A prograde sequence of corrensite and chlorite in pelitic rocks of the diagenetic zone, anchizone, and epizone (illite crystallinity indices = 0.17–0.58°Δ2θ) of the Gaspé Peninsula, Quebec, was studied by analytical and transmission electron microscopy (AEM and TEM). The data collectively suggest that diagenesis/metamorphism of chlorite and corrensite follows a sequence of phase transitions, compositional homogenization, and recrystallization, approaching a state of equilibrium for which chlorite is the stable phase.

Corrensite occurs as coalescing, wavy packets of layers intergrown with chlorite and illite in the diagenetic and low-grade anchizonal rocks. Intergrowths of discrete chlorite and corrensite crystals, interstratified packets of chlorite and corrensite layers, terminations of smectite-like layers by chlorite layers, and 2–3 repeats of R2- and R3-ordered chlorite-smectite mixed layers occur. These materials are alteration products of detrital biotite or other precursor phases like trioctahedral smectite. The crystal size and proportion of corrensite decrease significantly from the diagenetic zone to the anchizone. Deformed corrensite is crosscut by straight packets of chlorite and corrensite in the diagenetic sample. Some chlorite occurs as discrete, euhedral to subhedral crystals intergrown with or enclosed by other phases in the absence of corrensite. The crystal size of chlorite and definition of crystal boundaries increase whereas density of crystal imperfections and randomness in orientation decrease with increase in grade of diagenesis/metamorphism. Crystals that are kinked or bent, or display gliding along (001) form low-angle boundaries with relatively defect-free crystals, implying deformation during crystal growth. Abundant well-defined low-angle boundaries associated with dislocations are observed in the higher grade rocks, consistent with a stage of readjustment of crystal boundaries during crystal growth. The AEM analyses show that the corrensite has lower Fe/(Mg + Fe) and Al/(Si + Al) than the coexisting chlorite in the diagenetic sample, and that the ranges of composition of chlorite of different grades overlap and become smaller with increasing grade, implying prograde homogenization.

The data imply that corrensite is a unique phase that is metastable relative to chlorite: its conversion to chlorite occurred at a grade as low as that of the high-grade diagenetic zone. The textural relations suggest that the metamorphic crystallization and recrystallization were coeval with deformation processes due to tectonism, partially modified by subsequent contact metamorphism. The data, combined with those of previous reports, suggest that the Gaspé Ordovician rocks constitute a part of a regional distribution of trioctahedral phyllosilicate-rich rocks in the northern Appalachians. The regional occurrence of abundant chloritic minerals is thus directly related to a specific tectonic regime with precursor sediments largely derived from an andesitic arc system(s).

Hectorite and saponite are exchanged with [Al13O4(OH)24(H2O)12]7+ and the amount of Al3+ adsorbed and Na+ released are followed as a function of the exchange conditions. On saponite the reaction is a pure ion exchange with 2–2.15 mmol Al3+/g adsorbed and release of 0.80 mmol Na+/g. On hectorite the ion exchange is accompanied by supplementary hydrolysis-polymerization of Al13. When excess Al is offered in the form of Al13, ion exchange is incomplete and is accompanied by precipitation and polymerization of Al13 on the surface of both hectorite and saponite. The typical spacing of 1.8 nm is developed after washing, when at least 1.3–1.4 mmol Al3+/g is adsorbed. Above a loading of 2.2–2.5 mmol/g the 1.8 nm spacing is obtained without washing. Only pillared saponite with a loading of at least 1.9 mmol Al3+/g is thermally stable up to 550°C.

