Chlorite-like complexes of montmorillonite with magnesium hydroxide or aluminum hydroxide have been prepared under a variety of physical and chemical conditions. Requirements for the preparation of these complexes have been simplified considerably by the use of rapid mixing techniques. A complex may be formed either by precipitating the hydroxide in a clay suspension or by preparing the precipitate separately and mixing it immediately with the clay suspension. It is suggested that the process involves the adsorption of a layer of the precipitate over the entire surface of the montmorillonite unit layer rather than the direct formation of a structure in the interlayer space. It is considered that there is no appreciable permanent association of unit 10 Å layers of montmorillonite in a well stirred suspension, even in the presence of strong salt solution, but that instead most clay surfaces are exposed continually. The chlorite-like structure develops only upon association of the unit layers through aging or dehydration.

The aluminum hydroxide complex with montmorillonite differs somewhat from the magnesium type, but it has the approximate chlorite basal spacing. The complex shows a second-order basal diffraction spacing of low intensity, and forms regular expanded structures with water or ethylene glycol. A gibbsite structure for the interlayer material is most compatible with the x-ray data.

The occurrence of this process in sediments and soils is considered to be very probable, although it is premature to consider precise environments until more experimental data are available.