Micrite

Micrite is a microcrystalline calcite mud, generally considered to be less than 4 μm in crystal size. It is a common component of many sedimentary carbonate rocks, particularly limestones. Micrite forms through several processes, including the disintegration of algal and bacterial skeletons, the precipitation of calcium carbonate from seawater by microorganisms, and the physical abrasion of larger carbonate grains.

The term "micrite" (originally an abbreviation for "microcrystalline calcite") was coined by Robert Folk in the 1959 revision of his limestone classification system. It is a textural term, describing the fine-grained, muddy matrix of carbonate rocks.

Micrite is often dark in color due to the presence of organic matter and finely dispersed iron oxides. It can be distinguished from sparry calcite (sparite), which consists of larger, clear calcite crystals, typically cement. The presence and abundance of micrite provide valuable information about the depositional environment of carbonate sediments. For example, a high proportion of micrite might indicate a low-energy environment where fine particles can settle out of suspension.