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 addition, 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 frequency distribution or relative abundance of minerals in soils varies with the five principal classes of factors that govern soil formation. The characteristics of the minerals of the parent material, the time factor, climatic factors, relief factors and biotic factors each can be shown to have important independent effects on clay mineralogy of soils under proper circumstances. The soil parent material exerts a control over the frequency distribution of minerals in soils by introduction of the clay minerals into the soil directly, by controlling the course of chemical weathering in the soil through the relative susceptibility of its minerals to weathering, by furnishing abundant divalent metallic cations, by impediment of drainage, or by acceleration of leaching when highly permeable. The time factor is conspicuous as long times give an advanced degree of weathering even in temperate climates. Climate is important, since highly weathered materials inevitably occur as a result of intense leaching in warm tropical and equatorial climates. Relief is important in concentrating leaching water and metallic cations, in affecting oxidation or reduction. The biotic factor affects minerals conspicuously where an A0 horizon develops and resulting cheluviation moves R2O3 out of the A2 horizon.

Inherited minerals such as illite, quartz, feldspars, ferro-magnesian minerals, carbonates and gypsum are most abundant in clays of little-weathered parent materials and soils of the zonal Desert, Brown, Chestnut and Tundra soils as well as intrazonal Mountain groups and azonal Regosols and Lithosols. Secondary layer silicate minerals such as vermiculite, secondary chlorite, montmorillonite, kaolinite and halloysite are most abundant in clays of moderately weathered parent materials and soils of the zonal Chernozem, Prairie, Gray—Brown Podzolic, Podzol, Red—Yellow Podzolic, and Low Humic Latosol groups as well as intrazonal Planosol, Rendzina, Dark Magnesium soil, and Wiesenboden groups. Secondary sesquioxide minerals such as hematite, goethite, allophane, gibbsite and anatase and residual resistant primary minerals such as ilmenite and magnetite predominate in the more highly weathered parent materials and soils of the zonal Ferruginous Humic Latosols, Hydrol Humic Latosols, Latosolic Brown, and Ando soils and Laterites, as well as the intrazonal Tropical Savannah and Ground Water Podzol ortstein soils.

The effects of reduction and reoxidation of octahedral Fe3+ on the exchange of structural hydrogen in nontronite were determined using tritium (3H) as a label element. The uptake of H from the surrounding solution of nontronite suspensions increased as the reduction of structural Fe3+ increased. Similarly, the loss of H from the structure increased as the reduction increased. The results are generally consistent with a reduction mechanism involving the loss of structural OH, leaving the affected Fe sites with less than six-fold coordination. The attenuation of increased negative charge on the clay layer, however, was less than predicted by such a mechanism.

During the reoxidation of reduced nontronite in suspension, about one-third of the H remaining as part of the structure following reduction was lost, whereas twice that amount of H was incorporated into the structure from the surrounding solution. A reoxidation mechanism is proposed whereby H2O from the surrounding solution is incorporated into the mineral structure followed by the elimination of a hydrogen ion, returning the Fe to six-fold coordination. This mechanism implies the reversibility of Fe reduction in nontronite.

The crystal chemistry of Fe-Si scales deposited from geothermal brines at Salton Sea, California, was studied by powder X-ray diffraction and spectroscopic techniques including infrared, 57Fe Mössbauer, 27Al and 29Si nuclear magnetic resonance (NMR), and Fe and Si K-edge extended X-ray absorption fine structure (EXAFS). Scales precipitated at near 250°C from dissolved ferrous iron and silicic acid are composed of hisingerite. This phase is shown to possess the same local structure as nontronite and is a poorly-crystallized precursor of the ferric smectite. A clear distinction can be made at the local scale between hisingerite and 2-line ferrihydrite because, even in their most disordered states, the former possesses a two-dimensional and the latter a three-dimensional anionic framework. At temperature near 100°C Fe-Si scales are a mix of Al-containing opal and hydrous ferrous silicate, whose local structure resembles minnesotaite and greenalite. This hydrous ferrous silicate is very well ordered at the local scale with an average Fe coordination about Fe atoms of 6 ± 1. The difference in crystallinity between the ferrous and ferric silicate scales was related to variations of growth rates of clay particles precipitated from ferrous and ferric salt solutions. The low crystallinity of the ferric smectite suggests that the oxidation of ferrous iron occurs before polymerization with silica.

