![]() ![]() The carbonate minerals form the rock types: limestone, chalk, marble, travertine, tufa, and others. ![]() Calcium carbonate occurs as aragonite, calcite and dolomite as significant constituents of the calcium cycle. Surface precipitation of CaCO3 as tufa in Rubaksa, EthiopiaĬarbonate is found frequently in geologic settings and constitutes an enormous carbon reservoir. Magnesium carbonate (MgCO 3) has the calcite structure, whereas strontium carbonate and barium carbonate (SrCO 3 and BaCO 3) adopt the aragonite structure, reflecting their larger ionic radii. The vaterite structure is not fully understood. Calcite contains calcium atoms coordinated by six oxygen atoms in aragonite they are coordinated by nine oxygen atoms. The aragonite form can be prepared by precipitation at temperatures above 85 ☌ the vaterite form can be prepared by precipitation at 60 ☌. Other forms can be prepared, the denser (2.83 g/cm 3) orthorhombic λ-CaCO 3 (the mineral aragonite) and hexagonal μ-CaCO 3, occurring as the mineral vaterite. The thermodynamically stable form of CaCO 3 under normal conditions is hexagonal β-CaCO 3 (the mineral calcite). Water is added to give calcium hydroxide then carbon dioxide is passed through this solution to precipitate the desired calcium carbonate, referred to in the industry as precipitated calcium carbonate (PCC): CaO + H 2O → Ca(OH) 2 Ca(OH) 2 + CO 2 → CaCO 3↓ + H 2O Structure ![]() Pure calcium carbonate (such as for food or pharmaceutical use), can be produced from a pure quarried source (usually marble).Īlternatively, calcium carbonate is prepared from calcium oxide. The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. ![]() This reaction is important in the erosion of carbonate rock, forming caverns, and leads to hard water in many regions.Īn unusual form of calcium carbonate is the hexahydrate, ikaite, CaCO 3♶H 2O.
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