Editing Calcium carbonate (section)

== Polymorphs ==
Calcium carbonate crystallizes in three [[anhydrous]] [[Polymorphism (materials science)|polymorphs]],<ref>{{Cite journal |last1=Morse |first1=John W. |last2=Arvidson |first2=Rolf S. |last3=Lüttge |first3=Andreas |date=2007-02-01 |title=Calcium Carbonate Formation and Dissolution |url=https://pubs.acs.org/doi/10.1021/cr050358j |journal=Chemical Reviews |language=en |volume=107 |issue=2 |pages=342–381 |doi=10.1021/cr050358j |pmid=17261071 |issn=0009-2665 |access-date=15 December 2022 |archive-date=1 December 2022 |archive-url=https://web.archive.org/web/20221201024832/https://pubs.acs.org/doi/10.1021/cr050358j |url-status=live}}</ref><ref>{{Cite book |last=Lippmann|first= Friedrich |title=Sedimentary carbonate minerals |date=1973 |publisher=Springer |isbn=3-540-06011-1 |oclc=715109304}}</ref> of which [[calcite]] is the thermodynamically most stable at room temperature, [[aragonite]] is only slightly less so, and [[vaterite]] is the least stable.<ref name="Nahi-2022">{{Cite journal |last1=Nahi |first1=Ouassef |last2=Kulak |first2=Alexander N. |last3=Zhang |first3=Shuheng |last4=He |first4=Xuefeng |last5=Aslam |first5=Zabeada |last6=Ilett |first6=Martha A. |last7=Ford |first7=Ian J. |last8=Darkins |first8=Robert |last9=Meldrum |first9=Fiona C. |date=2022-11-20 |title=Polyamines Promote Aragonite Nucleation and Generate Biomimetic Structures |journal=Advanced Science |volume=10 |issue=1 |page=2203759 |doi=10.1002/advs.202203759 |pmid=36403251 |pmc=9811428 |s2cid=253707446 |issn=2198-3844}}</ref>

=== Crystal structure ===
The [[calcite]] crystal structure is [[trigonal]], with [[space group]] R{{overline|3}}c (No. 167 in the International Tables for Crystallography<ref>{{cite book | title=International tables for crystallography. | publisher=International Union of Crystallography | publication-place=Chester, England | date=2006 | isbn=978-0-7923-6590-7 | oclc=166325528 | doi = 10.1107/97809553602060000001| s2cid=146060934 | editor-last1=Welberry | editor-first1=T. R}}</ref>), and [[Pearson symbol]] hR10.<ref>{{Cite journal |last1=Chessin |first1=H. |last2=Hamilton |first2=W. C. |last3=Post |first3=B. |date=1965-04-01 |title=Position and thermal parameters of oxygen atoms in calcite |url=https://scripts.iucr.org/cgi-bin/paper?S0365110X65001585 |journal=Acta Crystallographica |volume=18 |issue=4 |pages=689–693 |doi=10.1107/S0365110X65001585 |bibcode=1965AcCry..18..689C |issn=0365-110X |access-date=15 December 2022 |archive-date=15 December 2022 |archive-url=https://web.archive.org/web/20221215201234/https://scripts.iucr.org/cgi-bin/paper?S0365110X65001585 |url-status=live}}</ref> [[Aragonite]] is [[Orthorhombic crystal system|orthorhombic]], with space group Pmcn (No 62), and Pearson Symbol oP20.<ref>{{Cite journal |last=Negro |first=AD |date=1971 |title=Refinement of the crystal structure of aragonite |url=http://www.minsocam.org/ammin/AM56/AM56_768.pdf |journal=American Mineralogist: Journal of Earth and Planetary Materials |volume=56 |pages=768–772 |via=GeoScienceWorld |access-date=15 December 2022 |archive-date=15 December 2022 |archive-url=https://web.archive.org/web/20221215200845/http://www.minsocam.org/ammin/AM56/AM56_768.pdf |url-status=live}}</ref> [[Vaterite]] is composed of at least two different coexisting crystallographic structures. The major structure exhibits [[Hexagonal crystal family|hexagonal]] symmetry in space group P6<sub>3</sub>/mmc, the minor structure is still unknown.<ref>{{Cite journal |last1=Kabalah-Amitai |first1=Lee |last2=Mayzel |first2=Boaz |last3=Kauffmann |first3=Yaron |last4=Fitch |first4=Andrew N. |last5=Bloch |first5=Leonid |last6=Gilbert |first6=Pupa U. P. A. |last7=Pokroy |first7=Boaz |date=2013-04-26 |title=Vaterite Crystals Contain Two Interspersed Crystal Structures |journal=Science |volume=340 |issue=6131 |pages=454–457 |doi=10.1126/science.1232139 |pmid=23620047 |bibcode=2013Sci...340..454K |s2cid=206546317 |issn=0036-8075}}</ref>

