Nacre is crystalline aragonite or calcium carbonate. Shellfish and mollusks excrete it when they are exposed to a parasite or a foreign body introduced into a shell. Nacre is noted for its shine and iridescence, and its coating on shells is called mother of pearl.

In some situations, production of nacre is induced or cultured by introducing a foreign body to a shellfish. This is the case with cultured pearls. Formation of pearls is accelerated by placing small foreign shell bits in oysters. This essentially “cultures” the production of nacre resulting in valuable and iridescent pearls. Alternately, fresh pearls, or naturally occurring pearls are usually an oyster’s or mussel’s response to parasitic agents. Since the methods for producing nacre are not externally controlled, quality and size of these pearls can vary.

Nacre also tends to line the inside of mollusk shells. You can even note it in garden snails, but it is most noticeable and impressive in sea mollusks. From time to time you can find shells that exhibit either a white or black shine on their interior, making them desirable to shell collectors.

Nacre when not in pearl form, has been used in a variety of decorative forms. Mother of pearl was traditional on shirt buttons, and some brands like Lacoste® still use nacre. Nacre also may be used on the keys or components of musical instruments. The dial on Rolex® watches, and on many other high end watches also employ mother of pearl.

Nacre may be worked into tiles, or form decorative boxes for jewelry, create cufflinks, or be used in jewelry like rings, necklaces and earrings. It may also be used with porcelain for kitchen and bathroom sinks. Quality of mother of pearl depends upon the thickness of the crystalline forms, and whether or not the nacre has been dyed to produce certain colors.

Though we often associate nacre with ocean dwelling mollusks, much of the nacre produced commercially is done so among fresh water shellfish like mussels. Though abalone is commonly thought a terrific source of nacre for decorative purposes, abalone harvesting can be limited in some areas. It often proves easier from a commercial sense to use smaller, easier to obtain, and less endangered animals to produce nacre or to grow pearls.