Calcareous concretions are pearl-like growths produced in mollusks that lack nacre. While still composed of calcite and aragonite, the crystals are much coarser. Some of these “pearls” may have a flame-like sheen on their surface. Calcareous concretions seen in jewelry include Conch Pearls and Quahogs.
Calcareous Concretion var. Conch Pearl.