We just acquired a "river pearl" festoon necklace which was billed as made up of Mississippi pearls. They look like others I've read about here and elsewhere but the accompanying GIA report they are (at least partially) identified only as "Unionidae family". Is there a way to further narrow the possibilities? My wife loves the necklace but would like to know where the pearls come from if ay all possible. As usual any info/input would be appreciated!