Limestone is a sedimentary rock composed of calcium carbonate (CaCO3). Calcite and aragonite are crystal forms of CaCO3. Limestone makes up approximately 10 percent of all the sedimentary rocks in the world. Limestone may form many erosional land formations when in contact with acid. Limestone is typically white; however, impurities present, such as iron oxide, can give limestone a red, brown or yellow color. The solubility of limestone in the presence of acid solutions leads to the formation of varied underground landscapes, including caves, sinkholes and underground drainage systems. Limestone may take various forms and textures, depending on the process of its formation.
Limestone is a sedimentary rock that has been deposited in layers over the Earth´s crust over millions of years. Most limestone is composed of crystal forms of the minerals calcite and aragonite. These minerals are skeletal fragments of marine animals, such as corals, diatoms, spicules, radiolarians and sponges. Like all sedimentary rocks, limestone is transported from one area to another by weathering and erosion. In the deposition of limestone, typically agents of denudation such as water, ice and wind may be involved. The deposition of limestone can take various forms, depending on how and where it is deposited, thus, limestone may take crystalline, clastic or granular forms.
The main source of the mineral calcite in limestone stems from the secretion of calcium carbonate by marine organisms. The secretion of CaCO3 by marine organisms produces enormous structures in the shallow marine habitats known as coral reefs. Limestone may also form in lakes and environments where the evaporation of water-soluble minerals produces the sedimentation of limestone. Calcite can be either deposited or precipitated by underground water, forming underground structures known as speleothems. Calcium carbonate is deposited where the evaporation of water leaves a solution saturated with the main elements of calcite.
Due to impurities such as iron oxide, organic matter and cay, limestone can take different colors and textures. Limestone may be crystalline, granular, clastic or massive rock, based on the process of formation. Travertine is a light-colored type of limestone that usually forms in streams, such as waterfalls and in cold springs. Tufa, which is a variety of travertine, is found in the same environment. Coquina is a poorly combined type of limestone formed by corals and marine shells, often found in coastal waters. Chalk is white to light gray and is usually formed by the calcareous remains of very small marine organisms.
Fossiliferous limestone if formed in the skeletal fossils of ancient organisms. Shelly limestone is a highly fossiliferous type of limestone composed mainly of the skeletal remains of marine animals, such as corals, sponges and mollusks. Lithographic limestone is a dense type of limestone composed of very fine particles of grain. Pisolitic limestone is made of pisolites, which are diminutive particles of calcium carbonate. Pisolitic limestone is white or yellow in color and forms due to the precipitation of calcite and other minerals from very high boiling water. Limestone may recrystallize into marble during regional metamorphism, which occurs during the formation of mountains.
Limestone is a very common type of material used in many building constructions in Europe and North America. Limestone is often cut into blocks and used in the construction industry and architecture; however, limestone is a very heavy type of material rarely used in very tall buildings. As an acid-neutralizing agent, limestone is often used in agriculture as a soil-treatment agent, and it is also given to cattle and chicken as a dietary supplement. According to hyperphysics.phy-astr.gsu.edu, limestone is a sedimentary rock formed inorganically or by biochemical processes. Limestone is a varied type of sedimentary rock due to the varied conditions in which it is formed.