Editing Limestone (section)

{{Short description|Type of sedimentary rock}}
{{Other uses}}
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{{Use dmy dates|date=October 2021}}
{{Infobox rock
|name = Limestone
|type = Sedimentary
|image = ElTorcal0408.jpg
|caption = Limestone outcrop in the [[Torcal de Antequera]] nature reserve of [[Málaga]], Spain
|composition = [[Calcium carbonate]]: inorganic crystalline [[calcite]] or organic calcareous material
}}
'''Limestone''' is a type of [[carbonate rock|carbonate]] [[sedimentary rock]] which is the main source of the material [[Lime (material)|lime]]. It is composed mostly of the [[minerals]] [[calcite]] and [[aragonite]], which are different [[Polymorphism (materials science)|crystal forms]] of [[calcium carbonate]] {{chem2|CaCO3}}. Limestone forms when these minerals [[Precipitation (chemistry)|precipitate]] out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years.<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=0-13-154728-3|edition=4th |pages=177, 181}}</ref><ref>{{Cite book|last=Leong|first=Goh Cheng|url=https://books.google.com/books?id=XhJ4RAAACAAJ&q=certificate+physical+and+human+geography|title=Certificate Physics And Human Geography; Indian Edition|date=1995-10-27|publisher=Oxford University Press|isbn=0-19-562816-0|pages=62|language=en}}</ref> Limestone often contains [[fossil]]s which provide scientists with information on ancient environments and on the [[evolution]] of life.{{sfn|Boggs|2006|p=159}}

About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone.<ref>{{cite book |last1=Blatt |first1=Harvey |last2=Tracy |first2=Robert J. |title=Petrology : igneous, sedimentary, and metamorphic. |date=1996 |publisher=W.H. Freeman |location=New York |isbn=0-7167-2438-3 |pages=295–300 |edition=2nd}}</ref>{{sfn|Boggs|2006|p=159}} The remaining carbonate rock is mostly [[Dolomite (rock)|dolomite]], a closely related rock, which contains a high percentage of the mineral [[Dolomite (mineral)|dolomite]], {{chem2|CaMg(CO3)2}}. ''Magnesian limestone'' is an obsolete and poorly-defined term used variously for dolomite, for limestone containing significant dolomite (''dolomitic limestone''), or for any other limestone containing a significant percentage of [[magnesium]].<ref>{{cite book |editor1-last=Jackson |editor1-first=Julia A. |title=Glossary of geology. |date=1997 |publisher=American Geological Institute |location=Alexandria, Virginia |isbn=0-922152-34-9 |edition=Fourth |chapter=Magnesian limestone}}</ref> Most limestone was formed in shallow marine environments, such as [[continental shelves]] or [[Carbonate platform|platforms]], though smaller amounts were formed in many other environments. Much dolomite is secondary dolomite, formed by chemical alteration of limestone.<ref>{{cite book |last1=Blatt |first1=Harvey |last2=Middleton |first2=Gerard |last3=Murray |first3=Raymond |title=Origin of sedimentary rocks |date=1980 |publisher=Prentice-Hall |location=Englewood Cliffs, N.J. |isbn=0-13-642710-3 |edition=2d |pages=446, 510–531}}</ref>{{sfn|Boggs|2006|p=182–194}} Limestone is exposed over large regions of the Earth's surface, and because limestone is slightly [[solubility|soluble]] in rainwater, these exposures often are eroded to become [[karst]] landscapes. Most [[cave]] systems are found in limestone bedrock.

Limestone has numerous uses: as a chemical [[feedstock]] for the production of [[Lime (material)|lime]] used for [[cement]] (an essential component of [[concrete]]), as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paint, as a [[soil conditioner]], and as a popular decorative addition to [[rock gardens]]. Limestone formations contain about 30% of the world's [[petroleum reservoir]]s.{{sfn|Boggs|2006|p=159}}