Nacre, also known as mother-of-pearl, is the iridescent substance that forms the shell lining of some fresh-water and salt-water mollusks. Just like the pearl, it is a mantle tissue secretion and is composed of alternating layers of calcium carbonate and conchiolin. It serves to both smooth the shell and defend it against parasitic organisms and damaging debris. Its iridescent beauty makes it a popular ornamentation in jewelry, watches and guitar inlays. What other decorative uses does it have? Discuss