Calcium

**Symbol:** Ca

**Atomic number:** 20

**International title:** calcium

**Relative Atomic Weight:** 40,80

**Information:** Calcium is a soft, light, reactive metal with a silver-like colour. Its properties are reminiscent of alkaline metals, although not so reactive. It exists in the form of calcium cation Ca²⁺.

**Use:** Calcium is used as a reducing agent (in organic synthesis as well as in the production of other more expensive metals, for example in the production of steel). It is also used in the production of lime glass. Oxide and calcium hydroxide are used in the building industry.

**Occurrence:** Calcium is among the top ten most popular elements on Earth. The most common rock is CaCO₃, which is composed of minerals of calcite and aragonite. Limestone varieties include chalk and marble. Chalk is almost a pure porous limestone, which originated from the shells of marine organisms. Marble is a highly prized variety of limestone used in construction and sculpture. Other major minerals of calcium are dolomite or magnesium carbonate CaMg(CO₃)₂, apatite Ca₅(PO₄)₃X (where X = OH, F or Cl), CaF₂ and gypsum CaSO₄·2H₂O. Calcium is a biogenic element (an essential part of bones and teeth).

**Structure:** Calcium crystallizes into a cubic (cubic) system (surface-centered cell).