The pearly, iridescent internal layer of certain mollusk shells, used as an inlay or veneer in jewelry, furniture, and other decorative objects. "Interference" caused by small surface grooves on the surface ? minute striations on thin layers of chitin ? results in an apparent bending of light. Thin film interference causes the coloration. The colors displayed are dependent on the thickness of the layer of chitin or its index of refraction.Also see intarsia, marquetry, and mosaic.