Pearl nacre, also known as mother-of-pearl, is the basic substance which is secreted by oysters and molluscs to form the inside of their shells. When nacre secretions are deposited around a foreign substance which has invaded the mollusc’s body, they build up to form a pearl. Nacre is composed of layers of calcium carbonate (in a crystalline form) and conchiolin (an organic protein substance which provides bonding). The specific lustre, iridescence and colouring of nacre - and, therefore, of any pearl which it forms - depends on the number and thickness of the various layers, as well as on whether or not the layers overlap each other. For more information on pearl nacre please visit:- http://www.pearl-guide.com/glossary-of-terms-n.shtml | 