Alteration experiments have been performed using RTT7 and synthetic basaltic glasses in MgCl2−CaCl2 salt solution at 190°C. The duration of experiments ranged from 0.25 to 463 days. The alteration products were studied by Scanning Electron Microscope (SEM), Scanning Transmission Electron Microscope (STEM), X-ray diffraction (XRD) and Electron Spectrometry for Chemical Analysis (ESCA). For both glasses, the early alteration product is a hydrotalcite-like compound [Mg6Al2CO3(OH)16·4H2O] in which HPO42−, SO42− and Cl− substitutes for CO32−. The measured basal spacing is 7.68 Å for the hydrotalcite formed from R7T7 glass and 7.62 Å for the hydrotalcite formed from basaltic glass which reflect the high Al/Al + Mg ratios x (0.34 ≤ x ≤ 0.46). The chemical microanalyses show that the hydrotalcite is subsequently covered by a silica-rich gel which evolves into saponite after a few months. These results support the use of basaltic glasses alteration patterns in Mg-rich solution, to understand the long-term behavior of R7T7 nuclear waste glass.

Surface diffusion, or migration within the electrical double layer next to mineral surfaces, is often invoked as a significant contributor to the overall diffusion coefficient in compacted clays, particularly where model predictions underestimate measured diffusion coefficients. The potential for surface diffusion of Sr2+, Ca2+ and Na+ on three clays compacted to dry bulk densities of 1.25 and 1.60 Mg/m3 was examined. The clays were a bentonite, an illite/smectite, and a glacial lake clay (composed mainly of smectite, illite, kaolinite and quartz). The clays were saturated with a Na-Ca-Cl-dominated synthetic groundwater solution with an effective ionic strength of 220 mol/m3. Total intrinsic diffusion coefficients for the cations were determined from their steady-state flux through compacted clays, and apparent diffusion coefficients were obtained from the time-lag technique. Models of diffusive transport in compacted clays, based only on diffusion in the pore solution, adequately described the diffusion data for all clays and diffusants, and there was no need to invoke other transport mechanisms, like surface diffusion. The data indicate that surface diffusion is not a significant transport mechanism in compacted clays at least to a clay density of 1.60 Mg/m3.

The crystal structure of cronstedtite-3T from Kutná Hora (Bohemia, Czechoslovakia), space group P31, was refined to Rw(all) = 3.1% for 1336 independent diffractions. There are two and three independent tetrahedral and octahedral positions, respectively, in this structure. The tetrahedra are occupied by 0.75 Si and 0.25 Fe while the octahedra are uniformly occupied by Fe. The refinement process was hindered by two problems: a “strong” superposition structure (all atoms of the octahedral sheets, i.e., ÷ 70% of the total diffraction power contribute almost solely to the family diffractions with mod(h–k, 3) = 0), and a slight disorder of the investigated crystal. The first problem was resolved by a preliminary block-diagonal refinement procedure where the atoms coinciding in the superposition structure were separated into individual blocks. The second problem was resolved by including two scale factors into the final full-matrix refinement: one for family diffractions, the other for the remaining ones which are characteristic for this polytype.

A new, well-ordered, thermally robust ethylene glycol intercalate of kaolinite was formed by refluxing the dimethyl sulfoxide intercalate of kaolinite (Kao-DMSO) with dry ethylene glycol (EG). This new phase (Kao-EG 9.4 Å) which is characterized by a d001 of 9.4 Å is distinct from a previously reported ethylene glycol intercalated phase of kaolinite (Kao-EG 10.8 Å) which has a d001 of 10.8 Å. The characterization of these two phases was studied by XRD, NMR, FTIR, and TGA/DSC. It was found that the concentration of water in the ethylene glycol reaction media played a crucial role in governing which of the phases predominated. Water favored Kao-EG 10.8 Å formation, while anhydrous conditions favored the formation of Kao-EG 9.4 Å. It is hypothesized that Kao-EG 9.4 Å is a grafted phase resulting from the product of the condensation reaction between an aluminol group on the interlamenar surface of kaolinite and the alcohol group of ethylene glycol. Ethylene glycol units would be attached to the interlamellar surface of kaolinite via Al-O-C bonds. The Kao-EG 9.4 Å phase was found to be resistant to both thermal decomposition up to 330°C and also, once formed, in the absence of interlamellar water molecules, to decomposition by hydrolysis in refluxing water.

