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Definition: pearl from Philip's Encyclopedia

Hard, smooth, iridescent concretion of calcium carbonate produced by certain marine and freshwater bivalve molluscs. It is composed of nacre, or mother-of-pearl, which forms the inner layer of mollusc shells. A pearl results from an abnormal growth of nacre around minute particles of foreign matter, such as a grain of sand.

Summary Article: Pearl
From The Encyclopedia of Tourism and Recreation in Marine Environments

Originally, and until the last century, one could only dive for pearls, and few of the shells collected during dives contained any. They were thus among the most precious items to be traded worldwide. Many legends have developed about pearls: in one, the Hindu god Krishna presents the first pearl to his daughter Pandaïa on her wedding day. China’s history has also long documented the importance of pearls.

Pearls form inside certain molluscs when a foreign particle irritates the body of the animal that then secretes layers of mother of pearl, the nacreous material that lines the shell. These increasing layers take a round, oval or pear-shaped form of the colour of the mother of pearl, which varies from different shades of white to dark green or blue. The thickness of the layering determines the durability and lustre of the pearl. It can be revealed only by X-ray.

As world population and technological know-how grew, pearls were cultivated to ensure a constant supply to jewellers. The ‘irritant’ has since been grafted by skilled workers who position a piece of oyster epithelial membrane (the lip of mantle tissue) and a nucleus (made from Mississippi shells: adopted following Mikimoto’s research for successful nuclei). These incite the creation of a pearl sac inside the mantle, within which the pearl develops for at least 18 months. Japan created, and later monopolized, the market for cultivated pearls (so that it remains a luxury product). The Mise-Nishikawa grafting needle is still used in pearl culture following changes introduced by Mikimoto, the founder of pearl cultivation. The Japanese cultivated mostly the pearl oyster Meleagrina margaritifera, of the Indian seas, which produces small, white pearls.

New production was initiated in the South Pacific in the early 1980s, where the warm waters of Australia and the lagoons of French Polynesia enabled the cultivation of Pinctada margaritifera, which produces the much larger ‘black’ pearl (10-21 mm in diameter). Their colour varies from white, to shades of green, grey or aubergine, to darkest black. Although French Polynesia over-produced in the 1990s, leading to massive decreases of price per gram of its non-processed black pearls (by 72% in the 1990s), the local government was slow to regulate production and quality because pearl production was used as a social development tool in the Tuamotu Archipelago.

Australia now produces 19.8% and French Polynesia 25.8% of the world’s pearls. Individual black pearls of high quality are worth US$1000 or more. Japan still dominates the international market of pearl, so that fluctuations in the value of the yen and the US dollar have repercussions on the volume of sales. In 2002, Japan bought 54.6% of the world’s pearls, Hong Kong 21.8% and the USA 9.2%. The production and sale of processed pearls is handled by Japan (30.6%), Australia (22.3%), Hong Kong (14.2%), China (10.3%) and French Polynesia (5.3%). China is best known for its freshwater pearls. Pearls have become an important tourist souvenir for visitors to Japan and French Polynesia.

Related internet sources

Robert Wan Tahiti:

Nova Online:

Anne-Marie d’Hauteserre
© CAB International 2008.

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