A discussion of the water content of vermiculite

Selected chemical and diffraction analyses from the literature, supplemented by thermal and thermogravimetric analyses and infrared absorption observations, are utilized to construct a rational model of the water arrangement i natural vermiculites. A super cell is arranged by simple modification ofthe Hendricks water nets to accom-modate the somewhat higher water contents, indicated by weight loss analyses, and the exchangeable cations. A three-cell unit (15.6 • 9/~) contains two Mg2+'6H~O octahedra centered at the corners and face centers and four 4H~O squares centered about ~5.2~k along a between the octahedra. The arrangement affords twenty hydrogen bonds near 2.75/~, twelve between silicate and water layers and eight between water layers, and thirty.two hydrogen bonds near 3.0/ ~ within water layers. The remaining four hydrogens are not active in the bonding system. The environment of each water molecule is a dis-torted tetrahedron. A broad infrared absorption band shows maxima t about 3600, 3450 and 3350 cm-