The effect of exchanging selected aryl and alkyl ammonium cations for sodium ions on the morphology and the hydrophobicity of a sodium montmorillonite was studied. It was found that the morphology of the organo-clays as observed by transmission electron microscopy depended on the type of and the amount of exchanged organic cation. An attempt was made to correlate the observed morphology of organo-clays with their hydrophobicity.

The tris(ethylenediamine) complex cations of chromium(III), cobalt(III), and copper(II) were exchanged onto sodium montmorillonite. The resulting cation exchanged clays were dried, ground, sieved and the 50/80 mesh size was retained for use as column packing material to be used in gas chromatographic analysis of light hydrocarbons and oxides of nitrogen. Studies indicated that the hydrocarbons were following a sieving action whereas the nitrogen oxides were involved in a surface adsorption process.

The changes in d001-spacing and surface area of tris(ethylenediamine)Cr(III)-montmorillonite were correlated with the changes in gas chromatographic retention time for the light hydrocarbons and the oxides of nitrogen.

Retention time was obtained for the 100 per cent exchanged montmorillonites containing cations of tris(ethylenediamine)Cr(III), tris(ethylenediamine)Co(III), and tris(ethylenediamine)Cu(II). A comparative study of the d001-spacing and surface area of the three clays is shown to be directly related to the retention time.

Heating effects were studied to determine thermal stability. Changes in retention times were compared with various structural changes. DTA and heating-oscillating X-ray powder diffraction analysis were used to help explain the relationship between retention time and structural change.

Lysine and vermiculite form a stable, ordered, interlamellar complex which has a well defined superlattice structure with respect to the ab-plane of vermiculite. The lysine molecules lie at a low angle to the silicate surfaces and establish a double layer network between such surfaces. I.R. and chemical data for the complex are given. The possible role of hydrogen bonds in linking the system together is considered.

Dioctahedral aluminum smectites from bentonite deposits in Argentina, Brazil, Czechoslovakia and Japan represent, according to the MgO content of the bulk samples, intermediate members in the montmorillonite-beidellite series. The smectite particles in these samples occur in a variety of forms such as; (a) laths and diamond-shaped units with a well developed crystal habit, (b) loosely folded aggregates with an irregular morphology and (c) flat and compact lamellae with well developed {001} forms but with complete lack of {hk0} forms. Such lamellae have been described in two groups: the thin ones (10–50 Å) and the thicker ones. Thin lamellae may give SAD spot patterns with a non-hexagonal symmetry. Lamellae having thicknesses greater than 50 Å resemble a single crystal but their SAD patterns indicate that they do not have a three-dimensional periodicity.

The question arises whether the morphologically different particles in a sample belong to the same intermediate phase or if they represent different members in the montmorillonite-beidellite series coexisting in the same sample.

Adsorption isotherms for water vapor, c-spacing and heat of immersion in water of Na- and Ca-montmorillonite were measured at 25°C at various r.h. The amount of water adsorbed as a function of the r.h. increased gradually, whereas the c-spacing increased, and the heat of immersion (per mole of adsorbed water) decreased in steps. There was good agreement between the calorimetric data, the heat calculated from the isotherms by use of BET equation, and the calculations from the ion-dipole model. A model is presented to describe the hydration of sodium and calcium montmorillonite.

Dissimilar fabrics, observed by scan electron micrography (SEM) on freshly broken surfaces of kaolins from weathered, water-laid material vs hydrothermally altered material in Mexico are illustrated, contrasted, and tentatively related to their respective environments of genesis. Coarse, open-textured, well-preserved books and vermiforms of kaolinite characterize the kaolin from water-laid material at Jacal, Mexico. Hydrothermal kaolins tend to have more tightly compacted crystals of either kaolinite flakes (individuals or in packets) or elongates (halloysite morphology) or mixtures of both in the same deposit. Variations in porosity of parent rock whether sedimentary or igneous, and dissimilar permeation by meteoric water and by vapor and liquids of hydrothermal fluids are deemed to be significant in the processes producing distinctive fabrics. The question is raised as to the fundamental distinction between kaolinite and halloysite and their nomenclature.

The electrical conductivity of Na-montmorillonite suspensions in various salt and clay concentrations was measured. The weight conductance of the clay suspension was found to decrease with increase in clay concentration between 0 and approximately 0·5 g clay/100 ml, then rose to a plateau at 6–10 g clay/100 ml. The weight conductance of the clay suspensions also increased with an increase in the salt solution concentration. If the model of two resistors in parallel is used in interpreting the experimental data, these changes can be attributed to an increase in the mobility of the adsorbed Na ions. It is proposed that the two resistors in series model is more realistic in describing the conductivity of the suspensions. This model predicts the observed weight conductance changes of the suspensions, while the mobility of the adsorbed ions remains constant. A constant mobility of the adsorbed Na ions in clay-water systems of low to medium salt and clay concentrations also is predicted by the diffuse double layer.

