We describe the results of a set of brittle sliding and wear experiments on thin sheets of polycrystalline sodium nitrate. We have built a new brittle deformation apparatus that allowed us to simultaneously observe the microstructural evolution under the microscope, and measure the mechanical response of the material. The microstructural history was recorded using a video microscopy technique and selected frames were then digitized and analysed. Fault gouge in these experiments was the direct product of frictional wear and was produced dominantly by intense intergranular fracturing and accompanying grain surface erosion. Although an increase in displacement was accompanied by an increase in gouge zone width, the development of a gouge zone is not a constant process either with respect to displacement, or with respect to the spatial distribution along the fault zone.