As products of living animals, pearls are unique among gems. In size, shape and even color, pearls exist in a stunning diversity of forms--far more than just small, round and white. Depending on the fashions of the era, the most sought-after pearls may be perfectly spherical, pear-shaped or irregular. A single large pearl may provide special elegance, or a cluster of seed pearls may light up a garment or object of art. With their long and lustrous history, pearls are more popular than ever.