Limestone

overlaid by limestone. Cumberland Plateau, Tennessee]]

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 (ground water that reaches earth's surface as precipitation), as is evidenced by the creation of stalagmites and stalactites. Limestone makes up approximately 10 percent of the total volume of all sedimentary rocks.

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.

Karst and caves are often formed in limestone.

It is quarried for roadbeds and gravel roads, building and landscape construction, and cement manufacture.