Mother of Pearl Mother-of-pearl is an organic gemstone that comes from the inside of some mollusk shells. Mother-of-pearl is made from nacre, which is mainly calcium carbonate. Like pearls, mother-of-pearl exhibits a pearly luster and an attractive iridescence. Mother-of-pearl tends to be the same color as the pearls produced by the mollusk and their color varies. Mother-of-pearl gemstones may be white, yellow, blue-green, bronze, pink, red, brown, black or banded. Mother-of-pearl gemstones can be natural (occurring without human intervention) or cultured, and may come from saltwater or freshwater. Sometimes mother-of-pearl is called "Cachalong opal" and abalone shell mother-of-pearl is sometimes called "sea opal". Such trade names are due to the play of color seen in both mother-of-pearl and opal.