Different types of pearl producing species (first two columns), trade names of their pearls (third column) and characteristic color nuances of the pearls (last column). The pearls produced by the species of the first four rows are true pearls as they consist mainly of aragonite layers. The pearl produced by the Melo melo sea snail (last column) consist mainly of calcite prisms and is hence a non-nacreous pearl. Image properties: Gemological Institute of America.
