Zircon (ZrSiO4), hafnon (HfSiO4) and five intermediate compositions were synthesized from a Pb silicate melt. The resulting crystals were 20–300 µm in size and displayed sector and growth zoning. Raman spectra were acquired at locations in the sample for which preceding electron microprobe (EMP) analyses revealed sufficient compositional homogeneity. The dataset documents shifts of Raman bands with changing composition. In this study, bands that have previously not been reported were found for the intermediate compositions and for pure hafnon, in particular at wavenumbers less than 200 cm−1. For these external modes, the dataset provides new insight into the compositional dependence of their frequencies. Density-functional theory calculations support the observations and are used for a detailed interpretation of the spectra. The pitfalls of the EMP analysis along the zircon–hafnon join are highlighted.