Mother-of-pearl sources are the two answers to the crossword puzzle, NACRES and ABALONES. Nacres is a French word for mother-of-pearl, and abalones are a type of sea snail whose shells produce mother-of-pearl. Mother-of-pearl is an iridescent material that is used in jewelry, furniture, and other decorative items. It is made from the inner layer of certain mollusk shells, such as those of abalones and oysters.