Natural freshwater pearls occur in mussels for the same reason that saltwater pearls occur in oysters. Foreign material, usually a sharp object or parasite, enters a mussel and cannot be expelled.

Most pearls come from oysters, which thrive in both freshwater and saltwater environments. Oysters are bivalves that means their shell is composed of two valves connected by an elastic ligament.

Pearls are made by marine oysters and freshwater mussels as a natural defence against an irritant such as a parasite entering their shell or damage to their fragile body. The oyster or mussel slowly ...

The Pinctada maxima oyster can take up to five years to produce a single South Sea pearl, whereas more common freshwater oysters can take as little as three months and create dozens of pearls.