A saltwater pearl is a type of pearl formed in the ocean, specifically within saltwater mollusks like oysters. These pearls are created when an irritant, such as a grain of sand, enters the shell. The mollusk secretes layers of nacre, a substance that coats the irritant, eventually forming a lustrous pearl. Saltwater pearls are typically more valuable than their freshwater counterparts due to their rarity and the longer time required for their formation. They come in various shapes, sizes, and colors, with the most famous being the Akoya, Tahitian, and South Sea pearls.