The solubility of amorphous sodium aluminosilicate solid and zeolite A crystals in sodium hydroxide and nitrated/nitrited sodium aluminate solutions has been determined at temperatures of (303.15, 338.15, and 403.15) K and as a function of solution NaOH, NaNO3, NaNO2, and Al(III) concentrations. Similar solubilities were measured when equilibrium was approached from below (via dissolution in undersaturated liquor) and above (by precipitation from supersaturated liquors). The solubility (expressed in terms of SiO2 and Al(III) concentrations) increased monotonically with increasing temperature, solution ionic strength, and hydroxide concentration for both amorphous and zeolite A phases. However, the solubility decreased with increasing solution AI(III), NO3, and NO2- concentrations and was significantly higher for the amorphous than the zeolite phase at all temperatures and solution conditions.