|Density (at 0oC)||1.54 g/cm3|
|Boiling point||1757 K|
|Melting point||1115 K|
Calcium is an alkaline Earth mineral. It is naturally found in bones, teeth, shells, rocks, and minerals. Calcium carbonate is a naturally occurring compound that is the basis for limestone, marble, and chalk. Stalagmites and stalactites in caves form from calcium carbonate precipitating out of solution.
Calcium is used as a reducing and/or alloying agent for metals. It is used primarily in the creation of steel to improve the steel's mechanical properties. Historically, calcium was used to create lime (a calcium oxide and/or hydroxide compound), which was used as a building material. Lime is still used today in substances like paints, concrete, cement, and plaster.
Calcium compounds (such as calcium carbonate or calcium magnesium pills) are often used as calcium supplements for human consumption. Calcium carbonate is also used as an antacid for indigestion.
Calcium carbonate compounds (limestone, shells, etc.) are natural carbon sinks in two ways:
Through weathering and human activities, the calcium carbonate can be made to break down, releasing the stored carbon dioxide. Acidified solutions (e.g. acid rain) and heat (especially from human processign) are particularly good at breaking down calcium carbonate and bicarbonate into calcium oxide and carbon dioxide (and water, in the case of bicarbonate breakdown).