Mixed-layer clays of variable composition and structure occur in core samples from two drillholes (WK207 and WK210) drilled into the Te Mihi sector of the Wairakei geothermal field. These were identified by X-ray diffraction analysis of glycolated and oriented sample fractions at less than 2 μm and less than 0.2 μm.

Low permeability lacustrine sediments encountered by drillhole WK207 contain a well-developed sequence of mixed-layer clays. The shallowest downhole appearance of mixed-layered illite/smectite (I0.6/Sm) occurs at 146 m depth where temperature is only 100°C. Discrete illite is present only below 297 m (200°C) in the finer size fraction (less than 0.2 ¼m). Chlorite first appears downhole, in association with illite-smectite, at 177 m depth (110°C).

Drillhole WK210 encountered predominantly ignimbrites and rhyolites, and fluid flow here is mainly in channels. Within these rocks, a sequence of interlayered clays is poorly developed. Discrete illite and chlorite are present in core from only 244 m (180°), but the measured temperatures where interlayer clays occur ranges from 140 to 209°C.

Differences in the identity of clay minerals present in the Wairakei reservoir, where conditions are otherwise the same, demonstrate the strong control that the type of fluid flow has on their formation. In poorly-permeable sediments, where diffuse fluid flow prevails, a clearly-defined sequence of mixed-layer clays occurs. These are absent where channel flow dominates, the discrete chlorite and illite deposit directly from solution.

The hydroxyl deformation modes of kaolins have been studied by Fourier transform (FT) Raman spectroscopy. Kaolinites showed well-resolved bands at 959, 938 and 915 cm−1 and an additional band at 923 cm−1. For dickites, well-resolved bands were observed at 955, 936.5, 915 and 903 cm−1. Halloysites showed less-resolved Raman bands at 950, 938, 923, 913 and 895 cm−1. The first 3 bands were assigned to the librational modes of the 3 inner-surface hydroxyl groups, and the 915-cm−1 band was assigned to the libration of the inner hydroxyl group. The band in the 905 to 895 cm−1 range was attributed to “free― or non-hydrogen-bonded inner-surface hydroxyl groups. The 915-cm−1 band contributed ~65% of the total spectral profile and was a sharp band with a bandwidth of 11.8 cm−1 for dickite, 14.0 cm−1 for kaolinites and 17.6 cm−1 for halloysites. Such small bandwidths suggest that the rotation of the inner hydroxyl group is severely restricted. For the inner-surface hydroxyl groups, it is proposed that the hydroxyl deformation modes are not coupled and that the 3 inner-surface deformation modes are attributable to the three OH2-4 hydroxyls of the kaolinite structure. For intercalates of kaolinite and halloysite with urea, a new intense band at ~903 cm−1 was observed with concomitant loss in intensity of the bands at 959, 938 and 923 cm−1 bands. This band was assigned to the non-hydrogen-bonded hydroxyl libration of the kaolinite-urea intercalate. Infrared reflectance (IR) spectroscopy confirms these band assignments.

Due to their unique polarity, pore-size distribution, and high surface areas, pillared and delaminated clays are potentially useful materials for the adsorption of environmental toxicants. To determine their properties for adsorption of chlorinated phenols, alumina-pillared montmorillonite (APM), chromia-pillared montmorillonite (CPM), and alumina-delaminated Laponite (ADL) were reacted with aqueous pentachlorophenol (PCP) solutions in batch equilibrium experiments. An hydroxy-Al Laponite (HAL) in which the Na+ exchange ions were replaced by ions of the type Al13O4(OH)(24+x)(H2O)(12-x)(7-x)+ was included in the study. With ADL as the adsorbent, the extent of PCP adsorption increased with decreasing pH, and then became constant at pH ≤ pKa. Thus, the neutral phenol was preferred over the phenolate form. Binding of neutral PCP at pH 4.7 to all adsorbents never reached saturation values, and the loadings achieved were limited by the water solubility of the adsorbate. Among the pillared and delaminated clays investigated, ADL exhibited the largest capacity for physical adsorption of PCP at pH 4.7. Differences in the PCP binding capacities for APM, CPM, and ADL suggested that adsorption was dependent on the pore structure and surface composition of the modified clay adsorbent, not on surface area alone. HAL exhibited quantitative uptake of PCP at the 8 µmole/g level, indicating that a chemi-sorption mechanism may operate for PCP binding to this adsorbent. Adsorption of 3-chlorophenol, 3,5-dichlorophenol, and 3,4,5-trichlorophenol by ADL at pH 7.4 increased as the degree of hydrophobicity and chlorination of the phenol increased; hence, the binding capacity was not limited by the molecular size of the adsorbate. In contrast to the adsorption properties observed for pillared, delaminated, and hydroxy-interlayered clays, Na+-montmorillonite and Na+-Laponite did not adsorb PCP from aqueous solution.

