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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.[1][2]

The term pelite is not to be confused with pilite, a rarely used name for an altered olivine that has been partially pseudomorphically replaced by an assemblage of carbonate–chlorite–actinolite and can be identified only in a thin section.

Pettijohn (1975)[3] 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 Greek terms are more commonly used for metamorphosed rocks, and the Latin for unmetamorphosed:

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


  1. ^ 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
  2. ^ 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
  3. ^ Pettijohn, F. J. (1975), Sedimentary Rocks, Harper & Row, ISBN 0-06-045191-2.