In this paper atomic force microscopy-studies are reported suggesting the existence of vicinal faces on the (100) plane of artificially grown goethite. Goethite crystals are commonly regarded to have boundary planes of (100), (010) and (001) faces. In contradiction to these theoretical models TEM and SEM images exhibit (110) and (021) faces to be dominating. These goethite particles consist of many crystallographic coherent domains so that the existence of dislocations on the surfaces has to be assumed. These sites on the surfaces may serve as a nucleation site for the formation of steps. The vicinal faces on the (100) face found with the AFM are (021) faces. They influence the growth velocity of the (100) face to such a degree, that this face vanishes and only (110) faces remain as stable boundary surfaces. The (021) faces are also stable, but have the highest growth rate among the faces considered.

The compositions, fabrics and structures of authigenic minerals that formed recently from silicic volcanic ash layers from a 1300-meter sediment column obtained at ODP Site 808 of the Nankai Trough were studied using XRD, STEM, AEM and SEM. Smectite and zeolites were first detected as alteration products of volcanic glass with increasing depth, as follows: smectite at 200 m below seafloor (mbsf) (20 °C), clinoptilolite at 640 mbsf (60 °C) and analcime at 810 mbsf (75 °C).

A primitive clay precursor to smectite was observed as a direct alteration product of glass at 366 mbsf (approximately 30 °C). High defect smectite with lattice fringe spacings of 12 to 17 Å and having a cellular texture filling pore space between altering glass shards occurs at 630 mbsf. Packets of smectite become larger and less disordered with increasing depth and temperature. The smectite that forms as a direct alteration product of volcanic glass has K as the dominant interlayer cation.

With increasing depth, smectite becomes depleted in K as the proportion of clinoptilolite increases, and then becomes depleted in Na as the proportion of analcime increases. The composition of the exchangeable interlayer of smectite appears to be controlled by the formation first of K-rich clinoptilolite and then Na-rich analcime, via the pore fluid, giving rise at depth to Ca-rich smectite. Smectite reacted to form illite in the interbedded shales but not in the bentonites. Paucity of K in smectite and pore fluids, due to formation of clinoptilolite under closed system conditions, is believed to have inhibited the reaction relative to shales.

The changes in amount and location of layer charge during diagenetic alteration have been investigated for smectites and smectite layers of illite/smectite interstratified minerals (I/S) by X-ray powder diffraction analysis with various expansion behavior tests: 1) ethylene glycol (EG) solvation (XRD); 2) K-saturation and EG solvation; 3) Li-saturation, heating at 250 °C and glycerol or EG solvation (Greene-Kelly test); and 4) alkylammonium saturation. In the course of low-temperature diagenesis but before the onset of illitization, mean layer charge of smectites continuously increases from approximately 0.56 to 0.73 per O20(OH)4 with increasing depth, and tetrahedral charge also increases continuously from approximately 0.21 to 0.38 per O20(OH)4 (beidellitization). The continuous increase in tetrahedral charge without change in peak intensity and shape suggests that the solid-state Al for Si substitution mechanism appears to predominate within beidellitization. After illitization, the content of the beidellitic layers continuously decreases, while the mean layer charge of expandable layers and the content of illite layers in I/S increase. This suggests that the conversion of a beidellitic layer to an illitic layer preferably occurs during early illitization. Thus, before illitization, beidellite-like layers are formed from precursor smectite, and during the early stage of illitization, the high charged beidellitic layers are probably consumed to form illite layers.

Continuous wave and pulsed electron paramagnetic resonance spectroscopies combined with thermal and chemical methods were used to identify and characterize V(TV), Fe(III), Mn(II) and Cr(III) in a multimineral system that consists of vermiculite and impurities of carbonates. All of these transition metals were structure-bound in mineral phases. The V(IV) was located in octahedral layers of the vermiculite and became oxidized to V(V) during the transformation of the host mineral to enstatite at about 800 °C. The Fe(III) was associated with the vermiculite as well as the carbonate impurities. The Fe(III) identified in the vermiculite was transferred into the enstatite structure during the thermal conversion. An indirect proof of Fe(III) and Cr(III) in the impurities was found in the heated samples in which these cations occurred in Ca and/or Mg oxides that were formed by transformation of the carbonates. The Mn(II) in the untreated samples was associated with the impurities and was also detected in oxides formed from the samples heated at 600 °C.

