The statistical techniques of multiple regression analysis have been used to obtain more reliable formulae relating the cell dimensions especially the b-axis) of layer-lattice silicates to their composition or structural formulae. This allowed the significance of each coefficient to be expressed precisely and so provided rigorous tests for certain structural concepts about the different factors affecting cell dimensions. More recently an explicit theory has been developed about the various forces controlling the layer-lattice silicate structures which (a) removes some anomalies, (b) explains many variations in accurate bond lengths and angles, and (c) has several interesting structural implications for properties such as polymorphism, composition limits, crystal morphology, and stability under weathering. This paper summarizes work now being published in extenso elsewhere.

Quantitative measurement of the relative degree of crystal perfection among 144 samples of Coastal Plain kaolin shows that the deposits are nonhomogeneous with respect to crystallinity and that the hard and soft types can be distinguished at the 0.95 probability level by an analysis of variance. The nonhomogeneity of the deposits and the distinction between the hard and soft types agrees with the results obtained for other properties not reported here. Although on the basis of pulverizing ease there may be a single population with hard and soft end members, in terms of origin the evidence indicates the existence of two distinct clay populations.

Experimental data are presented to show that the current auxilliary procedures adopted for identification of kaolinite in the presence of chlorite are not generally valid because the procedures often fail to give an explicit condition for distinguishing both the minerals.

As the result of an examination of numerous infrared spectra in the OH region of clay minerals, obtained by using Nippon Bunko DS-401G Grating Speetrophotometer, it turned out that the absorption band at 3698±2 cm−1 is effective for distinguishing kaolinite from other clay minerals without the use of any additional techniques. The absorption band seems to be less affected by variation of particle size and crystallinity than is the X-ray diffraction pattern. The band is detectable to a few weight percent of kaolinite in total amounts of clay minerals. Identification of kaolinite by its absorption spectrum in clay samples from sedimentary rocks was successful.

More than one hundred sets of direct shear tests were conducted on soils composed of four reference clay minerals and various combinations of the four clay minerals of the Columbia University Clay Mineral Standards Project (A.P.I. 49) to illustrate with quantitative results the influence of clay mineralogy on the stress-strain characteristics of soils and hence the practical importance of clay mineralogy in soil mechanics. The soils tested consisted of various amounts by weight of Bedford Indiana Halloysite, Mesa Alta New Mexico Kaolinite, Santa Rita New Mexico Montmorillonite and Fithian Illinois Illite prepared with distilled water. The experimental results agree quite well with hyperbolic stress-strain relations previously developed by the author. The Hvorslev strength parameters are written as exponential functions of the clay mineral content and are included in the hyperbolic stress-strain law. The ultimate shear strength of the soils are mathematically expressed in terms of the stress history, confinement, and mineralogy.

Swelling pressures of oriented samples of sodium montmorillonite at 10−4 and 10−2 M NaCl in the pore-water were measured at controlled temperatures ranging from 1°C to 23°C. The specially designed apparatus allowed swelling against a movable piston connected to a mercury manometer through which the ambient pressure was applied.

A decrease in swelling pressure with decrease in temperature is predicted theoretically from the Gouy-Chapman theory, taking the variation of temperature and dielectric constant into account. At a salt concentration of 10−4 M NaCl, the measured swelling pressure at 120 Å average interparticle distance decreased from 48 cm of mercury at 23°C to 35 cm at 1°C, while the corresponding calculated pressure decrease was from 48 to 40 cm. While the measured pressures fell below calculated values at higher distances, the influence of temperature remained consistent.

At 10−2 M NaCl, a decrease in measured swelling pressure with decreasing temperature also occurred, but the measured swelling pressures were much higher than those predicted theoretically. Corrections were calculated, based upon the salt concentrations required by the theory to give the experimentally measured swelling pressures at room temperature. These were substituted into the approximate Langmuir solution of the combined Poisson-Boltzmann equation to describe the swelling pressure at 10−2 M NaCl. With these corrections, the calculated swelling pressure at 120 Å average interparticle distance decreased from 30 cm at 23°C to 26 cm at 1°C while the measured pressure decreased from 30 to 23 cm. This agreement between the corrected, calculated pressure and measured pressure held from 100 to 250 Å interparticle spacing.

Four natural bentonites, from Texas, Wyoming, Mexico, and Puerto Rico, have been fractionated by use of a super-centrifuge. The fractions have been investigated for base exchange capacity, apparent density, X-ray diffraction character and gel strengths of their suspensions.

