Pearl is a hard, dense, variously colored lustrous concretion formed of concentric layers of mother-of-pearl as an abnormal growth within the shell of some mollusks and used as a gem. It is composed of calcium carbonate (mainly aragonite or a mixture of aragonite and calcite. The characteristic luster of pearls is due to reflection, refraction, and diffraction of light from the thin overlapping translucent layers. Pearls are believed to help balance emotions, reduce stress and anxiety. They are associated with purity and innocence and encourage honesty, wisdom and personal integrity.