A sedimentary rock consisting mainly of carbonates, primarily calcite (calcium carbonate, CaCO3) or dolomite (CaMg(CO3)2), with some sand or clay as impurities. Most limestones are organically formed from the secretions, shells, or skeletons of plants and animals such as corals and molluscs. Inorganic limestones are formed by precipitation from water containing dissolved carbonates. Limestone is of economic importance as a building material, and as a source of lime and cement.
Limestones often contain variable amounts of silica in the form of chert or flint, as well as varying amounts of clay, silt and sand as disseminations, nodules, or layers within the rock. The primary source of the calcite in limestone is most commonly marine organisms. Another form taken by calcite is that of oolites (oolitic limestone) which can be recognised by its granular appearance. Limestone makes up about 10 percent of the total volume of all sedimentary rocks.Pure limestones are white or almost white. Because of impurities, such as clay, sand, organic remains, iron oxide and other materials, many limestones exhibit different colors, especially on weathered surfaces.
Travertine is a banded, compact variety of limestone formed along streams, particularly where there are waterfalls and around hot or cold springs.
During regional metamorphism that occurs during the mountain building process (orogeny) limestone recrystallizes into marble.
Limestone is a parent material of Mollisol soil group.
Limestone landscape
Limestone is partially soluble, especially in acid, and therefore forms many erosion landforms. Limestone is less resistant than most igneous rocks, but more resistant than most other sedimentary rocks. Limestone is therefore usually associated with hills and downland and occurs in regions with other sedimentary rocks, typically clays.
Bands of limestone emerge from the Earth's surface in often spectacular rocky outcrops and islands.
Unique habitats are found on alvars, extremely level expanses of limestone with thin soil mantles.
Uses of limestone
Limestone is especially popular in architecture, and many landmarks around the world, especially in North America and Europe, are made primarily of the material.
Limestone was most popular in the early 20th and late 19th centuries. Train stations, banks and other structures from that era are normally made of limestone. Limestone is used as a facade on some skyscrapers, but only in thin plates for covering rather than solid blocks. In the United States, Indiana, most notably the Bloomington area, has long been a source of high quality quarried limestone, called Indiana limestone.
Limestone was also a very popular building block in the middle ages in the areas where it occurred since it is hard, durable, and commonly occurs in easily accessible surface exposures. Many medieval churches and castles in Europe are made of limestone. Beer stone was a popular kind of limestone for medieval buildings in southern England.
Limestone and marble are very reactive to acid solutions, making acid rain a significant problem. Many limestone statues and building surfaces have suffered severe damage due to acid rain.
Other uses include:
the manufacture of quicklime (calcium oxide)and slaked lime (calcium hydroxide) cement and mortar pulverized limestone is used as a soil conditioner to neutralize acid soil conditions crushed for use as aggregate - the solid base for many roads geological formations of limestone are among the best petroleum reservoirs as a reagent in desulfurizations glass making toothpaste
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