pelite

{{Short description|Metamorphic rock}}

{{about|the metamorphic rock|the sedimentary rock|Argillite}}

File:Petrogenetic grid for Metapelites.png for metapelites (click to zoom).{{cite journal |last1=Wei|first1=Chunjing |last2=Powell|first2=Roger |date=2003 |title=Phase relations in high-pressure metapelites in the system KFMASH (K2O–FeO–MgO–Al2O3–SiO2–H2O) with application to natural rocks |journal=Contributions to Mineralogy and Petrology |volume=145 |issue=3 |pages=301–315 |doi=10.1007/s00410-003-0454-1|s2cid=129368566}} {{cite journal |last1=Wei|first1=Chunjing |last2=Powell|first2=Roger |last3=Clarke|first3=Gordon |date=2004 |title=Calculated phase equilibria for low‐ and medium‐pressure metapelites in the KFMASH and KMnFMASH systems |journal=Journal of Metamorphic Geology |volume=22 |issue=5 |pages=495–508 |doi=10.1111/j.1525-1314.2004.00530.x |s2cid=128393826}} Each line represents a metamorphic reaction. Metamorphic facies included are: BS = Blueschist facies, EC = Eclogite facies, PP = Prehnite-Pumpellyite facies, GS = Greenschist facies, EA = Epidote-Amphibolite facies, AM = Amphibolite facies, GRA = Granulite facies, UHT = Ultra-High Temperature facies, HAE = Hornfels-Albite-Epidote facies, Hbl = Hornblende-Hornfels facies, HPX = Hornfels-Pyroxene Facies, San = Sanidinite facies ]]

A pelite ({{etymology|grc|{{wikt-lang|grc|πηλός}} ({{grc-transl|πηλός}})|clay, earth}}){{LSJ|phlo/s|πηλός|ref}}. or metapelite is a metamorphosed fine-grained sedimentary rock, i.e. mudstone or siltstone. The term was earlier used by geologists to describe a clay-rich, fine-grained clastic sediment or sedimentary rock, i.e. mud or a mudstone, the metamorphosed version of which would technically have been a metapelite. It was equivalent to the now little-used Latin-derived term lutite.Potter, P.E., J.B. Maynard, and P.J. Depetris (2005) Muds and Mudstones. New York, New York, Springer. 279 pp. {{ISBN|978-3-540-22157-9}}Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) Glossary of Geology (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. {{ISBN|0-922152-76-4}}{{cite book |last=Whitten|first=D. G. A. |title=The Penguin Dictionary of Geology |date=1972 |publisher=Penguin Books |location=London |isbn=0140510494 |page=[https://archive.org/details/penguindictionar0000whit/page/342 342] |url-access=registration |url=https://archive.org/details/penguindictionar0000whit/page/342}} A semipelite is defined in part as having similar chemical composition but being of a crystalloblastic nature.{{cite web |url=https://webapps.bgs.ac.uk/bgsrcs/rcs_details.cfm?code=SEMPEL |title=Semipelite |year=2023 |author=British Geological Survey |website=BGS Rock Classification Scheme |publisher=UK Research and Innovation |access-date=2023-01-21}}

Pettijohn (1975)Pettijohn, F. J. (1975), Sedimentary Rocks, Harper & Row, {{ISBN|0-06-045191-2}}. gives the following descriptive terms based on grain size, avoiding the use of terms such as clay or argillaceous which carry an implication of chemical composition. The Ancient Greek terms are more commonly used for metamorphosed rocks, and the Latin for unmetamorphosed:

class="wikitable" |+Descriptive size terms
Texture	Common	Ancient Greek	Latin
Coarse | gravel(ly) || psephite (psephitic)|| rudite (rudaceous)
Medium | sand(y) || psammite (psammitic)|| arenite (arenaceous)
Fine | clay(ey) || pelite (pelitic)|| lutite (lutaceous)