A method is described whereby differentiation between clay minerals may be rapidly effected. The method depends upon the differential moisture adsorption of clay minerals. There seems no reason why reasonably quantitative results may not be obtained. An application to the Etruria Marl is given.

Examination of the differential thermal characteristics of a normal montmorillonite saturated with a series of monovalent and divalent cations shows that the temperature of the main dehydroxylation peak is independent of valency but is apparently a parabolic function of ionic radius. NH4 +, Cs+, Zn2+ and Cd2+ give anomalous results, but the apparent discrepancy of the former two ions can be fully accounted for. The results are believed to be consistent with evolution of water molecules through the hexagonal holes in the sheet surface and diffusion between the layers to the micelle edge. The significance of variation in the 800–1000°C region of the curve is briefly considered.

A description is given of the widespread development in the U.S.S.R. of deposits of clay, largely kaolinitic in mineralogical content. These deposits also may be traced outside the U.S.S.R. Their origin is believed related to a period of intense weathering in Mesozoic times. It is pointed out that this thesis of an ancient crust of weathering would well repay application in other countries, where deposits normally regarded as of pneumatolytic origin might possibly be due to intense weathering.

A chloritic mineral found in close association with vermiculite from the Yoshino mine, Kochi Prefecture, agrees well with penninite but shows remarkable exfoliation on heating. Its mineralogical properties were studied by chemical, thermal and X-ray methods.

Under certain circumstances, both glycerol and ethylene glycol form interlayer complexes with vermiculites resembling those formed with the smectites. The rate and degree of complex formation are related to the surface charge on the silicate layers, to the type of interlayer cation present and to crystal size. With glycerol, but not with ethylene glycol, the hydration state of the mineral immediately prior to complex formation is of some importance.