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. It 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, where the formation of pearls is accelerated by placing small foreign shell bits in oysters. It 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 this substance are not externally controlled, the quality and size of these pearls can vary.
Nacre also tends to line the inside of mollusk shells. It can even be seen in garden snails, but it is most noticeable and impressive in sea mollusks. From time to time, people can find shells that exhibit either a white or black shine on their interior, often making them appealing to shell collectors.
When not in pearl form, this substance has been used in a variety of decorative forms. Mother of pearl was traditional on shirt buttons, and some brands still use it. It may also be used on the keys or components of musical instruments. The dial on Rolex® and many other high end watches also use mother of pearl.
Nacre may be worked into tiles, designs in the wood of 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. The 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 most people associate nacre with ocean-dwelling mollusks, much of what is produced commercially is found among fresh water shellfish like mussels. Though abalone is commonly thought a terrific source for decorative purposes, harvesting of the sea snails can be limited in some areas. Commercial producers often find it easier to use smaller, easier to obtain, and less endangered animals for this purpose.