PAUL D STEWART / SCIENCE PHOTO LIBRARY PAUL D STEWART / SCIENCE PHOTO LIBRARY
Inner polished surface of an Abalone shell. Structural colour arising from light scattering by complex nanostructures rather than simple absorption, refraction or reflection. The nacre is made up of polygonal tiles of a very hard crystalline form of calcium carbonate, aragonite, cemented in a matrix of conchiolin. The tiles are each a single crystal tessellated in stacked layers. Each layer is 0.5 micron thick. The individual tiles are about 10 micron across and their optical axes are all perpendicular to the layer. Nacre appears iridescent because the thickness of the aragonite platelets is close to the wavelength of visible light. These structures interfere constructively and destructively with different wavelengths of light at different viewing angles, creating structural colours. This beauty is hidden within the shell and cannot serve any purpose than strength for the Abelone.
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