A pearl is a hard glistening object produced within the soft tissue of a living shelled mollusk or another animal, such as a conulariid. Just like the shell of a mollusk, a pearl is composed of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. Pearl, concretion formed by a mollusk consisting of the same material (called nacre or mother-of-pearl) as the mollusk’s shell. It is a highly valued gemstone.
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