Freshwater pearls from China are traditionally “tissue nucleated”. They are grown in man-made ponds and lakes throughout China, typically on small family-owned farms.
This means that tiny, 1.0mm square pieces of mantle tissue are inserted into small incisions made throughout the soft body of the host mussel. These pieces of donor tissue serve as organic nuclei that stimulate pearl sac formation, and eventually, form our beloved, colorful Freshwater pearls.
As the Freshwater mussel begins to create the pearl, it envelops the mantle tissue nucleus in a pearl sac and the donor tissue square inside slowly begins to degrade. This will continue throughout the 2-3 year formation period, until nothing remains in the core of the pearl …
Basically, it creates a pearl made up of 100% solid crystalline nacre (so they're very, very durable little gems).
Freshwater pearl mussels can be nucleated up to 25 times on each side of the shell, so a potential pearl harvest from even a single mussel absolutely dwarfs that of any other pearl type.This larger harvest volume accounts in large part for their less expensive prices.