Pearl

Pearl is a hard, rounded gem produced within the soft tissues of certain mollusks, most commonly oysters. Pearls form when an irritant, such as a grain of sand or a parasite, becomes coated with nacre, the layered, iridescent coating secreted by the mollusk. Over time these concentric layers accumulate into a pearl, composed mainly of calcium carbonate in the form of aragonite (or, less commonly, calcite) held together by organic matrix proteins.

Natural pearls occur without human intervention in the wild, but today most are cultured. In pearl farming, a nucleus or tissue is implanted into a mollusk, which then secretes nacre around it. The major cultivated pearl types are Akoya (saltwater, typically white to silver-gray), South Sea (large pearls from Pinctada maxima, often white or golden), Tahitian (dark hues from Pinctada margaritifera), and freshwater pearls (produced in Hyriopsis or Cristaria species, primarily in China).

Pearls vary in size, shape, and color. Sizes range from a few millimeters to over 12 millimeters; shapes include perfectly round, near-round, oval, or baroque. Colors span white, cream, pink, gold, and black, with a characteristic luster and nacreous iridescence that can intensify with quality and thickness of nacre.

Economic and cultural significance has varied across history. Natural pearls were highly valued in ancient times, while modern production expanded rapidly with cultured pearls in the 20th century. Today, China is the leading producer of freshwater pearls, with other major supplies from Japan, Australia, and the broader Asian and Pacific regions. Pearl grading typically considers luster, surface quality, shape, size, color, and symmetry.