The Gourougou volcanic massif (northeastern Morocco) is actively prospected for bentonite deposits. Five bentonites originating from different environments were selected for the present study: hydrothermal alteration of obsidian perlite glass inside the volcanoes themselves (Providencia and Tribia deposits); alteration of pyroclastic flows in a marine shallow water to lagoonal lacustrine environment (Ibourhardayn deposit); ash falls in marine or lacustrine systems (Moulay Rachid and Melg el Ouidan (formerly Camp Berteau) deposits). All of these bentonites were probably formed from volcanic glass originating from a rhyolitic magma at different stages of differentiation as shown by slight variations of REE and incompatible element abundances. The crystal-chemical characteristics of the smectite vary according to alteration conditions: beidellite predominates in hydrothermal systems, whereas montmorillonite predominates in lagoonal and lacustrine environments, and mixed-layer beidellite-montmorillonite in the sea-water-altered pyroclastic flows. All these dioctahedral smectites exhibit a heterogeneous distribution of charge as shown by the presence of partially expandable (1 EG) or non- expandable (0 EG) layers in the K-saturation state. The proportion of the collapsed or partially expandable layers is not related to the average layer charge or to the cation exchange capacity. This militates for an overall heterogeneous charge distribution. Compared to other natural or experimental alteration systems of similar rhyolitic glass, the formation of beidellite or montmorillonite appears to be controlled by the amounts of Mg in the system.

The effects of chemical reduction of structural Fe3+ in nontronite SWa-1 (ferruginous smectite) on intervalence electron transfer (IT) and magnetic exchange were investigated. Visible absorption spectra in the region 800-400 nm of a chemical reduction series of the SWa-1 nontronite revealed an IT band near 730 nm (13,700 cm−1). Both the intensity and position of this band were affected by the extent of Fe reduction. The intensity increased until the Fe2+ content approached 40% of the total Fe, then decreased slightly with more Fe2+. The position of the band also shifted to lower energy as the extent of reduction increased.

Variable-temperature magnetic susceptibility measurements showed that the magnetic exchange in unaltered nontronite is frustrated antiferromagnetic, but ferromagnetic in reduced samples. Magnetic ordering temperatures are in the range 10–50 K, depending on the extent of reduction. The ferromagnetic component in the magnetization curve increased with increasing Fe2+ in the crystal structure. The positive paramagnetic interaction likely is due to electron charge transfer from Fe2+ to Fe3+ through such structural linkages as Fe2+-O-Fe3+ (perhaps following a double exchange mechanism), which is consistent with the visible absorption spectra.

Vernadite (MnO2·nH2O) is a mineral with a poorly ordered structure. Its synthetic analogue is designated δ-MnO2. Birnessite and vernadite are independent mineral species and cannot be described further under the same name. They have similar hexagonal unit-cell parameters, a0, but different c0 parameters. Rancieite has a structure similar to that of birnessite. Calcium bearing, 14-Å birnessite occurring in nature was first described by the authors. In addition to the todorokite having the parameters a0 = 9.75 Å, b0 = 2.84 Å, and c0 = 9.59 Å, other species of natural todorokite are known having a0 parameters that are multiples of 4.88 Å equal to 14.6 and 24.40 Å, the b0 and c0 parameters being the same.

Diffuse reflectance spectra of kaolins have been recorded in samples from different environments. They show the systematic presence of Fe-oxides, even in bleached kaolins, with no contribution from the Fe3+ ions substituted in kaolinite. Second derivative spectra of various Fe-phases (hematite, goethite, lepidocrocite, maghemite, akaganeite, ferrihydrite and Fe-polymer) may be differentiated by the position of a diagnostic band corresponding to the 2(6A1) → 2(4T1(4G)) transition. The systematic comparison of diffuse reflectance spectra of unbleached and bleached kaolins has demonstrated the differences between the Fe-oxides occurring as coatings and as occluded phases. The features observed in second derivative spectral curves are consistent with assignments of crystal field transitions to goethite, hematite, akaganeite, and aged hydrous ferric oxides. The optical determination of the Fe-phases associated to kaolins assists in the interpretation of the formation conditions of these minerals.

