Editing Gypsum

{{Short description|Soft calcium sulfate mineral}}
{{About|the mineral|}}
{{Use American English|date=May 2022}}
{{Use dmy dates|date=July 2014}}
{{Infobox mineral
| name        = Gypsum
| category    = [[Sulfate mineral]]s
| boxwidth    = 
| boxbgcolor  = 
| image       = Gypse Caresse.jpg 
| imagesize   = 260px
| caption     = 
| formula     = {{chem2|CaSO4*2H2O}}
| IMAsymbol   = Gp<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>
| molweight   = 
| strunz      = 7.CD.40
| system      = [[Monoclinic]]
| class       = Prismatic (2/m) <br/>[[H-M symbol]]: (2/m)
| symmetry    = Monoclinic <br/>[[Space group]]: ''I''2/a
| unit cell   = a = 5.679(5), b = 15.202(14) <br/>c = 6.522(6)&nbsp;Å; β = 118.43°; Z&nbsp;=&nbsp;4
| 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
| habit       = Massive, flat. Elongated and generally prismatic crystals
| twinning    = Very common on {110}
| cleavage    = Perfect on {010}, distinct on {100}
| fracture    = Conchoidal on {100}, splintery parallel to [001]
| tenacity    = Flexible, inelastic
| mohs        = 1.5–2 (defining mineral for 2)
| luster      = Vitreous to silky, pearly, or waxy
| refractive  = ''n''<sub>α</sub> = 1.519–1.521<br/> ''n''<sub>β</sub> = 1.522–1.523<br/> ''n''<sub>γ</sub> = 1.529–1.530
| opticalprop = Biaxial (+)
| birefringence = δ = 0.010
| pleochroism = None
| 2V          = 58°
| streak      = White
| gravity     = 2.31–2.33
| melt        = 
| fusibility  = 5
| diagnostic  = 
| solubility  = Hot, dilute HCl
| diaphaneity = Transparent to translucent
| other       = 
| references  = <ref>{{cite book|editor1=Anthony, John W. |editor2=Bideaux, Richard A. |editor3=Bladh, Kenneth W. |editor4=Nichols, Monte C. |title= Handbook of Mineralogy|publisher= Mineralogical Society of America|place= Chantilly, VA, US|chapter-url=http://rruff.geo.arizona.edu/doclib/hom/gypsum.pdf |archive-url=https://web.archive.org/web/20060206190607/http://rruff.geo.arizona.edu/doclib/hom/gypsum.pdf |archive-date=2006-02-06 |url-status=live|chapter=Gypsum|isbn=978-0962209703 |volume=V (Borates, Carbonates, Sulfates)|year=2003}}</ref><ref>[http://www.mindat.org/min-1784.html Gypsum]. Mindat</ref><ref name=Cornelis>{{citation |first1= Cornelis |last1= Klein | first2= Cornelius S. Jr. |last2= Hurlbut |year= 1985 |title= Manual of Mineralogy |publisher= John Wiley |edition= 20th |pages= [https://archive.org/details/manualofmineralo00klei/page/352 352–353] |isbn= 978-0-471-80580-9 |url-access= registration |url= https://archive.org/details/manualofmineralo00klei/page/352 }}</ref>
| var1 = Satin spar|var1text = Pearly, fibrous masses
| var2 = [[Selenite (mineral)|Selenite]]|var2text = Transparent and bladed crystals
| var3 = [[Alabaster]]|var3text = Fine-grained, slightly colored
}}
'''Gypsum''' is a soft [[sulfate mineral]] composed of [[calcium sulfate]] [[Hydrate|dihydrate]], with the [[chemical formula]] {{chem2|CaSO4*2H2O}}.<ref name=Cornelis/> It is widely mined and is used as a [[fertilizer]] and as the main constituent in many forms of [[plaster]], [[drywall]] and [[blackboard]] or [[sidewalk chalk]].<ref>{{Cite web |last=Institute |first=Canadian Conservation |date=2017-09-14 |title=Care of Objects Made of Plaster of Paris – Canadian Conservation Institute (CCI) Notes 12/2 |url=https://www.canada.ca/en/conservation-institute/services/conservation-preservation-publications/canadian-conservation-institute-notes/care-plaster-paris.html |access-date=2023-01-20 |website=www.canada.ca}}</ref><ref>Make your own sidewalk chalk. (1998, July 21). Christian Science Monitor. 13.</ref><ref>{{Cite web |title=Plaster {{!}} Definition, Uses, Types, & Facts |url=https://www.britannica.com/technology/plaster |access-date=2023-01-20 |website=Britannica |language=en}}</ref><ref>{{Cite web |title=drywall — definition |url=https://www.merriam-webster.com/dictionary/drywall |access-date=2023-01-20 |website=Merriam-Webster |language=en}}</ref> Gypsum also [[Crystallization|crystallizes]] as translucent crystals of [[selenite (mineral)|selenite]]. It forms as an [[evaporite]] mineral and as a [[Mineral hydration|hydration]] product of [[anhydrite]]. The [[Mohs scale of mineral hardness]] defines gypsum as hardness value 2 based on [[Scratch hardness|scratch]] [[hardness comparison]].

Fine-grained white or lightly tinted forms of gypsum known as [[alabaster]] have been used for [[sculpture]] by many cultures including [[Ancient Egypt]], [[Mesopotamia]], [[Ancient Rome]], the [[Byzantine Empire]], and the [[Nottingham alabaster]]s of [[Medieval England]].

