formations of spherical or irregular shape formed in the bodies of certain mollusks. Pearls consist of the same material as the shells, that is, mainly of calcium carbonate. The formation of a pearl is due to a foreign body (sand particle, parasite) falling into the wall of the mantle or between the mantle and the shell; nacre is then deposited around it.

Pearls are white, rose, yellowish, or sometimes black; their size varies from microscopic to that of a pigeon’s egg. A large and regularly shaped pearl is valued very highly (the largest pearl, weighing 34 carats, is believed to have belonged to the Spanish king Philip II). Pearls are obtained mainly from pearl oysters, whose shells have beautiful mother-of-pearl. Marine pearls are gathered in the Red Sea and Persian Gulf and off the shores of Ceylon, Australia, Japan, and Venezuela. Freshwater pearls have long been gathered in Russia, Scotland, Germany, China, and North American countries.

Because of its decorative properties—its smooth mat surface and soft iridescent sheen—the pearl has long been used by jewelers, often combined with precious stones and metals, to make necklaces, signet rings, brooches, and other jewelry (in India for many centuries before Christ, in Japan probably from the sixth century A.D. , and in Western Europe from the 15th and 16th centuries). In Russia, from the llth and 12th centuries and particularly in the 15th–18th centuries, decorative pearl embroidery was used widely to ornament linen, silk, brocade, and velvet and to beautify articles used in church and the ceremonial dress of the tsar, the nobles and the people.

The fall in natural supply and the great demand for pearls has led, in the 20th century, to their artificial cultivation on a large scale (mainly in Japan). Small mother-of-pearl spheres are inserted into the mantles of marine pearl oysters to serve as the foundations of future pearls.