One of the only gemstones formed within a living organism, pearls have an iridescent, milky quality that the ancient Chinese associated with the power of the moon.
Pearls are formed when mantle tissue in a mollusk is damaged, and nacre is secreted into the wounded area until it eventually hardens into a sphere. Natural pearls are caused by chance, and are relatively rare, but today pearls are cultured and harvested in farm-like settings. Over 99 percent of all available pearls are of the cultured variety.
The value of pearls is determined by the size, shape, luster, symmetry, and lack of flaws. Generally, the larger the pearl, the higher the value, as pearls take many years to reach maturity inside the mollusk. Used in beaded necklaces, pendants, and many other jewelry types, the pearl is a symbol of dignified elegance, with a long history stretching back to Hebrew and Hindu scriptures.
Different hues can be achieved through the use of dyes, heat treatment, bleaching and irradiation, though must cultured pearls are not altered from their original color. Because they are formed from organic matter, pearls are sensitive to chemicals and acids and should be treated with care for the life of the piece.