Mother-of-pearl, also called nacre, is an organic–inorganic composite material produced by some mollusks as an inner shell layer. It is also the material of which pearls are made. The characteristic iridescence seen in mother-of-pearl is due to presence of hexagonal platelets of aragonite which is itself a form of calcium carbonate. The thickness of aragonite platelets corresponds to the wavelength of visible light. At different viewing angles and with different wavelengths, the platelets interfere constructively and destructively with light resulting in the characteristic iridescent patterns. Mother-of-pearl is believed to promote calmness, clarity, and protection from negative energy, as well as enhancing intuition and creativity.