Calcareous rock also refers to sediments derived near land. The carbon content is high due to life-derived sediments. The farther from land sediments fall, the less calcareous they are, usually. There are of course exceptions. Some areas can have inter bedded calcareous sediments due to storms or changes in ocean currents.

Limestone often contains variable amounts of silica in the form of chert or flint, as well as varying amounts of clay, silt and sand as disseminations, nodules, or layers within the rock. The primary source of the calcite in limestone is most commonly marine organisms. These organisms secrete shells that settle out of the water column and are deposited on ocean floors as pelagic ooze or alternatively is conglomerated in a coral reef (see lysocline for information on calcite dissolution). Secondary calcite may also be deposited by supersaturated meteoric waters (groundwater that precipitates the material in caves). This produces speleothems such as stalagmites and stalactites. Another form taken by calcite is that of oolites (oolitic limestone) which can be recognized by its granular appearance. Limestone makes up about 10% of the total volume of all sedimentary rocks.

During the XIth plan emphasis to be given for locating SMS and BF grade limestone along with cement grade limestone from the states of Meghalaya, Rajasthan, Madhya Pradesh, Gujarat, Orissa and Assam.