In nature, carbon atoms join with oxygen to form the carbonate ion, CO3. These ions combine with metal cations to form carbonate minerals. These minerals are commonly formed in sedimentary and oxidizing environments.

The carbonates fall into three groups: the calcite group, the dolomite group, and the aragonite group. The copper carbonate minerals, azurite and malachite, are the only important economic carbonates.

Minerals of the carbonate class:

• Are transparent.
• Are lightly-colored with a white streak.
• Have average to above average specific gravity.
• Are soft with good to perfect cleavage.
• Soluble in acidic solutions.