A natural pearl is a precious gemstone formed within the soft tissue of a living mollusk, such as an oyster or a clam. Unlike cultured pearls, which are created through human intervention, natural pearls develop spontaneously when an irritant, like a grain of sand, enters the shell. The mollusk secretes layers of nacre, a substance that coats the irritant, eventually forming a pearl. Natural pearls are rare and highly valued for their unique shapes, colors, and luster. They can be found in various types of mollusks, and their sizes can range from tiny to large. Due to their scarcity, natural pearls are often considered more valuable than cultured pearls in the jewelry market.