Editing Concretion (section)

===Moqui Marbles===
[[Image:MoquiMarble1.jpg|thumb|Moqui Marbles, hematite, goethite concretions, from the Navajo Sandstone of southeast Utah. The "W" cube at the top is one cubic centimeter in size.|left]]
[[Moqui Marbles]], also called Moqui balls or "Moki marbles", are iron oxide concretions which can be found eroding in great abundance out of outcrops of the [[Navajo Sandstone]] within south-central and southeastern Utah. These concretions range in shape from spheres to discs, buttons, spiked balls, cylindrical forms, and other odd shapes. They range from pea-size to baseball-size.<ref name=ChanParry2002>{{cite journal |last1=Chan |first1=M.A. |first2=W.T. |last2=Parry |year=2002 |title=Mysteries of Sandstone Colors and Concretions in Colorado Plateau Canyon Country |journal=Utah Geological Survey Public Information Series |volume=77 |pages=1–19 |url=https://ugspub.nr.utah.gov/publications/public_information/PI-77.pdf |access-date=18 August 2021}}</ref><ref name="Catling2004">{{cite journal |last1=Catling |first1=David C. |title=On Earth, as it is on Mars? |journal=Nature |date=June 2004 |volume=429 |issue=6993 |pages=707–708 |doi=10.1038/429707a|pmid=15201892 |s2cid=4393420 |doi-access=free }}</ref>

The concretions were created by the precipitation of iron, which was dissolved in groundwater. The iron was originally present as a thin film of iron oxide surrounding sand grains in the Navajo Sandstone. Groundwater containing [[methane]] or [[petroleum]] from underlying rock beds reacted with the iron oxide, converting it to soluble [[reduced iron]]. When the iron-bearing groundwater came into contact with more oxygen-rich groundwater, the reduced iron was converted back to insoluble iron oxide, which formed the concretions.<ref name=ChanParry2002/><ref name="Catling2004"/><ref>{{cite journal |last1=Chan |first1=M.A. |first2=B.B. |last2=Beitler |first3=W.T. |last3=Parry |first4=J. |last4=Ormo |first5=G. |last5=Komatsu |year=2005 |title=Red Rock and Red Planet Diagenesis: Comparison of Earth and Mars Concretions |journal=GSA Today |volume=15 |number=8 |pages=4–10 |doi=10.1130/1052-5173(2005)015[4:RRARPD]2.0.CO;2 |url=https://www.geosociety.org/gsatoday/archive/15/8/pdf/i1052-5173-15-8-4.pdf |access-date=18 August 2021}}</ref> It is possible that reduced iron first formed [[siderite]] concretions that were subsequently oxidized. [[Iron-oxidizing bacteria]] may have played a role.<ref>{{cite journal |last1=Loope |first1=David B. |last2=Kettler |first2=Richard M. |last3=Weber |first3=Karrie A. |title=Morphologic Clues to the Origins of Iron Oxide–Cemented Spheroids, Boxworks, and Pipelike Concretions, Navajo Sandstone of South-Central Utah, U.S.A. |journal=The Journal of Geology |date=September 2011 |volume=119 |issue=5 |pages=505–520 |doi=10.1086/661110|bibcode=2011JG....119..505L |s2cid=10139364 |url=http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1197&context=bioscifacpub |url-access=subscription }}</ref>