LIMESTONE

Limestone is a sedimentary rock made up largely of the mineral calcite (calcium carbonate: CaCO₃). The solubility of limestone in water and weak acid solutions leads to important phenomena. Most well-known natural cave systems are as a result of limestone. 

Areas overlying limestone substratum tend to have smaller quantities of visible groundwater sources (ponds and rivers), as surface water effortlessly drains downward through cracks in the limestone. While draining, water gradually (over thousands or millions of years) expands these cracks; dissolving the calcium-carbonate and moving it away in solution.

Karst topography and caves develop in carbonate rocks due to their solubility in dilute acidic groundwater. Cooling groundwater or mixing of different groundwaters will also create conditions suitable for cave formation.

Coastal limestone is often eroded by organisms which bore into the rock by an assortment of means. This progression is known as bioerosion. It is most widespread in the tropics.

Because of contamination, such as clay, sand, organic remains, iron oxide and other materials, many limestone display diverse colors, particularly on weathered surfaces. Limestone may be crystalline, clastic, granular, or immense, depending on the process of formation. Crystals of calcite, quartz, dolomite or barite may line small cavities in the rock.

Calcium (along with nitrogen, phosphorus, and potassium) is a key mineral to plant nutrition: soils overlying limestone bedrock tend to be pre-fertilized with calcium.

Limestone is an important stone for masonry and architecture, vying with only granite and sandstone to be the most commonly used architectural stone. Limestone is a key ingredient of quicklime, mortar, cement, and concrete.

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