Lutite is old terminology, which is not widely used, by Earth scientists in field descriptions for fine-grained,
sedimentary
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
rocks, which are composed of
silt
Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel ...
-size
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...
,
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
-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
A pelite ( Greek: ''pelos'', "clay") 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, ...
.
[Potter, P.E., J.B. Maynard, and P.J. Depetris (2005) Muds and Mudstones. New York, New York, Springer. 279 pp. ][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. ] Lutite was first used in 1904 by Grabau,
[Grabau, A.W. (1904) ''On the classification of sedimentary rocks.'' American Geologist. vol. 33, pp. 228-247.] who derived it from ''lutum'', the Latin word for mud. 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.
Pettijohn
[ Pettijohn F. J. (1975), ''Sedimentary Rocks'', Harper & Row, ] 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:
References
{{reflist
Sedimentary rocks
Mudstone