Editing Chert (section)

===Other occurrences===
The [[banded iron formation]]s of [[Precambrian]] age are composed of alternating layers of chert and [[iron oxide]]s.{{sfn|Boggs|2006|pp=217-218}}{{sfn|Blatt|Tracy|1996|pp=339-343}}

Nonmarine cherts may form in saline alkaline lakes as thin lenses or nodules showing sedimentary structures suggestive of [[evaporite]] origin. Such cherts are forming today in the alkaline lakes of the [[East African Rift Valley]].{{sfn|Blatt|Tracy|1996|pp=336-337}} These lakes are characterized by [[sodium carbonate]] brines with very high [[pH]] that can contain as much as 2700 ppm silica. Episodes of runoff of fresh water into the lakes lowers the pH and precipitates the unusual [[sodium silicate]] minerals [[magadiite]] or [[kenyaite]], After burial and [[diagenesis]], these are altered to Magadi-type chert.{{sfn|Blatt|Middleton|Murray|1980|p=576}} The [[Morrison Formation]] contains Magadi-type chert that may have formed in the alkaline Lake T'oo'dichi'.<ref>{{cite journal |last1=Dunagan |first1=Stan P |last2=Turner |first2=Christine E |title=Regional paleohydrologic and paleoclimatic settings of wetland/lacustrine depositional systems in the Morrison Formation (Upper Jurassic), Western Interior, USA |journal=Sedimentary Geology |date=May 2004 |volume=167 |issue=3–4 |pages=269–296 |doi=10.1016/j.sedgeo.2004.01.007|bibcode=2004SedG..167..269D }}</ref>

Chert may also form from replacement of [[calcrete]] in fossil soils ([[paleosols]]) by silica dissolved from overlying [[volcanic ash]] beds.<ref>{{cite journal |last1=Smith |first1=Gary A. |last2=Huckell |first2=Bruce B. |title=The geological and geoarchaeological significance of Cerro Pedernal, Rio Arriba County, New Mexico |journal=New Mexico Geological Society Field Conference Series |date=2005 |volume=56 |page=427 |url=https://nmgs.nmt.edu/publications/guidebooks/downloads/56/56_p0425_p0431.pdf |access-date=10 July 2021}}</ref>