Which animals produce pearls?

The shimmering spheres known as pearls are indeed a remarkable natural phenomenon, primarily formed within the soft tissue of certain mollusks. When an irritant, such as a parasite (Review), a piece of shell, or even a grain of sand, finds its way into the shell of one of these creatures, the animal responds by coating the intruder with layers of nacre. This lustrous substance, also known as mother-of-pearl, builds up over time, eventually creating the beautiful gem we recognize.

While many immediately associate pearls with oysters, these marine bivalves are indeed the most famous and prolific producers of the high-quality, iridescent pearls valued in jewelry. Specific species like the Pinctada oyster family are renowned for their output, particularly for saltwater (Deals) pearls. However, it's a common misconception that only oysters can create pearls. Other bivalve mollusks, including mussels and clams, are also capable of forming these concretions.

The pearls produced by other mollusks, such as freshwater mussels, are often less iridescent or perfectly spherical than their saltwater oyster counterparts, though they can still be quite beautiful and valuable. The vast majority of pearls available today, whether from oysters or mussels, are actually cultured. This means humans intentionally introduce an irritant into the mollusk to stimulate pearl formation, a process that has made these natural wonders more accessible than ever before. Natural pearls, formed without human intervention, remain exceedingly rare and highly prized.