Limestones

Limestone is a sedimentary rock composed of the mineral calcite (calcium carbonate) . The primary source of this calcite is usually marine organisms. These organisms secrete shells that settle out of the water column and are deposited on ocean floors as pelagic ooze (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. Limestone makes up approximately 10 percent of the total volume of all sedimentary rocks.