Calcite

**Chemical name:** Calcium carbonate **Formula:** CaCO₃ **Molar mass of compound CaCO₃:** 100.087 g/mol **Mohs scale hardness:** 3 **Crystal system:** Rhombohedral system **Arrangement of atoms:** The calcium carbonate structure consists of planar coordination groups of CO₃ and calcium ions, which are arranged in a six-fold coordination with oxygen atoms. **Crystal habit:** Calcium carbonate can crystallize in columnar, rhombohedral or scalenohedral forms. **Description:** Calcite is a mineral formed by the crystallization of magma and hydrothermal fluids. It is a primary component of rocks such as limestone, marble and travertine, and exhibits various colors depending on impurities. Transparent varieties of calcite are known as Iceland spar. **Applications:** Calcium carbonate is used in the production of lime and cement and as a building material. Iceland spar is used as a polarizing prism in optical devices.