Minerals aragonite

The choice of selected raw materials is very wide, but they must provide calcium oxide (lime), iron oxide [1309-37-1/, siHca, and aluminum oxide (alumina). Examples of the calcereous (calcium oxide) sources are calcium carbonate minerals (aragonite [14791-73-2] calcite [13397-26-7] limestone [1317-65-3] or mad), seasheUs, or shale. Examples of argillaceous (siHca and alumina) sources are clays, fly ash, mad, shale, and sand. The iron oxide commonly comes from iron ore, clays, or mill scale. Some raw matedals supply more than one ingredient, and the mixture of raw matedals is a function of their chemical composition, as deterrnined by cost and availabiHty. 

It is the case that in surface seawater at 25°C, the ion activity products of all the minerals aragonite, magnesian calcite (15 mole %), calcite and dolomite are... 

Solution caverns or caves often contain deposits of recrystallized calcium carbonate, usually in the form of the mineral aragonite. Stalactites, stalagmites, and other cave formations are called speleothems. Created gradually by the precipitation of aragonite from groundwater, many speleothems display a layered structure. Recent study shows that bacteria and other simple life forms may contribute to the formation of cave deposits. 

Calcium (3.4% of lithosphere) occurs as carbonate in the minerals aragonite and calcite and the rocks limestone, chalk and marble, and as sulphate in anhydrite, CaS04, and gypsum, CaS04.2H20. All are plentiful and widely distributed. The metal, which has both h.c.p. and c.c.p. forms, is made (Fig. 138) by electrolysing the fused chloride, CaClg, a by-product of the Solvay process. 

The porosity associated with the exinitic maceral of the splint coal can be seen more clearly in Figure 4. The large, irregularly shaped pores often form distinct tubular channels, which extend from the apparent center of the spore exine to the boundary between the spore and the surrounding inertinite. Commonly the channels contain spherical particles, who.se identity as the mineral aragonite (CaC03) was based on... 

Calcium does not occur as a free element in nature. It is much too active and always exists as a compound. The most common calcium compound is calcium carbonate (CaC03). It occurs in the minerals aragonite, calcite, chalk, limestone, marble, and travertine, and in oyster shells and coral. 

Calcium carbonate is prepared by double decomposition of calcium chloride and sodium bicarbonate in aqueous solution. Density and fineness are governed by the concentrations of the solutions. Calcium carbonate is also obtained from the naturally occurring minerals aragonite, calcite, and vaterite. 

Sedimentary calcium carbonates are formed as the shells of marine plants and animals. Biologically produced CaCOs consists primarily of two minerals aragonite and calcite. Shallow-water carbonates, primarily corals and shells of benthic algae (e.g. Halimeda) are heterogeneous in their mineralogy and chemical composition but are composed mainly of aragonite and magnesium-rich calcite (see Morse and Mackenzie (1990) for a discussion). Carbonate tests of microscopic plants and animals, most of which hve in the surface ocean (there are also benthic animals that produce carbonate shells), are primarily made of the mineral calcite, which composes the bulk of the CaCOs... 

Calcium Carbonate, Carbonic acid calcium sail (1 1) Calcichew Calcidia Citrical. CCaOj mol wt 100.09. C 12.00%, Ca 40.04%, O 47.96%. CaCOj. Exists in nature as the minerals aragonite, calcite and vaterite. 

The most important carbonate mineral is calcium carbonate, CaCOs. This substance occurs in beautiful colorless hexagonal crystals as the mineral calcite. Marble is a microcrystalline form of calcium carbonate, and limestone is a rock composed mainly of this substance. Calcium carbonate is the principal constituent also of pearls, coral, and most sea shells. It also occurs in a second crystalline form, as the orthorhombic mineral aragonite. 

Mother-of-pearl is an iridescent form of the calcium carbonate mineral aragonite (and occasionally vaterite) forming on the inside of molluscan shells. It is technically referred to as nacre. Field (1835) describes the use of true mother-of-pearl as an opalescent pigment. 

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