Berthierine (formerly chamosite) occurs as concretions, lenses, and bands in carbonaceous, kaolinitic shale of freshwater coal-swamp deposits in Paleogene and Upper Triassic coal measures of Japan. Textural relations in thin sections of the Triassic berthierine rocks and a siderite-kaolinite-berthierine-quartz assemblage in Paleogene rocks indicate that the berthierine formed by reaction of siderite with kaolinite. The transformation of siderite and kaolinite to berthierine and quartz occurs progressively under reducing conditions between 65° and 150°C and at burial depths of 2–5 km. Utatsu berthierine is an aluminous, low-Mg variety as compared with berthierine pellets in modern marine and estuarine sediments and in ancient marine ironstones. Fe is the dominant octahedral cation with Fe2+ ≫ Fe3+. The composition of the berthierine varies between different morphological types. Utatsu berthierine transformed to ferrous chamosite when kaolinite in the host shale changed to pyrophyllite. These transformations are estimated to have occurred at ∼160°C and at a burial depth of ∼3 km.

Imogolites in which a part or all of Si was substituted with Ge were synthesized from solutions containing aluminum ion and silicic and/or germanic acid. The products were similar to natural imogolite in their tubular morphology, electron diffraction patterns, and differential thermal analysis curves. However, the external diameter of the tube increased with increasing Ge substitution up to about 33 Å, and associated changes appeared in the X-ray powder diffraction patterns, suggesting that the substitution of Ge for Si caused a decrease in the curvature of the gibbsite sheet with which SiO- or GeO-tetrahedra are associated. Infrared absorption bands at 995 and 930 cm−1 in imogolite disappeared and new bands appeared at 910 and 810 cm−1 on substitution of Ge for Si, whereas those in the region between 700 and 300 cm−1 remained unchanged or changed little. The former two bands were assigned to Si-O vibrations and the latter bands to Al-O vibrations.

The transformation of ferrihydrite to goethite and/or hematite, as influenced by the presence of co-precipitated Si, was investigated by infrared spectroscopy (IR), X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). Ferrihydrite samples having Si/Fe molar ratios ranging from 0 to 1 were synthesized by reacting Fe2(SO4)3 with NaOH to an equilibrium pH of 8.2 in the presence of Na2SiO3. The XRD pattern of the Si-free sample contained five distinct but weak peaks, whereas the patterns of ferrihydrite samples containing Si had only two broad bands. With an increase of the Si/Fe molar ratio from 0.10 to 1.0, the 2.54-Å XRD peak shifted to 2.97 Å, and broad IR bands were observed at 990 cm−1 (Si-O stretching region) and 450 cm−1 (silicate bending region). The intensities of both IR bands increased with increasing Si/Fe molar ratio.