This paper deals with the use of Stern theory as applied to a clay-water electrolyte system, which is more realistic to understand the force system at micro level than the Gouy-Chapman theory. The influence of the Stern layer on potential-distance relationship has been presented quantitatively for certain specified clay-water systems and the results are compared with the Gouy-Chapman model. A detailed parametric study concerning the number of adsorption spots on the clay platelet, the thickness of the Stern layer, specific adsorption potential and the value of dielectric constant of the pore fluid in the Stern layer, was carried out. This study investigates that the potential obtained at any distance using the Stern theory is higher than that obtained by the Gouy-Chapman theory. The hydrated size of the ion is found to have a significant influence on the potential- distance relationship for a given clay, pore fluid characteristics and valence of the exchangeable ion.

Aqueous suspensions of allophane show relatively high viscosity, presumably because of strong particle interaction between the unit particles. To test this hypothesis, we measured the particle weight and particle size of allophane during a dispersion using the light scattering method. The particle weight was more than several hundred times larger than that of the unit particle, and the size was 100–400 nm, whereas the Stokes’ diameter of the particles in the sample was less than 50 nm. Particle weight and size varied with the pH of the sample. Particle sizes were cross-checked by ultrafiltration through membrane filters. The experimental findings show that the unit particles of allophane within dilute dispersions appear to be associated like strings of beads, forming domains (primary floccules) about 100 nm in diameter. When these domains coagulate under certain conditions, they do not grow analogously but form clusters, such as secondary floccules, then precipitate. Formation of secondary flocculation of loose structure accounts for the maximum relative viscosity at the transition pH between dispersion and coagulation.

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.

Trimethylammonium ions (TMA+) with formula CH3(CH2)n-1N+(CH3)3, with n = 4, 8, 12, 16, 18 and 22 were intercalated into synthetic Li-fluorotaeniolite (Li-FTN) and Li-fluorohectorite (Li-FHT) by cation exchange. The products were analyzed by thermogravimetric (TGA) and X-ray powder diffraction (XRD). XRD patterns exhibited variable (001) spacings of the TMA+/mica complexes depending upon the exchange ratio of TMA+/Li+ and the carbon number of TMA+. Detailed inspection of these XRD patterns clarified the structures of the complexes and also the intercalation mechanism, as follows: The fundamental structure of the complexes is the commonly known intercalation structure where the “paraffin-type bilayers” of TMA+ are in the mica interlayer and their long chains incline at approximately 30° to the silicate sheet. This structure appeared at the final stage of the intercalation reaction. During the intermediate stage of the reaction, units of this structure and those of hydrated mica formed randomly and regularly interstratified structures. Variable (001) spacings in XRD patterns showed the structural change of the complex with an increasing number of TMA+-intercalated units.

Synthetic hectorite clay minerals were hydrothermally crystallized with direct incorporation of a series of five water-soluble polyvinyl alcohols (PVA) of molecular weights from 9000-146,000. The molecular weight of PVA had little effect on the success of hydrothermal hectorite synthesis, d-spacing or the amount of polymer incorporated. The basal spacings range from 19.5 Å to 20.8 Å and the amount of polymer incorporated ranges from 20 wt.% to 23 wt.%. Incorporation of PVA within the clay inter-layers, along with Li(I) ions to compensate the lattice charge, is indicated. Thermal gravimetric analysis and small angle neutron scattering were used to further examine the polymer-clay systems. Small PVA-clay crystallites that are coated with excess PVA are indicated. Removal of the polymer does not alter the extended synthetic clay network, and the nitrogen BET surface area increases from <5 m2/g to >200 m2/g.

