The structure of natural shell samples has for many years been of significant interest, not only to researchers in the biological sciences but also to material scientists. This is primarily because the shells often have physical properties far exceeding those of their constituent minerals: in particular the mother of pearl structure, or “nacre”, consists of small, interlocking tablets of aragonite (orthorhombic CaCO3) separated by organic matrix membranes. Nacre has a very high strength when compared to single aragonite crystals and researchers are mimicking this structure in order to produce similarly high-strength materials. The fact that the aragonite tablets have a thickness similar to the wavelength of visible light (e.g. ~ 500 nm) results in nacre’s characteristic iridescence but poses significant challenges for effective microstructural characterisation.
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