- Most carbonate rocks are formed by the precipitation of calcium carbonate from seawater. This occurs when the concentration of calcium ions and carbonate ions in the water is high enough to exceed the solubility of calcium carbonate.

Biochemical precipitation:

- Some carbonate rocks are formed by the biochemical precipitation of calcium carbonate by organisms such as corals, mollusks, and algae. These organisms extract calcium and carbonate ions from the water and use them to build their shells and skeletons.

Lithification:

- Once the calcium carbonate has been precipitated, it must be lithified, or turned into rock. This occurs when the sediment is compacted and cemented together by minerals such as calcite or aragonite.