Showing papers in "Clays and Clay Minerals in 1971"

Mechanisms Controlling the Permeability of Clays

Abstract: Coefficients of permeability, calculated using Terzaghi’s theory of one-dimensional consolidation, are reported for smectite, illite, and kaolinite, in water, methyl and ethyl alcohol, benzene, and carbontetrachloride. When the pore fluid was water the clays were homoionized to either the sodium or calcium form and the pore water electrolyte concentration was varied. The coefficients of permeability are evaluated in terms of both mechanical and physico-chemical variables. It appears that the coefficients of permeability are mainly influenced by mechanical effects, particularly the distribution of void sizes and the tortuosity of the channels. The coefficient of permeability is maximized if the flow channels consist of many small channels and a relatively few large ones, through which the main flow occurs. Physico-chemical variables exert great influence on the coefficient of permeability through their influence on dispersion or aggregation of the clay particles.

Cation migration into empty octahedral sites and surface properties of clays

Abstract: The migration of small cations into the empty octahedral sites of dioctahedral clays allows one to study the local effects in the trioctahedral structure and the consequences of the exchange capacity decrease on the solvation properties. The results concern essentially the montmorillonite saturated by lithium. Computations based on a point charge model shows the necessity for the OH groups to undergo a reorientation when the lithium ions are within the octahedral sites. This change of orientation was studied by i.r. spectroscopy which permits one to estimate the amounts of lithium present in the structure. By analogy with i.r. results obtained for the Li, Mg, Ca and K montmorillonites, one can say that the non-exchangeable lithium which is not within the octahedral sites must be in the bottom of the hexagonal cavities. Moreover, it is shown that the solvation properties of the clay depend on the number of exchangeable cations and on the nature of the solvent. The clay does not swell with water when the amount of exchangeable cation is lower than 50 per cent of the exchange capacity. This limit is 30 per cent with glycerol, and 20 per cent with ethylene glycol.

Reactivity of Clay Minerals With Acids and Alkalies

Abstract: One-g samples of a montmorillonite, a metabentonite, an illite, two kaolinites, and three halloysites were treated with 50 ml of hydrochloric acid (6·45 N, 1: 1), acetic acid (4·5 N, 1: 3), sodium hydroxide (2·8N), sodium chloride solution (pH 6·10; Na = 35‰; Cl = 21·5‰), and natural sea water (pH 7·85; Na = 35·5‰; Cl = 21·5‰) for a 10-day period in stoppered plastic vials. The supernatant solutions were removed from the clay minerals and analyzed for SiO2, Al2O3, CaO, MgO, Na2O, and K2O. All the solutions removed some SiO2, Al2O3, and Fe2O3 from the samples, but the quantities were small. Sodium hydroxide attacked the kaolin group minerals more strongly than it did montmorillonite, metabentonite, or illite. Halloysite was more strongly attacked by hydrochloric acid than was any of the other experimental minerals. Hydrochloric acid removed iron oxide coatings from soil clay minerals, but acetic acid did not remove them completely. The samples most strongly attacked by HCl and NaOH were examined by X-ray diffraction. Acid treatment did not destroy the structure of the clays, but the halloysite structure was partially destroyed. Sodium hydroxide attacked the halloysite structure, as shown by chemical analysis and X-ray diffraction. These experiments show that treatment in dilute acids has no harmful effect in the preparation of clays for X-ray diffraction. Acetic acid is preferred to hydrochloric acid for this purpose. Hydrochloric acid cleans clay minerals by removing free iron oxide from the surface; acetic acid is less effective.

