mother-of-pearl

[muhth -er-uh v-purl] /ˈmʌð ər əvˈpɜrl/
noun
1.
a hard, iridescent substance that forms the inner layer of certain mollusk shells, used for making buttons, beads, etc.; nacre.
adjective
2.
of or having the qualities of mother-of-pearl, as being iridescent or pearly:
mother-of-pearl buttons.
Origin
1500-10; compare Italian madreperla, obsolete French mère perle
British Dictionary definitions for mother-of-pearl

mother-of-pearl

noun
1.
a hard iridescent substance, mostly calcium carbonate, that forms the inner layer of the shells of certain molluscs, such as the oyster. It is used to make buttons, inlay furniture, etc Also called nacre, related adjective nacreous
mother-of-pearl in Science
mother-of-pearl  
The hard, smooth, pearly layer on the inside of certain seashells, such as abalones and certain oysters. It is used to make buttons and jewelry. Also called nacre.