Editing Concretion (section)

==Origins==
[[File:Concretion_rock_from_Middle_Jurassic_of_Iran.jpg|thumb|Concretion rock with white core from the Middle Jurassic of Iran]]
Detailed studies have demonstrated that concretions form after sediments are buried but before the sediment is fully lithified during [[diagenesis]].<ref>{{Cite journal|title=The Moeraki Boulders; anatomy of some septarian concretions|url=https://pubs.geoscienceworld.org/sepm/jsedres/article-abstract/55/3/398/97797/the-moeraki-boulders-anatomy-of-some-septarian|journal=Journal of Sedimentary Research|date=1985-05-01|issn=1527-1404|pages=398–406|volume=55|issue=3|doi=10.1306/212F86E3-2B24-11D7-8648000102C1865D|language=en|first1=P.|last1=Dale|first2=C. A.|last2=Landis|first3=J. R.|last3=Boles|url-access=subscription}}</ref><ref>{{Cite journal|title=Isotopic evidence for origin of the Moeraki septarian concretions, New Zealand|url=https://pubs.geoscienceworld.org/sepm/jsedres/article-abstract/59/2/272/113809/isotopic-evidence-for-origin-of-the-moeraki|journal=Journal of Sedimentary Research|date=1989-03-01|issn=1527-1404|pages=272–279|volume=59|issue=2|doi=10.1306/212F8F6C-2B24-11D7-8648000102C1865D|language=en|first1=James R.|last1=Boles|first2=Geoffrey D.|last2=Thyne|url-access=subscription}}</ref><ref>{{Cite journal|title=The geochemistry of concretions from the Kimmeridge Clay Formation of southern and eastern England|journal=Sedimentology|date=1991|issn=1365-3091|pages=79–106|volume=38|issue=1|doi=10.1111/j.1365-3091.1991.tb01856.x|language=en|first=I. C.|last=Scotchman|bibcode=1991Sedim..38...79S}}</ref><ref>{{cite journal |last1=Mozley |first1=Peter S. |last2=Burns |first2=Stephen J. |title=Oxygen and Carbon Isotopic Composition of Marine Carbonate Concretions: An Overview |journal=SEPM Journal of Sedimentary Research |date=1993 |volume=63 |doi=10.1306/D4267A91-2B26-11D7-8648000102C1865D |url=https://www.researchgate.net/publication/279585759 |access-date=19 August 2021}}</ref><ref>{{cite journal|title=Calcite-Cemented Concretions in Cretaceous Sandstone, Wyoming and Utah, U.S.A.|url=https://pubs.geoscienceworld.org/sepm/jsedres/article-abstract/73/3/462/99315/calcite-cemented-concretions-in-cretaceous|journal=Journal of Sedimentary Research|date=2003-05-01|issn=1527-1404|pages=462–483|volume=73|issue=3|doi=10.1306/111602730462|language=en|first1=Kitty L.|last1=Milliken|first2=M. Dane|last2=Picard|first3=Earle F.|last3=McBride|bibcode=2003JSedR..73..462M|url-access=subscription}}</ref><ref>{{cite journal|title=Internal structure and mode of growth of elongate calcite concretions: Evidence for small-scale, microbially induced, chemical heterogeneity in groundwater|journal=GSA Bulletin|date=2005-11-01|issn=0016-7606|pages=1400–1412|volume=117|issue=11–12|doi=10.1130/B25618.1|language=en|first1=J. Matthew|last1=Davis|first2=Peter S.|last2=Mozley|bibcode=2005GSAB..117.1400M}}</ref> They typically form when a mineral precipitates and cements sediment around a nucleus, which is often organic, such as a leaf, tooth, piece of shell or [[fossil]]. For this reason, fossil collectors commonly break open concretions in their search for fossil animal and plant specimens.<ref>{{cite book |last1=Prothero |first1=Donald R. |last2=Schwab |first2=Fred |title=Sedimentary geology : an introduction to sedimentary rocks and stratigraphy |date=2004 |publisher=W.H. Freeman |location=New York |isbn=0716739054 |page=118 |edition=2nd}}</ref> Some of the most unusual concretion nuclei are [[World War II]] military [[Shell (projectile)|shells]], [[bomb]]s, and [[Shrapnel shell|shrapnel]], which are found inside [[siderite]] concretions found in an English coastal [[salt marsh]].<ref>{{cite journal|title=Complex cementation textures and authigenic mineral assemblages in Recent concretions from the Lincolnshire Wash (east coast, UK) driven by Fe(0) to Fe(II) oxidation|url=http://iugspace.iugaza.edu.ps/xmlui/bitstream/handle/20.500.12358/26050/Al-Aghaetal1995RecentconcretionsfromtheWash.pdf?sequence=1&isAllowed=y|journal=Journal of the Geological Society|date=1995-02-01|issn=0016-7649|pages=157–171|volume=152|issue=1|doi=10.1144/gsjgs.152.1.0157|language=en|first1=J.|last1=Esson|first2=C. D.|last2=Curtis|first3=S. D.|last3=Burley|first4=M. R.|last4=Al-AGHA |bibcode=1995JGSoc.152..157A |s2cid=129359274|archive-url=https://web.archive.org/web/20191213005520/http://iugspace.iugaza.edu.ps/xmlui/bitstream/handle/20.500.12358/26050/Al-Aghaetal1995RecentconcretionsfromtheWash.pdf?sequence=1&isAllowed=y|archive-date=2019-12-13|url-status=dead}}</ref>

Depending on the environmental conditions present at the time of their formation, concretions can be created by either concentric or pervasive growth.<ref>{{cite journal|title=Relationship between oriented calcite concretions and permeability correlation structure in an alluvial aquifer, Sierra Ladrones Formation, New Mexico|url=https://pubs.geoscienceworld.org/sepm/jsedres/article-abstract/66/1/11/98701/relationship-between-oriented-calcite-concretions|journal=Journal of Sedimentary Research|date=1996-01-01|issn=1527-1404|pages=11–16|volume=66|issue=1|doi=10.1306/D4268293-2B26-11D7-8648000102C1865D|language=en|first1=J. Matthew|last1=Davis|first2=Peter S.|last2=Mozley|url-access=subscription}}</ref><ref>{{Cite journal|title=Mudrock-hosted carbonate concretions: a review of growth mechanisms and their influence on chemical and isotopic composition|url=https://jgs.lyellcollection.org/content/157/1/239|journal=Journal of the Geological Society|date=2000-01-01|issn=0016-7649|pages=239–251|volume=157|issue=1|doi=10.1144/jgs.157.1.239|language=en|first1=Q. J.|last1=Fisher|first2=R.|last2=Raiswell|bibcode=2000JGSoc.157..239R|s2cid=128897857|url-access=subscription}}</ref> In concentric growth, the concretion grows as successive layers of mineral precipitate around a central core. This process results in roughly spherical concretions that grow with time. In the case of pervasive growth, cementation of the host [[sediments]], by infilling of its pore space by precipitated minerals, occurs simultaneously throughout the volume of the area, which in time becomes a concretion. Concretions are often exposed at the surface by subsequent erosion that removes the weaker, uncemented material.