Editing Chert (section)

==Varieties==
There are numerous varieties of chert, classified based on their visible, microscopic and physical characteristics.<ref name="roberts-etal-1990"/><ref name="mitchell-1985"/> Examples are:
* [[Flint]] is a compact microcrystalline quartz. It was originally the name for chert found in [[chalk]] or marly limestone formations formed by a replacement of calcium carbonate with [[silica]]. Commonly found as nodules, this variety was often used in past times to make bladed tools. Today, some geologists refer to any dark gray to black chert as flint.{{sfn|Bates|Jackson|1984|loc="Flint"}}<ref>George R. Rapp, "Archaeomineralogy", 2002. {{ISBN|3-540-42579-9}}</ref><ref>Barbara E. Luedtke, "The Identification of Sources of Chert Artifacts", American Antiquity, Vol. 44, No. 4 (Oct., 1979), 744–757.</ref> The dark color is from inclusions of organic matter.{{sfn|Blatt|Middleton|Murray|1980|p=571}} Among non-geologists, the distinction between "flint" and "chert" is often one of quality – chert being lower quality than flint. This usage of the terminology is particularly prevalent in Great Britain where most true flint (found in chalk formations) was of better quality than "common chert" (from limestone formations).<ref>{{cite book |last1=Luedtke |first1=Barbara E. |title=An archaeologist's guide to chert and flint |date=1992 |publisher=Institute of Archaeology, University of California |location=Los Angeles |isbn=0-917956-75-3 |url=https://escholarship.org/uc/item/7j8387sj |access-date=8 October 2020}}</ref>

* "Common chert" is a variety of chert which forms in limestone formations by replacement of calcium carbonate with silica. This is the most abundantly found variety of chert. It is generally considered to be less attractive for producing gem stones and bladed tools than flint.

* [[Jasper]] is a variety of chert formed as primary deposits, found in or in connection with magmatic formations, and owes its typical red color to hematite inclusions. Jasper frequently also occurs in black, yellow and green, depending on the type of iron it contains. Jasper is usually opaque to near opaque.{{sfn|Bates|Jackson|1984|loc="Jasper"}} Jasper is also present in banded iron formation, where it is described as jaspilite.{{sfn|Boggs|2006|p=207}}

* Radiolarite is a variety of chert formed as primary deposits and containing [[radiolarian]] microfossils.{{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|pp=209–210}}

* [[Chalcedony]] is a microfibrous quartz.{{sfn|Boggs|2006|pp=206–207}}

* [[Agate]] is distinctly banded chalcedony with successive layers differing in color or value.<ref>{{cite book |last1=Klein |first1=Cornelis |last2=Hurlbut | first2=Cornelius S. Jr. |title=Manual of mineralogy : (after James D. Dana) |date=1993 |publisher=Wiley |location=New York |isbn=047157452X |edition=21st |page=529}}</ref>

* [[Onyx]] is a banded agate with layers in parallel lines, often black and white (''sardonyx'').{{sfn|Klein|Hurlbut|1993|p=529}}

* [[Magadi-type chert]] is a variety that forms from a sodium silicate precursor in highly alkaline lakes such as [[Lake Magadi]] in Kenya.<ref>{{cite journal |last1=Leet |first1=Kennie |last2=Lowenstein |first2=Tim K. |last3=Renaut |first3=Robin W. |last4=Owen |first4=R. Bernhart |last5=Cohen |first5=Andrew |title=Labyrinth patterns in Magadi (Kenya) cherts: Evidence for early formation from siliceous gels |journal=Geology |date=3 June 2021 |volume=49 |issue=9 |pages=1137–1142 |doi=10.1130/G48771.1|bibcode=2021Geo....49.1137L |s2cid=236292156 }}</ref>

* [[Novaculite]] is a very dense, fine-grained, and uniform form of very pure white chert with a high content of extracrystalline water.{{sfn|Blatt| Middleton | Murray |1980|p= 571}} It is most common in the mid-[[Paleozoic]] rocks of [[Texas]], [[Oklahoma]], and [[Arkansas]] in the south-central United States, where it has undergone some [[metamorphism]].{{sfn|Boggs|2006|p=207}}

* Porcelanite is a term used for fine-grained siliceous rocks with a texture and a fracture resembling those of unglazed porcelain. It likely forms in shallow water and is composed mostly of opal-CT.{{sfn|Boggs|2006|pp=207, 214}}

* [[Rotten stone|Tripolitic chert]] (or tripoli) is a light-colored porous friable siliceous (largely chalcedonic) sedimentary rock, which results from the weathering (decalcification) of chert or siliceous limestone.{{sfn|Bates|Jackson|1984|loc="Tripoli"}}

* [[Siliceous sinter]] is porous, low-density, light-colored siliceous rock deposited by waters of hot springs and geysers.{{sfn|Boggs|2006|p=207}}

* [[Mozarkite]] a varicolored, easily polished Ordovician chert that takes a high polish. It is the state rock of Missouri.{{sfn|Bates|Jackson|1984|loc="Mozarkite"}}

Other lesser used archaic terms for chert are firestone and silex.{{sfn|Bates|Jackson|1984}}