2H NMR spectra of synthetic deuterated kaolinite have been collected in the temperature range from 150 K to 350 K. Hydroxyl groups show a Pake doublet pattern with an asymmetry factor of 0. They are almost fixed spatially, and undergo a wobbling motion with increasing temperature. The quadrupole coupling constant is 273 ± 3 kHz at 150 K, which indicates that interlayer hydrogen bonding is relatively weak.

Magnetic fractionation, chemical, and structural analyses prove that alteration of ilmenite from Manavalakurichi deposit extends only up to the formation of pseudorutile with traces of rutile. The data indicate that ferrous to ferric iron transformation, ferric iron oxide formation, and iron removal contribute to the alteration sequence. The first two highly magnetic fractions are not unaltered ilmenite. A reduction in ilmenite unit cell volume indicates the ferrous-ferric conversion occurred during alteration.

Oxygen isotope composition of three types of unique nodules which consist of amorphous silica-apatite, cristobalite-apatite and tridymite-apatite associations interspersed amidst basaltic pyroclastics from the Har Peres volcano, Golan Heights, Israel is reported. Unusual isotopic temperature (75°C estimated from oxygen isotope fractionation between cristobalite (δ18O = +25.5‰)-apatite (δ18O = +12.9‰) pair suggests that the nodule was not formed by present-day pedogenesis as has been previously proposed, but was a xenolith incorporated probably from the underlying siliceous phosphorites at a higher temperature. An observed negative oxygen isotopic fractionation (δ18O = −5.1‰) between tridymite (δ18O = +9.9‰) and associated apatite (δ18O = +15.0‰) is indicative of the nodular formation under disequilibrium conditions. A plausible mechanism of formation of the apatite (and calcite) associated with tridymite is an epitaxial overgrowth on template tridymite of magmatic origin under the current weathering regime. Oxygen isotopic evidence indicates a complicated origin for the nodules.

A kaolin clay occurring in Carboniferous mudstone near the Jiangshan-Shaoxing deep fault in Zhejiang Province, eastern China was characterized by XRD and IR. Although the dominant mineral appeared to be kaolinite, IR also suggested the possible occurrence of nacrite. This was confirmed by forming intercalation complexes with potassium acetate and with hydrazine hydrate, both water complexes having the same characteristic spacing at 8.35 Â. Different particle size fractions of the kaolin clay were studied and the results indicated that nacrite content increased with increasing particle size. This occurrence of nacrite is consistent with previous findings of the polytype in high temperature and pressure environments.

Poorly crystalline authigenic alteration products of basic pyroclastics from the Golan Heights, Israel, were investigated by XRD, DTA, TGA, FTIR and chemical analysis. Modeling XRD patterns with the use of NEWMOD code provided a way to identify these clays as random interstratified illite/smectites (I/S) with ∼70% of illitic interlayers. Their characteristic features were very poor basal reflections, distinct hk bands, high CEC and low (∼2%) K2O content. Crystallite thickness distribution was found to follow Ergun's model with a weight-average thickness of 2.7–2.8 layers. A new method was proposed to calculate the proportion of kaolinite and 2:1 minerals in their mixtures and the average crystallochemical formula of 2:1 minerals in the presence of kaolinite. The method starts from data of chemical analysis and TGA and assumes that the anionic frameworks of kaolinite and 2:1 minerals are exactly O10(OH)8 and O10(OH)2 respectively. The number of OH-groups per ten oxygens not bonded to H in the empirical formula of the mixture is used to evaluate the proportion of kaolinite. Formation of I/S in well-drained environments under humid mediterranean climatic conditions was attributed to long dry seasons. Interstitial water composition was shown to be consistent with authigenic formation of I/S.

