A low-defect kaolinite of 7.18-Angstrom basal spacing was expanded upon intercalation with hydrazine. The 001 d-spacing was broad and the peak resolved into components at 10.28, 9.48, and 8.80 Angstrom. It was found that the ordered kaolinite predominantly expanded to 9.48 Angstrom with 31.2% and 10.28 Angstrom with 38.0% of the total peak area. A high-defect kaolinite-showed expansion by hydrazine in identical steps with d-spacings of 10.27, 9.53, and 8.75 Angstrom. It is proposed that the intercalation of the kaolinite by hydrazine occurs according to the orientation of the hydrazine molecule and that water plays an integral part in the process of kaolinite expansion. For the hydrazine-intercalated kaolinite, hydroxyl stretching bands attributed to water are observed at 3413, 3469, and 3599 cm(-1) for the low-defect kaolinite and at 3600 and 3555 cm(-1) for the high-defect kaolinite. Upon the exposure of the low-defect hydrazine-intercalated kaolinite to air, an additional water band is observed at 3555 cm(-1), Water bending modes are observed at 1578, 1598, 1612, 1627, 1650, and 1679 cm(-1) for the hydrazine-intercalated low-defect kaolinite and at 1578, 1598, 1613, 1627, 1652, and 1678 cm(-1) for the hydrazine-intercalated high-defect kaolinite. The intensities of these bands are a function of the exposure to air and measurement time. The 1650- and 1679 cm(-1) bands increased in intensity as the intensity of the 1612 cm(-1) band decreased. Even after exposure to air for 24 h, water remained in the kaolinite interlayer space and only after heating was the water removed. The 1578, 1598, and 1612 cm(-1) bands as well as the 1627 cm(-1) band are attributed to (a) free or non-hydrogen-bonded water held in the interlayer spaces of the kaolinite, (b) water in the hydration spheres of the hydrazine, and (c) adsorbed water on the kaolinite surface. In kaolinites additional bands at 1650 and 1679 cm(-1) are attributed to water coordinated to the siloxane surface.