I have been finding some freshwater pearls out of the Duck River and Tennessee freshwater shells. Although I have not found a "perfect pearl" I have found a 75carat pearl that appears to be black underneath a relatively thin whit nacre covering. It is shaped like a teardrop. The shells we get are used to produce most freshwater cultured pearls in the world. I repeat, these are not cultured pearls. They aren't GIA certified, but I personally don't need it being I know they are real cause I took them out of the shells myself. What would the rough estimate be for that pearl?