Despite the fact that virtually all pearls sold today are cultured pearls, there tends to be some confusion as to exactly what cultured pearls are and how they compare to natural pearls. Moreover, there are differenct types of cultured pearls -- saltwater versus freshwater and all-nacre versus bead-nucleated.

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Natural Pearls

 

Contrary to what you may have heard, naturally occurring pearls rarely result from a grain of sand becoming lodged between the shell and body tissue of an oyster or mussel. Usually, a pearl forms when an organic irritant such as a parasite or wayward food particle becomes trapped in the animal. Unable to expel the irritant, the animal develops a pearl sac of soft mantle tissue around the object and over time coats it with layers of nacre secreted by the pearl sac.

Nacre is composed of alternating very thin layers of the mineral aragonite (a form of calcium carbonate crystal) and conchiolin, a thin protein membrane. These two materials form the same substance from which the animals shell is built.

 

Theoretically, any mollusk that produces a shell can produce a pearl. However, naturally occurring pearls are very rare. Only about one of every 10,000 animals will produce a pearl. Moreover, the process is slow. An 8mm pearl can take up to eight years to form, depending on the species of mollusk.

 

Decades ago, over harvesting and pollution depleted natural pearls to levels that have made finding and collecting them uneconomical.