Water Layers in Vermiculite

Abstract

GRUNER¹ has shown that vermiculite consists of talc-like layers, 9·26 A. high, alternating with water layers (4·95 A.), the total water content of the mineral being in the region of 20 per cent. Theories^2,3 as to the nature of the water layers have found difficulty in explaining the observation^1,2,3 that, when vermiculite is heated at 110° C., about half the water is removed without apparently affecting the diffraction pattern. It can be shown, however, that a change in the structure does, in fact, take place during this treatment ; but that the rapid rehydration which occurs on contact with normal atmospheric conditions tends to obscure it. Thus, while the diffraction patterns of unheated and rehydrated samples are identical, a powder specimen heated at 110° C, and sealed in a thin glass tube before rehydration can occur does not give the usual 14·2 A. basal reflexion of vermiculite but one at 11·8 A. corresponding to a water-layer thickness of 2·54 A., which is about half the original value. A single flake similarly treated shows the 11·8 A. reflexion to be associated with a regular sequence of higher orders ; that is to say, it represents a real spacing and is not a diffraction effect from intimately mixed layers of different sizes⁴. It is clear, therefore, that removal of half the water is accompanied by replacement of an original double water-layer by a single layer.