Carbonates, Anhydrous Carbonates - Calcite Group

The carbonates are grouped into two divisions: (1) Anhydrous Carbonates; (2) Acid, Basic and Hydrous Carbonates.

Anhydrous Carbonates

Calcite Group
The Calcite Group consists of a series of carbonates of the bivalent metals, calcium, magnesium, ferrous iron, manganese and zinc. The all crystallize in the rhombohedral class of the Hexagonal System with closely agreeing crystal constants. They all show a perfect rhombohedral cleavage, with the angle between the cleavage faces varying from 105° to 108°. The Calcite Group forms one of the most marked and important groups of isomorphous minerals, its chief members being as follows:

• Calcite, CaCO₃.
• Dolomite, (Ca,Mg)CO₃.
• Magnesite, MgCO₃.
• Siderite, FeCO₃.
• Rhodochrosite, MnCO₃
• Smithsonite, ZnCO_3.