The Orient phenomena is also a form of iridescence. With pearls there is a delicate, shifting iridescent color layer that is quite distinct from the main body color. The luster as well as the orient relates closely to the thickness of the nacre layer on the pearl’s surface.
Orient is also found in mother-of-pearl in the lining of shells on the outside as well as the inside of the shell. In abalone shells the color is vivid and comes in many hues.
Orient is caused by the interference of colors within the different thin layers of the pearl or mother-of-pearl shell.