Fabric of Kaolinite and Illite Floccules

Abstract: A scanning and high voltage electron microscope study of the fabric of laboratory sedimented moist uncompressed kaolinite and illite floccules reveals an abundance of face-face flake orientation in the porous clay network. Clays were flocculated in the laboratory in both distilled water and slightly saline (1 g/l. NaCl) water using various clay concentrations. Floccules taken from the moist clay mass were prepared for study by freeze-drying and impregnation with polyethylene glycol. There is little difference in the fabric of kaolinite flocculated in distilled or slightly saline water. The fabric is dominated by a 3-dimensional network of twisted chains of face-face oriented flakes having the appearance of a stair-stepped cardhouse. Illite floccules in distilled water also consist of abundant face-face oriented overlapping flakes. However, in salt water there is a more even mixture of fabrics—edge-to-face flocculation of individual platelets and also stepped clusters of face-to-face oriented flakes, the latter being more abundant. It is suggested that under the experimental conditions the double layer of each clay particle is compressed resulting in an increase in the importance of van der Waals forces of attraction. As a result flakes approach each other and rotate into a parallel or subparallel position. The resultant dominant fabric is that of a stepped cluster of overlapping flakes.

Swelling Characteristics of Compacted, Expansive Soils

Abstract: Abstraet-The limitations of existing methods for the prediction of swelling behavior of compacted softs are examined. Both the purely theoretical approach and the purely empirical approach are found to be inadequate. The present study is based on a semi-empirical approach in which a model of swelling behavior is developed leading to equations relating swelling potential or swelling pressure of a compacted soil to its plasticity index, clay content and initial molding water content. The model is based on the concepts of the diffuse double layer, modified by introducing empirical constants to account for elastic swelling effects and other limitations involved in the direct application of double layer theory to real soils. The empirical constants are evaluated from the results of experimental investigations carried out on a large number of soil samples representing a wide variation of clay content as well as consistency limits. It is shown that the predicted values of the swelling potential and swelling pressure based on the proposed model agree closely with the experimental results of this study and those reported in the literature. Furthermore, the equations developed in this study are of a more general nature and appear to be applicable to a larger range of soil types than those previously published.

Preparation and solvation properties of some variable charge montmorillonites

Abstract: Li-, Na-, K- and Ca-saturated Wyoming montmorillonites have been prepared and used to obtain Li.Na-, Li,K-, and Li,Ca-montmorillonites with a range of Li contents. These were heated at 220°C for 24 hr, causing the Li+ ions to migrate mainly into the layer structure and leaving varying amounts of Li+, Na+, K+, and Ca2+ ions in the interlayer positions as determined by exchange with NH4+ ions. The results are only partially consistent with a migration of the Li+ ions into vacant octahedral sites up to the limit of the octahedral layer charge. Solvation of the resulting clays with water and various organic liquids showed the following results: With water, acetone and 3-pentanone, expansion of the montmorillonites increased in a step-wise manner with increasing numbers of interlayer cations qualitatively in accord with the field strength of the cations and the dipole moments of the molecules. With ethanol, ethylene glycol and morpholine, swelling with each liquid was practically independent of the number of interlayer cations, within the limits of the prepared materials. It is suggested that for the second group of liquids some mechanism additional to cation-dipole interactions, such as hydrogen bonding to silicate oxygen surfaces, may play an important part.

Mixed-Layer Kaolinite—Montmorillonite from the Yucatan Peninsula, Mexico

Abstract: Clay beds 1–2 m thick and interbedded with marine limestones probably of early Eocene age are composed of nearly pure mixed-layer kaolinite-montmorillonite Particle size studies, electron micrographs, X-ray diffraction studies, chemical analyses, cation exchange experiments, DTA, and TGA indicate that clays from three different localities contain roughly equal proportions of randomly interlayered kaolinite and montmorillonite layers The montmorillonite structural formulas average K0·2Na0·2Ca0·2Mg0·2(Al2·5Fe 1·0 3+ Mg0·5)(Al0·75Si725)O20+(OH)4−, with a deficiency of structural (OH) in either the montmorillonite or kaolinite layers Nonexchangeable K+ indicates that a few layers are mica-like Crystals are mostly round plates 1/10 to 1/20 µ across The feature most diagnostic of the mixed-layer character is an X-ray reflection near 8 A after heating at 300°C The clays are inferred to have developed by weathering of volcanic ash and subsequent erosion and deposition in protected nearshore basins

