Calcite is a carbonate mineral of secondary formation that is common to sedimentary rocks, including limestone, yet much of which is formed from the shells of long dead marine organisms.

Calcite forms in two stages. The particles from amorphous calcium carbonate dehydrate and crystallize to appear as individual particles of vaterite in the first stage. The second stage is slower where the vaterite transforms through a dissolution and reprecipitation mechanism, into calcite.