A pearl is a hard, glistening object produced within the soft tissue of a living shelled mollusk or other animals, such as fossil conulariids. It is composed of calcium carbonate in minute crystalline form, which is deposited in concentric layers similar to the shell of a mollusk.
While perfectly round and smooth pearls are considered more commercially valuable, many other shapes exist known as baroque pearls. For centuries, high-quality natural pearls have been highly valued as gemstones and objects of beauty, leading them to become a metaphor for things that are rare, fine, admirable, and valuable.