It is much more stable than aragonite, so the original hard parts of these creatures are commonly found as fossils, millions of years after they sank to the sea floor. Calcite was used to make the shells and skeletons of extinct groups of corals, articulate brachiopods, bryozoans, echinoderms and most trilobites. During fossilisation, aragonite shells either dissolve away completely, or the aragonite recrystallizes to form calcite. Aragonite, found in the shells of molluscs such as ammonites, gastropods and bivalves, is unstable and doesn’t usually survive for millions of years. Invertebrates use two main forms of calcium carbonate to make their shells and exoskeletons, and the one they use influences how likely they are to be immortalised as fossils. Many of the 700,000 fossils in the Museum’s collections are also made of calcium minerals. The museum’s collections holds nearly 750,000 marine invertebrates, including crustaceans, corals and bristleworms. They are found on either side of the stomach and provide calcium for essential parts of the cuticle such as mouthparts and legs. Calcium required after moulting in lobsters, crawfish, crayfish and some land crabs is provided by gastroliths (sometimes referred to as gizzard stones, stomach stones or crab’s eyes). Crustaceans such as crabs and lobsters have a hard exoskeleton strengthened with both calcium carbonate and calcium phosphate. Coral reefs and some marine bristle worm tubes (Serpulidae, Spirorbinae) rely on the reinforcing nature of calcium carbonate to provide support and protection to their soft bodies. Mollusc shells are created as protective shields by their soft-bodied owners and this is true of other invertebrates, especially in the world’s oceans. In the pearl industry the oyster or mussel is ‘seeded’ with a tiny orbs of shell to ensure that the resulted pearl is totally spherical. The mantle around the soft bodied animal secretes calcium carbonate and conchiolin that surrounds the invading body and imitates its shape so they are not all perfectly spherical. In nature pearls are the result of the molluscs’ reaction against a parasitic intruder or a piece of grit. Pearls, also made of aragonite and calcite, are produced by bivalves such as oysters, freshwater mussels and even giant clams. An international collection it contains many rare, beautiful and scientifically important specimens and is utilised by worldwide scientists for their research. The 5 th most common element in the earth’s crust, calcium forms many useful rocks and minerals such as limestone, aragonite, gypsum, dolomite, marble and chalk.Īragonite and Calcite, the two most commonly crystalised forms of calcium carbonate, helped form the 2 million shells in our mollusc collection, the core of which is the Melvill-Tomlin collection, donated to the museum in the 1950s. It is crucial for life today and commonly forms a supporting role in plants and animals. Known by most as the fundamental element in bone-forming or limestone, it has a host of other applications and is present in seabeds and marine life past and present.Ĭalcium (Ca) is a light-coloured metallic element with an atomic number of 20. Continuing the international year of the periodic table of chemical elements, for April we have selected Calcium.

Calcium periodic table