Nacre - (pronounced like acre) - a secretion by the mantle from certain mollusks. It forms an iridescent layer on the surface inside the mollusk shell of both the pearl and mother-of-pearl.
Navette - a gemstone with pointed ends and having a boat shaped profile. A good example would be the shape of a football.
Nucleus - the core of a natural or cultured pearl. This is the irritant which triggers the formation of the pearl.
