Editing Calcium carbonate (section)

==Occurrence==
[[File:Silfurberg.jpg|thumb|[[Calcite]] is the most stable [[polymorphism (materials science)|polymorph]] of calcium carbonate. It is transparent to opaque. A transparent variety called [[Iceland spar]] (shown here) was used to create [[polarized light]] in the 19th century.<ref name="Russell2008">Russell, Daniel E . 17 February 2008. Retrieved December 31, 2010. "[http://www.mindat.org/article.php/190/Helgustadir+Iceland+Spar+Mine Helgustadir Iceland Spar Mine] {{Webarchive|url=https://web.archive.org/web/20190508192834/https://www.mindat.org/article.php/190/Helgustadir+Iceland+Spar+Mine |date=8 May 2019}}" ''[[mindat.org]]''</ref>]]

===Geological sources===
[[Calcite]], [[aragonite]] and [[vaterite]] are pure calcium carbonate minerals. Industrially important source rocks which are predominantly calcium carbonate include [[limestone]], [[chalk]], [[marble]] and [[travertine]].

===Biological sources===
[[File:Calcium carbonate chunks.JPG|thumb|Calcium carbonate chunks from [[clam]]shell]]
[[Eggshell]]s, [[snail]] shells and most [[seashell]]s are predominantly calcium carbonate and can be used as industrial sources of that chemical.<ref>{{cite web |title=How are seashells created? |last=Horne |first=Francis |date=23 October 2006 |website=Scientific American |access-date=25 April 2012 |url=http://www.scientificamerican.com/article.cfm?id=how-are-seashells-created |archive-date=19 March 2011 |archive-url=https://web.archive.org/web/20110319230625/http://www.scientificamerican.com/article.cfm?id=how-are-seashells-created |url-status=live}}</ref> [[Oyster]] shells have enjoyed recent recognition as a source of dietary calcium, but are also a practical industrial source.<ref>{{cite web |url=http://www.webmd.com/drugs/drug-16642-Natural+Oyster+Shell+Calcium+Oral.aspx?drugid=16642&drugname=Natural+Oyster+Shell+Calcium+Oral| title=Oyster shell calcium |website=WebMD| access-date=25 April 2012}}</ref><ref>{{cite web|title=Oyster Shell Calcium Carbonate|publisher=Caltron Clays & Chemicals|url=http://caltronclays.in/Oyster_CC.html|access-date=25 April 2012|archive-url=https://web.archive.org/web/20130910033017/http://caltronclays.in/Oyster_CC.html|archive-date=10 September 2013}}</ref> Dark [[green vegetables]] such as [[broccoli]] and [[kale]] contain dietarily significant amounts of calcium carbonate, but they are not practical as an industrial source.<ref>{{cite journal|last=Mangels|first=Ann Reed|date=June 4, 2014|title=Bone nutrients for vegetarians|journal=The American Journal of Clinical Nutrition|volume=100|issue=1|pages=469S–475S|doi=10.3945/ajcn.113.071423|pmid=24898231|doi-access=free}}</ref>

[[Annelid]]s in the family [[Lumbricidae]], earthworms, possess a regionalization of the digestive track called [[calciferous glands]], Kalkdrüsen, or glandes de Morren, that processes calcium and [[Carbon dioxide|{{chem2|CO2}}]] into calcium carbonate, which is later excreted into the dirt.<ref>{{Cite web |title=The Function of the Calciferous Glands of Earthworms |url=https://journals.biologists.com/jeb/article/13/3/279/4425/The-Function-of-the-Calciferous-Glands-of |access-date=2024-02-05 |website=The company of biologists |archive-date=5 February 2024 |archive-url=https://web.archive.org/web/20240205140813/https://journals.biologists.com/jeb/article/13/3/279/4425/The-Function-of-the-Calciferous-Glands-of |url-status=live}}</ref> The function of these glands is unknown but is believed to serve as a {{chem2|CO2}} regulation mechanism within the animals' tissues.<ref>{{Cite journal |title=Stable isotopes reveal that the calciferous gland of earthworms is a CO2-fixing organ |url=https://www.sciencedirect.com/science/article/pii/S0038071707003872 |access-date=2024-02-05 |journal=Soil Biology and Biochemistry |date=2008 |doi=10.1016/j.soilbio.2007.09.012 |archive-date=29 January 2012 |archive-url=https://web.archive.org/web/20120129144311/http://www.sciencedirect.com/science/article/pii/S0038071707003872 |url-status=live |last1=Briones |first1=María Jesús Iglesias |last2=Ostle |first2=Nicholas J. |last3=Piearce |first3=Trevor G. |volume=40 |issue=2 |pages=554–557 }}</ref> This process is ecologically significant, stabilizing the [[Soil pH|pH of acid soils]].<ref>{{Cite web |title=Ecological functions of earthworms in soil |url=https://edepot.wur.nl/352649 |access-date=2024-02-05 |website=eDepot |archive-date=5 February 2024 |archive-url=https://web.archive.org/web/20240205140817/https://edepot.wur.nl/352649 |url-status=live}}</ref>

