Pearls have been featured in jewelry for centuries. Today, they are regarded as both classic and contemporary, coming in many more fashionable styles than your mother's traditional strand of pearls.
Pearls, be they natural or cultured, are formed when a mollusk produces layers of nacre (pronounced NAY-kur) around some type of irritant inside its shell. In natural pearls, the irritant may be another organism from the water. In cultured pearls, a mother-of-pearl bead or a piece of tissue is inserted (by a human) into the mollusk to start the process.
For both natural and cultured, the quality of the nacre dictates the quality of the luster, which is very important to the final beauty and value. The surface of the pearl should be smooth and free of marks while the overall shape could be round, oval, pear-shaped, or even misshapen. Misshapen pearls are called baroque pearls and have their own unique style, making for beautiful jewelry.