There are five types of freshwater pearls: Biwa pearls, mabe pearls, blister pearls, Chinese freshwater pearls, and seed pearls.
Biwa pearls are known for their good quality, smooth surface, and high, even luster. Biwa pearls originate from Lake Biwa which is the largest lake in Japan and the first freshwater culturing site. The freshwater mussels don't accept a nucleus and, as a result, Biwa pearls have interesting shapes. The colors of these pearls ranges from creamy white to white-rose, salmon orange, dark wine red and violet.
Chinese freshwater pearls resemble Biwa pearls but they use a nucleus made from the mantle tissue of another oyster which is cut into a desired shape. The colors range from rose, white, green-white, green-rose, salmon orange, wine red and violet.
Mabe pearls are cultured by gluing a half-bead nucleus against the inside of a mollusk's shell. When the hemispherical nucleus is covered in nacre, it is cut out. The hole in the nucleus is filled and the pearl is backed with mother-of-pearl. Mabe pearls are not as durable as other types of pearls. Over time, the nacre coating might lift off, become damaged, or discolored.
Blister pearls grow attached to the inner surface of the shell rather than loose in the mollusk's mantle. The blister pearl has the same iridescent nacre as the inner surface of the shell and the back is flat.
Seed pearls are small natural pearls that measure two millimeters or less. These pearls are usually drilled and strung together.
Freshwater pearls range in size from 2.5 mm to 9 or 10 mm. The largest freshwater pearls are 10-12 mm.