pearl

Strand of akoya pearls from China

A pearl is a hard, smooth, rounded (not necessarily round), lustrous object made of nacre (mother-of-pearl) that is organically produced by certain hard-shelled mollusks, principally oysters and mussels. Pearls are valued as gemstones and are used in jewelry. Pearls can also be crushed and used in cosmetics or paint formulations.

Pearls are formed inside the shell of certain bivalve mollusks when nacre is secreted in successive thin, translucent, concentric layers around a foreign particle or irritant. Nacre is a natural substance used in forming the inner layer of a mollusk shell. It is made up of successive layer of inorganic calcium carbonate and organic conchiolin.

Natural pearls are made up of 100 percent nacre (except for the foreign particle at the center). Cultured pearls are produced when a large, round bead is inserted inside the mollusk and it is then coated with nacre.

The "queen of gems," pearls have had a long history of importance to human beings. Rare, treasured for their beauty, and one of the most expensive gems in the world, natural pearls have been tied to historical events and revered in religious texts. Their history has reflected the best of the human capacity for treasuring beauty and uniqueness, offering gifts to others, and creativity, with the invention of cultured pearls and diverse jewelry. However, they also have been a focus of human greed, as people have stolen, plundered, and fought over pearls.

Pearls may come in various shapes and colors. They may be round, semi-round, button, drop, pear, oval, baroque, and ringed. While usually white, pearls also may have a creamy or pinkish tinge, or tinted with various colors such as yellow, green, and blue. Black pearls are highly valued because of their rarity. The shape of the pearl varies according to the irritant at the center of the pearl, and the color varies according to the inside of the shell of the mollusk that produces it.

The largest pearl ever found came from the Philippines in 1934. It weighed 14 pounds (6.36 kilograms) when it was discovered by an anonymous Muslim Filipino diver off the island of Palawan. Later, a Palawan chieftain gave the pearl to Wilbur Dowell Cobb in 1936 as gift for having saved the life of his son. It was first called the “Pearl of Allah” and is now officially named the “Pearl of Lao Tzu” (Imperial-Deltah 2006).

Pearls fit into two categories: freshwater and saltwater. As their name implies, freshwater pearls are formed in freshwater mussels that live in lakes, rivers, ponds, and other bodies of fresh water. Most freshwater cultured pearls sold today come from China. By contrast, saltwater pearls grow in oysters that live in the ocean, usually in protected lagoons. Akoya, South Sea, and Tahitian are the three main types of saltwater pearls. Overfishing and pollution have reduced pearl-producing oyster and mussel populations.