Abstract:

This paper discusses the regularity of evolution of clay minerals during the process starting from sedimentation,diagenesis to metamorphism.Because of the difference in measuring conditions of different X-ray diffractions,it is difficult to compare data obtained when taking the peak width of illete as half of 10Å reflections (Kubler,1966) as the crystallinity indexes.So the authors propose the opening index of illite instead of Kubler's index,that is,to take N_a=b/a at half 10Å reflection and C_R=h/N_s(see fig.4) to discribe opening illite and the parameter of diagenetic strength. Based on the study of sepiolite-talc from Permian,Jiangxi Province,the authors suggest that the sepiolite changes towards talc when its layer-chain structure collapses.Since there is no distinct low limit for diagenesis,it is suggested to abandon the term anadiagenesis as a stage of diagenesis,but it could be used as a relative description term.The division of stages according to transforming marks of clay minerals are as follows.