=== Crystallization ===
[[File:Calcite+Aragonite.png|thumb|234x234px|Crystal structure of calcite and aragonite]]
All three polymorphs crystallize simultaneously from aqueous solutions under ambient conditions.<ref name="Nahi-2022" /> In additive-free aqueous solutions, calcite forms easily as the major product, while aragonite appears only as a minor product.

At high saturation, vaterite is typically the first phase precipitated, which is followed by a transformation of the vaterite to calcite.<ref>{{Cite journal |last1=Bots |first1=Pieter |last2=Benning |first2=Liane G. |last3=Rodriguez-Blanco |first3=Juan-Diego |last4=Roncal-Herrero |first4=Teresa |last5=Shaw |first5=Samuel |date=2012-07-03 |title=Mechanistic Insights into the Crystallization of Amorphous Calcium Carbonate (ACC) |url=https://pubs.acs.org/doi/10.1021/cg300676b |journal=Crystal Growth & Design |language=en |volume=12 |issue=7 |pages=3806–3814 |doi=10.1021/cg300676b |issn=1528-7483 |access-date=15 December 2022 |archive-date=15 December 2022 |archive-url=https://web.archive.org/web/20221215200842/https://pubs.acs.org/doi/10.1021/cg300676b |url-status=live}}</ref> This behavior seems to follow [[Ostwald's rule]], in which the least stable polymorph crystallizes first, followed by the crystallization of different polymorphs via a sequence of increasingly stable phases.<ref>{{Cite journal |last1=Cardew |first1=Peter T. |last2=Davey |first2=Roger J. |date=2019-10-02 |title=The Ostwald Ratio, Kinetic Phase Diagrams, and Polymorph Maps |url=https://pubs.acs.org/doi/10.1021/acs.cgd.9b00815 |journal=Crystal Growth & Design |language=en |volume=19 |issue=10 |pages=5798–5810 |doi=10.1021/acs.cgd.9b00815 |s2cid=202885778 |issn=1528-7483 |access-date=15 December 2022 |archive-date=15 December 2022 |archive-url=https://web.archive.org/web/20221215201316/https://pubs.acs.org/doi/10.1021/acs.cgd.9b00815 |url-status=live}}</ref> However, aragonite, whose stability lies between those of vaterite and calcite, seems to be the exception to this rule, as aragonite does not form as a precursor to calcite under ambient conditions.<ref name="Nahi-2022"/>
[[File:Calcite+Vaterite.png|thumb|Microscopic calcite and vaterite]]
Aragonite occurs in majority when the reaction conditions inhibit the formation of calcite and/or promote the nucleation of aragonite. For example, the formation of aragonite is promoted by the presence of magnesium ions,<ref>{{Cite journal |last1=Zhang |first1=Shuheng |last2=Nahi |first2=Ouassef |last3=Chen |first3=Li |last4=Aslam |first4=Zabeada |last5=Kapur |first5=Nikil |last6=Kim |first6=Yi-Yeoun |last7=Meldrum |first7=Fiona C. |date=June 2022 |title=Magnesium Ions Direct the Solid-State Transformation of Amorphous Calcium Carbonate Thin Films to Aragonite, Magnesium-Calcite, or Dolomite |url=https://onlinelibrary.wiley.com/doi/10.1002/adfm.202201394 |journal=Advanced Functional Materials |language=en |volume=32 |issue=25 |page=2201394 |doi=10.1002/adfm.202201394 |s2cid=247587883 |issn=1616-301X |access-date=15 December 2022 |archive-date=15 December 2022 |archive-url=https://web.archive.org/web/20221215200840/https://onlinelibrary.wiley.com/doi/10.1002/adfm.202201394 |url-status=live}}</ref> or by using proteins and peptides derived from biological calcium carbonate.<ref>{{Cite journal |last1=Metzler |first1=Rebecca A. |last2=Evans |first2=John Spencer |last3=Killian |first3=Christopher E. |last4=Zhou |first4=Dong |last5=Churchill |first5=Tyler H. |last6=Appathurai |first6=Narayana P. |last7=Coppersmith |first7=Susan N. |last8=Gilbert |first8=P. U. P. A. |date=2010-05-12 |title=Nacre Protein Fragment Templates Lamellar Aragonite Growth |url=https://pubs.acs.org/doi/10.1021/ja909735y |journal=Journal of the American Chemical Society |language=en |volume=132 |issue=18 |pages=6329–6334 |doi=10.1021/ja909735y |pmid=20397648 |issn=0002-7863 |access-date=15 December 2022 |archive-date=15 December 2022 |archive-url=https://web.archive.org/web/20221215200841/https://pubs.acs.org/doi/10.1021/ja909735y |url-status=live}}</ref> Some polyamines such as [[cadaverine]] and [[Polyethylenimine|Poly(ethylene imine)]] have been shown to facilitate the formation of aragonite over calcite.<ref name="Nahi-2022"/>

