A pearl is formed when a small irritant penetrates and lodges in the mantle tissue of a mollusk. In response nacre is secreted. Nacre is a combination of crystalline and organic substances. As nacre builds up in layers, it surrounds the irritant forming a pearl.Natural Pearls vs. Cultured Pearls
Natural pearls are pearls formed by chance. Cultured pearls have been given a helping hand. Today, nearly all pearls are cultured. By inserting a foreign object into a mollusk, pearl farmers can induce the creation of a pearl.