It's 'nacre'. The iridescent layer found on the inside of several shells is often called the mother of pearl. It is the name commonly given to shells coated in a deposit of nacre.
It is different from a pearl as it is formed in the linings of the shell while the pearl is formed by entombing a foreign object that has lodged inside the shell, albeit using the same material called nacre.
Furthermore, a pearl is usually round in shape while a mother of pearl follows the shape of the shell as it is created in its walls.
Mother of pearl is synonymous with nacre, a durable, glittering layer produced by mollusks and serves as an inner shell layer.
Generally, nacre is the first layer deposited by the pearl sac; conchiolin surrounds the bead nucleus or irritant and functions as a base coat that will cause the pursuant nacre layers to bind together.
Since the vast majority of modern pearl jewelry uses cultured pearls, a solid understanding of how they are valued will come in handy when shopping for a set of pearl earrings, a pearl bracelet or some other form of jewelry that uses pearls.
Here are some tips that will be helpful when selecting pearl jewelry shared by Zales.com.