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A detailed study of the conventional hydrothermal synthesis of zeolites in aqueous sodium alkaline solutions without the use of templates or organic bases is presented. Gel compositions representing most areas of the silica-rich half-triangle of the crystallization field that yield open-structure zeolites were prepared and were crystallized under different conditions in a design of a factorial experiment. The synthesized products were examined for their crystal structure and their Si/Al ratio. The data prove that the gel-alkalinity factor (a) increases the rate of crystallization to a point but further increase reveals a decrease of the phase transformation rate, thus stabilizing metastable structures, and (b) decreases the Si/Al ratio of the zeolitic framework. The increase of the gel-aluminicity (a) generates new crystalline structures that grow simultaneously with those that are formed in low-aluminicity gels and (b) decreases the slope of the framework Si/Al ratio versus alkalinity. An increase of crystallization temperature produces structures that are more dense and stable. Structure stability sequences were established in experiments performed at relatively high gel alkalinity and aluminicity.