Sodalite is a scarce mineral that can be rock forming. Sodalite is named in reference to its sodium content. It is used for carvings and some jewelry pieces. Its light to dark pure blue color is well known in the semi-precious stone trade. Sodalite is a member of the feldspathoid group of minerals. Mother-of-Pearl, hard, iridescent inner layer of certain shells, such as that of the abalone, pearl oyster, and mussel. Also called nacre, mother-of-pearl is composed chiefly of calcium carbonate deposited in thin, overlapping layers, together with some organic matter. The iridescent play of colors for which mother-of-pearl is known is caused by the interference of reflected light waves. In both Eastern and Western cultures, mother-of-pearl has a long history of use in decorative finishes and inlays for furniture, boxes, jewelry, buttons, and other ornamental objects.