Hydrothermal treatment of a mixture of silicic acid, cobalt chloride, sodium dithionite and sodium hydroxide at 250 °C under 500 psi of argon produced a pink solid. X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction data showed the product to be a well-crystallized smectite. SEM/EDX analysis gave a unit cell formula of [(Si8.05)(Co5.58)O20(OH)4]Na066. Heating the same mixture at 150 °C without argon gave a less well ordered smectite of composition [(Si7.93)(CO5.92)O20(OH)4]Na0.42. Two peaks were observed in the cyclic voltammograms of electrodes modified with films of these two clays recorded for the blank electrolytes in the absence of any adsorbed electroactive species. The first peak was attributed to the oxidation of a small fraction of the Co2+ sites within the clay lattices to Co3+. The second peak was assigned to further oxidation of these Co3+ to Co4+.

Shewanella putrefaciens is a species of metal-reducing bacteria with a versatile respiratory metabolism. This study reports that S. putrefaciens strain MR-1 rapidly reduces Fe(III) within smectite clay minerals. Up to 15% of the structural Fe within ferruginous smectite (sample SWa-1, Source Clays Repository of the Clay Minerals Society) was reduced by MR-1 in 4 h, and a range of 25% to 41% of structural Fe was reduced after 6 to 12 d during culture. Conditions for which smectite reduction was optimal, that is, pH 5 to 6, at 25 to 37 °C, are consistent with an enzymatic process and not with simple chemical reduction. Smectite reduction required viable cells, and was coupled to energy generation and carbon metabolism for MR-1 cultures with smectite added as the sole electron acceptor. Iron(III) reduction catalyzed by MR-1 was inhibited under aerobic conditions, and under anaerobic conditions it was inhibited by the addition of nitrate as an alternate electron acceptor or by the metabolic inhibitors tetrachlorosali-cylanilide (TCS) or quinacrine hydrochloride. Genetic mutants of MR-1 deficient in anaerobic respiration reduced significantly less structural Fe than wild-type cells. In a minimal medium with formate or lactate as the electron donor, more than three times the amount of smectite was reduced over no-carbon controls. These data point to at least one mechanism that may be responsible for the microbial reduction of clay minerals within soils, namely, anaerobic respiration, and indicate that pure cultures of MR-1 provide an effective model system for soil scientists and mineralogists interested in clay reduction. Given the ubiquitous distribution and versatile metabolism of MR-1, these studies may have further implications for bioremediation and water quality in soils and sediments.

Shortly after construction of a subdivision in the southwest Denver metropolitan area in 1986, a portion of the subdivision built directly on steeply-dipping strata of the Pierre Shale began experiencing damaging differential movements, causing house foundations to fail and pavements to warp and crack. This formation is a Late Cretaceous marine clay-shale composed predominantly of fluvial mixed-layer illite/smectite and quartz. During deposition of the shale, periodic and explosive volcanism generated thin beds of bentonite, consisting initially of volcanic ash and subsequently altered to nearly pure smectite. Some of these bentonite beds were exposed in a trench adjacent to the subdivision and perpendicular to the strike of the steeply-dipping strata. The thickest bentonite beds correlated well with linear heave features that these beds parallel the bedrock strike throughout the subdivision were mapped via severely deformed pavements. Mineralogical data show the bentonite bed that correlates with the worst damage within the subdivision consists of about 62% smectite by weight with mixed-layer illite/smectite expandability of 92%. By comparison, a sample of the typical silty claystone, which is fluvial mixed-layer illite/smectite mixed with detrital quartz from the adjacent strata, had about 23% smectite by weight with 70% to 90% illite/smectite expandability. Geotechnical tests for swell potential show that samples of 2 bentonite beds swelled 39% to 43% compared to 2% to 8% for samples of the typical silty claystone. It is proposed that differential swell resulting from stratigraphically-controlled differences in clay mineralogy and grain-size is the primary factor controlling extreme damage for this geologic setting.

