Calcilutite is a type of limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

 that is composed of predominately, more than 50 percent, of either clay-size or both silt-size and clay-size detrital (transported) carbonate

Carbonate rock

Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite and dolostone, which is composed of the mineral dolomite .Calcite can be either dissolved by groundwater or precipitated by...

 grains. These grains consist either of fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 fragments, ooids, intraclasts

Intraclasts

Intraclasts are irregularly-shaped grains that form by syndepositional erosion of partially lithified sediment.Gravel grade material is generally composed of whole disarticulated or broken skeletal fragments together with sand grade material of whole, disaggregated and broken skeletal debris...

, pellets

Pellets (petrology)

Pellets are small spherical to ovoid or rod-shaped grains that are common component of many limestones. They are typically 0.03 to 0.3 mm long and composed of carbonate mud . Their most common size is 0.04 to 0.08 mm. Pellets typically lack any internal structure and are remarkably uniform in size...

, other grains, or some combination of them. The term calcilutite was originally proposed in 1903 by Grabau as a part of his calcilutite, calcarenite

Calcarenite

thumb|250px|The [[Pietra di Bismantova]] in central [[Italy]] is an example of calcarenite formation.Calcarenite is a type of limestone that is composed predominately, more than 50 percent, of detrital sand-size , carbonate grains...

 and calcirudite

Calcirudite

Calcirudite is a type of limestone that is composed predominately, more than 50 percent, of carbonate grains that are larger in size than sand . The grains can consist of either fragments of fossils, fragments of older limestones and dolomites, other carbonate grains, or some combination of these...

 classification system based upon the size of the detrital grains composing a limestone. In the original classification of limestone according dominant grain-size, calcisiltite

Calcisiltite

Calcisiltite is a type of limestone that is composed predominately, more than 50 percent, of detrital silt-size carbonate grains. These grains consist either of the silt-size particles of ooids, fragments of fossil shells, fragments of older limestones and dolomites, intraclasts, pellets, other...

s were not named and are classified as calcilutite. In this classification, which the majority of geologists follow, a calcilutite consists of both silt- and clay-size, less than 0.062 mm in diameter, grains. It is the carbonate equivalent of a mudstone

Mudstone

Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...

. Calcilutites can accumulate in a wide variety of marine and lacustrine

Lacustrine

Lacustrine means "of a lake" or "relating to a lake".Specifically, it may refer to:*Lacustrine plain*Lacustrine delta-Fish:*Lacustrine goby , a type of small fish found in Philippine waters belonging to the Gobiidae family, known in Tagalog as dulong-See also:*Fluvial - of or relating a...

environments.