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Calcium carbonate (CaCO3) is found in large deposits of limestone, marble and chalk. People have used it for centuries as a building material and as an ingredient of cement. It is also widely used as an extender in paint, especially matte emulsion paints. The mineral is also a medicinal supplement known as antacids and a food additive. Synthetic calcium carbonate, commonly called precipitated calcium carbonate or PCC, is purified and often used when high purity is required, such as in medicine and dietary supplements.
Pure calcium carbonate can be obtained from a quarry, but it is more economical to extract it from the earth by burning in a kiln. This process, called calcination, is the same as that used to produce quicklime, which is the raw material for making builder’s lime. The resulting slaked lime can be further separated from impurities such as grit and feldspar, washed, dehydrated and dried to yield the low-solids PCC that is typically sold for papermaking, rubber, plastic, abrasives and paint manufacture.
The melting point of calcium carbonate is a function of its temperature and CO2 concentration. It is lower at higher temperatures, which results in more soluble water that can dissolve the more crystalline CaCO3. The rate at which calcium carbonate dissolves can be determined using a chemistry test known as the Langelier or Ryznar Index. Positive values indicate a scale-forming condition, while negative values suggest nonscaling and noncorrosive conditions. In order to improve the scaling and corrosion resistance of calcium carbonate, it can be surface treated by physical or chemical means to modify its particle size distribution and wettability.