==Etymology and history==

The word ''[[wikt:gypsum|gypsum]]'' is derived from the [[Greek language|Greek]] word {{lang|el|γύψος}} ({{transliteration|grc|gypsos}}), "plaster".<ref>{{cite web| url= http://www.askoxford.com/concise_oed/gypsum| archive-url= https://archive.today/20120719220246/http://www.askoxford.com/concise_oed/gypsum| url-status= dead| archive-date= 19 July 2012|title=Compact Oxford English Dictionary: gypsum |website=Oxford Dictionaries }}</ref> Because the [[quarry|quarries]] of the [[Montmartre]] district of [[Paris]] have long furnished burnt gypsum ([[calcination|calcined]] gypsum) used for various purposes, this dehydrated gypsum became known as [[plaster 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.<ref name=Szostakowski>{{Cite journal|last1=Szostakowski|first1=B.|last2=Smitham|first2=P.|last3=Khan|first3=W.S.|date=2017-04-17|title=Plaster of Paris–Short History of Casting and Injured Limb Immobilzation|journal=The Open Orthopaedics Journal|volume=11|pages=291–296|doi= 10.2174/1874325001711010291 |doi-access=free|issn=1874-3250|pmc=5420179|pmid=28567158}}</ref>

Gypsum was known in Old English as {{lang|ang|spærstān}}, "spear stone", referring to its crystalline projections. Thus, the word [[Spar (mineralogy)|spar]] 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 agriculturalist [[Johann Friedrich Mayer (agriculturist)|Johann Friderich Mayer]] investigated and publicized gypsum's use as a fertilizer.<ref>See:
*  {{cite book|last1=Thaer|first1=Albrecht Daniel|translator-last1=Shaw|translator-first1=William|translator-last2=Johnson|translator-first2=Cuthbert W.|title=The Principles of Agriculture |date=1844 |publisher=Ridgway |location=London, England |volume= 1 |pages=519–520 |url=https://books.google.com/books?id=zAhJAAAAMAAJ&pg=PA519}}
*  {{NDB|16|544|545|Mayer, Johann Friedrich|Klaus Herrmann|104138432}}  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.)
*  {{cite book |last1=Beckmann |first1=Johann |title=Grundsätze der deutschen Landwirthschaft |trans-title=Fundamentals of German Agriculture |date=1775 |publisher=Johann Christian Dieterich |location=Göttingen, (Germany) |page=60 |edition=2nd |url=https://books.google.com/books?id=q8w6AAAAcAAJ&pg=PA60 |language=de}}  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 the ''History 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.)
*  {{cite book |last1=Mayer |first1=Johann Friderich |title=Lehre vom Gyps als vorzueglich guten Dung zu allen Erd-Gewaechsen auf Aeckern und Wiesen, Hopfen- und Weinbergen |trans-title=Instruction in gypsum as an ideal good manure for all things grown in soil on fields and pastures, hops yards and vineyards |date=1768 |publisher=Jacob Christoph Posch |location=Anspach, (Germany) |url=https://books.google.com/books?id=lSlAAAAAcAAJ&pg=PA1 |language=de}}</ref>  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 [[Hants County, Nova Scotia#Plaster War|"Plaster War"]] of 1820.<ref>{{cite book|last=Smith|first=Joshua|title=Borderland smuggling: Patriots, loyalists, and illicit trade in the Northeast, 1780–1820|year=2007|publisher=UPF|location=Gainesville, FL|isbn=978-0-8130-2986-3|pages=passim}}</ref>

==Physical properties==
[[File:Gypsum deformed cristal-MCG 7747-P4150901-black.jpg|thumb|left|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&nbsp;g/L at 25&nbsp;°C)<ref name="Bock_1961">{{Cite journal| last = Bock| first = E.| year = 1961| title = On the solubility of anhydrous calcium sulphate and of gypsum in concentrated solutions of sodium chloride at 25&nbsp;°C, 30&nbsp;°C, 40&nbsp;°C, and 50&nbsp;°C| journal = Canadian Journal of Chemistry| volume = 39| issue = 9| pages = 1746–1751 | doi = 10.1139/v61-228| df = dmy-all| doi-access = free}}</ref> and, in contrast to most other salts, it exhibits [[Solubility#Factors affecting solubility|retrograde 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 anhydrous [[calcium sulfate]] ([[anhydrite]]).  As with anhydrite, the solubility of gypsum in saline solutions and in [[brine]]s is also strongly dependent on [[sodium chloride]] (common table salt) concentration.<ref name="Bock_1961"/>

The structure of gypsum consists of layers of calcium (Ca<sup>2+</sup>) and sulfate ({{chem2|SO4(2-)}}) ions tightly bound together. These layers are bonded by sheets of [[anion water]] molecules via weaker [[hydrogen bond]]ing, which gives the crystal perfect cleavage along the sheets (in the {010} plane).<ref name=Cornelis/><ref>{{cite journal| doi= 10.1016/S0008-8846(01)00675-5| last1= Mandal| first1= Pradip K|year=2002|pages=313|volume=32|journal=Cement and Concrete Research|last2=Mandal|first2=Tanuj K| title= Anion water in gypsum (CaSO<sub>4</sub>·2H<sub>2</sub>O) and hemihydrate (CaSO<sub>4</sub>·1/2H<sub>2</sub>O)|issue=2}}</ref>

==Crystal varieties==
{{main|Selenite (mineral)}}
Gypsum occurs in nature as flattened and often [[crystal twinning|twinned]] [[crystal]]s, and transparent, cleavable masses called selenite. In the form of selenite, gypsum forms some of the largest crystals found in nature, up to {{convert|12|m|ft|abbr=on}} long.<ref>{{cite journal |first1=Juan Manuel |last1= García-Ruiz |first2= Roberto |last2= Villasuso |first3= Carlos |last3= Ayora |first4= Angels |last4= Canals |first5= Fermín |last5= Otálora |title= Formation of natural gypsum megacrystals in Naica, Mexico |journal= Geology |volume=35 |issue=4 |pages=327–330 |year=2007 |doi= 10.1130/G23393A.1|bibcode = 2007Geo....35..327G |url=https://digital.csic.es/bitstream/10261/3439/1/garciaruiznaica.pdf |archive-url=https://web.archive.org/web/20170816122316/http://digital.csic.es/bitstream/10261/3439/1/garciaruiznaica.pdf |archive-date=2017-08-16 |url-status=live |hdl= 10261/3439 |hdl-access= free }}</ref> Selenite contains no significant [[selenium]]; rather, both substances were named for the ancient Greek word for the [[Moon]].