Ferrihydrite samples were incubated at room temperature in sodium acetate/acetic acid buffer solutions at pH 3, 5, 7, and 10 and in CaCO3 suspension at pH 8.3 for 10 months. Additional samples were incubated at pH 12.5 at 24°, 40°, 60°, and 91°C for 36 hr. Room-temperature incubation of ferrihydrite samples having Si/Fe molar ratios ≥0.1 at pH 3 for one week resulted in the dissolution of Fe and the precipitation of silica gel. Ferrihydrite samples having Si/Fe molar ratios ≤0.05 transformed to poorly crystalline goethite during room-temperature incubation at pH 5. The rate of transformation and the degree of crystallinity of the product were inversely related to Si/Fe molar ratio, and, with heat treatment, were also dependent on incubation temperature. Siliceous ferrihydrite samples having Si/Fe molar ratios ≥0.10 did not transform to phases having greater crystallinity during incubation at either room temperature in buffered solutions at pH ≥7 for as long as 10 months or at pH 12.5 at 91°C for 36 hr. The XRD peak at 2.97 Å did not shift significantly during incubation procedures, providing evidence that the structure of the high-Si ferrihydrite was not significantly altered.

Benzo(a)pyrene (B(a)P), and chlorophenols were sorbed from their respective aqueous solutions onto inorgano-organo-clays (IOCs). Cetyl pyridinium hydroxy-Al montmorillonite (CPC-hydroxy-Al montmorillonite), an IOC, containing only 11–12% surface organic carbon by weight, bound pentachlorophenol strongly, with an observed monolayer capacity of 0.08 mmole/g. The comparable value for granulated activated carbon (GAC) was found to be 0.12 mmole/g. On the other hand, cetyl pyridinium cation-exchanged montmorillonite (CPC-montmorillonite), containing 19.2% surface organic carbon by weight, did not bind pentachlorophenol as efficiently as did IOCs. For benzo(a)pyrene, CPC-hydroxy-Al montmorillonite was found to be a better adsorbent than GAC and CPC-montmorillonite. The significant difference in the sorption potential of the two types of surfactant-laden clays for pentachlorophenol and benzo(a)pyrene was probably due to the surface orientation of the adsorbed organic carbon. For 3,5-dichlorophenol, however, both types of organo-clays exhibited weak binding, which was probably due to the greater aqueous solubility of the dichlorophenol.

A process for treating smectite-bearing rock samples that utilizes LR White resin; allows TEM observation of expanded smectite interlayers and therefore preservation of original rock textures. Examples of several lattice fringe images are shown, including: (1) Dioctahedral smectite layers from a shale (1388.9 meter depth, Texas Gulf Coast) give fringes that consistently have spacings of 1.2–1.3 nm, yet duplicate other features previously observed in collapsed samples. (2) Packets of illite layers give fringes with 1.0-nm spacings coexisting with packets of (dominantly) R1 I/S having 2.1-nm lattice fringe spacings in a Gulf Coast shale from 4742.1 m. (3) Rectorite from Garland Co., Arkansas gives 2.3-nm lattice fringes. Samples with wide ranges of I/S ratios and lithologies have been found to be permanently expanded with retention of original textures, commonly leading to unambiguous identification of illite and smectite interlayers in lattice fringe images.

In an attempt to resolve the structure of opal-CT and opal-C more precisely, 24 opal samples from bentonites, Fuller's Earths, zeolite tuffs, biogenic silicas and silicified kaolins have been analyzed by high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). Results of this examination demonstrate that opal-C and opal-CT are part of a continuous series of intergrowths between end-member cristobalite and tridymite stacking sequences.

These findings are consistent with Flörke's (1955) interpretation of the most intense opal peak at ~4 Å as a combination of the (101) cristobalite and (404) tridymite peaks. The position and width of this peak are controlled by the relative volume of the two stacking types and the mean crystallite size. Direct evidence obtained by HRTEM provides data showing various stacking sequences in opals. Broadening due to crystallite size alone was determined by directly measuring crystallite size by TEM and comparing the measured size to the apparent size calculated using the Scherrer equation. XRD peak broadening is also described in terms of various contributions from structural disorder. The mean opal crystallite size ranges from 120 to 320 Å. For samples at either end of the size range, the crystallite size plays a larger role, relative to stacking disorder, in controlling peak broadening.

