the world > animals > invertebrates > subkingdom Metazoa > grade Triploblastica or Coelomata > class Pelecypoda or Conchifera > [noun] > bivalves > that produces pearls > pearl > substance (1)
pearla1393
The substance of which pearls are composed; = mother-of-pearl, n. 1. Also: an artificial imitation of this.