"nhydrous oxides, as follows:(y)M2/n :(z)L2 O3 :100SiO2 ; M is an alkali or alkaline earth metal having a valence n, y=0 to 2.0, z=0 to 5, and L is a tetrahedrally bound atom selected from Al, Ga, Fe, B or mixtures thereof. 7." . . . . .