Because of its shape and inscrutable luster pearl is true in many cultures as a symbol of eternity, beauty of spirit, wisdom and immortality. They are located on the inside of shells in response to a piece of sand which enters the shell. The mollusc then deposits a layer of calcium carbonate on the grain of sand, in the form of minerals. The layers are by a horn-like substance cemented together. It is estimated that a pearl is in one in 15,000 wild oysters. Therefore, nowadays cultivated almost all pearls. For this, put a small grain of pearl in the oyster and the pearl can be harvested after two years.