Mother of pearl is a shiny, iridescent substance that forms the inner lining of the shells of some mollusks, such as oysters and abalone.
It is also known as nacre and is composed of a combination of calcium carbonate, and other organic substances.
The mother of pearl itself consists of numerous thin layers of the mineral aragonite, separated by layers of organic material. This layered structure reflects light in a way that creates an iridescent effect.
Some fossils have iridescence and play of colour due to nacre – especially Ammolite, and the Madagascan iridescent Ammonites.