Both X-ray Rietveld and profile fitting structure analyses have been reviewed and discussed on the problems in the application to clay mineral samples. Both methods have established their positions in the crystal structure analysis of powder samples, but in the clay mineral samples, several characteristic features, which are inherent to clay minerals such as orientation effect and low symmetry in the sheet structure, have prevented to disclose the detailed structure of them. In order to overcome the problems, it is suggested to introduce more reliable synchrotron X-ray data as well as other auxiliary data, which is now popular in the field of zeolite structure analysis.
Finally, on the most fundamental problem of the crystal structure analysis, a local structure determined by X-ray method is compared and discussed with the result from molecular dynamic simulation.