Scanning electron microscopy of clays and clay minerals

Abstract: The scanning electron microscope (SEM) proves to be ideally suited for studying the configuration, texture, and fabric of clay samples. Growth mechanics of crystalline units — interpenetration and interlocking of crystallites, crystal habits, twinning, helical growth, and topotaxis — also are uniquely revealed by the SEM. Authigenic kaolins make up the bulk of the examples because their larger crystallite size, better crystallinity, and open texture make them more suited to examination by the SEM than most other clay mineral types.

Microstructure and Pore Structure of Impact-Compacted Clays

Abstract: The microstructures of impact-compacted kaolinite and illite clays, after drying, were investigated by pore size-distribution measurements, X-ray orientation determinations, and scanning electron microscopy. Clays compacted on the dry side of the optimum moisture content exhibited a domain structure with adjacent domains largely separated by micrometer-size interdomain voids; clays compacted at or above the optimum moisture content showed a more nearly massive structure, large interdomain voids being absent. Parallel orientation was observed within domains, but neighboring domains were generally tilted with respect to each other. In kaolinite compacted on the wet side of optimum, regions of local parallel orientation could be identified at high magnification as domain units. A significant volume of 200 A–800 A dia. pores in this clay was identified with spaces observed between the kaolinite plates within domains, for samples compacted both on the wet and dry sides of optimum. The subdomain structure was tentatively classified as “intergrown” in character. (001)/(020), (002)/(020), (001)/(060), and (002)/(060) orientation indices were calculated for the compacted kaolinite and compared with analogous measurements for fully-random and fully-oriented specimens of the same clay. The results indicated only a small degree of preferential orientation normal to the axis of compaction, with little difference between samples compacted either wet or dry of optimum. These results were consistent with scanning electron microscope interpretations, which suggested that the domains did not appear to orient themselves significantly under the influence of the compaction employed.

Clay Mineral Formation in an Alpine Environment

Abstract: Vermiculite, mixed-layer vermiculite-phlogopite, and smectite are presently forming from igneous and metamorphic bedrock in the alpine zone of the northern Cascades, Washington. In addi- tion, south-facing exposures of quartz-diorites and metadiorites above snow line are weathering to ferruginous bauxite. Calculations indicate that vermiculite is presently forming from phlogopite schists in this environment at a unit area rate that is approximately six times the average estimated rate of clay erosion for North America. The mineralogical data indicate that chemical weathering in this region is a quantitatively significant process, and suggest that in the development of current geomorphic concepts researchers may have generally underestimated the importance of chemical weathering in alpine environments.

The I.R. Spectra of Interlamellar Kaolinite-Amide Complexes—I. The Complexes of Formamide, N-Methyl-Formamide and Dimethylformamide

Abstract: The i.r. spectra of interlamellar kaolinite complexes with formamide, N-methylformamide and dimethylformamide have been examined. The spectra show that the amides hydrogen-bond, through the C=O group of the amide to the inner surface kaolinite hydroxyls and decrease the intensity of the kaolinite ν(OH) bands. Hydrogen-bonded kaolinite hydroxyl bands appear at lower frequencies and these have been correlated to the original kaolinite ν (OH) bands. Other kaolinite bands in the complexes show smaller perturbations of the kaolinite vibrations. Each amide hydrogen-bonds to different groups of hydroxyls. Formamide hydrogen-bonds to the 3690 and 3664 cm−1 hydroxyls, N-methylformamide to the 3690 and 3648 cm−1 hydroxyls. The interpretation for the dimethylformamide complex is less clear. The ν(NH) frequencies of formamide and N-methylformamide in the complexes are intermediate between that in dilute non-polar solution and in the liquid. This could arise from either or both a degree of intermolecular association of the amide when between the kaolinite lamellae, or to weak N—H … O hydrogen bonds to the tetrahedral oxygen sheet of the lamellae.