To study the physico-chemical activity of lichens on micaceous components of granitic rocks, samples covered by thalli of Parmelia conspersa (Ehrht) Ach. and Aspicilia intermutans (Nyl.) Arn. were collected and examined with Scanning Electron Microscopy (SEM) equipped with a Back Scattered Electron (BSE) detector and an Energy Dispersive Spectroscopy (EDS) microanalytical system. The bio-physical activity of both lichen species leads to a deep alteration of biotite, which results in detachment, separation and exfoliation of biotite plates. Chemically, the bioweathering process of biotite in the lichenmineral contact zone involves considerable depletion of potassium (K) from interlayer positions in biotite and removal of several elements, corresponding to a 9.7% loss in matter. The sequence of the loss of elements is: K+ » Fetot > Ti4+ ≅ Mg2+. There are also some gains in the order: Ca2+ > Na+ » Al3+ > Si4+ attributed to dissolution of co-existing Ca and Na rich minerals. Geochemical mass balance results suggest the transformation of K-rich biotite to scarcely altered biotite interstratified with a biotite-vermiculite intermediate phase in the lichen bioweathered contact zones.

The swelling property of smectite is dominated by the hydration of exchangeable cations in the interlayer spacing (‘interlayer hydration’). By investigating systematically the swelling behavior of various exchangeable cations with different valences and ionic radii, the interlayer hydration of smectite was explored. The swelling behavior of Li+-, K+-, Rb+-, Cs+-, Mg2+-, Sr2+-, Ba2+-, and La3+- montmorillonites in undersaturated conditions was measured precisely over the range 50–150°C by in situ X-ray diffraction (XRD) analyses. The systematic swelling behavior of ten homocationic montmorillonites, the aforementioned eight homoionic montmorillonites, plus Na+ and Ca2+ from a previous study, and the cation hydration energies were analysed by studying the changes occurring in the basal spacing and the 001 peak width. With decreasing cation hydration energy, swelling curves (i.e. plots of basal spacing vs. relative humidity (RH)) change from continuous (Mg2+, La3+, and Ca2+) to stepwise (Sr2+, Li+, Ba2+, and Na+) to one-layer only (K+, Rb+, and Cs+). For the first two groups, the RH at the midpoint between the one- and two-layer hydration states increased as the cation hydration energy decreased. Under low RH, with increasing temperature, the basal spacings of Mg-, La-, Ca-, Sr-, Li-, and Ba-montmorillonites decreased continuously to the zero-layer hydration state, whereas Na-, K-, Rb-, and Cs-montmorillonites swelled from the zero-layer hydration state even at the lowest temperature (50°C). A decrease in the basal spacing at the same RH but at different temperatures suggests the existence of metastable states or that the layer-stacking structure changes with temperature. The systematics of the swelling behavior of various homocationic montmorillonites as functions of RH and temperature (<150°C) at 1 atmare reported here.

High-resolution transmission electron microscopy (HRTEM) has been used to examine illite/smectite from the Mancos Shale; rectorite from Garland County, Arkansas; illite from Silver Hill, Montana; Na-smectite from Crook County, Wyoming; corrensite from Packwood, Washington; and diagenetic chlorite from the Tuscaloosa Formation. Thin specimens were prepared by ion milling, ultramicrotome sectioning, and/or grain dispersal on a holey carbon substrate. Some smectite-bearing clays were also examined after intercalation with dodecylamine hydrochloride (DH). Intercalation of smectite with DH proved to be a reliable method for HRTEM imaging of expanded smectite (d (001) = 16 Å) which could then be distinguished from unexpanded illite (d (001) = 10 Å). Lattice fringes of basal spacings of DH-intercalated rectorite and illite/smectite showed a 26-Å periodicity. These data support X-ray powder diffraction (XRD) studies which suggest that these samples are ordered, interstratified varieties of illite and smectite. The ion-thinned, unexpanded corrensite sample showed discrete crystallites containing 10-Å and 14-Å basal spacings corresponding to collapsed smectite and chlorite, respectively. Regions containing disordered layers of chlorite and smectite were also noted. Crystallites containing regular alternations of smectite and chlorite layers were not common. These HRTEM observations of corrensite did not corroborate XRD data. Particle sizes parallel to the c axis ranged widely for each sample studied, and many particles showed basal dimensions equivalent to more than five layers. For all illite, smectite, and illite/ smectite particles examined, crystallite sizes of about 20 Å in the basal dimension were not observed.

