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A dense, lustrous concretion, formed within the shell of certain molluscs, that is used as a gemstone and classified with precious stones.
The finest pearls (called oriental pearl) are produced by the pearl oyster. The pearl is composed of conchiolin and calcium carbonate (in the form of minuscule prisms of calcite or aragonite) that is secreted by the mantle of the mollusc and is deposited as nacre in very many thin concentric layers to surround some foreign particle (usually thought to be a grain of sand, but now believed possibly a cellular tissue that causes a resistance) that has entered the shell by nature (making a 'true pearl' or a 'wild pearl') or has been inserted by man (making a cultured pearl).
The pearl is either attached to the interior of the shell (blister pearl) or formed within the body of the mollusc (mantle pearl). The sizes vary (from seed pearl, to paragon pearl) as well as the form, from the finest, which are spherical, to the oval or egg-shaped or those that are irregularly shaped. The colours also vary, usually depending on the water where produced, from pink to various faint tints and blackish but some are artificially coloured. The finest specimens have a satin lustre.
Pearls are used as beads in a pearl necklace, suspended from brooches, earrings, and pendants, and set in finger rings, pins, brooches, etc. Probably the largest known round pearl is La Reine Perle, weighing 111 grains.
In addition to those of the pearl oyster, pearls are produced by other molluscs and are generally designated by the name of the mollusc, e.g. abalone pearl, clam pearl, conch pearl, mussel pearl.
Pearls are usually pierced through the centre for stringing or part-way for setting in earrings, pendants, studs, etc. Most drilling of oriental pearls is done in Bombay by means of a bow-drill. Pearls to be strung are drilled from each side to make a straight hole; those to be set are partially drilled and are cemented to a metal peg. Some inferior pearls are Chinese drilled.
The monetary value of a natural pearl is calculated by using the base system (once-the-weight method). Seed pearls are priced by the carat or ounce, and cultured pearls formerly by the momme.
The weight of a natural pearl is measured in grains, of a cultured pearl formerly by the momme. The size of a circular pearl is measured in millimetres. Pearls become damaged by acid (as from the skin or some hair-lotion or cosmetics), owing to the effect on the aragonite in the pearl, resulting in the pearl (especially a cultured pearl) becoming a barrel-shaped, with only two nacreous caps at the ends; by grease (as from the skin or certain cosmetics), the grease entering the drill-hole by capillary attraction from the string; and by dryness, from dry atmosphere or protracted storage, reducing the water content and causing surface cracking.
Frequent wearing is advisable, also frequent restringing by a jeweller (using a nylon string and tying a knot between individual pearls to prevent loss if the string should break) and occasional cleaning by an expert.
Among the most famous are: The Hanover pearls; Hope pearl; Mancini pearls; The Orange pearls; Peregrina, La.
From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson
A pearl is a hard, roundish object produced within the soft tissue (specifically the mantle) of a living shelled mollusk. Just like the shell of mollusks, a pearl is composed of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes of pearls (baroque pearls) occur.
The finest quality pearls have been highly valued as gemstones and objects of beauty for many centuries, and the word pearl has become a metaphor for something rare, fine, and admirable.
Almost any shelled mollusk can, by natural processes, produce some kind of "pearl" when an irritating microscopic object becomes trapped within the mollusk's mantle folds, but virtually none of these "pearls" are considered to be gemstones.
True iridescent pearls, the most desirable pearls, are produced by two groups of molluscan bivalves or clams. One family lives in the sea: the pearl oysters. The other, very different group of bivalves live in freshwater, and these are the river mussels; for example, see the freshwater pearl mussel.
Saltwater pearls can grow in several species of marine pearl oysters in the family Pteriidae. Freshwater pearls grow within certain (but by no means all) species of freshwater mussels in the order Unionida, the families Unionidae and Margaritiferidae. All of these bivalves are able to make true pearls because they have a thick inner shell layer composed of "mother of pearl" or nacre. The mantle of the living bivalve can create a pearl in the same way that it creates the pearly inner layer of the shell.
Fine gem-quality saltwater and freshwater pearls can and do sometimes occur completely naturally, but this is rare. Many hundreds of pearl oysters or pearl mussels have to be gathered and opened, and thus killed, in order to find even one pearl, and for many centuries that was the only way pearls were obtained. This was the main reason why pearls fetched such extraordinary prices in the past. In modern times however, almost all the pearls for sale were formed with a good deal of expert intervention from human pearl farmers.
A true pearl is made from layers of nacre, by the same living process as is used in the secretion of the mother of pearl which lines the shell. A "natural pearl" is one that formed without any human intervention at all, in the wild, and is very rare. A "cultured pearl", on the other hand, is one that has been formed on a pearl farm. The great majority of pearls on the market are cultured pearls.
Imitation or fake pearls are also widely sold in inexpensive jewelry, but the quality of the iridescence is usually very poor, and generally speaking, fake pearls are usually quite easy to distinguish from the real thing.
Pearls have been harvested, or more recently cultivated, primarily for use in jewelry, but in the past they were also stitched onto lavish clothing, as worn, for example, by royalty. Pearls have also been crushed and used in cosmetics, medicines, or in paint formulations.
Pearl is considered to be the birthstone for June.