Rare‐earth aluminosilicate glasses of the general formula 20R2O3· 20Al2O3· 60SiO2have been formed for 10 of the 14 possible rare‐earth oxides. Two series of “mixed‐rare‐earth” glasses were also formed (Nd/Er and Nd/Y). These glasses exhibit exceptionally high glass transformation temperatures, moderate thermal expansion coefficients, and refractive indices of approximately 1.65. The glass transformation temperature and thermal expansion coefficients vary linearly with the field strength of the rare‐earth ion. No evidence of a “mixed‐rare‐earth effect” was observed. MAS‐NMR indicates that the aluminum ions are tetrahedrally coordinated in at le