A Discussion of the Water Content of Vermiculite

W. F. Bradley and J. M. Serratosa1
Illinois Geological Survey, Urbana, Illinois
1 Permanent address: Instituto de Edafologia, CSIC, Madrid.

Abstract: 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 in natural vermiculites.

A super cell is arranged by simple modification of the Hendricks water nets to accommodate the somewhat higher water contents, indicated by weight loss analyses, and the exchangeable cations.

A three-cell unit (15.6 × 9 Å) contains two Mg2+·6H2O octahedra centered at the corners and face centers and four 4H2O squares centered about ±5.2 Å along a between the octahedra. The arrangement affords twenty hydrogen bonds near 2.75 Å, twelve between silicate and water layers and eight between water layers, and thirty-two hydrogen bonds near 3.0 Å within water layers. The remaining four hydrogens are not active in the bonding system. The environment of each water molecule is a distorted tetrahedron.

A broad infrared absorption band shows maxima at about 3600, 3450 and 3350 cm−1 at normal incidence, with increased activity in the highest and lowest energies when a flake is tilted. It is concluded that OH axes in the shortest bonds are more inclined to the cleavage planes than are the intermediate length axes.

Clays and Clay Minerals; 1958 v. 7; no. 1; p. 260-270; DOI: 10.1346/CCMN.1958.0070116
© 1958, The Clay Minerals Society
Clay Minerals Society (www.clays.org)