Nacre, also known as mother of pearl, is an organic-inorganic composite material prouced by some mollusks. It is strong, resilient, and iridescent. Pearls and the inside layer of the pearl oyster shells and the freshwater pearl mussel shells are made of nacre. Many other families of mollusks also have a shell layer which is nacreous, including the Trochidae and the Turbinidae.