Selenite may also occur in a silky, fibrous form, in which case it is commonly called "satin spar". 

Itmay 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, called [[alabaster]], 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 (crystal)|desert rose]].

==Occurrence==
Gypsum is a common mineral, with thick and extensive [[evaporite]] beds in association with [[sedimentary rock]]s. Deposits are known to occur in [[stratum|strata]] from as far back as the [[Archean|Archaean]] [[Aeon|eon]].<ref name="Cockell">{{cite journal| last1= Cockell| first1= C. S.|last2= Raven |first2= J. A.|year=2007|title=Ozone and life on the Archaean Earth|journal=Philosophical Transactions of the Royal Society A|volume=365|pages=1889–1901|doi=10.1098/rsta.2007.2049| pmid= 17513273|issue=1856|bibcode = 2007RSPTA.365.1889C | s2cid= 4716}}</ref><!--What about the Messinian evaporites?--> Gypsum is deposited from lake and sea water, as well as in [[hot spring]]s, from [[volcano|volcanic]] vapors, and sulfate solutions in [[Vein (geology)|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]]. Gypsum is the most common sulfate mineral.<ref name="DHZ1966">{{cite book |title=An Introduction to the Rock Forming Minerals | publisher=Longman |last1=Deer |first1=W.A. |last2=Howie |first2=R.A. |last3=Zussman |first3=J. |year=1966 |location=London |page=469 |isbn=978-0-582-44210-8}}</ref> 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 the [[White Sands National Park]] in the US state of [[New Mexico]] have created a {{convert|710|km2|adj=on|abbr=on}} expanse of white gypsum sand, enough to supply the US construction industry with [[drywall]] for 1,000 years.<ref name='The Albuquerque Journal 1999-02-07'>{{cite news |last = Abarr|first = James|title = Sea of sand |newspaper = The Albuquerque Journal|date = 7 February 1999|url = http://www.abqjournal.com/venue/travel/tourism/heritage_whitesands.htm|access-date = 27 January 2007|url-status=dead|archive-url=https://web.archive.org/web/20060630120616/http://www.abqjournal.com:80/venue/travel/tourism/heritage_whitesands.htm|archive-date=30 June 2006}}</ref>
Commercial exploitation of the area, strongly opposed by area residents, was permanently prevented in 1933 when President [[Herbert Hoover]] declared the gypsum [[dune]]s a protected [[National monument (United States)|national monument]].

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]]. This can lead to accumulation of elemental sulfur in oil-bearing formations,<ref>{{cite journal |last1=Machel |first1=H.G |title=Bacterial and thermochemical sulfate reduction in diagenetic settings — old and new insights |journal=Sedimentary Geology |date=April 2001 |volume=140 |issue=1–2 |pages=143–175 |doi=10.1016/S0037-0738(00)00176-7|bibcode=2001SedG..140..143M |s2cid=4606551 }}</ref> such as salt domes,<ref>{{cite journal |last1=Sassen |first1=Roger |last2=Chinn |first2=E.W. |last3=McCabe |first3=C. |title=Recent hydrocarbon alteration, sulfate reduction and formation of elemental sulfur and metal sulfides in salt dome cap rock |journal=Chemical Geology |date=December 1988 |volume=74 |issue=1–2 |pages=57–66 |doi=10.1016/0009-2541(88)90146-5|bibcode=1988ChGeo..74...57S }}</ref> where it can be mined using the [[Frasch process]]<ref name =Ullmann>{{Ullmann | title = Sulfur | author = Wolfgang Nehb, Karel Vydra | doi = 10.1002/14356007.a25_507.pub2}}</ref> Electric power stations burning coal with [[flue gas desulfurization]] produce large quantities of gypsum as a byproduct from the scrubbers.

Orbital pictures from the [[Mars Reconnaissance Orbiter]] (MRO) have indicated the existence of gypsum dunes in the northern polar region of Mars,<ref>[http://hirise.lpl.arizona.edu/nea.php High-resolution Mars image gallery]. University of Arizona</ref> which were later confirmed at ground level by the [[Mars Exploration Rover]] (MER) ''[[Opportunity rover|Opportunity]]''.<ref>[http://www.nasa.gov/mission_pages/mer/news/mer20111207.html NASA Mars Rover Finds Mineral Vein Deposited by Water] {{Webarchive|url=https://web.archive.org/web/20170615235154/https://www.nasa.gov/mission_pages/mer/news/mer20111207.html |date=15 June 2017 }}, NASA, 7 December 2011.</ref>
<gallery mode="packed" heights="100">
File:Lechuguilla Chandelier Ballroom.jpg|Large gypsum crystals in [[Lechuguilla Cave]]'s "chandelier ballroom" 
File:Cristales cueva de Naica.JPG|Gypsum crystals in the [[Cave of the Crystals]] in Mexico (person at lower right for scale)
File:GypsumCrystalsLakeLucerno.jpg|Gypsum crystals formed as the water evaporated in [[Lake Lucero]], White Sands National Park
File:White Gypsum - geograph.org.uk - 2503198.jpg|Gypsum veins in the silts/marls of the Tea Green and Grey Marls, [[Blue Anchor]], [[Somerset]], United Kingdom
File:Gypsum layers Caprock Canyons 1.JPG|Gypsum veins in [[Caprock Canyons State Park and Trailway]], Texas
File:Yardangs in dunes, White Sands National Park, New Mexico, United States.jpg|Dunes made of small crystals of gypsum, White Sands National Park
</gallery>

