The inner mother-of-pearl (nacre) layer of the abalone shell. Image credit: University of California, Riverside, Bourns College of Engineering.
Mother-of-pearl, also called nacre, is the iridescent substance (see iridescence) of which pearls and the inner coating of bivalve mollusc shells are made. It consists of alternate thin layers of aragonite (calcium carbonate) and conchiolin, a horny substance. Mother-of-pearl is valued for its beauty, and is used in thin sheets for ornament, jewelry, and buttons. See also abalone.