pearl

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Shiny, hard, rounded abnormal growth composed of nacre (or mother-of-pearl), a chalky substance. Nacre is secreted by many molluscs, and deposited in thin layers on the inside of the shell around a parasite, a grain of sand, or some other irritant body. After several years of the mantle (the layer of tissue between the shell and the body mass) secreting this nacre, a pearl is formed.

Although commercially valuable pearls are obtained from freshwater mussels and oysters, most precious pearls come from the various species of the family Pteriidae (the pearl oysters) found in tropical waters off northern and western Australia, off the Californian coast, in the Gulf, and in the Indian Ocean. Because of their rarity, large mussel pearls of perfect shape are worth more than those from oysters.

Artificial pearls were first cultivated in Japan in 1893. A tiny bead of shell from a clam, plus a small piece of membrane from another pearl oyster's mantle (to stimulate the secretion of nacre) is inserted in oysters kept in cages in the sea for three years, and then the pearls are harvested.

The top left trigram symbolizes summer, south, and heaven. The top right trigram represents autumn, west, and the moon. The bottom right trigram stands for winter, north, and the Earth. The bottom left trigram represents spring, east, and the sun. Effective date: 21 February 1984. >>