The calcium carbonate is a sedimentary rock which is mainly composed of calcite mineral (calcium carbonate: CaCo3). The calcium carbonate is often composed of various quantities of silica mineral in the form of chert or flint, as well as various amounts of clay, silt, and sand, as intercalations, nodules or interbedded layers. The main source of calcite in limestone is usually marine organisms, so that their shells deposit on the ocean floor. As well, the secondary calcite may be deposited by supersaturated meteoric waters (ground waters that cause the deposition in caves), and consequently cave deposited layers such as stalagmite and stalactite are formed.
Another form which is created due to calcite deposition is soils (soil calcium carbonate) that could be distinguished by their grain appearance.
Pure limestone is often found in white and whitish colors. Due to the presence of impurities such as clay, organisms remains, iron oxide and other components, most of the limestone are found in different colors, especially if they are weathered. Based on their formation process, limestone could be seen in crystalline, clastic, granular or massive forms in nature. The presence of calcite, quartz, dolomite or barite crystals may create some small cavities in rocks. The Folk and Dunham classifications are used to scrutinize the limestone in detail.
Travertine is a kind of calcium carbonate with a compact strip structure that is created through water currents, especially the waterfalls and as well, hot and cold springs. Due to the chemical composition of calcite, the calcium carbonate in places with high values of evaporation leaves supersaturated solutions. Tufa is a porous travertine that could be found near waterfalls. Coquina is also a type of calcium carbonate rock with a weak structure; it is composed of shells and corals fragments.
The calcium carbonate is soluble in some compounds such as acids, therefore many erosional structures such as calcareous caves, potholes, and deep valleys may be created. Some erosional features are known as karst. Although calcium carbonate is less resistant than igneous rocks, its resistance is higher than other sedimentary rocks. Usually, the Calcium carbonate is present in hills and sink hole structures, and often could be seen with other sedimentary rocks such as clay in different regions.
The calcium carbonate masses crop out with spectacular rocky landscapes. Some examples of these structures are Burren in Co Clare of Ireland, Verdon Gorge in France, Malham Cove in northern Yorkshire, England, Faro near the Swedish Island of Gotland, Niagara Fall in Canada/USA, and Ha Long Bay National in Vietnam.
The Calcium carbonate is especially used in architecture, and many historical masterpieces all around the world, especially in North America and Europe are made from this combination. Many buildings in Kingston, Ontario of Canada are made of calcium carbonate, so they are also called calcareous cities. Among the most important artworks of the world, the Abraham Lincoln Statue in Washington, the Parthenon Building in Athens, the Church ceiling of Kraków in Poland, and the Great Lion Statue of London’s Trafalgar Square are made of the calcium carbonate. Another feature of the calcium carbonate is that it could be easily crushed into smaller pieces. Meanwhile, its durability is long-lasting and could be well exposed on the surface. The application of the calcium carbonate in buildings was common in the early 20th and late 19th centuries. Train stations, banks, and other constructions of that time have been mainly made up of calcium carbonate. Besides, these rocks are used as façade of some skyscrapers. In the United States, buildings are made up of high-quality Indiana calcium carbonate, while in London, many well-known buildings are constructed by Portland calcium carbamate.
Although the application of the calcium carbonate in the buildings’ construction is more appropriate for humid regions, its resistance against acidic materials is low; the acidic rainfall is a significant problem in areas where calcium carbonate is widely used. The dissolved acid in acidic rainfall can damage the buildings, thus, soft limestone powder can be used to neutralize the effects of acidic rainfalls.