An innovative synthesis method for phase-pure Na-4-mica has been developed in this study.Phase pure Na-4-mica has been synthesized by using NaCl melt. In the newly developedmethod, not only could the postpreparation process be avoided but also the crystal size couldbe manipulated in the range of about 2−5 μm by the initial molar ratio of Al2O3/NaCl. Boththe hydrated and anhydrous Na-4-mica phases possess monoclinic crystal systems with thesame layer plane. The X-ray diffraction (XRD) patterns exhibited relatively strong h0l peaksalong with very strong 00l peaks. Changes in the cell parameters of β and c on hydration−dehydration indicate that the layer swelling is accompanied with a significant paralleldisplacement of layers. Furthermore, pure Na-4-mica has exhibited completely reversibledehydration−rehydration behavior up to 800 °C and extremely high Sr2+ uptake capacitywithout any layer collapse.