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.