Editing Gypsum (section)

==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>