Calcium carbonate

Calcium carbonate is a chemical compound, with chemical formula CaCO3.

It is commonly used as an antacid, and is the active ingredient in agricultural lime. It is a common substance found as rock in all parts of the world and is the main component of seashells and the shell of snails.

Occurrence
Calcium carbonate is found naturally as the following minerals and rocks:
 * Aragonite
 * Calcite
 * Chalk
 * Limestone
 * Marble
 * Travertine

Eggshells are composed of approximately 95% calcium carbonate.

To test whether a mineral or rock contains calcium carbonate, strong acids like hydrochloric acid can be dropped with a dropper onto it. If it does contain the chemical, it will fizz and produce carbon dioxide; otherwise, it probably wouldn't react vigorously. For example, all of the rocks/mineral mentioned above will react with acid.

Preparation
The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. When pure calcium carbonate is required (e.g. for food or pharmaceutical use), it is prepared by passing carbon dioxide into a solution of calcium hydroxide: the calcium carbonate precipitates out, and this grade of product is referred to as precipitated.
 * Ca(OH)2 + CO2 &rarr; CaCO3 + H2O

Chemical properties

 * See also: Carbonate

Calcium carbonate shares the typical properties of other carbonates. Notably:
 * 1) it reacts with strong acids, releasing carbon dioxide.
 * CaCO3 + 2HCl &rarr; CaCl2 + CO2 + H2O


 * 1) it releases carbon dioxide on heating (to above 825 °C in the case of CaCO3), to form calcium oxide.
 * CaCO3 &rarr; CaO + CO2

Calcium carbonate will react with water that is saturated with carbon dioxide to form the soluble calcium bicarbonate.
 * CaCO3 + CO2 + H2O &rarr; Ca(HCO3)2

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

Uses
The main use of calcium carbonate is in the construction industry, either as a building material in its own right (e.g. marble) or as an ingredient of cement.

Calcium carbonate is widely used in the pharmaceutical industry, either as an antacid, a calcium supplement (approximately 600 mg of calcium per gram of calcium carbonate), or as a base material for tablets of other pharmaceuticals.

Calcium carbonate is known as whiting in ceramics/glazing applications, where it is used as a common ingredient for many glazes in its white powdered form. When a glaze containing this material is fired in a kiln, the whiting acts as a flux material in the glaze.

It is commonly called chalk as it has been a major component of blackboard chalk. Chalk may consist of either calcium carbonate or gypsum, hydrated calcium sulfate CaSO4&middot;2H2O.

Recently, calcium carbonate has begun to replace kaolin in the production of glossy paper.

It is also the substance from which the lens of the mammalian eye is made.