Lutite

Not to be confused with latite, a type of volcanic rock.

Lutite is old terminology, which is not widely used, by Earth scientists in field descriptions for fine-grained, sedimentary rocks, which are composed of silt-size sediment, clay-size sediment, or a mixture of both. When mixed with water lutites often disintegrate into mud. Because this is a field term, there is a lack of any precise definition for it based upon specific grain-size characteristics. Lutites include a variety of fine-grained sedimentary rocks, including calcisiltite, calcilutite, claystone, mudstone, shale, and siltstone. It is equivalent to the term mudstone and the Greek-derived term pelite.[1][2] Lutite was first used in 1904 by Grabau,[3] who derived it from lutum, the Latin word for mud.[4] He also proposed a number of prefixes to be used with and attached to "lutite" in order to designate various types of lutites. None of these prefixes are used by Earth scientists nowadays.[1]

Pettijohn [5] 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:

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. ^ a b 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, J.A., eds. (2005) Glossary of Geology (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. ISBN 0-922152-76-4
  3. ^ Grabau, A.W. (1904) On the classification of sedimentary rocks. American Geologist. vol. 33, pp. 228-247.
  4. ^ lutum. Charlton T. Lewis and Charles Short. A Latin Dictionary on Perseus Project.
  5. ^ Pettijohn F. J. (1975), Sedimentary Rocks, Harper & Row, ISBN 0-06-045191-2