Mechanisms of Formation of Colored Clay-Organic Complexes. A Review

Abstract: The interactions of clay minerals with organic compounds which give rise to the formation of colored complexes, are discussed. The color reactions of clays can be ascribed to a charge transfer between the mineral and the adsorbed species. The active sites on the clay are aluminums exposed at crystal edges and/or transition metal cations in the higher valency state at planar surfaces both of which can act as electron acceptors. The pH of the system, the nature of the solvent and that of the exchangeable cation, influence the rate of color development and the final intensity and quality of the color produced. Steric factors also play a part in reactions involving bulky organics. Some practical applications based on color reactions of clays with electron-donating organic substances are described.

Cristobalite Authigenic Origin in Relation to Montmorillonite and Quartz Origin in Bentonites

Abstract: Three kinds of opal-cristobalite, differentiated by the sharpness of the 4·1 A XRD peak, were isolated from the Helms (Texas) bentonite by selective chemical dissolution followed by specific gravity separation. The δ18O value (oxygen isotope abundance) for these cristobalite isolates ranged from approximately 26–30‰ (parts per thousand), increasing with increased breadth of the 4·1 A XRD peak. Opal-cristobalite isolated from the Monterey diatomite had a δ18O value of 34‰. These δ18O values are in the range for Cretaceous cherts (approximately 32‰) and are unlike the values of 9–11‰ obtained for low-cristobalite (XRD peaks at 4·05, 3·13, 2·4, and 2·49) formed hydrothermally or isolated from the vesicles of obsidian. The morphology pseudomorphic after diatoms, observed with the scanning electron microscope, was more apparent in the opal-cristobalite from the Monterey diatomite of Miocene age (approximately 10 million yr old) than in the spongy textured opal-cristobalite from the Helms bentonite, reflecting the 40 million yr available for crystallization since Upper Eocene. The oxygen isotope abundance of Helms montmorillonite (δ18O = 26‰) indicates that it was formed in sea water while the δ18O values of the associated opal-cristobalite indicate that this SiO2 polymorph probably formed at approximately 25°C in meteoric water. Although both cristobalite and mont-montmorillonite in the bentonite were authigenic, the crystallization of the SiO2 phase apparently required a considerably longer period and occurred mainly after tectonic uplift. In contrast to the results for cristobalite, quartz from the Helms and Upton (Wyoming) bentonites had δ18O values of 15 and 21‰ respectively. Such intermediate values, similar to those of aerosolic dusts of the Northern Hemisphere, loess, and many fluvial sediments and shales of the North Central United States (U.S.A.), preclude either a completely authigenic or a completely igneous origin for the quartz. These values probably result from a mixing of quartz from high and low temperature sources, detritally added to the ash or bentonite bed.

I.R. Spectroscopic Evidence for Interaction Between Hydronium ions and Lattice OH Groups in Montmorillonite

Abstract: At low levels of hydration, exchangeable D+ in montmorillonite interacts with lattice OH groups and quantitatively converts AlMgOH groups to AlMgOD. Hydroxyl groups coordinated to two Al ions undergo a slower exchange, the extent of which is restricted by octahedral Fe3+ ions. The OH stretching vibration of AlMgOH groups in montmorillonite is assigned an unusually high frequency (3687 cm−1) compared with that of the same group in phengites (3602 cm−1).

