How Do Oysters Make Pearls?

The pearl-making process begins when a foreign particle, like a grain of sand or a tiny parasite, finds its way into the oyster’s shell. This uninvited guest irritates the oyster, much like a pebble in a shoe. To protect itself, the oyster’s mantle tissue, which is responsible for shell formation, starts to secrete nacre, also known as mother-of-pearl, around the irritant. This material, made largely of aragonite (CaCO₃) but also conchiolin, a hornlike organic substance that is the main constituent of the mollusk’s outer shell.

The oyster continues to coat the particle with layers of nacre over time. This process is akin to wrapping a gift. The layers of nacre build up gradually, creating a smooth, lustrous pearl. The more layers that are laid down, the larger and more lustrous the pearl becomes. This process can take several years, depending on the oyster species and environmental conditions.

The end result is a pearl, which can vary in shape, size, and color depending on the type of oyster and the conditions in which it lives. Pearls can be perfectly round, which are the most valued, or they can be irregularly shaped and known as baroque pearls. The color of the pearl can range from white to black, with various shades in between, influenced by the oyster’s environment and species.