The Raman spectra of nine 1-atm glass samples in the system nepheline-diopside are presented. Nepheline glass consists of a fully polymerized network structure with largely six-membered rings of Q4 tetrahedra. The structure of diopside glass contains Q0, Q1, Q2, and Q3 units. Intermediate compositions with up to 18 mol % nepheline have Q0, Q1, Q2, Q3, and Q4 structural units. Nepheline-rich compositions contain two discrete molecular structures with different polymerization modes (Q2 and Q4 units). This tendency to form molecular clusters is facilitated by the inability of Ca and Mg to compete with Na on nonframework sites in structural units having only bridged oxygens. ¿ American Geophysical Union 1990