Electron microscopic examination of montmorillonite from the deposit near Redhill shows that the particles of the so-called blue clay are predominantly lathshaped with an average length: width ratio of 5. The so-called yellow clay from Redhill also contains a high proportion of similar lath-shaped particles, but many smaller lamellar particles are present which appear to be the results of lateral fracture of the laths. The majority of particles of montmorillonite in the fullers' earth deposit near Bath, Somerset, are platy with a similar shape distribution to Wyoming Bentonite, although smaller in size.

The electron microscopic technique used is based on a positively charged supporting film which, immersed in a clay suspension, preferentially selects negatively charged montmorillonite from the predominantly uncharged impurities. A conventional replica technique also showed lath-shaped particles in the blue clay.

The possible practical consequences of the different particle shapes are discussed.

Dans ce travail, nous avons determine les caractéristiques des états d'équilibre de la montmorillonite calcique placée dans la phase vapeur délivrée par des solutions aqueuses d'éthane 1·2 diol, de propane 1·2 diol, de propane 1·3 diol, de butane 1·3 diol, de butane 1·4 diol et de butane 2-3 diol.

Les diagrammes de sélectivité, calculés à partir des isothermes d'adsorption, la diffraction des rayons X et la spectroscopic infrarouge mettent en evidence l'existence de deux phases adsorbées ayant des caractéristiques très différentes.

1. (1) Une phase interagrégat dont la composition est égale à celle de la solution d'équilibre.

2. (2) Une phase interfoliaire dont les caractéristiques sont étroitement liées à la stéréochimie de la molécule organique.

Les différents états stables mis en evidence s'expliquent par les energies mises en jeu par les interactions cations dipoles et les liaisons hydrogène intermoléculaires.

L'exploitation des diagrammes de sélectivité de la montmorillonite, en equilibra avec la phase vapeur délivrée par des solutions aqueuses d'éthane 1-2 diol, permet de montrer que la quantité de diol interfoliaire est supérieure a 25 % et qu'elle est directement reliée à la chaleur d'hydratation des cations compensateurs.

Les cinétiques de désorption, réalisées à plusieurs températures, permettent de retrouver les mèmes résultats, à savoir que l'encombrement moléculaire depend du cation compensateur.

Ainsi, la mesure des surfaces totales des minéraux argileux avec l'éthane 1·2 diol n'a de sens que si, d'une part, on opere toujours avec le mème cation (σm = cte) et, d'autre part, on determine la quantité de diol en contact avec la surface à partir de plusieurs cinétiques de désorption réalisées à différentes temperatures.

A semi-quantitative mineralogical analysis of colliery spoil by XRD has been developed and used to compare spoils from eight collieries, in connection with work on the production of synthetic dense aggregates from spoil. Phase analysis of clay, which constitutes over half of all these spoils, is carried out by comparing X-ray peak areas of oriented specimens after heating and treatment with ethylene glycol. Total clay is obtained by difference, after determination of quartz and other minerals by an internal standard technique, allowing calculation of the proportion of each clay mineral. The results are tested against chemical analysis and a semiquantitative X-ray analysis of the chlorite present indicated that it is a highly ferruginous variety. Differences are detected in the mineralogy of all eight spoils but, except for the predominance of kaolinite in the spoils from Scotland, these differences are small.

Partial chemical and X-ray analyses of specimens taken serially from three different rock types from the St. Austell granite show that potash feldspar is hydrothermally altered to a micaceous mineral. Sodic plagioclase alters to mica, montmorillonite and kaolinite. Furthermore, in the latter case the micaceous mineral and montmorillonite are intermediate products between feldspar and kaolinite. It is believed that the level of H+ ion activity in the altering solutions controlled the removal of alkalis, Al2O3 and SiO2 so as to leave appropriate concentrations of these constituents to re-form as mica or montmorillonite. Further alteration of a similar kind produced kaolinite.

Samples were collected from a 11·4 m deep weathered profile of a metamorphic rock. The mineralogy was determined from XRD powder patterns, differential thermal and thermogravimetric analyses with CEC determinations and chemical analyses.

Four stages in a weathering sequence from the profile base towards the surface are as follows : (i) a partially regular trioctahedral chlorite-chlorite mixed layer ; (ii) a random chlorite-vermiculite mixed layer; (iii) a random chlorite-smectite mixed layer, and finally (iv) a smectite. Some chloritic layers are therefore more resistant to chemical weathering than other chloritic layers. This profile indicates that the order of decreasing resistance to chemical weathering is talc > smectite > tremolite.