Tissue-Nucleated Pearl

A tissue-nucleated pearl is a cultured pearl grown without a bead at its centre. In the more common bead-nucleated method a round shell bead is implanted with a scrap of mantle tissue, and the mollusc coats the bead in nacre; in tissue nucleation only a small piece of mantle tissue is inserted, and the pearl that forms is nacre nearly all the way through. This is the standard technique for freshwater cultured pearls, in which a single mussel may be seeded many times, and it produces pearls of solid nacre but usually irregular, non-round shape.

Like all pearls it is an organic gem, aragonite platelets bound by the protein conchiolin, its glow the interference of light in those thin layers, and it is soft, hardness about 2.5, and dissolves in acid. The distinction matters for value and identification but not for symbolism: in tradition all pearls share the associations of the Moon, in Indian jyotisha the pearl is the primary lunar navaratna gem, and of purity, and the culturing methods that make them affordable are a twentieth-century development.