The effects of the adsorption of water vapour on fresh surfaces (cleaved under vacuum) of five alkali halides NaBr, NaCl, KBr, KCl et LiF have been studied. The decoration method made it possible to observe modifications in the topography of these cleavage surfaces. The study of the variation of superficial conductibility in relation to relative pressure allowed the determination of the isotherms of adsorption θ = f (p/p₀). Thus, it was possible to determine three domains in the field of relative pressures between 0 and 0,8. The first corresponds to physical adsorption of water on the surface, the second to hydration of the cations Na⁺ or K⁺ by the water molecules, and the third to dissolution. For LiF, only one region has been observed.

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SUMMARY A catalogue of the Schlegel graphs of all the three‐valent tetrakaidecahedra with faces having at least four edges and at most six edges is presented. These fifty‐nine polyhedra can be used for all purposes in stereology, either as morphological models of grains in microscopic studies of all kinds of materials where the unit cells are supposed in equilibrium, for the experimental and theoretical study of three‐dimensional packing and non‐packing problems or as a conceptual basis for the theoretical frequency computation of occurrences of the different types of polygons in materials observed in slides or polished sections.

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Packing polyhedra into geometric models is a useful approach to the description of sub-polyhedric rock textures. When a packed aggregate of polyhedra is cut, a mosaic of individual polygons is obtained. Crystallographic concepts, enabling to predict what kinds of mosaics are obtained along any section plane in the polyhedral aggregate, are introduced. Thus, the shape (regular or irregular), the number of sides of the polygons in a given mosaic and likewise, the pattern of a mosaic — whether the mosaics made up of polygons of one type only, or a mixture of several types — can be determined by crystallographic operations. A few mosaics, obtained when packed aggregates of tetrakaidecahedra, rhombododecahedra, and cube-rhombododecahedra are cut along preferred planes of orientation, are presented. Geometric models are compared to the textural pattern of a few rocks, ceramics and metals. The frequency distribution of the mosaic types obtained by cutting across packed aggregates of tetrakaidecahedra is looked into it. Lastly, the spatial random distribution of two, and also the three mineral phases in the aggregate is graphically illustrated.