An homogenous 8.4 Aa hydrate was obtained after washing intercalated KAc-nacrite. X-ray diffraction analysis based on comparison of the experimental and calculated profiles enabled the amount of water (one molecule per Si 2 Al 2 O 5 (OH) 4 ) and the z coordinate along c (super *) (6.5 Aa) to be determined. The hydration state was accompanied by a decrease in the coherent domain along c (super *) in the order nacrite > KAc-nacrite > H 2 O-nacrite. The IR spectrum of the hydrated nacrite showed an evolution of the structure with a shift of nu (OH) from 3702, 3649 and 3630 cm (super -1) to 3690, 3641 and 3620 cm (super -1) , respectively for the nacrite hydroxyls. The nu (OH) stretching bands of the interlayer water appeared at 3602 and 3545 cm (super -1) and their bending band at 1655 cm (super -1) . The TGA/DTG analysis of the air-dry hydrated nacrite showed a loss of water at 245 degrees C, the weight loss (1 molecule per Si 2 Al 2 O 5 (OH) 4 ) corresponding to the interlamellar water, in agreement with that determined by XRD.