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White pearl necklace. A pearl nucleus or a bead for cultured pearl is a sphere (usually) or other shape (occasionally) formed only by cutting and polishing a nacreous shell used to accommodate the nacre secreted from a graft of mantle tissue, that eventually forms the centre of a beaded cultured pearl. [2]
The iridescent nacre inside a nautilus shell Nacreous shell worked into a decorative object. Nacre (/ ˈ n eɪ k ər / NAY-kər, also / ˈ n æ k r ə / NAK-rə), [1] also known as mother-of-pearl, is an organic–inorganic composite material produced by some molluscs as an inner shell layer. It is also the material of which pearls are composed.
(A) Optical overview of a nonbeaded keshi–cultured pearl showing iridescence. (B) Cross-section showing CaCO3 growth begins onto an organic center. (C) Mature nacre (purple box in B) showing the ordered state in their thickness and interface curvature.
The original Japanese cultured pearls, known as akoya pearls, are produced by a species of small pearl oyster, Pinctada fucata martensii, which is no bigger than 6 to 8 cm (2.4 to 3.1 in) in size, hence akoya pearls larger than 10 mm in diameter are extremely rare and highly priced. Today, a hybrid mollusk is used in both Japan and China in the ...
Although these are a variety of cultured saltwater pearls, the amount of time that the pearls are cultured dramatically increases the depth of the nacre, and the likelihood of producing a baroque pearl. Most Tahitian pearl farm harvests, which, for example, produce more than 40 percent baroque and semi-baroque pearls.
Most molluscs with shells can produce pearls, but only the pearls of bivalves and some gastropods, whose shells are lined with nacre, are valuable. [4] [5] The best natural pearls are produced by marine pearl oysters, Pinctada margaritifera and Pinctada mertensi, which live in the tropical and subtropical waters of the Pacific Ocean.
They have a very strong inner shell layer composed of nacre, also known as "mother of pearl" and are important to the cultured pearl industry as they are cultivated to produce South Sea pearls. The South Sea pearl or Philippine pearl was declared by Philippine President Fidel Ramos as the national gem in 1996 through Proclamation No. 905.
Black South Sea pearls, or Tahitian pearls come from the black-lip oyster; gold and silver South Sea pearls from the gold-lip and silver-lip oysters; and Akoya cultured pearls from Pinctada fucata martensii, the Akoya pearl oyster. Pearls are also obtained in commercial quantities from some species of the closely related winged oyster genus Pteria.