Editing Chert (section)

====Subvarieties====
Bedded cherts can be further subdivided by the kinds of organisms that produced the silica skeletons.{{sfn|Boggs|2006|p=208}}

''Diatomaceous chert'' consists of beds and lenses of [[diatomite]] which were converted during [[diagenesis]] into dense, hard chert. Beds of marine diatomaceous chert comprising [[strata]] several hundred meters thick have been reported from sedimentary sequences such as the [[Miocene]] [[Monterey Formation]] of California and occur in rocks as old as the [[Cretaceous]]. Diatoms were the dominant siliceous organism responsible for extracting silica from seawater from the [[Jurassic]] and later.{{sfn|Boggs|2006|pp=208-209}}

''[[Radiolarite]]'' consists mostly of remains of radiolarians. When the remains are well-cemented with silica, it is known as ''radiolarian chert''.{{sfn|Boggs|2006|pp=209-210}} Many show evidence of a deep-water origin, but some appear to have formed in water as shallow as {{convert|200|m||sp=us}},{{sfn|Boggs|2006|p=210}} perhaps in [[shelf sea]]s where upwelling of nutrient-rich deep ocean water support high organic productivity.{{sfn|Blatt|Tracy|1996|p=336}} Radiolarians dominated the extraction of silica from seawater prior to the Jurassic.{{sfn|Boggs|2006|p=213}}

''Spicularite'' is chert composed of spicules of glass sponges and other invertebrates. When densely cemented, it is known as ''spicular chert''. They are found in association with [[glauconite]]-rich [[sandstone]], [[black shale]], [[clay]]-rich [[limestone]], [[phosphorite]]s, and other nonvolcanic rocks typical of water a few hundred meters deep.{{sfn|Boggs|2006|p=210}}

Some bedded cherts appear devoid of fossils even under close microscopic examination. Their origin is uncertain, but they may form from fossil remains that are completely dissolved in fluids that then migrate to precipitate their silica load in a nearby bed.<ref>{{cite journal |last1=Murray |first1=Richard W. |last2=Jones |first2=David L. |last3=Brink |first3=Marilyn R. Buchholtz ten |title=Diagenetic formation of bedded chert: Evidence from chemistry of the chert-shale couplet |journal=Geology |date=1 March 1992 |volume=20 |issue=3 |pages=271–274 |doi=10.1130/0091-7613(1992)020<0271:DFOBCE>2.3.CO;2|bibcode=1992Geo....20..271M }}</ref>{{sfn|Boggs|2006|pp=215-216}} [[Aeolian processes|Eolian]] quartz has also been suggested as a source of silica for chert beds.<ref>{{cite journal |last1=Cecil |first1=C. Blaine |last2=Hemingway |first2=Bruce S. |last3=Dulong |first3=Frank T. |title=The Chemistry of Eolian Quartz Dust and the Origin of Chert |journal=Journal of Sedimentary Research |date=26 June 2018 |volume=88 |issue=6 |pages=743–752 |doi=10.2110/jsr.2018.39|bibcode=2018JSedR..88..743C |s2cid=134950494 }}</ref> [[Precambrian]] bedded cherts are common, making up 15% of middle Precambrian sedimentary rock,{{sfn|Blatt|Middleton|Murray|1980|p=571}} and may have been deposited nonbiologically in oceans more saturated in silica than the modern ocean. The high degree of silica saturation was due either to intense volcanic activity or to the lack of modern organisms that remove silica from seawater.{{sfn|Boggs|2006|p=216}}