such as duringbrackish waterdesalination of water with high concentrations ofcalcium andsulfate. Scaling decreases membrane life and productivity.[33] This is one of the main obstacles in brackish water membrane desalination processes, such asreverse osmosis ornanofiltration. Other forms of scaling, such ascalcite scaling, depending on the water source, can also be important considerations indistillation, as well as inheat exchangers, where either the saltsolubility orconcentration can change rapidly.
A new study has suggested that the formation of gypsum starts as tiny crystals of a mineral calledbassanite (2CaSO4·H2O).[34] This process occurs via a three-stage pathway:
homogeneous nucleation of nanocrystalline bassanite;
The production ofphosphate fertilizers requires breaking down calcium-containingphosphate rock with acid, producing calcium sulfate waste known asphosphogypsum (PG). This form of gypsum is contaminated by impurities found in the rock, namelyfluoride,silica, radioactive elements such asradium, and heavy metal elements such ascadmium.[35] Similarly, production oftitanium dioxide produces titanium gypsum (TG) due to neutralization of excess acid withlime. The product is contaminated with silica, fluorides, organic matters, and alkalis.[36]
Impurities in refinery gypsum waste have, in many cases, prevented them from being used as normal gypsum in fields such as construction. As a result, waste gypsum is stored in stacks indefinitely, with significant risk of leaching their contaminants into water and soil.[35] To reduce the accumulation and ultimately clear out these stacks, research is underway to find more applications for such waste products.[36]
People can be exposed to gypsum in the workplace by breathing it in, skin contact, and eye contact. Calcium sulfateper se is nontoxic and is even approved as a food additive,[38] but as powdered gypsum, it can irritate skin and mucous membranes.[39]
Gypsum works,Valencian Museum of EthnologyOldAlfarb kiln for making plaster as a construction materialBritish Gypsum,Kirkby ThoreMap of gypsum deposits in northern Ohio, black squares indicate the location of deposits, from"Geography of Ohio", 1923
Gypsum board[40] is primarily used as a finish for walls and ceilings, and is known in construction as plasterboard, "sheetrock", or drywall. Gypsum provides a degree of fire-resistance to these materials, and glass fibers are added to their composition to accentuate this effect. Gypsum has negligible heat conductivity, giving its plaster some insulative properties.[41]
Gypsum blocks are used like concrete blocks in construction.
Gypsum mortar is an ancient mortar used in construction.
A component ofPortland cement used to prevent flash setting (too rapid hardening) ofconcrete.
A wood substitute in the ancient world: For example, when wood became scarce due to deforestation onBronze AgeCrete, gypsum was employed in building construction at locations where wood was previously used.[42]
Fertilizer: In the late 18th and early 19th centuries, Nova Scotia gypsum, often referred to as plaster, was a highly sought fertilizer for wheat fields in the United States.[43] Gypsum provides two of thesecondary plant macronutrients, calcium and sulfur. Unlike limestone, it generally does not affect soil pH.[44]
Othersoil conditioner uses: Gypsum reduces aluminium and boron toxicity in acidic soils. It also improves soil structure, water absorption, and aeration.[44]
Soilwater potential monitoring: a gypsum block can be inserted into the soil, and its electrical resistance can be measured to derive soil moisture.[48]
Asalabaster, a material for sculpture, it was used especially in the ancient world before steel was developed, when its relative softness made it much easier to carve.[49] During theMiddle Ages andRenaissance, it was preferred even tomarble.[50]
In the medieval period,scribes andilluminators used it as an ingredient ingesso, which was applied to illuminated letters and gilded with gold in illuminated manuscripts.[51]
Used in baking as a dough conditioner, reducing stickiness, and as a baked goods source of dietary calcium.[54] The primary component of mineral yeast food.[55]
Used in mushroom cultivation to stop grains from clumping together.
^Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (2003)."Gypsum"(PDF).Handbook of Mineralogy. Vol. V (Borates, Carbonates, Sulfates). Chantilly, VA, US: Mineralogical Society of America.ISBN978-0-9622097-0-3.Archived(PDF) from the original on 6 February 2006.