Adsorption of Cu2+ and Co2+ by synthetic imogolite, synthetic allophanes with a range of SiO2/ Al2O3 ratios, and allophanic clay fractions from volcanic ash soils was measured in an ionic medium of 0.05 M Ca(NO3)2. The effect of pH (and metal concentration) on adsorption was qualitatively similar for the synthetic and natural allophanes with relatively minor changes in behavior caused by variable SiO2/Al2O3 ratios. Cu and Co were chemisorbed by allophane at pH 5.0–5.5 and 6.9–7.2 (pH values for 50% adsorption level), respectively, with concomitant release of 1.6–1.9 protons/metal ion adsorbed. Quantitatively, adsorption by imogolite was less than that by the allophanes, presumably because of fewer sites available for chemisorption on the tubular structure of imogolite. Electron spin resonance studies of the imogolite and allophanes revealed that Cu2+ was adsorbed as a monomer on two types of surface sites. The preferred sites were likely adjacent AlOH groups binding Cu2+ by a binuclear mechanism; weaker bonding occurred at isolated AlOH or SiOH groups. These chemisorbed forms of Cu2+ were readily extracted by EDTA, CH3COOH, and metals capable of specific adsorption, but were not exchangeable. In addition, the H2O and/or OH− ligands of chemisorbed Cu2+ were readily displaced by NH3, with the formation of ternary Cu-ammonia-surface complexes.

A new method is proposed for applying the chlorite geothermometer using X-ray diffraction (XRD) data. A linear correlation has been found between the (001) basal spacing of chlorite and its “crystallization” temperature. The basal spacing values were corrected for an increase of Al(IV) with Fe enrichment (Fe/Fe + Mg), when the Fe(II) value of chlorite is >2.6 in the formula unit. The regression coefficient of the best fit is r = 0.95. Only 2 Bragg lines need to be measured for application of the proposed technique: the (001) and (060) X-ray spacing. The proposed method is applied to 19 chlorite samples from 4 different geothermal fields. The temperatures of chlorite formation obtained with the present method and those calculated by the expressions formulated by Cathelineau (1988) and Kranidiotis and MacLean (1987) are presented. The method's validity was also tested on geothermal chlorites from the literature, and the results show good agreement with previous experimental trials.

A field-mapping and crystal-chemical study of two alunite- and halloysite-rich deposits in the Turplu area, situated northwest of Balıkesir on the Biga Peninsula of northwest Turkey reveals a mineralogically diverse and a potentially economic clay deposit. The mineral assemblage along fault zones is dominated by halloysite and sometimes alunite. The alunite is nearly end-member in composition (a = 6.995 Å, c = 17.195 Å) often occurring with a minor Ca phosphate phase. Of the two deposits studied, the more northerly mine contains more alunite relative to halloysite. Geochemical alteration indices suggest that the northern mine has experienced a slightly greater degree of hydrothermal modification. Halloysite is found in both hydrated and dehydrated states and assumes a tubular morphology. Observations by transmission and scanning electron microscopy are consistent with a model of halloysite dehydration, where the shapes transform from an open-hole tubular morphology to a closed-hole unfurled morphology.

Mineral paragenesis includes the effects of initial deposition of volcanic tuffs and andesite on top of karstic terrain. The contact between altered volcanics and underlying limestones is irregular and appears to have provided a mechanism to flush both hydrothermal and meteoric waters through the volcanics. Periods of hydrothermal alteration (hypogene) contemporaneous with extensional and strike-slip faulting have resulted in alunite and halloysite deposits. Hydrothermal alteration is concentrated near the fault zones. Because of subsequent weathering (supergene) away from the fault zones, much of the andesitic volcanic rocks have been altered to a more smectite-rich and kaolinite-bearing assemblage. The deposits continue to be both plastically deformed in the alunite/halloysite regions and to undergo brittle deformation in the saprolitized volcanics. Tectonic deformation has mixed the contacts, such that limestone blocks are entrained into parts of the alteration zones. Gibbsite and gypsum are common weathering products associated with limestone block inclusions. Genetic models for the origins of alunite-halloysite deposits in NW Turkey should consider as possible influencing factors the underlying lithologies, the extent of hydrothermal alteration, and recent weathering by meteoric fluids. In the case of the Turplu deposits, karstic limestones, hydrothermal circulation of sulfate-rich waters, and a post-alteration history of meteoric weathering were all important factors in their formation.

Feldspars in granitic saprolite in southwestern Australia have altered to halloysite, kaolinite, and gibbsite with no evidence of noncrystalline material. The secondary minerals are commonly present as intimate mixtures within altered feldspar grains, but discrete zones of gibbsite or halloysite-kaolinite also are present. Variations in the chemical microenvironment within micrometer-size zones in grains apparently controlled the type and distribution of secondary minerals. The alteration of both plagioclase and alkali feldspars involved congruent dissolution by soil solution and crystallization of halloysite, kaolinite, and gibbsite from this solution. Highly altered feldspar grains consist of etched feldspar fragments embedded within a highly porous framework of subhedral to euhedral platy crystals of kaolinite and gibbsite, or of spherical and felted aggregates of halloysite.