The large contents of octahedral vacancies in published formulae of chlorite from hydrothermal systems and clastic sequences are shown to be largely caused by inclusion of other minerals. Verification is provided by analytical electron microscope (AEM) analyses of chlorite in pelitic rocks from the Gaspé Peninsula, Quebec and the Gulf Coast, Texas. The Gaspé chlorite occurs as discrete crystals locally coexisting with corrensite, and the Gulf Coast chlorite is free of mixed layers other than local serpentine-like 7-Å layers. Unlike most electron microprobe analyses (EMPA), but like other AEM analyses, the reported chlorite formulae do not have significant octahedral vacancies, are not Si-rich and (Fe + Mg)-poor relative to classic metamorphic chlorite, and have nearly equal amounts of tetrahedral and octahedral Al. The studied chlorites and those in metabasites and clastic rocks that could be positively identified as containing no or minimal mixed layering or submicroscopic intergrowths have little or no Ca or alkalis. In contrast, EMPA of chlorite reported for other clastic sequences show variable amounts of Na + K + 2Ca that exhibit a poorly defined positive correlation with the proportion of octahedral vacancies. The EMPA of chlorite from the Salton Sea and Los Azufres geothermal fields that were suggested to contain temperature-dependent amounts of tetrahedral Al (and thus used as “chlorite geothermometers”) show compositional characteristics similar to those reported for several saponite-chlorite transition series in metabasites.

Continuous increases in octahedral occupancy and tetrahedral Al with increasing metamorphic grade are attributed to decreases in abundance of mixed layers or fine-grained intergrown minerals that commonly occur as a result of increasing crystal size and homogeneity in prograde sequences. Use of “chlorite geothermometry” based on the proportion of apparent octahedral vacancies or tetrahedral Al is therefore unwarranted and leads to inaccurate temperature estimates.

The hydrolytic behavior of Fe solutions at room temperature under acidic conditions was investigated. In the presence of Al ions, with Cl and NO3 as associated anions, the Fe hydrolysis began almost instantaneously and a crystalline β-FeOOH (akaganeite) was formed in the AlCl3/FeCl3 system within a short period. Initially the particles were small with large surface area. However, with time the particles grew in size and the surface area decreased. After about 42 days of equilibration, the akaganeite particles grew to 60–300 nm long, 10–50 nm wide and with a surface area of 55 m2/g, which is similar to other reports for akaganeite prepared at higher temperatures. In the NO3 system [Al(NO3)3/Fe(NO3)3], lepidocrocite (γ-FeOOH) and goethite (α-FeOOH) were formed. In a mixed anion system (Cl/NO3) solid phases identified were akaganeite (β-FeOOH) and lepidocrocite (γ,-FeOOH). The introduction of poly-nuclear hydroxy-Al along with monomer Al in Cl and NO3 systems of Fe affected the quantity and quality of the solid phase. The crystallinity of β-FeOOH formed in the presence of polynuclear hydroxy-Al ions in a Cl-system was more disordered than when it formed in the presence of monomer Al-ions alone. In NO3 systems, polynuclear hydroxy-Al hindered the formation of goethite (α-FeOOH). Our experiments showed that Fe oxyhydroxides crystallize readily under acidic conditions in the presence of Al ions and the data also indicated that the Cl was essential for the crystallization of akaganeite, whereas goethite was formed in those systems when Cl was absent.

The swelling of n-butylammonium vermiculite in water was investigated as a function of the sol concentration (r), the salt concentration (c) and the temperature (T).

The interlayer spacing in the gel phase was investigated as a function of r and c by neutron diffraction and by laboratory experiments which measured how many times its own volume a crystal would absorb. The salt concentration was found to be the stronger variable with the interlayer spacing decreasing proportional to c0.5, which is consistent with previous results and with the Coulombic attraction theory. The sol concentration was found to affect the swelling for two reasons, the salt fractionation effect and the trapped salt effect. Both of these cause the salt concentration in the supernatant fluid to be greater than that originally added to the crystals and so reduce the swelling.

