Determination of the mineralogical composition of six highly weathered soils of the Central Plateau of Brazil showed that the sand content (predominantly quartz) was not related to the relative amounts of gibbsite and kaolinite in the clay (< µm) fractions. The latter is in agreement with kinetic considerations of the involved mineral species, but in disagreement with thermodynamic considerations. However, that dissolution of quartz has been operative in these soils is indicated by an excellent relationship (r2 = 0·96) between the amount of sand-size quartz and the reactive SiO2 content of the clay fractions.

A specimen of Kenya vermiculite contained no mica or chlorite layers either as separate phases or as components of an interstratifled structure. Dehydroxylation occurred in two stages, at 550° and 850°C, with approximately equal amounts of hydroxyl liberated in each stage. Al-saturated Kenya vermiculite showed low temperature dehydration characteristics similar to those of the natural Mg-saturated specimen, but the DTA, TGA and oscillating-heating X-ray diffraction patterns showed that the three stage dehydration process was not as clear-cut with the Al-saturated specimen.

As with montmorillonite, when small amounts of aluminum were precipitated by the addition of Ca(OH)2 in the presence of vermiculite, the Al(OH)x, was taken up and held indefinitely by the clay, the ion product (Al)(OH)3 in solution was maintained at 10-33∙0 and no gibbsite was formed with time. With large amounts, 800 and 1600 me Al(OH)x per 100g vermiculite, the hydroxide was held initially in the interlayer space, but gibbsite was eventually formed as (Al)(OH)3 approached the solubility product of gibbsite. Unlike montmorillonite, the vermiculite specimens retained an appreciable amount of the interlayer hydroxide and did not regain the original C.E.C. values as gibbsite was formed.

Al-vermiculite which was repeatedly suspended in AlCl3 with (Al)(OH)3 maintained at a value less than 10-33∙8 liberated 435 me Mg, took up 208 me Al as an interlayer hydroxide and caused a reduction in C.E.C. from 130 to 28 me per 100g clay. With vermiculite an appreciable amount of the interlayer Al(OH)x was stable with respect to gibbsite whereas with montmorillonite it was not.

Mössbauer spectroscopy of dioctahedral phyllosilicates showed that on dehydroxylation iron which originally occupied M(2) and M(l) sites became, respectively, 5- and 6-coordinated. The 6-coordinated sites are very distorted. No migration of cations occurs in the course of heating the specimens for 1–3 hr at 600°–700°C.

By using a combination of several physicochemical methods, different successive stages of the dehydroxylation process could be distinguished: (1) migration of protons; (2) localized dehydroxylation of individual associations without significant change in the overall configuration of the octahedral sheets; and (3) loss of most of the hydroxyl groups with concomitant changes in the cell dimensions. Penetration of Li into the octahedral sheets does not affect the course of the reaction, but reduces the dehydroxylation temperature and the stability of the products.

Dehydroxylation was preceded by or associated with the oxidation of any divalent iron present. Fe3+ derived from Fe2+ was indistinguishable by Mössbauer spectroscopy from iron initially present in the trivalent form. High concentrations of Fe lower the dehydroxylation temperature and reduce the stability of the dehydroxylate to the extent that partial disintegration may precede complete dehydroxylation.

There is a wrinkle in the story of common features in West Syrian anaphoras, which John Fenwick called “the Missing Oblation.” In this article, I argue that the importance of the “missing oblation” highlighted by Fenwick, Robert Taft, Stefano Parenti and others needs to be balanced against the verbs of oblation that are present. The emphasis on the missing oblation, combined with the tendency to summarize the Antiochene structure with little reference to the importance of these verbs, results in an inaccurate and unbalanced sense of the degree to which the anaphora expresses the belief that the action of offering bread and wine is constitutive of the eucharistic action. This should lead to a caution with the unhelpful heuristic about the spiritualization of sacrifice in contemporary scholarship and the underemphasis of the belief in the materiality of the eucharistic sacrifice in writers such as John Chrysostom and earlier anaphoras.

