It is suggested (1) that large amounts of Al, Fe and Si carried in solution by fresh water are chemically precipitated as hydroxide gels in the brackish water environment of estuaries and deltas, and (2) that these gels are subsequently deposited in both the brackish water environment and in the neighbouring seas, where they become parental material for the neoformation of clay minerals, and various other silicate and iron minerals. The types of neoformed minerals will depend upon both the composition of the parental gels and the physico-chemical milieu of their crystallization. Evidence is discussed supporting this hypothesis from the following sources (1) the concentrations of Al, Fe and Si dissolved in fresh water and in sea-water, (2) experimental work on the crystallization of alumino-siliceous gels, and (3) a study of the precipitation of Si from the waters of the Mississippi River delta.

Because of the unusual sediment pattern of present times, this source of neoformed clay minerals and other minerals contributes only a small proportion of the sediments of the brackish parts of estuaries, deltas and the adjacent seas, which are dominated by fine-grained continental detritus. In earlier geological eras, when the world's river systems carried only relatively minor amounts of fine-grained continental detritus, this source of neoformed minerals is likely to have contributed a considerable proportion of the fine-grained sediments of these areas of sedimentation. Three possible examples are discussed.

The Cretaceous fuller's earth of Southern England has been studied using sedimentological, petrographical and X-ray diffraction techniques, and by 40Ar-39Ar radiometric dating. The results indicate that the ultimate sources of the fuller's earth were basic to intermediate, alkaline pyroclastic materials, perhaps stemming from volcanicity associated with the Mesozoic rifting of the North Atlantic. The Wolf Rock phonolite is considered as a potential pyroclastic source. Deposition occurred under normal sedimentary processes, with partial re-working of land-fall ash, and incorporation of orthoclastic debris.

A thick deposit of flint clay in the Permian I llawarra Coal Measures of the southern part of the Sydney Basin, New South Wales, is described. The flint clays which have affinities with those of the Pennsylvanian of North America and with the kaolin coal tonsteins of the Westphalian, are associated with red-brown claystones that contain in addition to hematite, an abundance of a regular mixed layer clay mineral. Pyrophyllite generally forms a minor constituent only of the flint clays but in one part of the deposit it is more abundant than kaolinite. Although there are many puzzling aspects concerning the origin of the deposit, evidence suggests that the kaolinite and the pyrophyllite in the flint clays are detrital.

The use of HF digestion to concentrate minerals of the plumbogummite group is discussed. Prolonged treatment is shown to result in solution of plumbogummite minerals, and in precipitation of HCl-insoluble, complex fluorides. These yield X-ray diffraction spacings that may be confused with those of plumbogummite minerals. The presence of fluorides in digestion residues is confirmed by X-ray diffraction, DTA and by identifying the products formed when such residues are heated to 600°C.

Fixation of K by soil clays and selected reference clay minerals was induced by dry heat and hydrothermal procedures, at 100°C, 200°C and 380°C. Appreciable amounts were fixed at all temperatures. In the cases of the samples treated hydrothermally the amounts fixed increased with pressure.

Fixation by dry heating at 380°C was significantly greater than at 100°C and 200°C respectively. Fixation under hydrothermal conditions increased in order 380°C > 200°C > 100°C.

Reductions in cation exchange capacities (and surface areas) were associated with fixation, indicating that some fixation was due to ion exchange. Changes in mineralogy in some of the samples also support the conclusion that ion exchange was partly responsible for fixation. Some of the fixation under hydrothermal conditions was due to the formation of insoluble K-compounds - as for example the synthesis of a new mineral when one sample was treated.

The lattice-iron content of the clays may have influenced their hydrothermal behaviour. Thus the Princes Town Clay ( > 7-5 % lattice-iron) and three nontronites (≫ 7-5 % lattice-iron) showed appreciable lattice collapse after hydrothermal treatment, while Wyoming bentonite and hectorite (<3-5%) lattice-iron) showed no collapse at all.

The degree of crystallinity of the mineral may also have influenced its hydrothermal reaction. For example, the highly disordered soil kaolinite (St John's) was much more reactive than the more ordered Georgia kaolinite. Also, the more-ordered reference clays fixed relatively less K at 380°C than the less-ordered soil clays.

The soils examined are from alluvial sheet deposits in a high valley where they are subjected to alternate wetting and drying, leading to desiccation. They are principally derived from shale and limestone bedrock in the surrounding mountains which are rapidly eroded and transported down valley mainly when the snow melts. The soils have engineering properties of fairly low density, high permeability, high plasticity with the plasticity index above the A line (CH range). These properties are correlated with the size grading and the clay mineralogical composition – about 30% calcite, 45-50 % clay minerals, dominated by Fe3+ and Mg-smectites and fine-grained muscovite. The clay mineralogy is explained in terms of Millot's zone of smectitization affecting biotite from detrital shale fragments, the muscovite remaining substantially unaltered. Calcite solution and redeposition account for the chalky texture and strong bond.