Based on (001) spacings from X-ray diffraction and cation composition from ammonium acetate base exchange data, it was found that upon fractionation, clays of heterogeneous cation composition divide into two groups. Fractions larger than 0.150 micron contain the divalent cations Ca2+-Mg2+, while the finer fractions contain the monovalent cation Na+. Based on indirect evidence provided by X-ray diffraction, particle size fractionation, and gel strength, and correlation of the data with the literature, it is concluded that Na+ clays exist as unit layers in suspensions while Ca2+-Mg2+ particles are aggregates of a few layers.

Base exchange capacity and density were found to be independent of particle size.

A new structure is postulated and proposed for aqueous montmorillonite gels. This structure, descriptively called “hinge,” comprises clay particles oriented randomly to form a network in which each particle is hinged to other particles through sharing of bound particle-water.

Dry, homoionic systems of two montmorillonites and a kaolinite were treated with NH3 and then evacuated exhaustively to eliminate any physically adsorbed ammonia. It was concluded that the NH3 retained by the minerals was associated with the exchangeable cations. The mechanism of this adsorption process is the same as that which leads to the formation of inorganic ammines, namely, the mutual attraction between unshared electrons in the NH3 molecules and ionic centers of positive charge. This sorption process is reversible at elevated temperatures and is described by the equation, nNH3 + CX ⇄ (nNH3 · C)X, where n is the number of NH3 molecules associated with each exchangeable cation, C, on exchange complex X. Accordingly, n is a coordination number and has the following values for the cations indicated: NH4, 0; K, 0; H, 1; Ca, 2; Mg, 2; Alin, 3; Alex, 6. Here in and ex refer to interior and exterior exchange sites respectively. The retention of NH3 by cations which saturate the exchange complex of clays was shown to be analogous to the formation of ammoniates by reaction of NH3 with inorganic salts.

A reduced retention of NH3 by the Mg and Al 1:1 systems was ascribed to the possibility that exchangeable Mg and Al on kaolinite occur as hydroxy complexes.

A significant amount of NH3 was adsorbed to the weak acid hydroxyl groups on the broken clay edges, Relative to exchange capacities this phenomenon was greater in magnitude on the 1:1 than on the 2:1 clays.

Energies of NH3 adsorption on CaCl2, Ca-bentonite and NH4-bentonite were determined. Values of △H as a function of temperature were shown to be different for the Ca and NH4-clay systems. The data indicated stronger energies of retention of NH3 by the Ca-clay than for the NH4 clay. The thermodynamic data thus support the mechanisms proposed here.

Kaolinite, to which iron oxides had been added by heating with FeCl3 solution, was studied with regard to its cation exchange capacity. It was observed that net cations held (cations less anions) varied directly with pH. Cations and anions are removed in equivalent amounts when the clays are washed with water. Removal of exchangeable cations proceeds as the last anions are removed. As a consequence, the negative sites may become saturated with non-exchangeable hydroxy-aluminum ions. To obtain the true CEC of a kaolinite-iron oxide system, it is necessary to estimate the amount of nonexchangeable hydroxy-aluminum by conductometric titration.

Volcanic activity was important in Spain during the second half of the Cenozoic Era. It was closely related to the late kinematic and subsequent periods of the Alpidic orogenic cycle. Manifestations of the volcanic activity are seen in several parts of the Iberian Peninsula, but the main ones were confined to a few rather individualized zones. Cabo de Gata, Cartagena, and Mazarrón show a strong similarity, as does the Guelaya volcanic province, Morocco. The rocks (rhyolites, dacites and andesites) are clearly calcalkaline and, in many places, strong contamination processes have been demonstrated. The eruptions were, at least in part, fissural and fill important fractures, mainly northeast-southwest. They occurred just after the more important folding in the Betic-Riffien orogen. In these regions bentonite has formed by alteration of volcanic material.

The most important deposits are in Sierra of Nijar and Gata (Almería, Spain) and in the Monte Tidinit (Morocco). The Cabo de Gata bentonites are composed mainly of calcic and calcosodic montmorillonites. Palygorskite has been found in some places.

The bentonite of the Monte Tidinit is mainly calcium montmorillonite but some samples contain cristobalite. In Monte Maazza there is also a sedimentary deposit, consisting of a complex mixture of endellite, halloysite, gibbsite, montmorillonite and alunite—probably of hydrothermal origin. Halloysito is the main component: it is accompanied by gibbsite in the bottom layers and by montmorillonite and alunite in the top ones.

The ground clay, after processing by cation exchange or acid activation, is used for several industrial products, such as soaps and detergents, cosmetics and pharmacy; but the main use is for drilling muds, foundry molds, and clarification of mineral and vegetable oils.

All the bentonites are amenable to acid activation but the natural mixture of halloysite and montmorillonite from Monte Maazza gave the best results in tests on lubricating oils at a laboratory scale.

Research still in progress on the rheology of suspensions of the Almeréa bentonite contaminated with electrolytes gave interesting results using several thinner and filter oss control agents.