==Mining==
{| class=wikitable style="text-align:right; float:right;"
|+ Estimated production of Gypsum in 2015<br/>(thousand metric tons)<ref>{{cite web |publisher=U.S. Geological Survey |title=GYPSUM |url=https://minerals.usgs.gov/minerals/pubs/commodity/gypsum/mcs-2016-gypsu.pdf |archive-url=https://web.archive.org/web/20161212180411/http://minerals.usgs.gov/minerals/pubs/commodity/gypsum/mcs-2016-gypsu.pdf |archive-date=2016-12-12 |url-status=live}}</ref>
|-
! Country || Production || Reserves
|-
| style=text-align:left;| [[China]]||132,000||{{N/A}}
|-
| style=text-align:left;| [[Iran]]||22,000||1,600
|-
| style=text-align:left;| [[Thailand]]||12,500||{{N/A}}
|-
| style=text-align:left;| [[United States]]||11,500||700,000
|-
| style=text-align:left;| [[Turkey]]||10,000||{{N/A}}
|-
| style=text-align:left;| [[Spain]]||6,400||{{N/A}}
|-
| style=text-align:left;| [[Mexico]]||5,300||{{N/A}}
|-
| style=text-align:left;| [[Japan]]||5,000||{{N/A}}
|-
| style=text-align:left;| [[Russia]]||4,500||{{N/A}}
|-
| style=text-align:left;| [[Italy]]||4,100||{{N/A}}
|-
| style=text-align:left;| [[India]]||3,500||39,000
|-
| style=text-align:left;| [[Australia]]||3,500||{{N/A}}
|-
| style=text-align:left;| [[Oman]]||3,500||{{N/A}}
|-
| style=text-align:left;| [[Brazil]]||3,300||290,000
|-
| style=text-align:left;| [[France]]||3,300||{{N/A}}
|-
| style=text-align:left;| [[Canada]]||2,700||450,000
|-
| style=text-align:left;| [[Saudi Arabia]]||2,400||{{N/A}}
|-
| style=text-align:left;| [[Algeria]]||2,200||{{N/A}}
|-
| style=text-align:left;| [[Germany]]||1,800||450,000
|-
| style=text-align:left;| [[Argentina]]||1,400||{{N/A}}
|-
| style=text-align:left;| [[Pakistan]]||1,300||{{N/A}}
|-
| style=text-align:left;| [[United Kingdom]]||1,200||55,000
|-
| style=text-align:left;| Other countries||15,000||{{N/A}}
|-
| style=text-align:left;| World total||258,000||{{N/A}}
|}

Commercial quantities of gypsum are found in the cities of [[Araripina]] and [[Grajaú]] in Brazil; in Pakistan, Jamaica, Iran (world's second largest producer), Thailand, Spain (the main producer in Europe), Germany, Italy, England, Ireland, Canada<ref name='Mining Canada'>{{cite web |url=http://mmsd1.mms.nrcan.gc.ca/mmsd/producers/commodityCompany_e.asp?nId=51&mineType=nonMetal |title=Mines, mills and concentrators in Canada |access-date=27 January 2007 |date=24 October 2005 |publisher=Natural Resources Canada |url-status=dead |archive-url=https://web.archive.org/web/20050313183544/http://mmsd1.mms.nrcan.gc.ca/mmsd/producers/commodityCompany_e.asp?nId=51&minetype=nonMetal |archive-date=13 March 2005 |df=dmy-all }}</ref> and the United States. Large open pit quarries are located in many places including [[Fort Dodge, Iowa]], which sits on one of the largest deposits of gypsum in the world,<ref>{{Cite book|title=The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide|publisher=Helion|year=2018|via=Credo Reference}}</ref> and [[Plaster City, California]], United States, and East [[Kutai]], [[Kalimantan]], Indonesia. Several small mines also exist in places such as [[Kalannie]] in [[Western Australia]], where gypsum is sold to private buyers for additions of calcium and sulfur as well as reduction of aluminium toxicities on [[soil]] for agricultural purposes.<ref>{{Cite web |title=Australia - Gypsum industry news from Global Gypsum |url=https://www.globalgypsum.com/news/itemlist/tag/Australia?start=70&utm_source=chatgpt.com |access-date=2025-05-15 |website=www.globalgypsum.com}}</ref><ref>{{Cite web |title=Livebearing Aquarium Fish—Habitat, Diet, and Breeding |url=https://www.thesprucepets.com/livebearing-aquarium-fish-1378599?utm_source=chatgpt.com |access-date=2025-05-15 |website=The Spruce Pets |language=en}}</ref>

Crystals of gypsum up to {{convert|11|m|abbr=on}} long have been found in the caves of the [[Naica Mine]] of [[Chihuahua (state)|Chihuahua]], Mexico. The crystals thrived in the cave's extremely rare and stable natural environment. Temperatures stayed at {{cvt|58|C}}, and the cave was filled with mineral-rich water that drove the crystals' growth. The largest of those crystals weighs {{convert|55|t|ST}} and is around 500,000 years old.<ref>{{cite news|newspaper = The Telegraph| url = https://www.telegraph.co.uk/news/newstopics/howaboutthat/3269047/Worlds-largest-crystal-discovered-in-Mexican-cave.html| title =World's largest crystal discovered in Mexican cave| access-date=6 June 2009|location=London|first=Richard|last=Alleyne|date=27 October 2008}}</ref>
<gallery widths="220px" heights="200px" perrow="3">
File:Gypsum-24382.jpg|Golden gypsum crystals from [[Winnipeg]]
File:WhiteSandsGypsum.jpg|Gypsum [[sand]] from [[White Sands National Park]], [[New Mexico]]
</gallery>

==Synthesis==
[[Chemical synthesis|Synthetic]] gypsum is produced as a waste product or by-product in a range of industrial processes.

