The characteristics of minerals,such as illite,etc.in fault gouge from Xiaowan Fault are studied with X-ray diffraction and chemical analysis. The results show that :( 1) X-ray diffraction features of illite are?[(002)?(001)]>8?,Ir>1,BB1 <4?,belonging to orderly mixed layer.Expansive layer accounts are smaller than 15%.The crystal cell parameters b0=8.991 ?,1M polytype structure.(2)KO2 content varies from 4.18%to 5.56%.( 3) There is negative correlation exists between K2 O and Fe2O3. There is a positive cor...