Using a simple ionic model, the energy necessary to expand a layer structure by a certain distance can be calculated. This has been done for a series of 15 structures including hydroxides, 2:1 and 1:1 structures of various types. Plots of energy versus separation distance show three major groups which have common bonding properties. For large separations, the group with the strongest interlayer bonds contains the brittle micas, the hydroxides, and the 1:1 structures. Intermediate bonding structures are the normal micas and the weakest bonds occur in the zero layer charge 2:1 structures. The relative energies needed for a given separation are not constant so that for small separations the zero layer charge structures such as talc and pyrophyllite are more strongly bonded than the normal micas. These groupings correlate very well with the expandability of the structures by water and other substances. It is proposed that this approach to the study of the layer structures will provide a simple theory explaining the expansion properties of layer silicates.

The adsorption isotherms of quinoline from aqueous solutions by some clays and oxides varied from the S type for silica to a form somewhat similar to the Langmuir type for montmorillonite and silica-alumina. The adsorption reaction reached equilibrium in about 2 hr and was irreversible. X-ray powder diffraction studies showed that a single layer of molecules is adsorbed on montmorillonite and that the molecules lie either flat or in an upright position depending on surface coverage. The adsorption showed high sensitivity towards pH, attaining a maximum at pH 6. The decrease below pH 6 was due to competition with protons as well as to problems inherent in surface packing of positively charged quinoline molecules. The decrease above pH 6 is probably due to more exchangeable metallic cations on the surface leading to a favored sorption of water over organic molecules.

A simple electrostatic model has been used to demonstrate that the inner surface hydroxyls in kaolinite, dickite and nacrite are responsible for the interlayer bonding in these minerals. The contribution to the interlayer bonding of an individual hydroxyl hydrogen depends on the orientation of the hydroxyl group relative to the 1:1 layer since this orientation determines the H—O interlayer distance. If this distance is much greater than the sum of the van der Waals radii, 2·60 Å, there is essentially no bond. As the distance becomes less than 2·60 Å, the strength of the interlayer bond increases.

The sorption of U and Ra on finely ground biotite, muscovite, and phlogopite was adequately described by the Freundlich adsorption equation, (x/m) = KCn, at low U and Ra concentrations despite Ra precipitation at the higher temperature. Radium and U sorption-efficiency curves derived from the Freundlich constants generally showed decreased distribution coefficients in response to increasing temperature and increasing Ra or U concentrations. Temperatures investigated were 5°C, 25°C, and 65°C. Solution compositions used were 0.1 M NaCl and 0.01 M NaHCO, for U, and 0.01 M NaCl for Ra. Uranium initial solution concentrations ranged from 1.00 × 10−4 M to 4.00 × 10−7 M; the Ra initial solution concentration range was 6.80 × 10−7 M to 8.60 × 10−9 M.

In 0.01 M NaHCO3 solutions, anionic uranyl carbonate complexes were prevalent, and because they are weakly sorbed relative to free uranyl ion and uranyl hydroxy complexes, the result was a relatively low U sorption efficiency on biotite and phlogopite and excellent sorption efficiency on muscovite. Uranyl carbonate complexes decreased in solubility with increasing temperature, so that U sorption efficiency on biotite increased with increasing temperature. Sorption of uranyl ion and uranyl hydroxy cations on biotite decreased with incresaing temperature.

The degree of preferred orientation of mineral grains in powder X-ray diffraction (XRD) samples prepared by standard techniques has been evaluated by means of a correction model implemented in the Rietveld program, BGMN. It is demonstrated that neither front- nor side-loading of mineral powders obtained by wet grinding in a McCrone micronizing mill yield powder mounts with randomly oriented particles. Despite fine grinding, the primary sizes and shapes of mineral grains contained in multi-phase samples influence the degree of preferred orientation in XRD powder mounts. Two minerals, both of platy habit, were found to show different degrees of preferred orientation in front- and side-loaded samples. In contrast to these methods of sample preparation, the spray-drying technique yielded perfect randomness of the particles. The experiments on artificial mineral mixtures demonstrate that the model applied can effectively correct for preferred orientation allowing reliable Rietveld quantitative phase analysis of moderately textured samples prepared by standard techniques.