# Protolith

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{{Short description|Rock from which a metamorphic rock is formed}}
{{Refimprove|date=January 2021}}

A '''protolith''' ({{etymology|grc|''πρωτο'' (prōto)|first||''λίθος'' (líthos)|stone}}) is the original, unmetamorphosed [rock](/source/rock_(geology)) from which a given [metamorphic rock](/source/metamorphic_rock) is formed.<ref>{{Cite web |title=Basics--Rocks-Metamorphic |url=https://commons.wvc.edu/rdawes/g101ocl/basics/metamorphic.html |access-date=2022-10-17 |website=commons.wvc.edu}}</ref><ref>{{cite encyclopedia |url=http://encyclopedia2.thefreedictionary.com/protolith |title=protolith |encyclopedia=[The Free Dictionary](/source/The_Free_Dictionary) |publisher=[Farlex](/source/Farlex)}}</ref>

For example, the protolith of a [slate](/source/slate) is a [shale](/source/shale) or [mudstone](/source/mudstone). Metamorphic rocks can be derived from any other kind of non-metamorphic rock and thus there is a wide variety of protoliths. Identifying a protolith is a major aim of metamorphic [geology](/source/geology). 

Protoliths are non-metamorphic rocks and have no protoliths themselves. The non-metamorphic rocks fall into two classes: [sedimentary rock](/source/sedimentary_rock)s, formed from sediment, and [igneous rock](/source/igneous_rock)s, formed from [magma](/source/magma). The source of the sediment of a sedimentary rock is termed its [provenance](/source/provenance_(geology)). 

Magmatic protoliths can be further divided into three categories: [ultramafic](/source/Ultramafic_rock) rock, [mafic](/source/mafic) rock, and quartzo-feldspathic rock. Similarly, sedimentary protoliths can be classified as quartzo-feldspathic, [pelitic](/source/Pelite), [carbonate rocks](/source/Carbonate_rock), or some mixture of the three.<ref>{{Citation |last=Hoinkes |first=G. |title=Classification, Nomenclature, and Formation☆ |date=2014-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780124095489090497 |work=Reference Module in Earth Systems and Environmental Sciences |publisher=Elsevier |language=en |doi=10.1016/b978-0-12-409548-9.09049-7 |isbn=978-0-12-409548-9 |access-date=2022-10-17 |last2=Hauzenberger |first2=C. A. |last3=Schmid |first3=R.|url-access=subscription }}</ref> 

On a geological time scale, the first protoliths were first formed{{how|date=September 2024}} shortly after the formation of the Earth during the [Hadean](/source/Hadean) eon.{{cn|date=September 2024}} 

==References==
{{Reflist}}

Category:Petrology

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