A new method was used for extracting the solution from inside the gels by collapsing the gels by the addition of potassium hydrogen carbonate. The Volhardt titration was carried out on the extracted and supernatant solutions from about 250 gels. The ratio of the external to the internal chloride concentration was found to be approximately constant across the range of salt concentrations. Its average value was equal to 2.6, again in agreement with Coulombic attraction theory and showing the surface potential to be constant at about 70 mV.

The (r, c, T) boundary of the two phase colloid region was investigated by three methods. A plot of log c against Tc was linear within experimental accuracy, with a gradient of 0.077 K−1 or 13 K per log unit. This shows that the surface potential varies by only 1 mV per decade in the salt concentration. The system is therefore governed by the Dirichlet boundary condition and not by the Nernst equation.

Synthetic, relatively well-crystallized aluminum-substituted maghemite samples, γ-(Aly·Fe1−y)2O3, with y = 0, 0.032, 0.058, 0.084, 0.106 and 0.151 have been studied by X-ray diffraction and zero-field Mössbauer spectroscopy in the range 8 K to 475 K, and also with an external field of 60 kOe at 4.2 K and 275 K. It was found that there are two different converging models for fitting the zero-field spectra of the maghemites with a superposition of two Lorentzian-shaped sextets, both resulting in inconsistent values for the hyperfine fields (Hhf) and/or the center shifts (δ) of the tetrahedral (A) and octahedral (B) ferric ions. From the applied-field measurements it is concluded that there is a constant difference of 0.12 ± 0.01 mm/s between δB and δA, regardless of the Al content. For the Al-free sample the center shifts are found as: δA = 0.370 mm/s and δB = 0.491 mm/s at 4.2 K and δA = 0.233 mm/s and δB = 0.357 mm/s at 275 K (relative to metallic iron), with an estimated error of 0.005 mm/s. Both δA and δB are observed to decrease with increasing Al concentration. The effective hyperfine fields for the non-substituted maghemite sample are: Heff,A = 575 kOe and Heff,B = 471 kOe at 4.2 K and Heff,A = 562 kOe and Heff,B = 449 kOe at 275 K, with an error of 1 kOe. The B-site hyperfine field remains approximately constant with Al substitution, while for the A site a slight decrease with increasing Al content was observed.

Pillared structures with an interlayer opening of ∼0.3 nm were obtained after successive heat treatments of the PILC precursor in reducing and oxidizing conditions. This precursor was prepared by reacting a Na+-montmorillonite with an intercalant containing Al and Fe oxo-hydroxides (Al/Fe = 1). Powder X-ray diffraction, elemental analysis, 57Fe Mössbauer spectroscopy, catalytic activity measurements and surface area data were used to characterize the samples. On the basis of Mössbauer spectra taken at temperatures between 4.2 and 300 K, it is deduced that oxidizing steps produce Al substituted maghemite which converts into Al substituted magnetite upon reducing heat treatment. Firing the precursor in oxidizing atmosphere forms pillars of few nm in diameter. However, heating under reducing conditions yields pillars of smaller diameter. This later behaviour is maintained even after reheating the material in oxidizing atmosphere. From the temperature dependence of Mössbauer spectra it is deduced that the diameter of the Fe oxide particles in the pillars is smaller than 10 nm.

A number of smectitic samples from Almeria (SE Spain) were studied by chemical analysis, DTA, TG, XRD (oriented aggregates with ethylene glycol treatment and Greene-Kelly test), FTIR and MAS NMR. Chemically they resembled a beidellite-montmorillonite series, displaying DTA/TG characteristics already quoted in the literature in beidellite descriptions. They did not swell after the Greene-Kelly test, as it has also been reported for some beidellites. Nevertheless XRD of the oriented, glycolated samples, FTIR, MAS NMR and revision of the chemical analysis demonstrated that they were mixed-layered kaolinite/montmorillonite. It is possible that some of the reported beidellites in the literature are kaolinite/montmorillonite. Beidellite characterization must be supported by several different techniques.