The Carbonates

 

The Carbonates belong to one group of salts of various oxygen acids; they can be divided into two classes viz. (a) the anhydrous carbonates and (b) the acid, basic and hydrous carbonates.           

·       The anhydrous carbonates include two distinct, isomorphous group and the aragonite group. The metallic elements present in the former are calcium, barium, and cobalt; in the latter they are calcium, barium, strontium and lead.

·       Calcite (CaCO3), Dolomite (CaCO3. MgCO3) Magnesite (MgCO3), siderite (FeCO3) Rhodochrosite (MnCO3) and Smithsonite (ZnCO3) belong to the Calcite group.

·       Aragonite (CaCO3) Strontianite (SrCO3) and Cerussite (PbCO3) are minerals; that belong to the Aragonite group.

·       The calcite group is characterised by rhombohedral crystallisation; the aragonite group crystallize in orthorhombic system. Malachite (CuCO3.Cu(OH)2) and Azurite (2 CuCO3. Cu (OH) 3) are minerals that fall. Under the. acid, basic and hydrous carbonates group.

·       Calcite is the most common and widespread of the carbonate minerals; has many and varied crystal forms; it frequently grades into dolomite; great masses of calcite occur in limestones.

·       Transparent crystals are used in rangefinders and polarizing microscopes. Calcite also occurs as vein mineral in many rocks. Crystalline limestones in Precambrian terrains are used in cement making.

       i.          Classification of carbonates: 

·       Hexagonal carbonates include:

Ø  Calcite

Ø  Magnesite

Ø  Dolomite

Ø  Siderite

Ø  Rhodochrosite

Ø  Smithsonite

Ø  Ankerite

·       Orthorhombic Carbonates Include:

Ø  Aragonite

Ø  Cerussite

Ø  Strontianite

Ø  Witherite