pearl

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.

In an effort to decrease the time taken for farmed oysters to produce pearls, US biotechnologists inserted growth-promoting proteins into oysters. The first generation in 1997 were more than twice as fast to grow larger pearls.

Pearl

Town in Rankin County, southern-central Mississippi, USA, 11 km/7 mi southeast of downtown Jackson; population (1990 est) 19,600. It is principally a residential suburb of Jackson.

Pearl

River of southern Mississippi and eastern Louisiana, USA; length 781 km/485 mi. Rising in the Red Hills, Mississippi, northeast of Philadelphia, it winds in a southwesterly direction past Jackson, before turning southeast to cross the Coastal Plain. Near Picayune, Mississipi, it divides into two parallel channels 48 km/30 m from its mouth; the East Pearl, the main channel, empties into Lake Borgne on the Gulf of Mexico, and the West Pearl enters the Rigolets, an outflow of Lake Pontchartrain. The river forms the Louisiana–Mississippi border for the last 187 km/116 mi of its course.

In its upper reaches the Pearl passes through the Ross Barnett Reservoir, where it is joined by the Yockanookany River, above Jackson. On the Coastal Plain, it flows through Piney Woods and past Monticello, Morgantown, and Columbia, Missouri. Bogalusa, Louisiana, is the largest town on the state boundary. The river's name refers to the pearl oysters formerly abundant on its banks.