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Reference.org
Calcium carbonate
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<p>Calcium carbonate is a <a href="/facts/Chemical_compound/37FXqqtv">chemical compound</a> with the <a href="/facts/Chemical_formula/hghUtthl">chemical formula</a> <a href="/facts/Calcium/hf252CC0">Ca</a><a href="/facts/Carbonate/FES1QHkN">CO3</a>. It is a common substance found in <a href="/facts/Rock_(geology)/FXCJkmop">rocks</a> as the <a href="/facts/Mineral/LkUFbNmv">minerals</a> <a href="/facts/Calcite/gKMHYQJo">calcite</a> and <a href="/facts/Aragonite/QGcD3SLs">aragonite</a>, most notably in <a href="/facts/Chalk/b6hepsNS">chalk</a> and <a href="/facts/Limestone/8ntvtFnR">limestone</a>, <a href="/facts/Eggshell/eWg3KsVh">eggshells</a>, <a href="/facts/Gastropod_shell/HIIBd2oQ">gastropod shells</a>, <a href="/facts/Shellfish/JjTSlMgw">shellfish</a> skeletons and <a href="/facts/Pearl/7ombxKgg">pearls</a>. Materials containing much calcium carbonate or resembling it are described as <a href="/facts/Calcareous/sGpRISvY">calcareous</a>. Calcium carbonate is the active ingredient in <a href="/facts/Agricultural_lime/5UgLrVED">agricultural lime</a> and is produced when calcium <a href="/facts/Ion/3bePpDna">ions</a> in <a href="/facts/Hard_water/Ay4aksF4">hard water</a> react with <a href="/facts/Carbonate_ion/FES1QHkN">carbonate ions</a> to form <a href="/facts/Limescale/1BNaIVAH">limescale</a>. It has medical use as a <a href="/facts/Calcium/hf252CC0">calcium</a> supplement or as an <a href="/facts/Antacid/CP9PeyQ8">antacid</a>, but excessive consumption can be hazardous and cause <a href="/facts/Hypercalcemia/kdEeLaVd">hypercalcemia</a> and digestive issues. </p>