Difficulties in the interpretation of X-ray diffractograms of soil clays are discussed with reference to clay fractions obtained from glacial till and lacustrine soil parent materials. Diffracto-grams of the coarse clay fractions are readily interpreted by conventional means but it is difficult to determine if the dominant mineral species of the fine clay fraction is an interstratified mineral or a mixture of discrete montmorillonite and mica. A number of methods of interpretation of diffractograms of interstratified minerals are used with varying results. In the case of clays of small particle size, diffraction peaks crucial to the recognition of interstratification are not resolved due to the peak broadening. This phenomenon causes the diffractogram of a mixture of discrete minerals to resemble that of an interstratified mineral.

The mineral in monomineralic glauconite pellets is an iron-rich mixed-layer illite-smectite (here called glauconite), often composed almost entirely of illite layers. The nature of the interlayering is closely analagous to that of aluminous illite-smectite and varies with the proportions of the layer types: >30 per cent smectite, randomly interstratified; 15–30 per cent smectite, allevardite-like ordering; < 15 per cent smectite, ‘IMII’ ordering.

Glauconite is analagous to aluminous illite-smectite chemically as well as structurally. A good correlation has been found between the number of potassium atoms per O10(OH)2 in structural formulas calculated from the chemical analyses and the proportion of illite layers as determined by X-ray powder diffraction methods. This relationship indicates a remarkably systematic increase in the potassium content of the illite layers with an increasing proportion of illite layers. This feature and the existence of ordered interlayering at high proportions of illite layers can be explained by crystal-chemical effects of illite layers on neighboring smectite layers. Glauconite differs from aluminous illite-smectite in that glauconite contains significantly less potassium per illite layer than does aluminous illite-smectite with the same proportion of illite layers except near the pure illite composition. The strength with which the interlayer potassium is held and the ease of conversion of smectite to illite layers in glauconite may be attributed to its 1M structure and, perhaps, to its high octahedral iron content, which lead to stronger bonding of potassium by allowing a higher tilt angle of the O-H axis of hydroxyls adjacent to the potassium ion.

The apparent octahedral cation occupancy in excess of two-thirds of the octahedral positions in many glauconites appears largely attributable to the presence of significant amounts of interlayer hydroxy-iron, aluminum and magnesium complexes in the smectite layers.

It is shown that order-disorder relations in the distribution of the isomorphous substitutions are important in the characterization of different 2/1 phyllosilicates and in the determination of their behavior. These order-disorder relations are shown by selected area diffraction patterns obtained from single crystals. The range of layer charges corresponding to smectites (charge per half-cell <0.6) is that for which phyllosilicates are stable with disordered substitutions. Phyllites with charge >0.6 show anomalous diffusions which indicate that the distributions of exchangeable Ba ions are partially ordered; this result is taken as evidence that the isomorphous substitutions also are partially ordered.

Plagioclase feldspar is one of the outermost minerals destroyed in the hydrothermal alteration of quartz monzonite of the Butte district, Montana. Single grains of andesine plagioclase showing varying stages of fringe alteration were selected to show the sequence of events leading from the fresh plagioclase tectosilicate to the phyllosilicate montmorillonite, and to evaluate the role of petrographically-identified allophane in the alteration process.

Replicas of fresh, incipiently, and thoroughly montmorillonitized grains reveal a complex sequence of events which may follow alternate equivalent paths. Quantitatively most important is the formation of a hobnail texture composed of sparse to dense ~0.5 μ discoids of amorphous material on feldspar cleavage surfaces. These discoids appear to fuse laterally to form amoeboid or lobate amorphous clusters. Some assume progressively more polygonal outlines characterizing the montmorillonite morphology, or their fringes become flake-like montmorillonite which peels away in wisps from the pitted feldspar surface. Wisps may persist singly, they may form minute ropy granules, they may develop into wispy ridges, or the entire surface may convert to ragged, wispy, or compact montmorillonite. Far less commonly, plagioclase appears to develop without a discernible amorphous stage. The alternative paths are probably influenced by the chemical activity of magnesium in the system.

Crude sedimentary kaolin clay from central Georgia, U.S.A., which had a wide distribution of particle size, was divided into several size fractions by repeated sedimentation in water. The resulting fractions had approximately a 2:1 ratio in dia. between their upper and lower limits. Each fraction was then studied by transmission and scanning electron microscopy and characterized in terms of surface area (both geometric and by gas adsorption), particle shape and impurity analysis.

