One surprising pearl fact is that most pearls sold today are actually cultured pearls.   What!   Nature creates an infinite variety of pearls however humans assist nature by enhancing pearl shape and quantity.   Natural pearls were common until overharvesting ruined the natural pearl ecosystem.  Today almost all pearls are cultured pearls.  Cultured pearls insert round beads, shells and foriegon tissue into oysters (salt water pearls) and mussels (freshwater pearls).  Mussels produce as many as 50 pearls per mussel while oysters usually produce one pearl which is one reason saltwater pearls are so much more expensive.  Cultured pearls have a much better chance of forming round pearls, most natural pears are irregular shapes known as “baroque” pearls making round natural pearls extremely rare.