Pearls independently if they are marine or freshwater, follow the same basic process of formation, this occurs when a piece of debris like sand or other particles, even some parasites enter into the mollusk, this particle gets into the interior of the mollusk valves, once this strange body is stuck, the mollusk produces a lustrous substance called nacre as a defense mechanism, the layers of nacre are accumulated increasing the size of the pearl, take around two to four years to form. Nacre is mainly composed of calcium carbonate (CaCO₃).