Editing Concretion (section)

==Appearance==
[[File:Rock concretions from Hells Hollow State Park, Pennsylvania.jpg|thumb|Samples of small rock concretions found at [[McConnells Mill State Park]] in Pennsylvania]]
Concretions vary in shape, hardness and size, ranging from objects that require a magnifying lens to be clearly visible<ref>{{cite book |last1=Allaby |first1=Michael |title=A dictionary of geology and earth sciences |date=2013 |publisher=Oxford University Press |location=Oxford |isbn=9780199653065 |edition=Fourth |chapter=concretion}}</ref> to huge bodies three meters in diameter and weighing several thousand pounds.<ref>{{cite book |last1=Boggs |first1=Sam |title=Principles of sedimentology and stratigraphy |date=2006 |publisher=Pearson Prentice Hall |location=Upper Saddle River, N.J. |isbn=0131547283 |edition=4th |page=114}}</ref> The giant, red concretions occurring in [[Theodore Roosevelt National Park]], in [[North Dakota]], are almost {{convert|3|m|ft|abbr=on|sp=us}} in diameter.<ref>{{cite web |url=http://www.parkrec.nd.gov/byways/theodore/theodore.html |title=Theodore Roosevelt National Park North Unit Scenic Byway |access-date=2012-05-13 |url-status=dead |archive-url=https://web.archive.org/web/20120508204512/http://www.parkrec.nd.gov/byways/theodore/theodore.html |archive-date=2012-05-08 }}</ref> Spheroidal concretions, as large as {{convert|9|m|ft|abbr=on|sp=us}} in diameter, have been found eroding out of the [[Qasr el Sagha Formation]] within the [[Faiyum depression]] of Egypt.<ref>{{cite journal |last1=Abdel-Wahab |first1=A. |last2=McBride |first2=E. F. |title=Origin of Giant Calcite-Cemented Concretions, Temple Member, Qasr El Sagha Formation (Eocene), Faiyum Depression, Egypt |journal=Journal of Sedimentary Research |date=1 January 2001 |volume=71 |issue=1 |pages=70–81 |doi=10.1306/031700710070|bibcode=2001JSedR..71...70A }}</ref> Concretions occur in a wide variety of shapes, including spheres, disks, tubes, and grape-like or soap bubble-like [[Aggregate (geology)|aggregate]]s.<ref>{{cite journal |last1=Todd |first1=J. E. |title=Concretions and their geological effects |journal=Geological Society of America Bulletin |date=1 January 1903 |volume=14 |issue=1 |pages=353–368 |doi=10.1130/GSAB-14-353|bibcode=1903GSAB...14..353T |url=https://zenodo.org/record/1671335 }}</ref>