The arrangement of water molecules in the vicinity of clay mineral surfaces has been the subject of much speculation. Vermiculite offers a promising line of approach to this problem since, in addition to its occurrence in soil-clays, it is available as relatively large flakes which can be studied by single-crystal X-ray diffraction methods. This note reports an as yet incomplete structure analysis of vermiculite. A two-dimensional Fourier synthesis has been carried out and a determination of atomic parameters in the third dimension is in progress. The results obtained so far would appear to justify a preliminary statement.

The (h0l) set of reflexions for a natural Mg-saturated vermiculiet were recorded on two multiple-film packs exposed to MoKα radiation in a Weissenberg camera for 100 hours and 5 hours respectively. Intensities were estimated visually by comparison with a set of standards obtained from the (00·10) reflexion.