=== Selection by organisms ===
Organisms, such as [[mollusca|molluscs]] and [[arthropod]]s, have shown the ability to grow all three crystal polymorphs of calcium carbonate, mainly as protection (shells) and muscle attachments.<ref>{{Cite book |last1=Lowenstam |first1=H.A. |title=On Biomineralization |last2=Weiner |first2=S. |publisher=Oxford University Press |year=1989 |isbn=978-0-19-504977-0}}</ref> Moreover, they exhibit a remarkable capability of phase selection over calcite and aragonite, and some organisms can switch between the two polymorphs. The ability of phase selection is usually attributed to the use of specific macromolecules or combinations of macromolecules by such organisms.<ref>{{Cite journal |last1=Belcher |first1=A. M. |last2=Wu |first2=X. H. |last3=Christensen |first3=R. J. |last4=Hansma |first4=P. K. |last5=Stucky |first5=G. D. |last6=Morse |first6=D. E. |date=May 1996 |title=Control of crystal phase switching and orientation by soluble mollusc-shell proteins |url=https://www.nature.com/articles/381056a0 |journal=Nature |language=en |volume=381 |issue=6577 |pages=56–58 |doi=10.1038/381056a0 |bibcode=1996Natur.381...56B |s2cid=4285912 |issn=1476-4687 |access-date=15 December 2022 |archive-date=15 December 2022 |archive-url=https://web.archive.org/web/20221215212206/https://www.nature.com/articles/381056a0 |url-status=live}}</ref><ref>{{Cite journal |last1=Falini |first1=Giuseppe |last2=Albeck |first2=Shira |last3=Weiner |first3=Steve |last4=Addadi |first4=Lia |date=1996-01-05 |title=Control of Aragonite or Calcite Polymorphism by Mollusk Shell Macromolecules |url=https://www.science.org/doi/10.1126/science.271.5245.67 |journal=Science |language=en |volume=271 |issue=5245 |pages=67–69 |doi=10.1126/science.271.5245.67 |bibcode=1996Sci...271...67F |s2cid=95357556 |issn=0036-8075 |access-date=15 December 2022 |archive-date=15 December 2022 |archive-url=https://web.archive.org/web/20221215212206/https://www.science.org/doi/10.1126/science.271.5245.67 |url-status=live}}</ref><ref>{{Cite journal |last=Marin |first=Frédéric |date=October 2020 |title=Mollusc shellomes: Past, present and future |journal=Journal of Structural Biology |language=en |volume=212 |issue=1 |page=107583 |doi=10.1016/j.jsb.2020.107583|pmid=32721585 |s2cid=220850117|doi-access=free}}</ref>