Étude Structurale d'une Nacrite Tunisienne

X-ray diffraction based on the comparison between the experimental and the calculated (20,11) and (02,31) powder profiles enabled determination of the structural characteristics of a Tunisian nacrite. The nacrite has space group Cc and the stacking mode is 2M. The two-layer periodicity could be described by a rotation of adjacent layers by 60° with the same interlayer shift between all layers (t = -0.35a along the 8.9 Å axis). Because the 60° rotated layer can be deduced from the nonrotated one by a mirror plane parallel to the 8.9 Å axis, the nacrite can also be described by the stacking of two symmetric layers. This better explains the unique translation between layers and is coherent with the previous description of stacking faults in the other members of the kaolinite family, i.e. kaolinite and dickite.