Lime Stone

Limestone is a sedimentary rock composed largely of the mineral calcite (Calcium carbonate: CaCo3). Limestone’s often contain variable amounts of silica in the form of chart or flint, as well as varying amounts of clay, silt and sand as dissemination, nodules, or layers within the rock. 

The primary source of the organisms secretes 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)