More than 8000 different derivatives of mica-type layer silicates (muscovite, biotite, illite, vermiculite, beidellite, montmorillonite) with alkylammonium ions and different organic molecules as swelling liquids were prepared and characterized analytically by X-ray and chemical methods. The following results have been discussed in some detail.

Layer-lattice compounds are formed in simple stoichiometric relations. In n-alkyl-ammonium compounds, for instance, the sum (n-Cx,H2x+1NH3++n-CxH2x+1Y) per (Si, Al)4O10 is equal to 2.0 (Y = OH-, Cl-, Br-, NH2-, COH-, CONH2-, CN-).

The layer distance of the pure n-alkylammonium derivatives enables one to determine the charge density in the silicate layers. But in soils the ability of humic acids to undergo two-dimensional intracrystalline swelling and to react with alkylammonium ions must also be considered.

The properties of n-alkylammonium layer silicates are similar to those of alkyl-ammonium-uranium micas and of swelling vanadates (e.g. hewettite and pascoite). The swelling properties of alkyl-(α, ω)-diammonium ions are markedly influenced by the opportunities for hydrogen bonding. Mica-type layer silicates may show catalytic properties like protease or oxidase with ammonium ions, which are of general interest.

Al-substituted goethites were prepared by rapid oxidation of mixed FeCl2-AlCl3 solutions at pH 6.8 in the presence of CO2 at 25°C. A combination of Al substitution and adsorption of CO2 reduced crystal size (except for an increase at small additions of Al) and produced unusual thin, porous particles. Product goethites had surface areas up to 283 m2/g and unit-cell expansions induced by hydration. Substitution of Al for Fe reduced the 111 spacing and increased infrared OH-bending vibrational frequencies. Al substitution split the goethite dehydroxylation endotherm during differential thermal analysis into a doublet and increased the temperature of all reactions. Both cold and hot alkali solutions dissolved Al from the goethite structure.

After drying the product in vacuo at 110°C. X-ray powder diffraction data indicated minimal deviation from Vegard's law for the goethite-diaspore solid solution up to about 30 mole % Al substitution. Goethite prepared in the presence of 40 mole % Al had a 111 spacing of 2.403 Å corresponding to 36 mole % structural Al if Vegard's law was obeyed. Rapid oxidation of mixed FeCl2-AlCl3 solutions appears to be conducive to a higher degree of Al substitution in goethite than alkaline aging of hydroxy-Fe(III)-Al coprecipitates.

The pH of aqueous bentonite suspensions is known to be influenced by carbonates present even in minor amounts. On the other hand, at high solid:liquid ratios (at standard pH measurement conditions: 2% w/w suspension), the type of exchangeable cation in the smectite is also known to determine pH (particularly Na+ or Ca2+). By cation-exchange tests we proved that exchanging the Ca2+ for Na+ results in an increase in the pH. However, this increase in pH was only found if excess salts were removed from the system (by washing or dialysis, respectively). The effect of the type of exchangeable cation can, at least partially, be explained by hydrolysis of Ca2+. On the other hand, a pronounced alkalinity of Na bentonites is observed which can, at least partially, be attributed to the hydrolysis of montmorillonite (Na+ is exchanged for H+ of water). The increase in the volume of the Stern layer, caused by increasing the degree of delamination, is also suggested to play a role. H+ and Na+ are concentrated in the Stern layer. Hence, increasing the Stern layer volume decreases the amount of H+ and Na+ in solution and thus increases pH. Unfortunately, both processes, montmorillonite hydrolysis and delamination, depend on the ionic strength. Distinguishing the processes quantitatively, therefore, is an analytical challenge, and impossible based on the data presented here.

To model the pore-water chemistry of clays and clay stones, all of the above-mentioned processes have to be considered. It is possible that other reactions, not identified in the present work, contribute toward the pH values of aqueous bentonite suspensions.

Mössbauer spectra of 15 smectites were investigated. In these samples, ferric iron occupies both M(1) and M(2) octahedral sites, the distribution being partly determined by the relative covalency of the bonds formed.