Particle diameter determined from measurements made on electron micrographs showed considerable deviation from the diameter obtained by Stokes sedimentation. This deviation was especially large for the coarser particles and could be explained by the microscopically observed porosity of the kaolinite booklets. Imperfect stacking of the crystallites within a kaolinite booklet leads to a moderately regular array of slit-like voids. Effective particle densities as low as about 1·6 have been observed. The pore structure was also investigated by use of mercury intrusion porosimetry.

Boron adsorption by Ca forms of montmorillonite, illite, and kaolinite was determined as a function of pH and boron concentration in solution. Data from batch experiments were compared with results computed for each clay according to fitted adsorption coefficients (maximum boron adsorption and affinity constants related to the binding energy). The agreement between calculated values and experimental results indicates that a phenomenological equation can be used to predict boron adsorption on clays as a function of both of these variables. For the solution-to-clay ratios examined, the water content does not affect the boron-surface interaction as expressed by the above adsorption parameters. Because the affinity of clays for B(OH)4− is much stronger than for B(OH)3 , the adsorption maximum was obtained only under alkaline conditions at approximately pH 9.0 to 9.7. It is suggested that the pH of maximum adsorption is a function of the ratios of affinity coefficients of the three species B(OH)3, B(OH)4−, and OH− competing for the same adsorption sites. The adsorption coefficients indicate that in some cases the difference in the amount of adsorbed boron between montmorillonite and kaolinite could be either small or large, depending on the circumstances. The main factor that would affect this difference is the total amount of boron in the suspension. Estimated value of the adsorption maximum was 2.94, 11.8 and 15.1 µmole/g for Ca-kaolinite, Ca-montmorillonite, and Ca-illite, respectively.

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.

Mica particles approximately 10 or 25 mm square and 0.5 mm thick were placed in NaCl-NaTPB solutions to make visual observations of the changes that occur in micas when the interlayer K is replaced by Na. Samples of muscovite, biotite, phlogopite, lepidolite, and lepidomelane were used, and the effects of different degradation periods were photographed.

An increase in the thickness of the particles due to basal planes splitting apart was observed with all micas. This exfoliation released interlayer K and in some cases caused the particles to cleave into separate flakes. Lepidomelane particles remained intact despite a 20-fold increase in thickness in 7 days. Even muscovite and lepidolite exfoliated and cleaved, but much longer degradation periods were needed.

There was a distinct change in the color of the dark biotite, phlogopite and lepidomelane particles when K was removed. Therefore, the initial stages of K depletion at holes, scratches, and edges of the particles were easily followed. As the degradation of the mica particles progressed, however, the color of the mica became a less reliable index of the stage of K depletion. Visual evidence of K depletion at the edges of particles was also obtained with muscovite, but not with lepidolite.

Transverse sections of 25-mm particles of K-depleted biotite were photographed to show the edge expansion that occurred when interlayer K was replaced by Na.

The hypothesis tested was that macroscopic swelling of montmorillonitic clays is reduced by the presence of interlayer minerals. Fine and coarse clay fractions of Camargo and Panther Greek bentonite samples were artificially interlayered by reaction of Al2(SO4)3 and NaOH in 0∙5% suspensions of the clays. All four clay fractions reacted similarly to artificial interlayering. At an Al:clay ratio of 16 meq Al/g clay the CEC was completely lost, surface area was reduced and X-ray basal spacings were altered. No macroscopic swelling occurred in samples treated with 16 meq of Al/g of clay. At smaller concentrations of hydroxy-aluminum 8 and 2 meq Al/g clay, the clay properties were less drastically altered. Extraction of interlayered clays with Na citrate restored the original C.E.C., surface area, and basal spacings of all samples and resulted in some slight enhancement of C.E.C. and surface areas of the coarse fractions. Treatment with hot Na citrate resulted in an increase in swelling ability but only slight increases in C.E.C. and surface area. Evidence presented supports the hypothesis that macroscopic swelling of montmorillonitic clays is greatly reduced by interlayer materials. Reduced swelling due to interlayering occurs even when other clay properties may be slightly different from those of nontreated samples. Indications are that interlayer material occurs naturally in the clays studied and this may apply to other bentonite deposits.