Pelite

Pelite (Greek pelos, clay) is an old and currently not widely used field geological term for a clay-rich, fine-grained clastic sediment or sedimentary rock, i.e. mud or a mudstone. It is equivalent to the Latin-derived term lutite. More commonly, metamorphic geologists currently use pelite for a metamorphosed fine-grained sedimentary rock, i.e. mudstone or siltstone, which should technically be called a metapelite.