Nacre
![Fossil nautiloid shell with original iridescent nacre in fossiliferous asphaltic limestone, Oklahoma. Dated to the late Middle Pennsylvanian, which makes it - by far - the oldest deposit in the world with aragonitic nacreous shelly fossils.[17]](/uploads/202501/28/Fossil_nautiloid_shell_with_original_iridescent_nacre_in_fossiliferous_asphaltic_limestone0809.jpg)
Nacre (/ˈneɪkər/ NAY-kər also /ˈnækrə/ NAK-rə), also known as mother of pearl, is an organic-inorganic composite material produced by some molluscs as an inner shell layer; it also makes up the outer coating of pearls. It is strong, resilient, and iridescent.