pearl
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Pearl oyster
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A white spherical gem produced by a bivalve
mollusk, particularly the Pearl oyster, Pinctada. In response to
an irritation by foreign matter within the shell, the mantle secretes calcium
carbonate in the form of mother-of-pearl
(nacre) around the irritant body. Over several years, the encrustation forms
the pearl. Cultured pearls may be obtained by "seeding" the oyster with
an artificial irritant, such as a small bead. Pearls are variable and may
be black or pink as well as the usual white. Another bivalve group producing
marketable pearls is the freshwater Pearl mussel, Margaritifera margaritifera.
Related category
• ZOOLOGY
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