1. (lime mud) Microcrystalline calcite, with a grain size finer than 4 μm. This may originate from biogenic sources in the form of aragonitic calcareous algae, by bioerosion and physical erosion of coarser carbonate fragments, inorganic precipitation from carbonate saturated waters, and biochemical precipitation by algal activity.
2. Limestones consisting mainly of lithified lime mud. See folk limestone classification; leighton–pendexter classification.