Optical and Electron Microscopic Investigation of Shear Induced Structures in Lightly Consolidated (Soft) and Heavily Consolidated (Hard) Kaolinite

Abstract: A review of fabric studies of clays suggests the need for relating those fabric characteristics which are revealed at the two levels of magnification provided by optical and electron microscopy, and a technique to achieve this has been developed and is described within the context of the initial stages of a long term study of the interrelation between fabric and engineering behaviour. Two kaolinitic clays with contrived fabrics were prepared by controlling particle size, moisture content and pH of suspension, and consolidation load and were subjected to shear loading to failure. Resin impregnation techniques which permit the kaolinite to be cut into thin sections for transmission electron microscopy have been optimized with the object of minimizing fabric strain and damage during ultratomy. The fabrics of the hard and soft ambient material are qualitatively compared by means of electron micrographs and are explained in terms of the preparatory procedures adopted for fabric control. The fabrics of the two types of shear induced structures are also qualitatively compared and explained in terms of the original fabrics and the subsequent shear loading.

Dodecylammonium- mica complexes- i factors affecting the exchange reaction

Abstract: Dodecylammonium chloride (DAC) is used as a reagent to displace potassium from a wide range of mica minerals. Displacement is rapid and essentially complete for trioctahedral micas even in dilute solutions (0·02N DAC) at low suspension concentrations. Increasing the suspension concentration, or the concentration of potassium in the extracting solution decreased the extent to which potassium could be displaced before equilibrium was established. Under standardized conditions of temperature and suspension concentration, the rate of potassium displacement increased as the particle size decreased although complete displacement was more difficult to achieve for the finest fraction (< 2µ) than for the coarser particles.

Diagenetic development of kaolinite

Abstract: Experimental solubility data for gibbsite and kaolinite are reviewed and applied to the pro- blem of gibbsite stability within the natural environment. It is concluded that free alumina compounds formed (only) in lateritic soils will tend to silicify spontaneously in all sedimentary environments. This metasomatic reaction should be accompanied by massive volume expansion: unusual textures are to be anticipated. Petrographic and field descriptions of a number of ancient kaolinitic sediments (some with, some without free alumina) are reviewed. It is concluded that silicification of hydrated aluminum oxides was an important mechanism of kaolinite formation in ancient sediments and that free alumina com- pounds persist only as a result of the unusual volume expansion associated with kaolinite formation.

Adsorption of Hydroxy-Al by Certain Phyllosilicates and its Relation to K/Ca Cation Exchange Selectivity

Abstract: The adsorption of hydroxy-Al by the 2–0•2 µ size fractions of muscovite, biotite, K-depleted micas, vermiculite and montmorillonite was studied. The differences in the amounts of hydroxy-Al adsorbed were apparently related to the expansibility and layer charge of minerals, the ionic saturation and degree of K-depletion, the basicity (OH/Al ratio) of the equilibrating hydroxy-Al solution, and the solution-clay ratio. The CEC reduction was not necessarily proportional to the amount of Al adsorbed because CEC reduction may occur through occupation of cation exchange sites by hydroxy-Al, or through hindrance to the entry of the replacing cation to these sites. Aluminum interlayering generally increases the K/Ca cation exchange selectivity (CES) of Na-vermiculite and K-depleted biotite, whereas the K/Ca CES of Na-montmorillonite was little affected. The basicity of the initial hydroxy-Al solution appeared to affect the K/Ca CES of Na-vermiculite and K-depleted biotite by controlling the amount of hydroxyl-Al adsorbed. The data indicate that in addition to the “propping effect”, hydroxy-Al interlayers may affect the K/Ca CES through the following mechanisms; (1) the “preferential occupation” of Ca adsorbing sites, and/or (2) the “retarding effect” on the entry of the more hydrated Ca ions.

