Colossal 10mm Silver Black Swirl Potato PearlsPrice is per 16 inch string of these huge pearls about 34 to the strand. Colour is a beautiful silver black grey and ringy. The least expensive cultured pearls today rival the most expensive natural pearls ever found Natural freshwater pearls occur in mussels for the same reason saltwater pearls occur in oysters. Foreign material inside a mussel can't be expelled. To reduce irritation, the mollusk coats the intruder with the same secretion it uses for