Abstract: According to results of analysis on some cases from coal fields in the eastern China and simulation by deformation expeiments under high temperature and confining pressure,it is indicated that in coal-bearing strata quartz C fabric is often of sparse small circle pattern and its axis is of obvious stress directing significance.This type of patterns of quartz C fabrics is related to the activation of basal slip systems of quartz.It is a middle stage pattern of maximum because of less plastic strain in quartz grains.Besides lower intensity of structural deformation,the widespread existence of soft minerals is an other major factor,which is responsible for the less plastic strain of quartz grains in sedimentary rocks,because soft minerals absorbed most of plastic strain.