The cation exchange capacity (C.E.C.) of nontronite was determined by titrating the acid clay, prepared by the action of H-resin on nontronite, in water and some nonaqueous solvents. The base-titratable acidities of the acid nontronite, freshly prepared as well as aged, were found to be greater than the acidities extractable with 1 N NaCl; the difference was attributed to the non-exchangeable pH-dependent component of C.E.C. In the freshly prepared sample, H+ and Fe3+ ions were the only exchangeable cations. Ageing produced basic Fe ions which were exchangeable and whose amount increased at the cost of H− and Fe3+ ions. Whatever the age, the total quantity of these exchangeable cations corresponding to the total isomorphous charge, remained constant. The amount of the pH-dependent acidity also remained unchanged. A likely mechanism to account for the observed pH-dependent component of the C.E.C, of nontronite is suggested.

A Tertiary mudstone from beneath worked coal among the basalts of the Faeroe Islands is mainly composed of aluminium-rich dioctahedral smectite, disordered kaolinite (amounting to about one quarter of the smectite) and probably about 13 ~ amorphous material. The texture is the result of crystallization in place. Chemical analysis suggests an ionic formula for the smectite of (Ca0.32Na0.10K0.04) (A13.88 Fe0.06+3Fe0.05+2Mg0.29) (Si6.71 A11.29) O20 (OH)4· 3·0 H20, which corresponds closely to beidellite. The total charge on the interlayer cations is 0·78 and cationexchange capacity is 52·5 meq/100g. DTA curves yielded endothermic peaks at 140°C, 220°C, and 555°C with an exothermic peak at 955°C. The nomenclature is discussed and the material considered to be a bentonitic beidellite-mudstone; the rock, which has crystallized in place has similarities with tonstein in its mode of formation.

The minus 1μm fraction of an argillized vitric tuff, overlying the Wallarah Coal Seam near Swansea, N.S.W. is a nearly monomineralic (95%+) expandite clay, which hydrates and reacts to glycerol and heat treatments like montmorillonite. Results of X-ray, differential thermal, thermogravimetric and infrared absorption analyses confirm the general montmorillonoid character of the mineral, but chemical data indicate that much of its structure charge arises from substitutions in the tetrahedral zones of the lattice, as in beidellite rather than montmorillonite. The structural fOrmula deduced for the Ca++-saturated form of the minus 0.1μm clay is:

The distinctive behaviours of the heat-treated NH4+- and Li+-saturated structures also suggest that the mineral is a 'beidellitic montmorillonite' rather than a montmorillonite.

Dispersions of Laponite clay in various electrolyte solutions have been studied. In the total absence of electrolyte the synthetic clay forms a sol at 2% concentration. All cations cause gelling and flocculation.

It has been found that for any given clay concentration the yield value of the dispersions at equivalent flocculation level is the same for all electrolyte solutions, making it possible to study all types of dispersions at a standard level of flocculation.

At standard level of flocculation, the yield values have been found to follow exponential relationships with clay concentration with a break in the curves occurring at about 1·6% clay concentration. It is postulated that the break in the yield value curve occurs when enough clay is present to form a card-house structure. The plastic viscosities show a linear relationship with concentration and indicate high effective dispersed volume fractions at low clay concentrations.

When comparing the flocculating effects of different cations at fixed clay concentration, an empirical relationship has been found between cation concentration giving standard flocculation level, cation valency and radius.

Two clay deposits, the Stafford Clay marker bed from the Middle Coal Measures of North Staffordshire and the Woolhope Bentonite from the Silurian, Woolhope Limestone near Woolhope in Herefordshire are described. These clays contain mixed-layer clay minerals which have been separated by sedimentation for mineralogical and chemical analysis. Both minerals are shown to be mica-montmorillonites with MacEwan stacking parameters PA = 0·59, PAA = 0·44 and PA = 0·56, PAA = 0·70 respectively. In both cases the average layer charge (1·22 and 1·46) is intermediate between that of montmorillonites and micas but the exchangeable cation layer charge (1·07 and 1·27/montmorillonite layer) and fixed cation layer charge (1·32 and 1·63/mica layer) of the component layers are higher and lower respectively than the normal range of montmorillonites and micas. Some chemical data are given for the raw material which yielded these minerals and for associated and related rocks. In particular K, U and Th determinations permit a discussion of the natural gamma-ray flux which is sufficiently more intense than that of the associ~.ted sediments to permit its detection by scintillation counter in the field.

Vermiculite single crystals immersed in aminoacid solutions of varying concentration and pH, form complexes characterized by discrete basal spacings. Organic molecules enter in the interlayer space as cations and as dipolar ions through mechanisms of ion exchange and dipole adsorption.

The basal spacings of the complexes were recorded. Based on these results the possible arrangements of the aminoacid molecules have been discussed.The main assumptions used are: (a) the electropositive groups NH3+ penetrate into the holes formed by the basal oxygens of the silicate; (13) the C-N bonds are perpendicular to the silicate sheets; (c) the hydrogen atoms of the —CH2 groups are directed towards the sheet surfaces; (d) the —COO− and —COOH groups are located in the middle plane of the interlayer space, halfway between the negative structural charges; and (e) double hydrogen bonds are formed between —COOH groups belonging to organic cations adsorbed onto opposite surfaces.

In solutions of higher concentration the crystals swell to the gel state. This phenomenon is due to: (a) the different nature of interlayer cohesion after substitution of the inorganic cations by the aminoacid cationic form; and (b) the appearance of repulsive forces between —COO− groups of adsorbed dipoles, that overcome cohesive forces.