Limestone is a sedimentary rock, mainly composed of mineral calcite. The primary source of the calcite is usually marine organisms, which settle out of the water column and are deposited on the ocean floors as pelagic ooze (but see lysocline for information on calcite dissolution). Secondary calcite may also be deposited in super-saturated meteoric waters, as is evidenced by the creation of stalagmites and stalactites.
Bands of limestone emerge from the Earth's surface in often spectacular rocky outcrops and islands. For example the Verdon Gorge in France, Malham Cove in North Yorkshire, England and the Ha Long Bay National Park in Vietnam.
It is quarried for roadbeds and gravel roads, building and landscape construction, and cement manufacture.
See also: marble, list of minerals, karst.