calcite group

The calcite group is a classification of minerals that share a common structure type, derived from the NaCl structure. In this group, carbonate (CO₃)²⁻ groups substitute for chlorine ions, and calcium cations replace sodium cations. This arrangement results in a rhombohedral structure due to the triangular shape of the CO₃ groups. Members of the calcite group exhibit perfect rhombohedral cleavage.

Calcite (CaCO₃) is the most common mineral in this group and is a polymorph with aragonite and vaterite. It is the stable form of calcium carbonate at most temperatures and pressures. Calcite is widely distributed in Earth's sediments and rocks, forming the primary component of limestones. It is identified by its effervescence when tested with dilute acid, a reaction that releases carbon dioxide gas. Calcite has numerous uses, including in cement, mortar, as a flux in metallurgy, and as crushed stone.12