The quadrupole splittings are linearly related to b−3. They show that Fe3+ octahedra are much more distorted in montmorillonite and beidellite than in nontronite and volkonskoite and that M(1) sites are more prone to change than M(2). Ferrous iron occurs in relatively undistorted octahedra in some otherwise distorted octahedral sheets and vice versa.

This work investigates unit cell dimensions, crystal size and specific surface area of aluminous goethite that was progressively dehydroxylated to form hematite. Goethite synthesized from the ferrous system altered to hematite with DTGA maximum increasing from 236° to 273°C for 0 to 30.1 mole % Al-substitution. Unit cell dimensions of goethite and hematite decreased as Al-substitution increased and increased as excess OH increased. The crystallographically equivalent a axis of goethite and c axis of hematite were more sensitive than other axes to the presence of excess structural OH associated with Al-substitution. Specific surface area increased from 147 to 288 m2/g for goethite and from 171 to 230 m2/g for hematite as Al-substitution increased. An increase in specific surface area on heating goethite at temperatures between 200° and 240°C is related to a decrease in the size of coherently diffracting domains of goethite crystals and to the development of pore and structural defects associated with the formation of hematite. The decrease in specific surface area for heating temperatures above 240°C is attributed to the growth of hematite crystals by diffusion.

Iddingsite rimming olivine in a basanite from the Limberg, Germany, is composed of saponite and goethite. Transmission electron microscopy of ion-thinned, oriented crystals suggests a two-stage alteration process. At first, the olivine breaks into a mosaic of 50-Å diameter {110} bounded needle-shaped domains which change to a metastable hexagonal phase having a = 3.1 Å and c = 4.6 Å, probably of close-packed, metal-oxygen octahedra. This reaction opens solution channels in the olivine which are detectable from about 20-Å diameter and are parallel to the olivine y-axis. Laths of smectite, one or two layers thick, 20 Å wide, and as much as 100 Å long parallel to their y-axis nucleate from the metastable phase and begin to fill in the solution channels. The laths orient with smectite (001) parallel to olivine (100). As the channels widen, prismatic {110} goethite crystals form directly from the metastable hexagonal phase. This first stage thus provides heterogeneous nuclei of smectite and goethite, formed epitactically and perhaps topotactically from a metastable intermediary.

In a second stage,these nuclei enlarge by deposition from solution as water migrates readily through the solution channels. A reduction in total volume allows smectite veins to form, misoriented with respect to the olivine. The reaction conserves iron, requires the addition of aluminum and water, and releases magnesium and silicon. Electron microprobe analyses of the iddingsite indicate that the smectite is saponite.

Imogolite is a tubular aluminosilicate which is common in Andosols and Spodosols. The high pH at point-of-zero charge at the outer parts of the tube and the anomalously high chloride adsorption of imogolite suggested that there may be structural charge associated with this mineral. The structural charge may arise because of changes in bond valence imposed by the incorporation of orthosilicate anions in a gibbsite-type sheet. By using a Basic Stem Model approach, it is shown that the surface charge properties of imogolite are explained if the mean Al-O bond valence of the outer -Al2OH groups is higher than the inner -Al2OHSiO3 groups. Hence, a weak positive charge is developed on the outer tube walls whereas a negative charge develops in the tubular pores. The best model fits were obtained where either one or two units of structural charge per unit cell of tube were assumed. The model may also explain why imogolite tubes are normally aggregated in large bundles in close hexagonal packing, because bound counterions may hold the tubes together. However, to arrive at good model descriptions, the deprotonation of -Al2OH groups must occur at a higher pH than that expected when assuming that all surface oxygens form two hydrogen bridges with H2O. A more precise structure of imogolite is required to test fully this hypothesis.

