Difference between revisions of "Limestone" - New World Encyclopedia
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'''Limestone''' is a [[Rock (geology)|sedimentary rock]] composed largely of the [[mineral]] [[calcite]]* (calcium carbonate, CaCO<sub>3</sub>). It makes up about 10 percent of the total volume of all sedimentary rocks. 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. | '''Limestone''' is a [[Rock (geology)|sedimentary rock]] composed largely of the [[mineral]] [[calcite]]* (calcium carbonate, CaCO<sub>3</sub>). It makes up about 10 percent of the total volume of all sedimentary rocks. 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 calcite in limestone is produced mainly by [[marine biology|marine organisms]] | + | The calcite in limestone is produced mainly by [[marine biology|marine organisms]], many of which secrete shells that settle out of the water column and are deposited on [[ocean]] floors. Moreover, coral reefs are made from the calcium carbonate skeletons of coral-building organisms. Secondary calcite may be precipitated from [[groundwater]]* and deposited in caves, producing formations such as [[stalagmite]]*s and [[stalactite]]*s. |
| − | Limestone can be found in | + | Limestone can be found in many varieties, depending on its mineral composition and physical structure. When composed of calcium carbonate alone, it is white or nearly white. Other colors are produced by the presence of minor constituents such as [[clay]], sand, organic remains, [[iron oxide]]*, and other materials. In addition, limestone may be crystalline, clastic, granular, or massive, depending on the method of formation. Crystals of calcite, [[quartz]]*, [[dolomite]]*, or [[barite]]* may line small cavities in the rock. |
[[Travertine]] is a banded, compact variety of limestone formed along streams, particularly where there are waterfalls, and around [[Hot spring|hot]] or cold springs. Calcium carbonate is deposited upon evaporation of the water. [[Tufa]]*, a porous or cellular variety of travertine, is found near waterfalls. [[Coquina]]* is a poorly consolidated limestone composed of pieces of [[coral]] or [[Animal shell|shell]]s. During [[Rock (geology)|regional metamorphism]] that occurs during the mountain-building process (orogeny), limestone recrystallizes into [[marble]]. | [[Travertine]] is a banded, compact variety of limestone formed along streams, particularly where there are waterfalls, and around [[Hot spring|hot]] or cold springs. Calcium carbonate is deposited upon evaporation of the water. [[Tufa]]*, a porous or cellular variety of travertine, is found near waterfalls. [[Coquina]]* is a poorly consolidated limestone composed of pieces of [[coral]] or [[Animal shell|shell]]s. During [[Rock (geology)|regional metamorphism]] that occurs during the mountain-building process (orogeny), limestone recrystallizes into [[marble]]. | ||
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== Limestone landscape == | == Limestone landscape == | ||
| − | + | [[Image:Limestone Hole.JPG|thumb|A limestone pothole.]] | |
| − | Limestone is partially soluble, especially in [[acid]], and therefore forms many | + | Limestone is partially soluble, especially in [[acid]]ic water, and therefore forms many [[landform]]*s produced by erosion. These include [[limestone pavement]]*s (horizontal surfaces of exposed limestone), [[cave]]s, [[gorge]]s, [[pothole]]*s, and [[cenote]]s (limestone sinkholes filled with freshwater). Such erosion landscapes are known as "karsts." |
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| + | Limestone is less [[resistance (geology)|resistant]]* to erosion 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 [[clay]]s. | ||
Bands of limestone emerge from the [[Earth]]'s surface in often spectacular rocky outcrops and [[island]]s. Examples include the Burren in Co. Clare, Ireland; the [[Verdon Gorge]] in [[France]]; [[Malham Cove]] in [[North Yorkshire]], [[England]]; on [[Fårö]] near the Swedish island of [[Gotland]], the [[Niagara Escarpment]] in [[Canada]]/[[USA]], Notch Peak in [[Utah]], and the [[Ha Long Bay]] National Park in [[Vietnam]]. | Bands of limestone emerge from the [[Earth]]'s surface in often spectacular rocky outcrops and [[island]]s. Examples include the Burren in Co. Clare, Ireland; the [[Verdon Gorge]] in [[France]]; [[Malham Cove]] in [[North Yorkshire]], [[England]]; on [[Fårö]] near the Swedish island of [[Gotland]], the [[Niagara Escarpment]] in [[Canada]]/[[USA]], Notch Peak in [[Utah]], and the [[Ha Long Bay]] National Park in [[Vietnam]]. | ||
Revision as of 21:59, 23 August 2006
Limestone is a sedimentary rock composed largely of the mineral calcite (calcium carbonate, CaCO3). It makes up about 10 percent of the total volume of all sedimentary rocks. 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 calcite in limestone is produced mainly by marine organisms, many of which secrete shells that settle out of the water column and are deposited on ocean floors. Moreover, coral reefs are made from the calcium carbonate skeletons of coral-building organisms. Secondary calcite may be precipitated from groundwater and deposited in caves, producing formations such as stalagmites and stalactites.
Limestone can be found in many varieties, depending on its mineral composition and physical structure. When composed of calcium carbonate alone, it is white or nearly white. Other colors are produced by the presence of minor constituents such as clay, sand, organic remains, iron oxide, and other materials. In addition, limestone may be crystalline, clastic, granular, or massive, depending on the method of formation. Crystals of calcite, quartz, dolomite, or barite may line small cavities in the rock.
Travertine is a banded, compact variety of limestone formed along streams, particularly where there are waterfalls, and around hot or cold springs. Calcium carbonate is deposited upon evaporation of the water. Tufa, a porous or cellular variety of travertine, is found near waterfalls. Coquina is a poorly consolidated limestone composed of pieces of coral or shells. During regional metamorphism that occurs during the mountain-building process (orogeny), limestone recrystallizes into marble.
Limestone containing bivalve fossils.
Various fossils collected from a limestone quarry in North Carolina, U.S.A. Clockwise from upper left: echinoids, bryozoans, and brachiopods.
A water-cooled limestone saw.
Limestone landscape
Limestone is partially soluble, especially in acidic water, and therefore forms many landforms produced by erosion. These include limestone pavements (horizontal surfaces of exposed limestone), caves, gorges, potholes, and cenotes (limestone sinkholes filled with freshwater). Such erosion landscapes are known as "karsts."
Limestone is less resistant to erosion 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. Examples include the Burren in Co. Clare, Ireland; the Verdon Gorge in France; Malham Cove in North Yorkshire, England; on Fårö near the Swedish island of Gotland, the Niagara Escarpment in Canada/USA, Notch Peak in Utah, and the Ha Long Bay National Park in Vietnam.
In Belgium and Holland there are several huge quarries, with a total gallery length of more than a hundred kilometers. An example of a hill with a lot of quarries is mount Saint Peter (Belgium/Netherlands) [1].
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. So many buildings in Kingston, Ontario, Canada were constructed from it, that it was nicknamed the 'Limestone City'. Limestone is readily available and relatively easy to cut into blocks or more elaborate carving. It is also long-lasting and stands up well to exposure. However, it is a very heavy material, making it impractical for tall buildings. It is also quite expensive.
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 has long been noted as a source of high quality quarried building Indiana limestone, while many famous buildings in London are built from Portland 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.
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
See also
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