Surface textures of quartz grains from about 250 fault gouge samples with various types of fault in Japan are examined by means of the scanning electron microscope. It is disclosed that the surface morphology of the grains is variable, but quartz grains extracted from one fault gouge sample commonly show a type of texture different from those observed on the grains from the other samples. The surface textures observed under the microscope are tentatively classified into eight types; subconcoidal, orange peel-like, fish scale-like, moss-like, motheaten, stalactitic, pot-hole, and coral-like textures. These textures can be classified into four groups of I to IV. Arranged in the order of their apparent features, it is interpreted that the progressive corrosion of quartz grains by ground water has taken place after faulting. The change of this surface feature can assist in estimating the time elapsed since the last fault activity.