A mixed layer kaolinite—smectite from Lower Silesia, Poland

Abstract: MODERN mineralogical literature contains many papers on interstratified minerals, hut very few in which 1:1 (one tetrahedral per one octahedral) layers participate in the interstratification. Brindley and Gillery (1954) reported a mixed-layer kaolin-chlorite, and Sudo and Hayashi (1956) and subsequently Shimoyama et al. (1969) described randomly interstratifled kaolin-montmoriUonite from an acid clay in Japan. In the last mentioned cases, 2:1 (two tetrahedral per one octahedral) expanding layers of montmoriiionite were distinguished from l : l layers, but no differentiation was made between halloysite, metahalloysite and kaolinite. In Jeglova, Lower Silesia, western Poland, kaolin clay and well developed quartz .crystals fill veins and cavities in metamorphic shield rocks associated with the granite intrusion known as the "Strzelin intrusion". This kaolin is a very plastic clay, fine grained and mostly white in color, but sometimes yellow or brown depending on the iron content. From the chemical composition and differential thermal curve (Morawiecki, 1953, 1962), the white clay was thought to be composed of kaolinie relatively free of chemical and mineral contaminations apart from quartz; a microscopic study found only well crystallized anatase, mica and quartz. Recently this kaolin clay has been carefully examined by X-ray diffraction and rather unusual properties were discovered which cannot be attributed to a. normal kaolinite. The X-ray diffraction pattern of a fully disoriented aggregate (Fig. 1) does not resemble that of a pure kaolinite. It differs in the number of reflections, their relative intensities, and the exact angular positions of the basal reflections. Such a pattern might result from a mechanical mixture of metahalloysite and kaolinite rather than pure kaolinite (Brindley et al. 1963). Electron micrographs, however, show a platy material (Fig. 2). The platy shape of the individual grains is the main reason for the excellent orientation obtained by sedimentation on a glass slide surface. These characteristics indicate a kaolinite rather than a haUoysite type mineral. It appeared during sample preparation, that the volume per gram of the wet clay from Jeglova was much greater than that of any other kaolin. Further swelling properties of the mineral in water and organic liquids were discovered. Swelling provides a good means for studying the nature of the structural layers. Oriented aggregates saturated with Na, Ca, ethylene glycol, glycerol were prepared. Samples also were heated to 380~ and to 600~ to check respectively on the layers after collapse and the remaining structure after kaolinite dehydroxylation. The oriented aggregates gave several orders of basal X-ray reflections. By comparing the results with those of the untreated and unheated sample, it was found that all the diffraction data were changed. The (00/) peaks were shifted very distinctly, some towards lower, some towards higher diffraction angles. Deviations from an integral series of a type d~ool}n, where n is an integer, were even greater than for the untreated sample. Interpretation of the X-ray data has been performed by a visual method (Meting, 1949). The peak positions have been represented in reciprocal space (Fig. 3), and the angular breadth (A0) ~ of the reflections measured at half maximum intensity is indicated. From considerations of the non-integral series of X-ray reflections, the directions of peak shifts and the (A0) values for four "orders" of reflection for the differently treated samples, I came to the conclusion that the,observed X-ray data are due to a statistically random mi~xture of non-swelling kaolinite and swelling smectite (Brindley, 1966) layers. To confirm this hypothesis, the theoretical positions of four (000 orders of basal spacing of kaolinite equal to 7-15 A (Brindley and Robinson, 1946) and (00|) orders of

Three Techniques for Fabric Viewing as Applied to Shear Distortion of a Clay

Abstract: A knowledge of the microscopic physical behavior of soils is important and necessary for the correct interpretation of observed macroscopic deformations in soil bodies. This study was designed to determine the particular pattern and distribution of extensive fabric alteration accompanying shear strains in a clay specimen subjected to triaxial stress combinations. The techniques used for observing these microscopic features were polarized light microscopy of thin sections from Carbowax-fixed clay samples, scanning electron microscopy of thinly coated cleavage surfaces in vacuum desiccated specimens, and transmission electron microscopy of metal-shadowed carbon replicas made of similar cleavage surfaces. All three methods showed that the zone of extensive fabric alteration in the triaxially sheared bodies was planar and had an average thickness of about 30 μ.

A Comparative Study of the Diagenetic Alteration of Clay Minerals in Mesozoic Shales from Papua, New Guinea, and in Tertiary Shales from Louisiana, U.S.A.

