Silver ion conductivity and microstructural changes during the crystallization process of the glass systems AgI-Ag2O-M(x)O(y) (M = V, P, Mo, B) have been investigated by impedance spectroscopy and high temperature X-ray diffraction. The observed anomalous increase of the conductivity depends sensitively on the variation of the grass crystal interface area, suggesting a high conductivity in the interface region. The involvement of silver ions with different co-ordination shells in the transport process is modelled by valence sum pseudo-potential maps for the vanadate system Ag8I4V2O7.