Keshi pearls are a gorgeous by-product of the pearl culturing process. Basically what happens with a keshi pearl is that the technician nucleates the pearl-bearing mollusk (this happens with both saltwater pearl oysters and Freshwater pearl mussels), and while the pearl is forming, a small piece of it breaks off within the body of the mollusk. The broken-off piece also irritates the mollusk into forming a pearl sac, and begin smoothing over the irritant with pearl nacre, creating an accidental pearl! These Freshwater keshi pearls are much more colorful than their saltwater cousins.
