Pelite
A pelite (from Ancient Greek πηλός (pēlós) 'clay, earth') 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. A semipelite is defined in part as having similar chemical composition but being of a crystalloblastic nature.
Pettijohn (1975) 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:
| 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) |