A pearl is a small, often round, object frequently used in jewelry. A pearl is created when a deposit forms around a grain of sand or other foreign matter that has entered inside the shell of an oyster or mussel or certain other varieties of mollusks. It is composed mainly of calcium carbonate and often has a smooth, lustrous surface. Another type of pearl with a "lumpy" or irregular shape, is the Biwa pearl, which comes from Lake Biwa, in Japan. Pearls often have a distinctive "off white" color and luminous quality, although there are pearls of a more pink or yellow hue, and another type which is a black pearl. The two most common types of pearls are natural pearls, (occurring in nature) and cultured pearls, (manufactured) which are formed when a foreign substance is introduced into an oyster for the purposes of creating a pearl. There are both freshwater and saltwater pearls.
A famous saying is: "Don't cast your pearls before swine."
China has overtaken Japan in cultured pearl production. Japan maintains its status as a pearl processing center, but at present imports the majority of them from China.