ln-situ grazing incidence X-ray diffractometry has been successfully applied to monitor phase change processes at silver in an aqueous halogenide interface. Crystalline silver halogenide films and islands equivalent to homogeneous films of several nanometers thick could be resolved. Major crystalline orientations independent of pH are AgI (002), AgBr (200), AgCl (200). Grain sizes increase with growth time (at fixed overpotential), but the crystalline percentage decreases with anodic overpotential and formation rate. The crystalline portion of the AgX phases is maximum in neutral electrolyte. The amorphous or nanocrystalline phases dominate at high pH. A dissolution-precipitation mechanism is valid. A strong pH dependence of the overall generation rate and the crystalline percentage of the AgX phases has been observed in contrast to thermodynamic expectations. A mechanistic model involving the modification of silver surfaces covered with specifically adsorbed halogenides species by hydroxyl ions is suggested.