=== Desulfurization ===
[[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.<ref name="pmid31561139">{{cite journal |last1=Koralegedara |first1=NH |last2=Pinto |first2=PX |last3=Dionysiou |first3=DD |last4=Al-Abed |first4=SR |title=Recent advances in flue gas desulfurization gypsum processes and applications – A review. |journal=Journal of Environmental Management |date=1 December 2019 |volume=251 |pages=109572 |doi=10.1016/j.jenvman.2019.109572 |pmid=31561139 |pmc=7396127}}</ref>

=== Desalination ===
Gypsum precipitates onto brackish water [[membrane]]s, a phenomenon known as mineral salt [[Fouling|scaling]], such as during [[brackish]] water [[desalination]] of water with high concentrations of [[calcium]] and [[sulfate]]. Scaling decreases membrane life and productivity.<ref>{{cite journal |last1=Uchymiak |first1=Michal |last2=Lyster |first2=Eric |last3=Glater |first3=Julius |last4=Cohen |first4=Yoram |title=Kinetics of gypsum crystal growth on a reverse osmosis membrane |journal=Journal of Membrane Science |date=April 2008 |volume=314 |issue=1–2 |pages=163–172 |doi=10.1016/j.memsci.2008.01.041}}</ref> 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 exchanger]]s, where either the salt [[solubility]] or [[concentration]] can change rapidly.

A new study has suggested that the formation of gypsum starts as tiny crystals of a mineral called [[bassanite]] (2CaSO<sub>4</sub>·H<sub>2</sub>O).<ref>{{Cite journal| last1 = Van Driessche| first1 = A.E.S.| first2 = L. G. | last2= Benning | first3= J. D. | last3= Rodriguez-Blanco| first4= M. | last4= Ossorio| first5= P. | last5= Bots | first6= J. M. | last6=  García-Ruiz| year = 2012| title = The role and implications of bassanite as a stable precursor phase to gypsum precipitation| journal = [[Science (journal)|Science]]| volume = 336| issue = 6077| pages = 69–72 | doi = 10.1126/science.1215648|bibcode = 2012Sci...336...69V| pmid=22491851| s2cid = 9355745}}</ref> This process occurs via a three-stage pathway: 
# homogeneous nucleation of nanocrystalline bassanite; 
# self-assembly of bassanite into aggregates, and 
# transformation of bassanite into gypsum.

=== Refinery waste ===
The production of [[phosphate]] fertilizers requires breaking down calcium-containing [[phosphate rock]] with acid, producing calcium sulfate waste known as [[phosphogypsum]] (PG). This form of gypsum is contaminated by impurities found in the rock, namely [[fluoride]], [[silica]], radioactive elements such as [[radium]], and heavy metal elements such as [[cadmium]].<ref name=Taylor>{{cite journal|doi=10.1016/j.jenvman.2009.03.007|pmid=19406560|title=Environmental Impact and Management of Phosphogypsum|journal=Journal of Environmental Management|volume=90|pages=2377–2386|year=2009|last1=Tayibi|first1= Hanan|last2=Choura|first2=Mohamed|last3=López|first3=Félix A.|last4=Alguacil|first4=Francisco J.|last5=López-Delgado|first5=Aurora|issue=8|bibcode=2009JEnvM..90.2377T |hdl=10261/45241|hdl-access=free}}</ref> Similarly, production of [[titanium dioxide]] produces titanium gypsum (TG) due to neutralization of excess acid with [[calcium hydroxide|lime]]. The product is contaminated with silica, fluorides, organic matters, and alkalis.<ref name="pmid26495867">{{cite journal |last1=Zhang |first1=Y |last2=Wang |first2=F |last3=Huang |first3=H |last4=Guo |first4=Y |last5=Li |first5=B |last6=Liu |first6=Y |last7=Chu |first7=PK |title=Gypsum blocks produced from TiO2 production by-products. |journal=Environmental Technology |date=2016 |volume=37 |issue=9 |pages=1094–100 |doi=10.1080/09593330.2015.1102329 |url=https://www1.cugb.edu.cn/uploadCms/file/20600/papers_upload/20161008164505966187.pdf |archive-url=https://web.archive.org/web/20220325023932/https://www1.cugb.edu.cn/uploadCms/file/20600/papers_upload/20161008164505966187.pdf |archive-date=2022-03-25 |url-status=live |pmid=26495867|bibcode=2016EnvTe..37.1094Z |s2cid=28458281 }}</ref>

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.<ref name=Taylor/> To reduce the accumulation and ultimately clear out these stacks, research is underway to find more applications for such waste products.<ref name="pmid26495867"/>

