MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY
The commercial top shell (Tectus niloticus) is a marine gastropod. This shell has had the outer layers removed revealing the nacre, or mother of pearl. It is an organic-inorganic composite material produced by some molluscs as an inner shell layer and which is also the outer coating of pearls. Strong, resilient, and iridescent, it was the raw material used to manufacture buttons until the advent of plastics. The industry nearly wiped out the species. Nacre is found in some ancient lineages of bivalves, gastropods, and cephalopods. The inner layer in most mollusc shells is porcellaneous, not nacreous, usually a non-iridescent shine. Rarely, it is a non-nacreous iridescence like the flame structure in conch pearls. A University of Cambridge group has produced the first man made nacre with potential applications in aircraft, car windscreens, tank and body armour.
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