Corrosion experiments on a number of rare earth di-silicates containing Y, Yb and Lu have been conducted in flowing air with 30 vol.% H2O at 1500°C. Nominally the corrosion rate is slower by a factor 5 to 10 compared to silica. However, alumina impurity incorporation has a profound influence on the process of corrosion as it masks not only the gravimetric results but also changes the surface phase assemblages to contain rare earth garnets and liquid phases. It is presumed that silica loss occurs under those conditions via the liquid phase and does not necessarily follow the same kinetics as direct silicate corrosion. Furthermore, atmospheric silicon hydroxide saturation effects contribute to the corrosion process. Currently all determined corrosion rates of rare earth silicates are viewed as system specific only.