mother-of-pearl; nacre
Technical and biological term for the iridescent inner layer of mollusk shells. Also used in jewelry and decorative contexts.
Mother-of-pearl is the beautiful layer inside a shell.
This button is made of mother-of-pearl.
Compound of 真珠 (pearl) + 質 (substance, quality). The exact historical derivation is uncertain, but the term transparently means 'pearl substance'.