Pelite

A pelite (from Ancient Greek πηλός (pēlós) 'clay, earth')[3] 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.

[4][5][6] A semipelite is defined in part as having similar chemical composition but being of a crystalloblastic nature.

The Ancient Greek terms are more commonly used for metamorphosed rocks, and the Latin for unmetamorphosed: In the late 1800s and early 1900s, George Barrow discovered the classic Barrovian-type metamorphic sequence in the southeastern Scottish Highlands.

He observed that as a pelitic rock undergoes higher pressures and temperatures, its mineral assemblage changes from predominantly chlorite to biotite to garnet to staurolite to kyanite to sillimanite.