Natural pearls form in freshwater and saltwater, in mollusks such as mussels, oysters and abalone. An intruder, such as a tiny worm or other material, gets into the mollusk and irritates the animal. Eventually these layers will form a pearl. The more nacre the animal secretes the smoother the coats will become. The more layers of nacre and the thinner the layers, the better the luster the pearl will have.
Natural pearls are extremely rare due to the polluted waters.
Cultured Pearls are a combination of man working with nature. Cultured pearls are formed by a human cultivator implanting a foreign matter into a mollusk. Once the shell is opened, a small incision is made in the mollusk's flesh. A small piece of tissue from another mollusk and a bead or piece of shell are inserted. Only about 2 out of 3 survive this process.