Sepiolite phase-transformation has been successfully imitated in laboratory for many years, but nonatural example has been reported yet. In this paper the authors intend to provide a good natural example insouthern China, especially in the Pingle depression, where the Permian sepiolite has been generallyconverted to talc and minor stevensite (magnesium montmorillonite) due to anadiagenesis during post-sedimentation. In our opinion, the degree of transformation can be indicated by the degree ofmetamorphism of coal (rank of coal). In order to study the relationship between clay transformation and coalrank, the authors have proposed some parameters of coalification correlated with sepiolite conversion. Ithappens that volatile matter in the Permian coal comprises 30-52% and a vitrinite reflectance ofapproximately 0.4-0.8% (R°) is reliable to indicate the existence of sepiolite. The consideration thatsepiohte phase-transformation has a linear relationship with the rank of coal can be justified on the trendsurface analysis diagrams which show that the areas of lower coal rank are obviously consistent with thesepiolite-distributed areas. Therefore, there is such a possibility as to predict new occurrences of sepiolite onthe basis of the distribution of the lower coal ranks. Sepiolite phase-transformation has been successfully imitated in laboratory for many years, but nonatural example has been reported yet. In this paper the authors intend to provide a good natural example insouthern China, especially in the Pingle depression, where the Permian sepiolite has been generallyconverted In our opinion, the degree of transformation can be indicated by the degree of metamorphism of coal (rank of coal). In order to study the relationship between clay transformation and coalrank, the authors have proposed some parameters of coalification correlated with sepiolite conversion. Ithappens that volatile matter in the permian coal comprises 30-52% and a vitrinite reflectance ofapproximately 0.4-0.8% (R °) is reliable to indicate the existence of sepiolite. The consideration that sepiohte phase-transformation has a linear relationship with the rank of coal can be justi fied on the trendsurface analysis diagrams which show that the areas of lower coal rank are obviously consistent with thesepiolite-distributed areas. Therefore, there is such a a potential as to predict new occurrences of sepiolite on the basis of the distribution of the lower coal ranks.