Abstract: Gradual change from 60% montmorillonite/40% illite randomly interstratified clay minerals at 3500 ft depth to 20% montmorillonite/80% illite at 10,200 ft can be observed in a complete section of Mesozoic shales at Barikewa in New Guinia. The top of a similar complete type Mesozoic section at 10,544 ft in the nearby Omati borehole contains 20–40% montmorillonite in randomly interstratified montmorillonite/illite. From 10,800 ft downward there is only 10–20% expandable material. Consequently depth of burial rather than stratigraphic level controls the proportion of expandable material present. Similar diagenetic alterations occur in the Wilcox Formation, Louisiana, also controlled by burial. The amount of illite 2M polymorphs in the Papuan samples is usually less than 5 per cent, the illite 10A peak sharpness ratio is about 1·4. Corresponding values for the Louisiana samples are 43% 2M polymorphs and about 2∙0 sharpness ratio. Chemical analysis of the Papuan shales show low MgO and K2O values when compared with the Louisiana samples. The latter sediments contain some chlorite, the former hardly any. Differences demonstrate a higher proportion of relatively unweathered material in the American samples. Increase of chlorite content, increase of magnesium content and decrease of kaolinite content from 12,368 ft down in the Louisiana samples suggests a change in sedimentation pattern.

Sodium-Lithium Exchange Equilibria on Vermiculite at 25° and 50°C*

Abstract: Sodium-lithium exchange equilibria between dilute aqueous chloride solutions and 0.2–62 µ Transvaal, South African vermiculite were studied at 25° and 50°C using a dialysis technique. The K content of the vermiculite was reduced to < 1% of the exchange capacity of 2·14 me/g by exhaustive extraction using Na-tetraphenylboron. The thermodynamic equilibrium constants and in turn the standard free energies and heats of exchange were evaluated from the equilibrium selectivity coefficients at the two temperatures. The standard entropy of exchange, ΔS°, was calculated according to the relationship ΔG° = ΔH° − TΔS°. Similar results were obtained for Na → Li and Li → Na exchange at 25°C, thus confirming the reversibility of the reaction. Sodium preference increased with Na saturation of the vermiculite and equilibrium selectivity coefficients ranged from 6·0 to 22·0 at 25°C. In comparison, selectivity coefficients for Na-Li exchange on montmorillonite ranged from 1·0 to 2·0 and became smaller with increasing Na saturation. The standard free energy and heat of exchange on vermiculite at 25°C were −1444 and −5525 cal mole−1, respectively, resulting in a ΔS° value of −13·7 e.u. This relatively large entropy change is probably due to differences in ion hydration in the solution and surface phases.

Structural factors controlling stacking sequences in dioctahedral micas

Abstract: Deviations in the symmetry of mica single layers from the ideal arrangement with all atoms in hexagonal arrays are caused by the structural factors such as compositional variation (substitutions), order-disorder, and distortions. The derivative crystal structure theory as applied to mica polymor- phism, implies that the ideal symmetry of the mica single layer (C2/m) can be altered to one of its standard subgroups by these structural factors. The "derivative structure" of the single layer may allow a unique interlayer and a specific intralayer configuration and result in a regular stacking sequence.

An analysis of x-ray diffraction line profiles of microcrystalline muscovites*

Abstract: Previous of the line profiles of the basal reflections of microcrystalline muscovites were refined by an adaptation of the method developed by Maire and Mrring. In order to evaluate the variation of interlayer spacings, the method required only relative values of Fourier coefficients, without the correction for instrumental broadening, which was the source of one of the moist critical problems previously. Instead of Ka radiation, K/3 radiation was used to record line profiles since difficulties associated with the separation of Kal and Kaz radiations could not be overcome satis- factorily. The data reconfirmed that the line broadening of 001 reflections was due not only to a small particle-size effect, but also to structural disorders involving the variation of the interlayer spacings. For the four specimens investigated here, the mean squares of the variation of interlayer spacings ranged from 0 to 0.0358, the square roots of which were inversely proportional to the total number of interlayer cations. It is considered that the observed distortions were mainly attributed to non- uniform interlayer spaces between silicate layers arising from an irregular distribution of interlayer cations. The data also indicated that the crystallites of all four specimens consisted of a similar number of layers. The method showed promise for the study of the nature and extent of structural disorders in micas or other silicate minerals.