== Occupational safety ==
{{NFPA 704 | H= 0 | F= 0 | R= 0 | S= |caption=Gypsum |ref=<ref name="MSDS">{{cite web |last1=Michigan Gypsum |title=MATERIAL SAFETY DATA SHEET Gypsum (Calcium Sulfate Dihydrate) |url=https://www.ncmissouri.edu/consumerinfo/wp-content/uploads/sites/26/2016/12/Gypsum-Calcium-Sulfate-msds.pdf |archive-url=https://web.archive.org/web/20211121062715/https://www.ncmissouri.edu/consumerinfo/wp-content/uploads/sites/26/2016/12/Gypsum-Calcium-Sulfate-msds.pdf |archive-date=2021-11-21 |url-status=live |website=Consumer Information |publisher=NorthCentral Missouri College |access-date=21 November 2021}}</ref>}}
People can be exposed to gypsum in the workplace by breathing it in, skin contact, and eye contact. Calcium sulfate ''per se'' is nontoxic and is even approved as a food additive,<ref name=pc>{{cite web |title=Compound Summary for CID 24497 – Calcium Sulfate |url=https://pubchem.ncbi.nlm.nih.gov/compound/calcium_sulfate#section=Food-Additives-and-Ingredients |publisher=PubChem}}</ref> but as powdered gypsum, it can irritate skin and mucous membranes.<ref name="cdc">{{Cite web|title = CDC – NIOSH Pocket Guide to Chemical Hazards – Gypsum|url = https://www.cdc.gov/niosh/npg/npgd0308.html|website = www.cdc.gov|access-date = 2015-11-03}}</ref>

===United States===
The [[Occupational Safety and Health Administration]] (OSHA) has set the legal limit ([[permissible exposure limit]]) for gypsum exposure in the workplace as TWA 15&nbsp;mg/m<sup>3</sup> for total exposure and TWA 5&nbsp;mg/m<sup>3</sup> for respiratory exposure over an eight-hour workday. The [[National Institute for Occupational Safety and Health]] (NIOSH) has set a [[recommended exposure limit]] (REL) of TWA 10&nbsp;mg/m<sup>3</sup> for total exposure and TWA 5&nbsp;mg/m<sup>3</sup> for respiratory exposure over an eight-hour workday.<ref name="cdc"/>

==Uses==
[[File:2.-Calera. Cal i guix (26561676342).jpg|thumb|upright=1.5|Gypsum works, [[Valencian Museum of Ethnology]]]]
[[File:Algepsar d'Alfarb. Forn primer, 1 (País Valencià).jpg|thumb|Old [[Alfarb]] kiln for making plaster as a construction material]]
[[File:KirkbyThoreGypsumPlant(SimonLedingham)May2005.jpg|thumb|upright=1.3|right|British Gypsum, [[Kirkby Thore]]]]
[[File:Geography of Ohio - DPLA - aaba7b3295ff6973b6fd1e23e33cde14 (page 96) (cropped2).jpg|thumb|upright=1.25|Map of gypsum deposits in northern Ohio, black squares indicate the location of deposits, from ''"Geography of Ohio"'', 1923]]
Gypsum is used in a wide variety of applications:

===Construction industry===
*[[Drywall|Gypsum board]]<ref>*[http://www.csinet.org/s_csi/docs/9400/9361.pdf Complimentary list of MasterFormat 2004 Edition numbers and titles] (large PDF document)</ref> 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.<ref name="Bonewitz-2008">{{Cite book |last=Bonewitz |first=Ronald |title=Rock and Gem: The Definitive Guide to Rocks, Minerals, Gems, and Fossils |publisher=DK |year=2008 |location=United States |pages=47 |language=English}}</ref>
*[[Gypsum block]]s are used like concrete blocks in construction.
*[[Gypsum mortar]] is an ancient mortar used in construction.
*A component of [[Portland cement]] used to prevent flash setting (too rapid hardening) of [[concrete]].
*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.<ref>{{cite journal| first= C. Michael |last= Hogan| url= http://www.themodernantiquarian.com/site/10854/knossos.html#fieldnotes |title= Knossos fieldnotes| journal= Modern Antiquarian | year= 2007}}</ref>

===Agriculture===
*[[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.<ref>{{cite journal |jstor=3739630|title=The Gypsum Trade of the Maritime Provinces: Its Relation to American Diplomacy and Agriculture in the Early Nineteenth Century |last1=Graham |first1=Gerald S. |journal=Agricultural History |year=1938 |volume=12 |issue=3 |pages=209–223 }}</ref> Gypsum provides two of the [[plant nutrition|secondary plant macronutrients]], calcium and sulfur. Unlike limestone, it generally does not affect soil pH.<ref name="soilsorg"/>
*[[Land reclamation|Reclamation]] of [[saline soils]], regardless of pH. When gypsum is added to sodic (saline) and [[acidic soil]], the highly [[soluble]] form of [[boron]] ([[sodium metaborate]]) is converted to the less soluble calcium metaborate. The exchangeable sodium percentage is also reduced by gypsum application.<ref>[https://books.google.com/books?id=ANCBDwAAQBAJ&dq=boron+sodium+soil&pg=PA99 Genesis and Management of Sodic (Alkali) Soils.] (2017). (n.p.): Scientific Publishers.</ref><ref>{{Cite journal |doi=10.2136/sssaj1980.03615995004400010010x |first1=J. D. |last1=Oster  |first2=H. |last2=Frenkel |year=1980 |title=The chemistry of the reclamation of sodic soils with gypsum and lime |journal=[[Soil Science Society of America Journal]] |volume=44 |issue=1 |pages=41–45 |bibcode=1980SSASJ..44...41O }}</ref> The [[Zuiderzee Works]] uses gypsum for the recovered land.<ref name="ley196110">{{Cite magazine |last=Ley |first=Willy |date=October 1961 |title=The Home-Made Land |department=For Your Information |url=https://archive.org/stream/Galaxy_v19n06_1961-08#page/n65/mode/1up |magazine=Galaxy Science Fiction |pages=92–106}}</ref>
*Other [[soil conditioner]] uses: Gypsum reduces aluminium and boron toxicity in acidic soils. It also improves soil structure, water absorption, and aeration.<ref name="soilsorg">{{cite web |title=Gypsum as an agricultural product {{!}} Soil Science Society of America |url=https://www.soils.org/news/science-news/gypsum-agricultural-product/ |website=www.soils.org}}</ref>
*Soil [[water potential]] monitoring: a gypsum block can be inserted into the soil, and its electrical resistance can be measured to derive soil moisture.<ref>{{cite encyclopedia |last1=Durner |first1=W. |last2=Or |first2=D. |year=2006 |chapter=Soil water potential measurement |title=Encyclopedia of hydrological sciences |editor-last1=Anderson |editor-first1=M.G. |publisher=John Wiley & Sons Ltd. |chapter-url=http://www.soil.tu-bs.de/download/downloads/pubs/2005.hsa077a.Durner-Or.SoilWaterPotentialMeasurement.pdf |archive-url=https://web.archive.org/web/20220616051818/http://www.soil.tu-bs.de/download/downloads/pubs/2005.hsa077a.Durner-Or.SoilWaterPotentialMeasurement.pdf |archive-date=2022-06-16 |url-status=live|access-date=23 May 2022 |isbn=978-0471491033}}</ref>

