Editing Concretion (section)

==Composition==
[[File:Concretions embedded in sandstone in Anza Borrego Desert State Park in California.jpg|thumb|upright|Spherical concretions embedded in sandstone in [[Anza-Borrego Desert State Park]] in the United States]]
Concretions are commonly composed of a mineral present as a minor component of the host rock. For example, concretions in [[sandstone]]s or [[shale]]s are commonly formed of a [[carbonate]] mineral such as [[calcite]]; those in [[limestone]]s are commonly an amorphous or microcrystalline form of [[silica]] such as [[chert]], [[flint]], or [[jasper]]; while those in black shale may be composed of [[pyrite]].{{sfn|Prothero|Schwab|2004|p=118}} Other minerals that form concretions include iron oxides or hydroxides (such as [[goethite]] and [[hematite]]),<ref>{{cite journal |last1=Busigny |first1=Vincent |last2=Dauphas |first2=Nicolas |title=Tracing paleofluid circulations using iron isotopes: A study of hematite and goethite concretions from the Navajo Sandstone (Utah, USA) |journal=Earth and Planetary Science Letters |date=February 2007 |volume=254 |issue=3–4 |pages=272–287 |doi=10.1016/j.epsl.2006.11.038|bibcode=2007E&PSL.254..272B }}</ref><ref>{{cite journal |last1=Parry |first1=W.T. |title=Composition, nucleation, and growth of iron oxide concretions |journal=Sedimentary Geology |date=January 2011 |volume=233 |issue=1–4 |pages=53–68 |doi=10.1016/j.sedgeo.2010.10.009|bibcode=2011SedG..233...53P }}</ref> [[Dolomite (mineral)|dolomite]], [[siderite]],<ref>{{cite journal |last1=Curtis |first1=C.D. |last2=Coleman |first2=M.L. |last3=Love |first3=L.G. |title=Pore water evolution during sediment burial from isotopic and mineral chemistry of calcite, dolomite and siderite concretions |journal=Geochimica et Cosmochimica Acta |date=October 1986 |volume=50 |issue=10 |pages=2321–2334 |doi=10.1016/0016-7037(86)90085-2|bibcode=1986GeCoA..50.2321C }}</ref> [[ankerite]],<ref>{{cite journal |last1=Strickler |first1=Michael E. |title=Fe Substitution for Al in Glauconite with Increasing Diagenesis in the First Wilcox Sandstone (Lower Eocene), Livingston Parish, Louisiana |journal=Clays and Clay Minerals |date=1990 |volume=38 |issue=1 |pages=69–76 |doi=10.1346/CCMN.1990.0380110|bibcode=1990CCM....38...69S |s2cid=140180525 }}</ref> [[marcasite]],<ref>{{cite journal|last1=Van Horn |first1=F.R. |last2=Van Horn |first2=K.R. |year=1933 |title=X-ray study of pyrite or marcasite concretions in the rocks of the Cleveland, Ohio, quadrangles |journal=American Mineralogist|volume=18 |number=7 |pages=288–294 |url=https://pubs.geoscienceworld.org/msa/ammin/article-abstract/18/7/288/536696/X-ray-study-of-pyrite-or-marcasite-concretions-in |access-date=10 August 2021}}</ref> [[barite]],<ref>{{cite journal |last1=Bréhéret |first1=Jean-G. |last2=Brumsack |first2=Hans-J. |title=Barite concretions as evidence of pauses in sedimentation in the Marnes Bleues Formation of the Vocontian Basin (SE France) |journal=Sedimentary Geology |date=February 2000 |volume=130 |issue=3–4 |pages=205–228 |doi=10.1016/S0037-0738(99)00112-8|bibcode=2000SedG..130..205B }}</ref><ref>{{cite journal |last1=Leśniak |first1=P.M. |last2=Łącka |first2=B. |last3=Hladı́kova |first3=J. |last4=Zieliński |first4=G. |title=Origin of barite concretions in the West Carpathian flysch, Poland |journal=Chemical Geology |date=June 1999 |volume=158 |issue=1–2 |pages=155–163 |doi=10.1016/S0009-2541(99)00010-8|bibcode=1999ChGeo.158..155L }}</ref> and [[gypsum]].<ref>{{cite journal |last1=Cruz |first1=Mar&#237 |last2=P&#237 |first2=A |title=Characterization of Gypsum Concretion in Loess: Some Geotechnical Considerations |journal=From Fundamentals to Applications in Geotechnics |date=2015 |issue=From Fundamentals to Applications in Geotechnics |pages=3248–3255 |doi=10.3233/978-1-61499-603-3-3248}}</ref>

Although concretions often consist of a single dominant mineral,{{sfn|Allaby|2013|loc="concretion"}} other minerals can be present depending on the environmental conditions that created them. For example, carbonate concretions, which form in response to the reduction of [[sulfates]] by [[bacteria]], often contain minor percentages of pyrite.<ref>{{cite journal |last1=Coleman |first1=Max L. |title=Microbial processes: Controls on the shape and composition of carbonate concretions |journal=Marine Geology |date=July 1993 |volume=113 |issue=1–2 |pages=127–140 |doi=10.1016/0025-3227(93)90154-N|bibcode=1993MGeol.113..127C }}</ref> Other concretions, which formed as a result of microbial sulfate reduction, consist of a mixture of calcite, barite, and pyrite.<ref>{{cite journal |last1=Raiswell |first1=R. |last2=Bottrell |first2=S. H. |last3=Dean |first3=S. P. |last4=Marshall |first4=J. D. |last5=Carr |first5=A. |last6=Hatfield |first6=D. |title=Isotopic constraints on growth conditions of multiphase calcite-pyrite-barite concretions in Carboniferous mudstones: Diagenetic history of septarian concretions in Carboniferous mudstones |journal=Sedimentology |date=25 April 2002 |volume=49 |issue=2 |pages=237–254 |doi=10.1046/j.1365-3091.2002.00439.x|s2cid=129664903 }}</ref>