36 Unusual Silver-White Square Pearl Beads - Beautiful Shiny LusterPrice is per 15 inch string of these massive lustrous pearls. Each measures 11mm square x 4. 5mm thick about 36 to the string. Beautiful shine! Cultured pearls Most pearls these days are cultured. These 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 shell