===Modeling, sculpture and art===
*[[Plaster]] for casting moulds and modeling.
*As [[alabaster]], 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.<ref>{{cite book |last1=Rapp |first1=George |title=Archaeomineralogy |chapter=Soft Stones and Other Carvable Materials |series=Natural Science in Archaeology |date=2009 |pages=121–142 |doi=10.1007/978-3-540-78594-1_6|isbn=978-3-540-78593-4 }}</ref> During the [[Middle Ages]] and [[Renaissance]], it was preferred even to [[marble]].<ref>{{cite journal |last1=Kloppmann |first1=W. |last2=Leroux |first2=L. |last3=Bromblet |first3=P. |last4=Le Pogam |first4=P.-Y. |last5=Cooper |first5=A. H. |last6=Worley |first6=N. |last7=Guerrot |first7=C. |last8=Montech |first8=A. T. |last9=Gallas |first9=A. M. |last10=Aillaud |first10=R. |title=Competing English, Spanish, and French alabaster trade in Europe over five centuries as evidenced by isotope fingerprinting |journal=Proceedings of the National Academy of Sciences |date=7 November 2017 |volume=114 |issue=45 |pages=11856–11860 |doi=10.1073/pnas.1707450114|pmid=29078309 |pmc=5692548 |bibcode=2017PNAS..11411856K |doi-access=free }}</ref> 
*In the medieval period, [[scribe]]s and [[Illuminated manuscript|illuminators]] used it as an ingredient in [[gesso]], which was applied to illuminated letters and gilded with gold in illuminated manuscripts.<ref>{{cite book |last1=Brown |first1=Michelle |title=Understanding illuminated manuscripts : a guide to technical terms |date=1995 |location=Los Angeles, California|publisher=Yale University Press |isbn=9780892362172 |pages=58}}</ref>

===Food and drink===
*A [[tofu]] (soy bean curd) coagulant, making it ultimately a significant source of dietary [[calcium]].<ref>{{cite book |last1=Shurtleff |first1=William |title=Tofu & soymilk production : a craft and technical manual |date=2000 |publisher=Soyfoods Center |location=Lafayette, CA |isbn=9781928914044|page=99}}</ref>
*Adding [[hard water|hardness]] to water used for [[brewing]].<ref>{{cite web|url=http://www.howtobrew.com/section1/chapter4-2.html| title= Water Chemistry Adjustment for Extract Brewing|access-date=15 December 2008|first= John |last=Palmer |publisher= HowToBrew.com}}</ref>
*Used in baking as a dough conditioner, reducing stickiness, and as a baked goods source of dietary calcium.<ref>{{cite web |url=http://www.usg.com/rc/technical-specifications/fillers/food-grade-calcium-sulfate-for-baking-industry-technical-specifications-en-IG130.pdf |work=United States Gypsum Company |title=Calcium sulphate for the baking industry |access-date=1 March 2013 |archive-url=https://web.archive.org/web/20130704125140/http://www.usg.com/rc/technical-specifications/fillers/food-grade-calcium-sulfate-for-baking-industry-technical-specifications-en-IG130.pdf |archive-date=4 July 2013 |url-status=dead }}</ref> The primary component of mineral yeast food.<ref>{{cite web |url=http://www.lesaffreyeastcorp.com/sites/default/files/products_files/Tech%20Sheet%20-%20RS%20Yeast%20Food.pdf |archive-url=https://web.archive.org/web/20131029185607/http://www.lesaffreyeastcorp.com/sites/default/files/products_files/Tech%20Sheet%20-%20RS%20Yeast%20Food.pdf|work=Lesaffre Yeast Corporation |title=Tech sheet for yeast food |access-date=1 March 2013 |url-status=dead |archive-date=2013-10-29}}</ref>
*Used in mushroom cultivation to stop grains from clumping together.

===Medicine and cosmetics===
*[[Plaster]] for surgical splints.<ref>{{cite journal |last1=Austin |first1=R.T. |title=Treatment of broken legs before and after the introduction of gypsum |journal=Injury |date=March 1983 |volume=14 |issue=5 |pages=389–394 |doi=10.1016/0020-1383(83)90089-X|pmid=6347885 }}</ref>
*Impression plasters in dentistry.<ref>{{cite journal |last1=Drennon |first1=David G. |last2=Johnson |first2=Glen H. |title=The effect of immersion disinfection of elastomeric impressions on the surface detail reproduction of improved gypsum casts |journal=The Journal of Prosthetic Dentistry |date=February 1990 |volume=63 |issue=2 |pages=233–241 |doi=10.1016/0022-3913(90)90111-O|pmid=2106026 }}</ref>

