Hopeite-type phosphate coatings in which zinc is replaced by other metals like nickel, manganese and magnesium are of great interest as conversion coatings on galvanized steel in the automotive and appliance industries. The anal. characterization of such coatings produced in special processes is not possible by XRD because the different types of hopeite are isomorphic. In this paper it is shown that the kind of metal substitution is responsible for certain specific features in the IR reflection spectra. Furthermore the structural changes caused by dehydration due to heating of the coatings were studied and differences in the thermal stability of the different coatings thus could be obsd.