Oysters and pearls

The next step in the grafting process is the insertion of a nucleus, the six to eight millimeter ball around which the pearl grows. The Japanese researchers who pioneered the grafting process decided that the shell of a wild mussel in the Mississippi river basin had the appropriate density for a pearl nucleus, and to this day most nuclei come from this unlikely mollusk. This practice leads not only to inferior pearls, but has also endangered the very existence of this North American mussel due to over-fishing.