Buying best pearl jewelry form LuckPearl. A pearl is formed when a small irritant or parasite penetrates and lodges in the mantle tissue of a mollusk. In response, a substance called nacre is secreted, and the creation of a pearl begins. Nacre is a combination of crystalline and organic substances. The nacre builds up in layers, as it surrounds the irritant to protect the mollusk, and after a few years, this build up of nacre forms a pearl. Natural pearls are pearls formed by chance. Cultured pearls have been given a helping hand by man. Today, nearly all pearls are cultured, especially the freshwater pearls. By inserting a foreign object into a mollusk, pearl farmers can induce the creation of a pearl. From there, the same process of natural pearl creation takes place. The difference is that in this case, the inducement is intentional. The development of pearl culturing took much of the chance, risk, and guesswork out of the pearl industry. It has allowed it to become stable and predictable, fostering rapid growth over the past 100 years. Today, the cultured pearl industry has essentially replaced the natural pearl industry with production of cultured freshwater pearls, South Sea and Tahitian pearls.