Thaer, Albrecht Daniel (1844).The Principles of Agriculture. Vol. 1. Translated by Shaw, William; Johnson, Cuthbert W. London, England: Ridgway. pp. 519–520.
Klaus Herrmann (1990)."Mayer, Johann Friedrich".Neue Deutsche Biographie (in German). Vol. 16. Berlin: Duncker & Humblot. pp. 544–545. (full text online). From p. 544:" … er bewirtschaftete nebenbei ein Pfarrgüttchen, … für die Düngung der Felder mit dem in den nahen Waldenburger Bergen gefundenen Gips einsetzte." ( … he also managed a small parson's estate, on which he repeatedly conducted agricultural experiments. In 1768, he first published the fruits of his experiences during this time as "Instruction about Gypsum", in which he espoused the fertilizing of fields with the gypsum that was found in the nearby Waldenburg mountains.)
Beckmann, Johann (1775).Grundsätze der deutschen Landwirtschaft [Fundamentals of German Agriculture] (in German) (2nd ed.). Göttingen, (Germany): Johann Christian Dieterich. p. 60. From p. 60:"Schon seit undenklichen Zeiten … ein Gewinn zu erhalten seyn wird." (Since times immemorial, in our vicinity, in the ministry of Niedeck [a village southeast of Göttingen], one has already made this use of gypsum; but Mr. Mayer has the merit to have made it generally known. In theHistory of Farming in Kupferzell, he had depicted a crushing mill (p. 74), in order to pulverize gypsum, from which a profit has been obtained, albeit with difficulty.)
^Smith, Joshua (2007).Borderland smuggling: Patriots, loyalists, and illicit trade in the Northeast, 1780–1820. Gainesville, FL: UPF. pp. passim.ISBN978-0-8130-2986-3.
^Mandal, Pradip K; Mandal, Tanuj K (2002). "Anion water in gypsum (CaSO4·2H2O) and hemihydrate (CaSO4·1/2H2O)".Cement and Concrete Research.32 (2): 313.doi:10.1016/S0008-8846(01)00675-5.
^Sassen, Roger; Chinn, E.W.; McCabe, C. (December 1988). "Recent hydrocarbon alteration, sulfate reduction and formation of elemental sulfur and metal sulfides in salt dome cap rock".Chemical Geology.74 (1–2):57–66.Bibcode:1988ChGeo..74...57S.doi:10.1016/0009-2541(88)90146-5.
^Graham, Gerald S. (1938). "The Gypsum Trade of the Maritime Provinces: Its Relation to American Diplomacy and Agriculture in the Early Nineteenth Century".Agricultural History.12 (3):209–223.JSTOR3739630.
^Brown, Michelle (1995).Understanding illuminated manuscripts: a guide to technical terms. Los Angeles, California: Yale University Press. p. 58.ISBN978-0-89236-217-2.
^Shurtleff, William (2000).Tofu & soymilk production: a craft and technical manual. Lafayette, CA: Soyfoods Center. p. 99.ISBN978-1-928914-04-4.
^Drennon, David G.; Johnson, Glen H. (February 1990). "The effect of immersion disinfection of elastomeric impressions on the surface detail reproduction of improved gypsum casts".The Journal of Prosthetic Dentistry.63 (2):233–241.doi:10.1016/0022-3913(90)90111-O.PMID2106026.
^Rodriguez, J. D.; Jimenez, A.; Prieto, M.; Torre, L.; Garcia-Granda, S. (2008). "Interaction of gypsum with As(V)-bearing aqueous solutions: Surface precipitation of guerinite, sainfeldite, and Ca2NaH(AsO4)2⋅6H2O, a synthetic arsenate".American Mineralogist.93 (5–6): 928.Bibcode:2008AmMin..93..928R.doi:10.2138/am.2008.2750.hdl:10651/5785.S2CID98249784.
^Rodríguez-Blanco, Juan Diego; Jiménez, Amalia; Prieto, Manuel (2007). "Oriented Overgrowth of Pharmacolite (CaHAsO4⋅2H2O) on Gypsum (CaSO4⋅2H2O)".Cryst. Growth Des.7 (12):2756–2763.doi:10.1021/cg070222+.
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