Mother-of-pearl is the iridescent inside lining of a mollusk shell. To protect the inside of their shells from parasites and foreign irritants, the mollusk coats it with nacre—an organic substance that builds up over many years to give the mother-of-pearl its iridescent effect and distinct beauty. This multicolored iridescence is caused by the way light reflects on the layers of nacre on the shell.
How is Mother of Pearl Different from Pearls?
Both are made in the same way from the same material, but mother of pearl refers specifically to the inner-shell of the mollusk. Whereas Pearls are made when a small irritant such as a grain of sand gets trapped inside the shell and over many years the mollusk coats this with layers of nacre until it grows into a pearl.