Limestone is a sedimentary rock; it occurs primarily on the seafloor where calcium carbonate-rich (‘calcareous’ material) material accumulates. This calcareous material can be originally organic, chemical, or detrital. About 10% of the sedimentary rocks are lime. Karst landscapes are caused by the solubility of limestone in water and poor acid solutions, in which water erodes limestone for thousands to millions of years. In limestone bedrock, most cave systems are located. There’s a granular feel on most limestone. Their constituent grains vary in size from 0.001 mm to visible particles (0.00004 inches). The grains are small fragments of fossil animal shells in many instances.
Marine species are most generally the main source of the calcite in limestone. Any of these species may create rock mounds known as reefs, building on generations that have passed. Over the past decade, the growth of the limestone market in the Asia Pacific region has been relatively rapid, mainly due to the presence of developing countries in the region, such as China, which holds the largest market share worldwide. In the past few years, many countries in the Asia Pacific have witnessed rapid urbanization, which has provided enough space for the limestone market to grow.
Limestones can also form in depositional environments of lacustrine and evaporite. At least a few hundred of all calcareous stones contain other materials. There may be quartz, feldspar, clay minerals, pyrite, siderite, and other minerals that are small particles. Wide nodules of chert, pyrite, or siderite may also be found. Limestone has important commercial value as well. To classify the forms of carbonate rocks collectively known as limestone, two main classification systems, the Folk and Dunham, are used.
- Folk Classification: A category gadget that places the number one focus on the basic composition of grains and interstitial fabric in carbonate rocks has been developed by Robert L. Folk. There are three primary additives based on composition: allochemicals (grains), matrix (often micrite), and cement (sparite). The Folk gadget uses names of elements; the main refers back to the grains, and the root is the second. When using the Folk system, it is helpful to have a petrographic microscope because the additives found in each pattern are miles simpler to decide.
- Dunham classification: In 1962, Robert J. Dunham released his limestone scheme. It relies on carbonate rocks’ depositional cloth. Based on the relative proportions of coarser clastic particles, Dunham divides the rocks into four major classes, based on factors such as whether the grains were initially in mutual contact and thus self-supporting or whether the presence of frame builders and algal mats characterizes the rock. Dunham deals with the initial porosity of the rock, unlike the Folk scheme. For hand samples, the Dunham scheme is more helpful because it is based on shape, not the grains in the sample.
Limestone is a stone with an incredible range of applications. It may be the one rock that is used more than any other in more ways. Here are some of the varieties used more often.
- Chalk: A soft limestone with a very fine texture, typically colored white or light gray. It is produced mainly from the remains of microscopic marine organisms such as foraminifers in the calcareous shell, or from various kinds of marine algae in the calcareous remains.
- Coquina: A poorly-cemented limestone that consists mostly of shell debris that is broken. It also forms on beaches where shell fragments of similar size are segregated by wave action.
- Fossiliferous Limestone: A limestone that contains fossils that are evident and plentiful. Typically, these are the shell and skeletal fossils of the limestone producing species.
- Lithographic Limestone: A thick limestone with a very fine and very uniform size of grain that occurs in thin beds that easily detaches to create a very smooth surface.
- Oolitic Limestone: A limestone consisting primarily of “oolites,” of calcium carbonate, small spheres created by condensed calcium carbonate precipitation on a sand grain or shell fragment.
- Travertine: A limestone that structures by evaporative precipitation, regularly in a cavern, to create developments, for example, cave rock formations, stalagmites, and flowstone.
- Tufa: A limestone formed by precipitation at a hot spring, lakeshore, or other location from calcium-laden waters.
In the late 19th and early 20th centuries, limestone was more common. Train stations, banks, and other buildings were usually built of limestone from that period. It is used on some skyscrapers as a façade, but only for covering thin plates rather than solid blocks. Used in blast furnaces, to pull them out of the iron, limestone joins with silica and various impurities. When heated to temperatures of 900 to 1,000 °C (1,650 to 1,800 °F), calcium carbonate will be dissociated from limestone, and carbon dioxide and lime will be formed, the latter having major applications in glass production and agriculture. Some types of limestone also act as a building stone; they are generally used for flooring, exterior and interior facings, and monuments.