Near-infrared Raman imaging microscopy (NIRIM) was used to produce chemical images of the distribution of elemental sulfur on oxidized pyrite and arsenopyrite surfaces. Analysis using Savitsky-Golay filtering permits an unambiguous identification of surface products even in the presence of broad background signals. Rather than forming a continuous, passivating layer at the mineral surface, the NIRIM images reveal that elemental sulfur forms in isolated patches on the order of tens of microns in diameter. The potential implications of this strongly heterogeneous distribution of chemical products for geochemical modeling of acid mine drainage (AMD) are discussed.