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Calcium carbonate

Calcium carbonate is a chemical compound with the formula CaCO₃. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime, and is usually the principal cause of hard water. It is commonly used medicinally as a calcium supplement or as an antacid, but excessive consumption can be hazardous.

Calcium carbonate shares the typical properties of other carbonates. Notably:

Calcium carbonate will react with water that is saturated with carbon dioxide to form the soluble calcium bicarbonate.

This reaction is important in the erosion of carbonate rocks, forming caverns, and leads to hard water in many regions.

The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. Pure calcium carbonate (e.g. for food or pharmaceutical use), can be produced from a pure quarried source (usually marble).

Alternatively, calcium carbonate is prepared by calcining crude calcium oxide. Water is added to give calcium hydroxide, and carbon dioxide is passed through this solution to precipitate the desired calcium carbonate, referred to in the industry as precipitated calcium carbonate (PCC):