Sequential active alteration of rhyolitic volcanic rock to endellite and a precursor phase of it at a spring in michoacan, mexico

Abstract: Sequential alteration of volcanic rock of rhyolitic composition to a precursor of endellite, and thence to tubular endellite, may be observed at a hot spring about 27 km north of Ciudad Hidalgo, Michoacan, Mexico. Ojo Caliente de Laguna Larga (or Verde) yields H2S-SO2-containing water, temperature about 45~ pH 3.5-3-7, from multiple orifices in vesicular and slabby rock with which the water reacts. First-stage alteration of the rock consisted of permeation and dissolution, accompanied by deposi- tion of clay substance in vesicle walls. The clay substance, although "amorphous" to X-rays, yields a weak DTA of endellite, and kaolinite. It is interpreted as a precursor of endellite. Further reaction included continued filling of vesicles and spreading argitlation which coalesced between vesicles and other rock pores. Ultimately, the rock was completely "digested" to well-defined endellites. Strong desilication and depotassication of the rock is indicated by the dissolved substances in the spring water: Si 59-1 (equivalent to 127 SiOz) ug/ml: A1, 1.63; Fe, 0.65: Mg, 0.21: Ca, 178: Na, 0-73: K, 13"7. Despite high K +, predominantly high H + and AP + induce formation of endellite. The clay- water system accords well with stability diagrams. Allophane-endellite in Indiana and endellite at Stanford, Kentucky, are formed from cold, strongly acid, meteoric-water solutions high in Si and AI relative to kaolinite dissolved in water. Factors of genesis common to both hot- and cold-water endellite are cited, suggesting that they are premissively critical, but not necessarily restrictive, to the origin of endellite.

Surface charge characterization of layer silicates by competitive adsorption of two organic divalent cations

Abstract: Diquat2+ (1, 1’-ethylene-2, 2’-dipyridinium ion) and paraquat2+ (1, 1’-dimethyl-4, 4’-di-pyridinium ion) were competitively adsorbed by Na-saturated kaolinites, smectites and expanded and collapsed vermiculites. The relative preference for one or the other cation varied with the surface charge densities of the adsorbents and the location of the adsorption site, i.e. internal or external. Minerals with high surface charge exhibited preference for diquat whereas minerals with low surface charge preferred paraquat. Expanded vermiculites preferentially adsorbed diquat on internal surfaces. Collapsed vermiculites generally showed a preference for paraquat. Smectites and kaolinites preferentially adsorbed paraquat.

Transformation of sericite into an interstratified mineral

Abstract: Sericite was K-depleted with molten LiNO3. The sample was changed into an interstratified structure in the presence of a small amount of LiN, Oa after prolonged treatment, and in the presence of a considerable amount of LiNO3 a similar structure was formed after about 3 hr of reaction. In the case of the presence of the proper amount of NaCI, a mixed-layer structure was easily obtained by treatment for a long period of time with a considerable amount of molten LiNO3. The interstratified mineral had a basal spacing of 22 A-23.3 ,~ which was expanded to 25 fit- 27.6 A by treatment with ethylene glycol.

I.R. Studies of Some Interstratified Minerals of Mica and Montmorillonite

Abstract: I.R. band shifts in the 830, 750 and 530 cm−1 regions that occur in interstratified layer silicates on heating were used to characterize the nature of the component layers. Two specimens showed shifts characteristic of 1 M illite and montmorillonite. Another specimen was similar to 2M illite even though the proportion of expanding layers was 0·4. The shifts for rectorite and allevardite resembled those of paragonite and 2 M illite.