The Boom Clay is an important raw material for the Belgian structural clay products industry. It can be divided into several lithological sub-units. In order to obtain an insight in the parameters which characterize these different units, and which affect the overall properties of the clay, a detailed chemical, physical and mineralogical analysis was carried out. Pearson correlation coefficients were calculated between the variables, which were then placed in four correlation groups: a quartz/clay mineral group, a reducing component group, a carbonate group and a feldspar group. This treatment of the data allowed three analysis parameters to be selected: <2 µm fraction, organic carbon and CO2. The other variables could be calculated fairly accurately from these by means of regression lines.

En utilisant des méthodes diffractométriques avec des smectites mal cristallisées, il n'est pas possible de déterminer de façon précise la répartition des atomes dans le feuillet. Il est particulièrement difficile de confirmer si le mineral est di- ou trioctaédrique, ou de déterminer la position de la vacance (position cis ou trans) dans la couche octaédrique. De même la nature polytypique de ces minéraux est difficile à preciser. La détermination de ces paramètres est difficile car les modulations (hkl) obtenues par diffraction des rayons X avec les smectites sont faibles et très peu marquées. Ce travail montre qu'en utilisant le césium comme cation interfoliaire, il y a non seulement augmentation de l'ordre dans l'empilement des feuillets mais aussi que son grand facteur de diffusion augmente l'intensité des modulations (hkl). En supposant que la substitution par du césium ne modifie pas la répartition des atomes dans le feuillet (il affecte seulement la distorsion de la couche tétraédrique), il est alors possible de déterminer cette répartition.

Transmission electron microscopy, X-ray radial distribution function analysis, chemical analysis, X-ray absorption edge spectroscopy, and Mössbauer spectroscopy combine to confirm an amorphous or gel structure for minerals of the hisingerite-neotocite series: (Fe,Mn)0.8SiO3.1.2H2O. A framework of (Fe,Mn)O6 octahedra and [SiO4] tetrahedra form hollow spheres, 50–100 Å in diameter, cross-bonded into a physically isotropic solid with as much as 10% interconnected pore space. The outer 10–20 Å of the spheres has a rudimentary structure, possibly marking the onset of segregation into Si-rich and (Fe,Mn)-rich layers. The Broken Hill mineral ‘sturtite’ is an intermediate member of the hisingerite-neotocite series.

Although seldom appreciated, the hydrocyclone offers several advantages over the more commonly used sedimentation/decantation method for clay separation. Large amounts of relatively concentrated clay suspensions may be separated in a matter of minutes. In addition, no dispersing agents are required and the shear conditions encountered by the suspension during passage through the hydrocyclone lead to particle disaggregation both in the silt and sub-micron size range. Formulae relating design factors of the hydrocyclone to separation performance exist but are of limited value as they are unable to predict the maximum particle size of the clay product or percentage recovery of any particular size of particle. Such data, determined from practical trials, are given for kaolinite, smectite and mixed-assemblage clay suspensions. Design limitations prevent the effective separation of clay products with ‘cut-off’ sizes finer than 5 µm.

Veins of intimately associated fibrous and granular saponitic clay occur in a basalt quarry at Orrock, Fife, Scotland. Preliminary X-ray diffraction studies suggested that both fibrous and granular forms consisted of pure saponite but chemical and thermal studies showed the presence of subsidiary amounts of interstratified chlorite. The fibrous clay, which is strongly oriented around the a axis but with a uniform distribution of the b and c poles, consists mainly of highly-crystalline laths with minor amounts of turbostratically-ordered particles. The granular clay consists of turbostratically-ordered particles only. The swelling behaviour of both types of clay in water and in ethylene glycol is similar to that of pure saponite. With glycerol, only the granular clay swells completely but the fibrous clay behaves similarly if first subjected to grinding or chemical pre-treatment. These observations are accounted for on the basis that the fibrous clay has better order than the granular form, thus enabling the interlamellar constituents to participate more fully in layer-to-layer bonding.

Clay mineral and trace element data indicate that sediments in the vicinity of the North Mid-Atlantic Ridge derive from material of both Icelandic and Canadian origin. These sources agree with the marine and atmospheric circulation patterns observed in this area.

Weathering products of a serpentinized Iherzolite were investigated using optical microscopy, X-ray diffraction, infrared spectroscopy, and electron microprobe and wet-chemical analysis methods. The original mineral assemblage of the rock was chrysotile-enstatite-diopside-picotite-magnetite-calcite. Rock porosity governed the types of chemical microsystems from which the clay minerals were derived. These microsystems were grouped into three types. (1) Grain microcracks and grain boundaries. These were the earliest manifestations of weathering. Only pyroxenes were affected and transformed into talc + iron oxides. (2) Plasma zones in which the rock structure was preserved. The talc + oxide and chrysotile were both altered into a saponitic mineral. Picotite was oxidized to oxipicotite. (3) Fissure zones. In the argillized zones the rock was restructured. Saponite was altered to nontronite + magnesium silicate gel. Talc was also transformed to the same gel. Fissures were often filled with clay cutans and some were edged with iron oxides. Mineral facies in the different zones have been plotted in Si-R2-R3 coordinates.

Basal X-ray peaks from normal and ethylene glycol-saturated tarasovite have been measured to 0.0.36 and 0.0.38, respectively; the mean basal spacings were 43·73 ± 0·44 and 46·05 ± 0·33 Å, with CV values of 1·31 and 0·97. The spacings indicate a near approach to a 3 : 1 illite-smectite but the CV values indicate a greater variability than is normally consistent with the allocation of a special name. Comparison of the observed spacings with those for illite showed that the more deviant values were always adjacent to positions of illite reflections. A modified Mering treatment of diffraction by mixed-layer sequences was used to estimate the proportion of illite layers; the average result was 79·9 ± 2·0%. The mineral is considered to have 3 : 1 illite-smectite units with randomly added illite layers, bringing the ratio from 75% for the ideally ordered sequence to near 80%.