Independant of the silica saturation, alumina saturation is based on the 1:1 alkali:alumina ratio of feldspars and feldspathoids. Any excess or deficiency in alumina in a rock is reflected in the mineralogy. Four classes of alumina saturation/undersaturation are:
Peraluminous - Al2O3 > (CaO + N2O + K2O)
corundum appears in the norm
Minerals present in the rock are: muscovite, topaz, tourmaline, spessartine-almandine, corundum, andalusite and sillimanite.