Otherwise known as Nacre, it is the thin, iridescent substance that lines the shell of a mollusk. It is composed of the same material that makes up a pearl, a combination of calcium carbonate and protein. When you look inside a shell and see that it is shiny, that is the Mother of Pearl. This substance is used to protect the mollusk from foreign organisms that enter its shell.Even if the pearls itself are usually more focused on, the Mother of Pearl is also used in crafting jewellery. They may not be as valuable as pearls, but they still allow jewellers to be creative and design beautiful pieces out of them.