Freshwater pearl mussel Freshwater pearl mussel The freshwater pearl mussel ("Margaritifera margaritifera") is an endangered species of freshwater mussel, an aquatic bivalve mollusc in the family Margaritiferidae. Although the name "freshwater pearl mussel" is often used for this species, other freshwater mussel species can also create pearls and some can also be used as a source of mother of pearl. In fact, most cultured pearls today come from "Hyriopsis" species in Asia, or "Amblema" species in North America, both members of the related family Unionidae; pearls are also found within species in the genus "Unio". The interior of the shell of "Margaritifera margaritifera"
Pearl are also commonly seen in necklaces. Circled pearls are characterized by concentric ridges, or rings, around the body of the pearl. In general, cultured pearls are less valuable than natural pearls, whereas imitation pearls have almost no value. One way that jewelers can determine whether a pearl is cultured or natural is to have a gemlab perform an X-ray examination of the pearl. If X-rays reveals a nucleus, the pearl is likely a bead-nucleated saltwater pearl. If no nucleus is present, but irregular and small dark inner spots indicating a cavity are visible, combined with concentric rings of organic substance,