Clay (<2 μm) and fine silt (2–20 μm) fractions of twenty seven soil samples from eight tropical ferruginous profiles of the Mysore Plateau (India) were analysed for kaolinite by dehydroxylation and selective dissolution. The considerable amounts of iron extracted by the procedure and the closeness of the SiO2/R2O3 molar ratios (2·00–2·18) to the ideal value of 2·00 indicated that iron was a structural constituent of the kaolinites. The calculated unit cell cation composition of the kaolinites showed a substitution of 0·11–0·82 atoms of Fe(III) for Al in every four octahedral sites. The kaolinites in these soils appear to be products of crystallization from weathering solutions.

Hisingerite occurs as a weathering product of iron-rich saponite in rhyolitic tuff of Oya, Tochigi Prefecture. The chemical composition: SiO2, 40·68%; Al2O3, 4·44%; Fe2O3, 28·54%; MgO, 1·85%; CaO, 1·42%; Na2O, 1·50%; K2O, 0·33%; H2O+, 6·43%; H2O−, 13·70%; total 98·89%. Very broad and weak X-ray powder reflections occur at 16, 4·5, 2·5, 1·7 and 1·5 Å, which correspond to the main peaks of nontronite. It is considered that trioctahedral iron-rich saponite was altered to hisingerite, a very poorly crystalline form of nontronite, by oxidation of iron and advanced leaching of octahedral Mg ions.

The idealized symmetry of kaolinite-type minerals (1:1 phyllosilicates) is analysed in detail. They can be considered as OD-structures consisting of three kinds of OD-layers. Each of them, taken separately, possesses higher symmetry than their combination. This explains the well-known tendency of kaolinite-type minerals to form a wide variety of ordered and disordered polytypes as well as twins. The possible stacking sequences result from the different kinds of pairs of kaolinite layers which are derived for dioctahedral, trioctahedral as well as ‘monoctahedral’ kaolinite-type minerals, the latter being defined as those in which the three octahedral positions are occupied by three different cations or two different cations and a void. The analysis makes use of a simple symbolism and a simplified pictorial representation.

A brief summary of the most important terms and definitions of the theory of OD-structures is given in an Appendix.

All MDO-polytypes (i.e. regular polytypes) of trioctahedral, dioctahedral and monoctahedral 1:1 phyllosilicates are derived from their OD-character using the results of our preceding paper. The terms ‘simple polytype’, ‘standard polytype’ and ‘regular polytype’ turn out to be synonyms of the term ‘MDO-polytype’ which has the advantage of being exactly defined. The method used to obtain the MDO-polytypes is also applicable to more complicated cases.

Chemical changes during the natural alteration of micas were studied by electron microprobe and classical chemical analyses of fresh and altered portions of mica flakes from 10 Canadian mineral deposits. Results of 50 new analyses are discussed in five examples, starting from simple changes in the interlayer followed by exsolution of titania and ending with complex replacements of anions and cations in all layers of the mica structure. Alteration of micas starts along 001 cleavage planes and fractures and gradually extends into the entire flake leaving some or no remnants of the host mica. The removal of ions from the mica structure and from the flake takes place by gradual depletion, by exsolution of oxides, and/or by alternating removal and redeposition of a newly-formed oxide, illustrated in the following example of the removal of Ti;

1. (1) removal of Ti from the mica structure and exsolution of rutile in the parent mica

2. (2) destruction of rutile and recrystallization as anatase on the surface of the mica; and

3. (3) destruction of anatase, removal of Ti from the surface of the host and crystallization of anatase away from the parent mica.

Residual minerals replacing the original micas are secondary and recrystallized micas, chlorite, vermiculite, serpentine, talc and depleted, optically amorphous flakes. Newly-formed minerals which may incorporate the released ions into their structures are rutile, anatase, sericite, hydronepheline, chlorite-serpentine aggregates, goethite and jarosite. The following partly-altered micas are indicative of sulphide mineralization;

1. (a) bright-green, partly altered phlogopite from ultrabasic rocks and from Co-Cu-Fe-Ni sulphide assemblages. The green phlogopite formed by replacement of K, Al and Ti by Fe, Mg and OH

2. (b) depleted mica coated with jarosite and Ni-goethite in the oxidation zone of a nickel deposit.

   The jarosite formed from released S and Fe from decomposed Fe-Ni sulphides and K released from the host mica; and

3. (c) chlorite-sericite-biotite alteration zones adjacent to Pb-Zn-Cu-Fe deposits.