Natural mother-of-pearl, such as mussels, is one of the hardest, most stable and stiff natural materials. Researchers have always been fascinated by it. The structure of mother-of-pearl is exquisite under the electron microscope; it looks like a miniature brick wall, the joints of which are filled with mortar. The bricks are composed of tiny Calcium carbonate plates stacked on top of each other and interconnected with mineral bridges, and filled with a mortar composed of an organic substance.