===Other===
*An alternative to iron oxide in some thermite mixes.<ref>{{cite journal |last1=Govender |first1=Desania R. |last2=Focke |first2=Walter W. |last3=Tichapondwa |first3=Shepherd M. |last4=Cloete |first4=William E. |title=Burn Rate of Calcium Sulfate Dihydrate–Aluminum Thermites |journal=ACS Applied Materials & Interfaces |date=20 June 2018 |volume=10 |issue=24 |pages=20679–20687 |doi=10.1021/acsami.8b04205|pmid=29842778 |hdl=2263/66006 |s2cid=206483977 |hdl-access=free }}</ref>
*Tests have shown that gypsum can be used to remove pollutants such as [[lead]]<ref>{{cite journal| doi=10.1016/j.apgeochem.2010.04.007| title=Interaction of gypsum with lead in aqueous solutions| journal=Applied Geochemistry| volume=25| issue=7| pages=1008| year=2010| last1=Astilleros| first1=J.M.| last2=Godelitsas| first2=A.| last3=Rodríguez-Blanco| first3=J.D.| last4=Fernández-Díaz| first4=L.| last5=Prieto| first5=M.| last6=Lagoyannis| first6=A.| last7=Harissopulos| first7=S.| bibcode=2010ApGC...25.1008A| url=https://eprints.ucm.es/18174/1/1000958.pdf |archive-url=https://web.archive.org/web/20170809180523/http://eprints.ucm.es/18174/1/1000958.pdf |archive-date=2017-08-09 |url-status=live}}</ref> or [[arsenic]]<ref>{{cite journal| doi=10.2138/am.2008.2750| title=Interaction of gypsum with As(V)-bearing aqueous solutions: Surface precipitation of guerinite, sainfeldite, and Ca<sub>2</sub>NaH(AsO<sub>4</sub>)<sub>2</sub>⋅6H<sub>2</sub>O, a synthetic arsenate| journal=American Mineralogist| volume=93| issue=5–6| pages=928| year=2008| last1=Rodriguez| first1=J. D.| last2=Jimenez| first2=A.| last3=Prieto| first3=M.| last4=Torre| first4=L.| last5=Garcia-Granda| first5=S.| bibcode=2008AmMin..93..928R| s2cid=98249784}}</ref><ref>{{cite journal| doi=10.1021/cg070222+|title=Oriented Overgrowth of Pharmacolite (CaHAsO<sub>4</sub>⋅2H2O) on Gypsum (CaSO<sub>4</sub>⋅2H<sub>2</sub>O)|author1=Rodríguez-Blanco, Juan Diego |author2=Jiménez, Amalia |author3=Prieto, Manuel  |journal=Cryst. Growth Des.|year= 2007|volume= 7 |issue=12|pages=2756–2763}}
</ref> from contaminated waters.

==Gallery==
<gallery widths="165" heights="130" caption="Unusual gypsum specimens from around the world">
File:Gypsum-71006.jpg|Green gypsum crystals from Pernatty Lagoon, Mt Gunson, [[South Australia]] - its green color is due to presence of [[copper]] ions.
File:Gypsum-162462.jpg|Unusual selenite gypsum from the [[Red River of the North|Red River]], Winnipeg, Manitoba, Canada
File:Gypsum-47190.jpg|Classic "ram's horn" gypsum from [[Santa Eulalia, Chihuahua]], Mexico, 7.5×4.3×3.8&nbsp;cm
File:Roses des Sables Tunisie.jpg|[[Desert rose (crystal)|Desert rose]], 47&nbsp;cm long
File:Gypsum-53691.jpg|Gypsum from Pernatty Lagoon, Mt Gunson, Stuart Shelf area, Andamooka Ranges - Lake Torrens area, South Australia, Australia
File:Copper-Gypsum-203925.jpg|Gypsum with crystalline [[native copper]] inside
File:Gypsum J1.jpg|Gypsum from Swan Hill, Victoria, Australia. The coloring is due to the copper oxide
File:Gypsum-21996.jpg|Waterclear twined crystal of the form known as "Roman sword". Fuentes de Ebro, Zaragoza (Spain)
File:Botryogen-Gypsum-199664.jpg|Bright, cherry-red gypsum crystals 2.5&nbsp;cm in height colored by rich inclusions of the rare mineral [[botryogen]]
File:Gypse Naica.jpg|Gypsum from Naica, Mun. de Saucillo, Chihuahua, Mexico
File:Gypsum-251118.jpg|Golden color gem, "fishtail"-twinned crystals of gypsum sitting atop a "ball" of gypsum which is composed of several single bladed crystals
</gallery>

==See also==
*[[Gypcrust]]
*[[Gypsum flora of Nova Scotia]]
*[[Gypsum recycling]]
*[[Phosphogypsum]]

==References==
{{Reflist|30em}}

==External links==
{{Commons}}
{{wiktionary}}
*[http://webmineral.com/data/Gypsum.shtml WebMineral data]
*[https://web.archive.org/web/20070814041825/http://mineral.galleries.com/minerals/sulfates/gypsum/gypsum.htm Mineral galleries – gypsum]
*[https://www.cdc.gov/niosh/npg/npgd0308.html CDC – NIOSH Pocket Guide to Chemical Hazards]
*{{Cite EB1911|wstitle=Gypsum|short=x}}
*{{Cite AmCyc|wstitle=Gypsum|short=x}}

{{Mohs}}
{{Authority control}}

[[Category:Calcium minerals]]
[[Category:Sulfate minerals]]
[[Category:Sedimentary rocks]]
[[Category:Evaporite]]
[[Category:Alchemical substances]]
[[Category:Monoclinic minerals]]
[[Category:Minerals in space group 15]]
[[Category:Alabaster]]
[[Category:Luminescent minerals]]
[[Category:Industrial minerals]]