Editing Limestone (section)

===Classification===
{{See also|List of types of limestone}}
[[File:Pamukkale 12.jpg|thumb|[[Travertine]] limestone terraces of [[Pamukkale]], [[Turkey]].]]
[[File:Luray Caverns, Dream Lake - mirror-lake of caverns (2015-05-09 14.03.28 by Stan Mouser).jpg|thumb|[[Cave formations|Cave limestone formations]] in the [[Luray Caverns]] of the northern [[Shenandoah Valley]]]]Two major classification schemes, the Folk and Dunham, are used for identifying the types of [[carbonate rocks]] collectively known as limestone.

====Folk classification====
{{main|Folk's carbonate classification}}
[[Robert L. Folk]] developed a classification system that places primary emphasis on the detailed composition of grains and interstitial material in [[carbonate rocks]].<ref>{{cite web| url = http://sepmstrata.org/page.aspx?pageid=89| title = Carbonate Classification: SEPM STRATA}}</ref> Based on composition, there are three main components: allochems (grains), matrix (mostly micrite), and cement (sparite). The Folk system uses two-part names; the first refers to the grains and the second to the cement. For example, a limestone consisting mainly of ooids, with a crystalline matrix, would be termed an oosparite. It is helpful to have a [[petrographic microscope]] when using the Folk scheme, because it is easier to determine the components present in each sample.<ref name="Folk">{{cite book |last=Folk |first=R. L. |year=1974 |title=Petrology of Sedimentary Rocks |publisher=Hemphill Publishing |location=Austin, Texas |isbn=0-914696-14-9}}</ref>

====Dunham classification====
{{main|Dunham classification}}
Robert J. Dunham published his system for limestone in 1962. It focuses on the depositional fabric of carbonate rocks. Dunham divides the rocks into four main groups based on relative proportions of coarser clastic particles, based on criteria such as whether the grains were originally in mutual contact, and therefore self-supporting, or whether the rock is characterized by the presence of frame builders and algal mats. Unlike the Folk scheme, Dunham deals with the original porosity of the rock. The Dunham scheme is more useful for hand samples because it is based on texture, not the grains in the sample.<ref name="Dunham">{{cite book |last=Dunham |first=R. J. |year=1962 |chapter=Classification of carbonate rocks according to depositional textures |editor-last=Ham |editor-first=W. E. |title=Classification of Carbonate Rocks |series=American Association of Petroleum Geologists Memoirs |volume=1 |pages=108–121 }}</ref>

A revised classification was proposed by Wright (1992). It adds some diagenetic patterns to the classification scheme.<ref name="Wright1992">{{cite journal |last1=Wright |first1=V.P.|year=1992 |title=A revised Classification of Limestones |journal=Sedimentary Geology |volume=76 |issue=3–4 |pages=177–185 |doi=10.1016/0037-0738(92)90082-3 |bibcode=1992SedG...76..177W}}</ref>

====Other descriptive terms====
[[File:Chalk ("Upper Chalk" Formation, Upper Cretaceous; White Cliffs of Dover, England, southern Britain).jpg|thumb|Chalk from the White Cliffs of Dover ([[Chalk Group]]), England]]
''[[Travertine]]'' is a term applied to calcium carbonate deposits formed in freshwater environments, particularly [[waterfall]]s, cascades and [[hot springs]]. Such deposits are typically massive, dense, and banded. When the deposits are highly porous, so that they have a spongelike texture, they are typically described as ''[[tufa]]''. Secondary calcite deposited by [[Supersaturation|supersaturated]] [[meteoric water]]s ([[groundwater]]) in caves is also sometimes described as travertine. This produces [[speleothem]]s, such as [[stalagmite]]s and [[stalactite]]s.{{sfn|Blatt|Middleton|Murray|1980|p=479-480}}

''[[Coquina]]'' is a poorly consolidated limestone composed of abraded pieces of [[coral]], [[Exoskeleton|shells]], or other fossil debris. When better consolidated, it is described as ''coquinite''.{{sfn|Boggs|2006|p=172}}

''[[Chalk]]'' is a soft, earthy, fine-textured limestone composed of the tests of planktonic microorganisms such as foraminifera, while
''[[marl]]'' is an earthy mixture of carbonates and silicate sediments.{{sfn|Boggs|2006|p=172}}
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