Two ferriphlogopite-1M crystals with a composition (K0.99Na0.01)Σ=1.00(Mg2.73Fe2+0.17Fe3+0.08-Ti0.01)Σ=2.299[(Fe3+0.95Si3.05)Σ=4.00O10.17](OH)1.79F0.04 (sample S1) and (K1.02)Σ=1.02(Mg2.68Fe2+0.20Fe3+0.11-Mn0.01)Σ=3.00[(Fe3+0.95Si3.05)Σ=4.00O10.18](OH)1.75F0.07 (sample S2) occur within an alkali-carbonatic complex near Tapira, Belo Horizonte, Minas Gerais, Brazil. Each crystal was studied by single-crystal X-ray diffraction. The least-squares refinements of space group C2/m resulted in R values of 0.031 for S1 and 0.025 for S2. Results showed that Fe3+ substitutes for Si within the tetrahedral sites and that the Fe distribution is fully disordered. The octahedral sites are preferentially occupied by Mg. The presence of Fe3+ within the tetrahedral sheet produces increased cell edge lengths. For sample S1, a = 5.362 Å, b = 9.288 Å, c = 10.321 Å and the monoclinic β angle was: β = 99.99°. For sample S2, a = 5.3649 Å, b = 9.2924 Å, c = 10.3255 Å and the monoclinic β angle was: β = 99.988°. The tetrahedral rotation angle of α = 11.5° is necessary for tetrahedral and octahedral sheet congruency. The enlarged tetrahedral sites are regular, with cations close to their geometric center. Ferriphlogopites have identical mean bond lengths for M1 and M2 sites within standard deviation. The M1-O3 and M2-O3 bond lengths are longer than the mean so that O3 may articulate with the tetrahedra.

Municipal solid waste incinerator (MSWI) bottom ash is the slag-like material produced by the incineration of municipal waste and is predominantly composed of glassy constituents, which include inherited manufactured glasses and glasses formed during incineration. Previous results indicate evidence of neoformation of well-ordered clay (illite) from glasses in MSWI bottom ash after 12 y of natural weathering. We investigated the mechanism and conditions of clay formation from glasses during natural weathering using transmission electron microscopy (TEM), experimental leaching experiments and ammonium oxalate extractions. It was concluded that the high surface area and initially high “active” Al and associated Si content predispose the ash to form clay minerals on a relatively short time scale. This work provides evidence that the composition of secondary amorphous aluminosilicate and thus, the type of clay mineral which may form, is determined by the pH of the pore solution rather than by the glass composition. Presumably alternate wetting and drying of the ash during disposal greatly accelerates the formation of well-ordered clays.

A macroscopic energy balance model for crystalline swelling of 2:1 phyllosilicates is presented. Crystalline swelling for a static system is modeled by a balance among the potential energies of attraction, repulsion and resistance. The potential energy of attraction is due to both the electrostatic interaction between the interlayer cations and the negative surface charge sites and to van der Waals attraction between layers. The potential energy of repulsion is due to the net hydration energy for the interlayer cations, the net hydration energy for the negative surface charge sites and Born repulsion. The potential energy of resistance represents irreversible work needed to overcome the mechanical resistance of the clay water system to both expansion and collapse. The potential energy of resistance is responsible for both hysteresis and the stepwise nature of crystalline swelling.

A numerical solution of the crystalline swelling model is presented and shown to yield reasonable estimates of basal spacings for octahedrally charged clays. Measured and predicted basal spacings are directly compared and are in general agreement (r2 = 0.39). Most of the scatter for the measured vs. predicted basal spacing relationship is attributed to inaccuracies of the assumptions used for the numerical solution. The crystalline swelling model readily accounts for the effects of layer charge and nature of the interlayer cations upon crystalline swelling, but does not account for the effect of charge site location upon crystalline swelling.