“Natural Pearls” is a very interesting phrase. It almost suggests that Cultured Pearls used in pearl jewelry are not natural. Natural Pearl simply pearls that have formed in nature. To this day natural pearls are being formed. The only problem is that you have find them somewhere at the bottom of the ocean. At this time in history to find enough “Natural Pearls” to complete pearl necklaces is almost an impossible accomplishment. When an "irritant" is lodged in the oysters' tissue, a natural pearl is formed. The process is actually a defense mechanism by the oyster, in which the irritant is covered with a substance called nacre. This mainly calcium carbonate compound covers the irritant one layer after another. Over a period of months to years, this eventually forms a Natural Pearl.