Natural calcium carbonate Limestone

Rainwater for instance will pick up atmospheric COg and react with calcium carbonate (limestone) to form a soluble substance, calcium bicarbonate. This reaction gives water its natural hardness . 

Occurrence. Carbon is distributed very widely in nature as calcium carbonate (limestone). Coal, petroleum and natural gas are chiefly hydrocarbons. Carbon is found as carbon dioxide in the atmosphere of the earth and dissolved in all natural waters. The atmosphere of Mars contains 96% C02. It is plentiful in the sun, stars, comets and the atmospheres of most planets. 

You have already seen on p. 122 in Table 8.2 that salts are useful substances. Some of the salts shown in that table occur naturally and are mined, for example calcium sulfate (gypsum) and calcium carbonate (limestone). Many of the others must be made by the chemical industry, for example ammonium nitrate, iron(n) sulfate and silver bromide. 

SYNS AGRICULTURAL LIMESTONE AGSTONE ARAGONITE ATOMIT BELL MINE PULVERIZED limestone CALCITE CARBONIC ACID, CALCIUM SALT (1 1) CHALK DOLOMITE FRANKLIN D LIMESTONE (FCC) LITHOGRAPHIC STONE MARBLE NATURAL CALCIUM CARBONATE PORTLAND STONE SOHNHOFEN STONE VATERITE... 

Calcite. A common crystalline form of natural calcium carbonate, caco3, that is the basic constituent of limestone, marble, and chalk. Also called calcspar. 

Calcium carbonate (limestone) occurs in nature as calcite, aragonite, valerite, dolomite (CaCOj MgCOj), chalk and travertine. An example of past use for limestone was in Egypt for construction of the Giza Pyramids and as marble - its highly crystalline form - somewhat later by the Greeks for statues and parts of buildings. The Romans used limestone extensively for road construction. Today, limestone is the... 

Test methods for limestone aggregates and natural calcium carbonates are specified in the relevant parts of BS 812 [6.3] and BS 6463 [6.5]. The former is being replaced by CEN Standards that are in preparation (see section 6.5). BS 6463, Part 102 (also in preparation) refers to CEN test methods, where appropriate (see below). 

Synonyms Agricultural limestone Calcite Calcium carbonate natural Chalk Cl 77220 Dolomite Franklin Limestone Lithographic stone Marble Natural calcium carbonate Paris white Pigment white 18 Portland stone Vaterlte Whiting Classification Inorganic salt... 

Sedimentary rocks are derived from weathered rock masses and deposited by the action of water or other means, or by the sedimentation of bioliths (mineral skeletons, shells, etc., of plants and animals) into layers, or, rarely, by chemical precipitation. Massive deposits of china clay or kaolin are found as a result of weathering, followed by movement and deposition. Limestone, the general term for natural calcium carbonate rocks, is the most abundant of the sedimentary rocks and is formed by the deposition of countless skeletons and shells. Gypsum and diatomaceous earths occur widely in sedimentary rocks. Sedimentary rocks are almost universally found in layered beds, which may have folded or otherwise been altered by subsequent geological events. Layers will differ from each other in texture, mineralogy and particle size. 

All commercial grades of natural calcium carbonate are based upon deposits of calcite, which vary in purity, colour and crystallite size. These factors depend upon genesis and subsequent temperature-pressure history. Chalk is usually off-white in colour and is composed of small crystals which are easily disintegrated. Marble, by metamorphosis, has large crystals and very white deposits can be found. Limestone is one of a number of intermediate forms and varies from white to grey or buff in colour, due mainly to iron impurities. 

Oyster shells were used as a white pigment in Japan, locally called gofun (q.v.). Further, according to Hall (1973) Oyster shell pigment, a fossUiferous form of limestone (like chalk), is a natural calcium carbonate that is finely gioimd for pigment use. See shell white. 

Whiting is a term commonly applied to natural prepared chalk and synthetically prepared calcium carbonate (qq.v.). Hall (1973), for example, states that The name whiting for natural calcium carbonate originally referred to a very finely pulverised form of chaUc but the term is now used more broadly to include all finely divided carbonates that are derived from high-calcium ordolomitic limestone [q.v.]. ... 

Calcium carbonates can occur naturally in the form of chalk, limestone, marble, etc., from which the filler is obtained by fine milling or synthesized by precipitation. Due to its low price and to the improvement of polymer properties and aging resistance, natural calcium carbonate is the most important filler used in plastics. Small amounts of finely dispersed CaC03, silica, or various silicates reduce sticking and improve the paperlike feel of PE films. 

Natural calcium carbonate is a very abundant material found in limestone and other minerals. There are about 2.5 billion pounds per year of ground calcium carbonate used in the world with about 20% going into rubber. 

