Synchrotron X-ray diffraction and small-angle X-ray scattering analyses of the nacre of the Nautilus shell

Abstract

The structure of a mollusk shell is studied by synchrotron X-ray diffraction and small-angle X-ray scattering methods using a two-dimensional detector. Scattering is measured in the momentum transfer range of q = 0.03–60 nm–1, which makes it possible to reveal structural features in the size range of 0.1–200 nm. At large q values Bragg scattering is observed whose character shows that aragonite plates are good single crystals without internal inclusions. At small angles scattering mainly occurs at the biopolymer film. This scattering, which has not previously been observed, is strongly anisotropic. The anisotropy type corresponds to the one-dimensional mesostructure of the polymer, which is formed by a system of parallel fibers packed with a step of ~100 nm and has no longitudinal structuring. Information on the biopolymer is obtained in situ without destruction of the nacre.