MOTHER OF PEARL
Also known as Nacre, is an organic–inorganic composite material produced by some mollusks as an inner shell layer; Mother of pearl is found in the outer layer of cultured pearls and the inside layer of pearl oyster and freshwater pearl oyster shells. It is strong, resilient, and iridescent.
Nacre is Secreted by the epithelial cells of the mantle tissue of various mollusks and continuously deposited onto the inner surface of the shell. The layers of nacre smooth the shell surface and help defend the soft tissues against parasites and damaging debris by entombing them in successive layers, forming either a blister pearl attached to the interior of the shell, or a free pearl within the mantle tissues. The process is called encystation and it continues as long as the mollusk lives.
Scientists from the University of Michigan and Australia’s Macquarie University crushed a minuscule mussel and used an electron microscope to observe the effects. Under compression, nacre’s binding organic layer dissipates to areas of lower pressure (like squeezing a bag of liquid and the liquid moves to everywhere but where you’re squeezing). Then the separated aragonite tablets that form it rigidify, blocking crack formation and lending the material its tensile strength. This functionality is similar to concrete, a material that is very good at resisting compression. Once decompressed, the structure fully restores its original build and mechanical strength as the organic material fills back in.