FTIR studies of six partially-deuterated montmorillonites (MS) reveal the presence of two O-D stretching bands, one between 2702–2728 cm-1 and another near 2680 cm-1. For homoionic (Li, Na, Mg, Ca, or La) Wyoming-type MS, the position of the higher frequency band, designated as (O-D)h, is between 2714–2728 cm-1, whereas for homoionic Cheto-type MS it is between 2702–2706 cm-1. The lower frequency band, designated as (O-D)1, is in the narrow range of 2674–2684 cm-1. Resolution of two corresponding O-H bands, appearing near 3670 and 3635 cm-1, was observed only after partial dehydroxylation of the smectites. The changes in the relative intensities of the two O-D stretching bands as a function of the smectite type and of the Lewis acidity (charge density) of the exchangeable ion were determined. For Wyoming-type MS, the intensity of the (O-D)h band is much lower than that of the (O-D)l band, whereas for Cheto-type MS, the intensity of the (O-D)h band is about equal or slightly higher than that of the (O-D)l band. The observed resolution can be ascribed tentatively to the presence of (at least) two types of octahedral OH groups in the smectites, the (O-D)h band being assigned to AlMgOH and the (O-D)1 band to AlAlOH groups. Pillaring of Cheto-type MS with hydroxy-Al13 oligocations resulted in products showing much higher thermal stability between 400–600°C compared to that of identically pillared Wyoming-type MS. Compositional and other factors, e.g., CEC values and mode of pillaring, may cause this difference in stability.

Fougerite (IMA 2003-057) is a mixed M(II)-M(III) hydroxysalt of the green rust group, where M(II) can be Fe or Mg, and M(III) is Fe. The general structural formula is: ${[{\text{Fe}}_{1-}^{2+}x{\text{Fe}}_x^{3+}{\text{Mg}}_y{(\text{OH})}_{2+2y}]}^{+x}{[x\text{/}n{A}^{-n}.m{\text{H}}_2\text{O}]}^{-x}$ where A is the interlayer anion and n its valency, with 1/4 ≼ x/(1+y) ≼ 1/3 and m ≼ (1−x+y). The structure of green rusts and parent minerals can accommodate a variety of anions, such as OH−, Cl−, ${\text{CO}}_3^{2-},{\text{SO}}_4^{2-}$${\rm{CO}}_3^{2 - },\;{\rm{SO}}_4^{2 - }$. The structure of the mineral was studied by Mössbauer, Raman and X-ray absorption spectroscopies (XAS) at the FeK edge. Mössbauer spectra of the mineral obtained at 78 K are best fitted with four doublets: D1 and D2 due to Fe2+ (isomer shift δ ≈ 1.27 and 1.25 mm s−1, quadrupole splitting ΔEQ ≈ 2.86 and 2.48 mm s−1, respectively) and D3 and D4 due to Fe3+ (δ ≈ 0.46 mm s−1, ΔEQ ≈ 0.48 and 0.97 mm s−1, respectively). Microprobe Raman spectra obtained with a laser at 514.53 nm show the characteristic bands of synthetic green rusts at 427 and 518 cm−1. X-ray absorption spectroscopy shows that Mg is present in the mineral in addition to Fe, that the space group is and the lattice parameter a ≈ 0.30–0.32 nm. The mineral forms by partial oxidation and hydrolysis of aqueous Fe2+, to give small crystals (400–500 nm) in the form of hexagonal plates. The mineral is unstable in air and transforms to lepidocrocite or goethite. The name is for the locality of the occurrence, a forested Gleysol near Fougères, Brittany, France. Its characteristic blue-green color (5BG6/1 in the Munsell system) has long been used as a universal criterion in soil classification to identify Gleysols. From a thermodynamic model of soil-solution equilibria, it was proposed that for the eponymous mineral, Fougères-fougerite, OH− may be the interlayer anion. In other environments, the interlayer anion may be different, and other varieties of fougerite may exist. Fougerite plays a key role in the pathways of formation of Fe oxides.

In the nearly 2000 occurrences of zeolites in sedimentary rocks of volcanic origin about 15 zeolite minerals have been identified. The mode of occurrence of six of these, clinoptilolite, erionite, chabazite, phillipsite, analcime, and mordenite, is described, and their morphology is illustrated with scanning electron micrographs.