A great irony of pearl history is that the least expensive cultured pearl product in the market
today rivals the quality of the most expensive natural pearls ever found. The price-value anomaly
is obvious to consumers as they hasten to buy Chinese freshwater bargains. Indeed, pearls from
freshwater mussels lie at the center of the liveliest activity in pearling today. Natural freshwater
pearls occur in mussels for the same reason that saltwater pearls occur in oysters. Foreign
material, usually a sharp object or parasite, enters a mussel and cannot be expelled. To reduce
irritation, the mollusk coats the intruder with the same secretion it uses for shell-building, nacre.
To culture freshwater mussels, workers slightly open their shells, cut small slits into the mantle
tissue inside both shells, and insert small pieces of live mantle tissue from another mussel into
those slits. In freshwater mussels that insertion alone is sufficient to start nacre production.
Most cultured freshwater pearls are composed entirely of nacre, just like their natural freshwater
and natural saltwater counterparts.