===Extraterrestrial===
Beyond Earth, strong evidence suggests the presence of calcium carbonate on [[Mars]]. Signs of calcium carbonate have been detected at more than one location (notably at [[Gusev crater|Gusev]] and [[Huygens (crater)|Huygens]] craters). This provides some evidence for the past presence of liquid water.<ref>{{cite journal | last1=Boynton | first1=W. V. | last2=Ming | first2=D. W. | last3=Kounaves | first3=S. P. | last4=Young | first4=S. M. | last5=Arvidson | first5=R. E. | last6=Hecht | first6=M. H. | last7=Hoffman | first7=J. | last8=Niles | first8=P. B. | last9=Hamara | first9=D. K. | last10=Quinn | first10=R. C. | last11=Smith | first11=P. H. | last12=Sutter | first12=B. | last13=Catling | first13=D. C. | last14=Morris | first14=R. V. | title=Evidence for Calcium Carbonate at the Mars Phoenix Landing Site | url=http://planetary.chem.tufts.edu/Boynton%20etal%20Science%202009v325p61.pdf | journal=Science | volume=325 | issue=5936 | pages=61–64 | year=2009 | pmid=19574384 | bibcode=2009Sci...325...61B | display-authors=3 | doi=10.1126/science.1172768 | s2cid=26740165 | access-date=7 January 2015 | archive-date=5 March 2016 | archive-url=https://web.archive.org/web/20160305022836/http://planetary.chem.tufts.edu/Boynton%20etal%20Science%202009v325p61.pdf | url-status=live}}</ref><ref name=Clark2007>{{cite journal |last1 = Clark |first1 = B. C. III |year = 2007 |title = Evidence for montmorillonite or its compositional equivalent in Columbia Hills, Mars |journal = [[Journal of Geophysical Research]] |volume = 112 |issue = E6 |pages = E06S01 |doi = 10.1029/2006JE002756 |last2 = Arvidson |first2 = R. E. |last3 = Gellert |first3 = R. |last4 = Morris |first4 = R. V. |last5 = Ming |first5 = D. W. |last6 = Richter |first6 = L. |last7 = Ruff |first7 = S. W. |last8 = Michalski |first8 = J. R. |last9 = Farrand |first9 = W. H. |last10 = Yen |first10 = A. |last11 = Herkenhoff |first11 = K. E. |last12 = Li |first12 = R. |last13 = Squyres |first13 = S. W. |last14 = Schröder |first14 = C. |last15 = Klingelhöfer |first15 = G. |last16 = Bell |first16 = J. F. |bibcode = 2007JGRE..112.6S01C |url = http://dspace.stir.ac.uk/bitstream/1893/17119/1/Clark2007_Evidence_for_montmorillonite_or_its_compositional_equivalent_in_Columbia_Hills_Mars.pdf |hdl = 1893/17119 |hdl-access = free |access-date = 20 April 2018 |archive-date = 29 July 2018 |archive-url = https://web.archive.org/web/20180729112107/https://dspace.stir.ac.uk/bitstream/1893/17119/1/Clark2007_Evidence_for_montmorillonite_or_its_compositional_equivalent_in_Columbia_Hills_Mars.pdf |url-status = live}}</ref>