protolith

{{Refimprove|date=January 2021}}

A protolith ({{etymology|grc|πρωτο (prōto)|first||λίθος (líthos)|stone}}) is the original, unmetamorphosed rock from which a given metamorphic rock is formed.{{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}}{{cite encyclopedia |url=http://encyclopedia2.thefreedictionary.com/protolith |title=protolith |encyclopedia=The Free Dictionary |publisher=Farlex}}

For example, the protolith of a slate is a shale or 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.

Protoliths are non-metamorphic rocks and have no protoliths themselves. The non-metamorphic rocks fall into two classes: sedimentary rocks, formed from sediment, and igneous rocks, formed from magma. The source of the sediment of a sedimentary rock is termed its provenance.

Magmatic protoliths can be further divided into three categories: ultramafic rock, mafic rock, and quartzo-feldspathic rock. Similarly, sedimentary protoliths can be classified as quartzo-feldspathic, pelitic, carbonate rocks, or some mixture of the three.{{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 }}

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 eon.{{cn|date=September 2024}}