Mother-of-Pearl

Mother-of-pearl, or nacre, is an organic gem material, not a mineral: the hard, iridescent inner layer of some mollusk shells, such as pearl oysters, mussels, abalone and some snails. It is mostly aragonite (calcium carbonate) held together by the protein conchiolin, the same material that makes up nacreous pearls. Mother-of-pearl is often used in its natural colors but is also frequently dyed.