Oxides and oxyhydroxides of iron, found in rust samples, yield distinct infrared absorption patterns which can be used in the identification of rust phases present. Standard IR absorption spectra of several forms of oxyhydroxides and oxides of iron are given, data compiled in tables and salient features that can be used in phase identification are discussed. Representative spectra of different types of rust samples from weathering steel bridge spans in Louisiana and from one 2500 year old iron axe are analysed and discussions of their characteristic features are included. Sharp peaks in well crystallized samples become broad, and progressively weaker, in samples lacking crystallinity. The technique can be used efficiently to determine the nature of phase changes that occur upon heating or otherwise treating rust specimens.