Cultured freshwater pearls are pearls that are farmed and created using freshwater mussels. ... Quality of cultured freshwater pearls is evaluated through a grading system of a series of A values, based on luster, shape, surface, color, and matching.
Nacre is composed of hexagonal platelets of aragonite (a form of calcium carbonate) 10–20 µm wide and 0.5 µm thick arranged in a continuous parallel lamina.