A pearl is a hard object produced within the soft tissue (specifically the mantle) of a living shelled mollusc. Just like the shell of a mollusc, a pearl is made up of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes of pearls (baroque pearls) occur. While white, and more recently black, saltwater pearls are by far the most popular, other colour tints can be found including pink, blue, champagne, green and purple.