For example, the formation of aragonite is promoted by the presence of magnesium ions, or by using proteins and peptides derived from biological calcium carbonate. Microscopic Calcite and VateriteĪragonite occurs in majority when the reaction conditions inhibit the formation of calcite and/or promote the nucleation of aragonite. However, aragonite, whose stability lies between those of vaterite and calcite, seems to be the exception to this rule, as aragonite does not form as a precursor to calcite under ambient conditions. This behavior seems to follow Ostwald's rule, in which the least stable polymorph crystallizes first, followed by the crystallization of different polymorphs via a sequence of increasingly stable phases. In additive-free aqueous solutions, calcite forms easily as the major product, while aragonite appears only as a minor product.Īt high saturation, vaterite is typically the first phase precipitated, which is followed by a transformation of the vaterite to calcite. Crystallization Crystal Structure of Calcite and AragoniteĪll three polymorphs crystallize simultaneously from aqueous solutions under ambient conditions. reacts with acids, releasing carbonic acid which quickly disintegrates into carbon dioxide and water:ĬaCO 3 ( s ) + 2 H + ( aq ) ⟶ Ca 2 + ( aq ) + CO 2 ( g ) + H 2 O ( l ), the minor structure is still unknown.Chemistry Ĭalcium carbonate shares the typical properties of other carbonates. It has medical use as a calcium supplement or as an antacid, but excessive consumption can be hazardous and cause hypercalcemia and digestive issues. Calcium carbonate is the active ingredient in agricultural lime and is produced when calcium ions in hard water react with carbonate ions to form limescale. Materials containing much calcium carbonate or resembling it are described as calcareous. It is a common substance found in rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skeletons and pearls. Chemical compound Crystal structure of calciteĬalcium carbonate is a chemical compound with the chemical formula Ca CO 3.
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