What are carbonates in mineralogy ?

Carbonates : definition

Carbonates constitute the most represented subclass of the mineralogical class of "carbonates, nitrates, borates". This subclass is in turn subdivided into anhydrous carbonates, the most common (calcite, siderite, magnesite ...), and hydrated carbonates (malachite, azurite...).

Carbonates are built on the basis of the anionic complex CO32- associated with different divalent cations, mainly Ca and Mg, sometimes Fe, Mn, etc...

The carbonate subclass includes about 210 minerals divided into 3 structurally different groups : that of calcite (CaCO3, rhombohedral), aragonite (CaCO3, orthorhombic) and dolomite (CaMg (CO3)2, rhombohedral). These three minerals are by far the most abundant of the carbonate class. Calcite and dolomite are essential minerals for the formation of carbonate rocks, sandstones abundant in the earth's crust.

Calcite from Rébenacq, Pyrénées, France
Siderite from Mont St-Hilaire, Canada
Azurite from Morocco
Malachite from Camarès, France