Textural analysis of eggshells

We discuss an experimental protocol to measure the degree of preferred orientation by using a textural index (tau) consisting of a single parameter easily derived from X-ray diffraction data recovered with a powder diffractometer. This textural index can be used for a quantitative characterization of the development of crystallographic orientation in biominerals and biomimetic materials which in many cases can be considered as layered structures showing preferred orientation across the structure but a quasi-homogeneous architecture in the normal to the growth direction. We demonstrate with the help of a computer simulation that the variation of the textural index with eggshell thickness and curvature arises from a competition for space between the mineral units growing outwards from the nucleation substrate.