Cultured freshwater pearls give us an amazing variety of colors and shapes.
Most freshwater pearls come from the triangular hyriopsis cumingi mussel native to China. The vast majority of freshwater pearls are cultured in China. A modest number are farmed in Japan's Lake Biwa and a small pearl farm also operates in the Tennessee River in the United States.
These freshwater mussels are amazing little pearl factories. They can be implanted with up to 40 nuclei! Sometimes they will accept a second nucleation. After implantation, they are left to do their thing for two to three years before harvesting. Pearls range from 2mm to 13mm with the average size of 6mm to 10mm. A very small amount, only 2%, are spherical.
In 2004, China produced 10 times the amount of cultured freshwater pearls than all the other pearl producers, salt and freshwater, combined. Because of their low price and abundance, they often come dyed in a wild variety colors and nucleated in many interesting shapes.
In the beginning, most of the Chinese goods were the highly textured rice shape. From the 1970's to the 1990's shape and surface quality improved. The market now offers round and near round cultured pearls of very high quality at a very reasonable price point.