We report the discovery of broad mid-infrared resonances in the outer regions of the Red Rectangle outflow (Markwick-Kemper et al. 2005). The peak position and the strength of the resonances vary spatially, but the full width at half maximum, as well as the shape of the feature, appears remarkably constant. While emission due to polycyclic aromatic hydrocarbons (PAHs) is also present at these locations, we show that PAHs cannot be the carriers of these new components. Instead, we argue that these resonances are caused by solid state components, perhaps simple Mg-Fe-oxides. The presence of such O-rich species in the otherwise C-rich outflows further complicates the picture of the formation and chemistry of the Red Rectangle nebula.