Calcitedolomite

Calcitedolomite is a term used to describe the calcite–dolomite continuum in carbonate rocks, representing the solid solution between the end-member minerals calcite (CaCO3) and dolomite (CaMg(CO3)2). It is not a discrete mineral but a range of compositions where calcium and magnesium substitute for one another within carbonate lattices. The system is typically described as a calcite–dolomite solid solution, with end members and intermediate compositions found in nature.

In terms of structure, both calcite and dolomite crystallize in a trigonal, rhombohedral lattice. Dolomite differs from calcite by containing alternating layers of calcium and magnesium; in calcitedolomite, varying Mg content produces continuous changes in lattice parameters and textural features. The carbonate framework remains CO3 groups, but the cation ordering and proportion shift with composition.

Calcitedolomite occurs widely in sedimentary rocks, particularly limestones and dolostones. It forms through diagenetic processes such as dolomitization, where magnesium-rich fluids partially replace calcium in limestone, producing mixed compositions. Intergrowths of calcite and dolomite can also occur, reflecting changes in chemical conditions during burial and burial-related metasomatism. The result is a rock that may display a mosaic of microcrystalline grains and a broad color range due to impurities.

Physical properties vary with composition. Pure calcite and pure dolomite have distinct reactions to acids, hardnesses, and densities, and calcitedolomite varieties exhibit intermediate or mixed characteristics. The material is economically important as a reservoir rock in carbonate basins and as a component in cement and aggregate materials. Its study helps.decode the diagenetic history and fluid interactions that shape carbonate rocks.