A mineral that forms in seawater from the skeletons of sea creatures?

A mineral that forms in seawater from the skeletons of sea creatures is calcium carbonate, often found in the form of aragonite or calcite. These minerals are produced by marine organisms such as corals, mollusks, and certain plankton as they create their shells and skeletons. Upon death, these organisms contribute to sediment that eventually compacts and can form limestone or other sedimentary rocks. This process plays a critical role in the carbon cycle and the geological carbon sequestration of the oceans.