THE CATION-EXCHANGE CAPACITY OF HYDRATED HALLOYSITE AND THE FORMATION OF HALLOYSITE-SALT COMPLEXES*

Examination of the cation-exchange capacity of a hydrated halloysite from Djebel Debar has disclosed no evidence for the proposed existence of exchangeable interlayer ions. A series of labile halloysite-salt com-plexes has been prepared. The requirements for effective intercalation of the salt are a high salt concentration i the external solution phase and a cation of low hydration energy. The view that the cation-exchange capacities of the kaolinite group of minerals arise from isomorphous substitutions within the crystal lattice rather than from broken bonds at the edge faces has been advanced by Samson and Schofield (1953) and by Robertson, Brindley and Mackenzie (1954). It would be expected that, if such substitutions occur, the electrical neutrality of the crystals would be preserved by cations located between the aluminosilicate layers as well as on the external surfaces of the crystals. In kaolinite itself