Many natural waters and municipal water supplies contain calcium carbonate (limestone, CaCOj) in solution. Limestone is dissolved in water to form soluble calcium bicarbonate (Ca(HC03)2). Limestone can be caused to precipitate again, forming a milky-white suspension, by making the calcium bicarbonate solution more alkaline or by adding more calcium. Usually, fime is added to accomplish both objectives. 

Synonyms Agricultural limestone Allied whiting Calcite Calcium carbonate (INCI) Calcium carbonate (1 1) Calcium carbonate, precipitated Calcium monocarbonate Carbonic acid calcium salt Carbonic acid calcium salt (1 1) Chalk Cl 77220 Dolomite Drop chalk English white Franklin Limestone Lithographic stone Marble Monocalcium carbonate Natural calcium carbonate Paris white Pigment white 18 Portland stone Precipitated calcium carbonate Precipitated chalk Prepared chalk Vaterite Vienna white White powder Whiting Classification Inorganic salt... 

Some carbonates are important industrial chemicals. Calcium carbonate occurs naturally in several forms, including limestone, and is used in the production of quicklime, calcium oxide CaO, slaked (or hydrated) lime, calcium hydroxide Ca(OH)2 and cement. 

Calcium. Calcium is the fifth most abundant element in the earth s cmst. There is no foreseeable lack of this resource as it is virtually unlimited. Primary sources of calcium are lime materials and gypsum, generally classified as soil amendments (see Calcium compounds). Among the more important calcium amendments are blast furnace slag, calcitic limestone, gypsum, hydrated lime, and precipitated lime. Fertilizers that carry calcium are calcium cyanamide, calcium nitrate, phosphate rock, and superphosphates. In addition, there are several organic carriers of calcium. Calcium is widely distributed in nature as calcium carbonate, chalk, marble, gypsum, fluorspar, phosphate rock, and other rocks and minerals. 

Whiting at one time coimoted only a very fine form of chalk of micrometer sizes but the term is now used more broadly to include all finely divided, meticulously milled carbonates derived from high calcium or dolomitic limestone, marble, shell, or chemically precipitated calcium carbonate. Unlike all of the above natural forms of limestone, it is strictly a manufactured product. 

The most common compound of calcium is calcium carbonate, CaC03, which occurs naturally in a variety of forms such as chalk and limestone. Marble is a dense form of calcium carbonate that can be given a high polish it is often colored... 

Limestone caverns are among nature s most spectacular displays. These caves occur in many parts of the world. Examples are Carlsbad Caverns In New Mexico, Jeita Caves in Lebanon, the Blue Grotto in Italy, and the Jenolan Caves In Australia. Wherever they occur, the chemistry of their formation involves the aqueous equilibria of limestone, which Is calcium carbonate. Three such equilibria, linked to one another by Le Chatelier s principle, play essential roles In cave dynamics. 

Historically, the alkali industry is based on limestone, or chalk. The chemical name for limestone is calcium carbonate (CaCOs). It is a very common mineral in seashells. Therefore, limestone is a naturally occurring sedimentary rock formed when seas or lakes evaporate. When limestone is heated, it produces carbon dioxide... 

Most elements, however, are naturally combined with one or more other elements, forming compounds. Water and calcium carbonate (also known as calcite, limestone, or marble) are examples of common compounds formed by the combination of two or more elements in water, one atom of oxygen is combined with two of hydrogen and in calcium carbonate, one atom of carbon is combined with three of oxygen and one of calcium. 

The composition of the particles is related to that of the source rocks. Quartz sand [composed of silica (silicon dioxide)], which makes up the most common variety of silica sand, is derived from quartz rocks. Pure quartz is usually almost free of impurities and therefore almost colorless (white). The coloration of some silica sand is due to chemical impurities within the structure of the quartz. The common buff, brown, or gray, for example, is caused by small amounts of metallic oxides iron oxide makes the sand buff or brown, whereas manganese dioxide makes it gray. Other minerals that often also occur as sand are calcite, feldspar and obsidian Calcite (composed of calcium carbonate), is generally derived from weathered limestone or broken shells or coral feldspar is an igneous rock of complex composition, and obsidian is a natural glass derived from the lava erupting from volcanoes see Chapter 2. 

Whenever natural water is heated and evaporates, some of the calcium bicarbonate reconverts to calcium carbonate and reprecipitates as limestone ... 

The action of carbonic acid on limestone produces a calcium bicarbonate solution that is exceedingly soluble in water. (For comparison, at 20°C the solubility of calcium carbonate in water is only 0.0145 g per liter while the solubility of calcium bicarbonate is 166 g per literJ ) Magnesium ions from dolomite are also released into aqueous solution according to the same mechanism. The weathering of gypsum, calcium sulfate, also releases calcium ions into natural water supplies. 

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