A simplified thermodynamic model is proposed assuming nepheline-like and trydimite-like structural units being major constituents of polymerized aluminosilicate melts. In the frame of the model, dissolution of albite in the melt can be described by the dissociation reaction AbL = NeL + QzL. Static 23Na NMR spectra recorded on glasses along the binary join Ab-Qz are consistent with the proposed structural units. The NMR spectra can be decomposed into two mixed (Lorentzian + Gaussian) components. The narrow line is comparable in chemical shift and width with the symmetric position of sodium in crystalline nepheline. The second much broader line is assigned to a more asymmetric albite-like environment. The proportions of both sites estimated from static NMR of glasses of the dry Ab-Qz binary are close to the calculated proportion in the melt at the glass transition. Using the new thermodynamic model, the liquidus of silica polymorphs in the system Ab-Qz can be described well by assuming non-ideal mixing of structural units in the melt with small interaction parameters.

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