Chlorite and corrensite are common clay minerals in lacustrine mudrocks from the Devonian Orcadian Basin, Scotland. The relationship of their occurrence to vitrinite reflectance data demonstrate that they are authigenic minerals, formed during burial diagenesis/metamorphism at temperatures of ≥120°C. Whole rock mineralogical and chemical analyses show that chlorite authigenesis occurred by reactions between the detrital dioctahedral clay mineral assemblage and dolomite that was formed under early evaporitic conditions in the lacustrine environment.

XRD and electron microprobe analyses indicate that phases intermediate between corrensite and chlorite are probably mixed-layer chlorite/corrensite with a tendency towards segregation of layer types. Chemically, the conversion of corrensite to chlorite involves an increase in Al for Si substitution in tetrahedral sites, but there is no change in the Fe/Mg ratio of octahedral cations. There is also no relationship of mixed-layer proportions to paleotemperature; only a general paleotemperature interval of approximately 120° to 260°C in which a range of phases between corrensite and chlorite occurs. Chlorite polytypes are exclusively IIb, indicating the formation of this polytype at diagenetic temperatures.

The occurrence of corrensite and Mg-rich chlorite in evaporite and carbonate successions is probably a reliable indicator of diagenetic alteration at temperatures of ≥ 100°C. Burial diagenetic reactions between dioctahedral clay minerals and Mg-rich carbonates may possibly explain many occurrences of corrensite and Mg-rich chlorite in such rocks.

A glass in the intermediate composition of montmorillonite and beidellite, 50/50 in mole ratio, was treated under a hydrothermal pressure of 100 MPa, in the temperature range from 250 to 500°C and durations from 2 to 129 days. The phases identified in the products were plotted in a time-temperature-transformation (TTT) diagram. The TTT diagram showed that the regularly interstratified montmorillonite-beidellite (r.i.M-B) was a metastable phase above the temperature of 350°C and changed to the assemblage of Na-rectorite + saponite + quartz, through the intermediate assemblage of beidellite + saponite + quartz. The TTT diagram suggested also that the r.i.M-B might be a stable clay mineral below the temperature of 300°C in the middle region of montmorillonite-beidellite pseudo-binary system, although the laboratory confirmation of the mineral stability was not easy for the sluggish reaction.

Additional well-crystallized kaolin from Washington County, Georgia, has been supplied to the Clay Minerals Society Source Clay Repository to replace the exhausted supply of KGa-1. This kaolin is called KGa-1B and is from a geographic location and stratigraphic position close to where KGa-1 was collected. Slight mineralogical and chemical differences are observed between KGa-1 and KGa-1B. KGa-1B crude appears slightly better crystalline than KGa-1, and it has a slightly higher titania content than KGa-1. The Al2O3, SiO2, Fe2O3, alkali, and alkaline earth contents appear similar for both samples. KGa-1 has a slightly coarser particle size than KGa-1B crude. More intensive post-depositional alteration may have cleansed and crystallized the KGa-1B material to a slightly greater degree than the KGa-1 material.

More than 40 samples of Al precipitation products formed in the presence of organic (aspartic, oxalic, citric, tartaric, malic, salicylic, and tannic acid, and acetylacetone) and inorganic (chloride, sulfate and phosphate) ligands, which were short-range-ordered materials after 2–5 months of aging, were analyzed by X-ray diffraction (XRD), infrared spectroscopy (IR), and transmission electron microscopic (TEM) examination after prolonged periods of aging in the mother liquids (from 7–15 years). Noncrystalline materials were found after 7–10 years of aging in samples formed in the presence of citrate, tartrate, and tannate at pH ≤ 8.0 and at ligand/Al molar ratios (R) ranging from 0.05–0.1; they were found as well in the presence of phosphate and malate at ligand/Al molar ratios from 0.1–0.5. Poorly crystalline Al-oxyhydroxides (pseudoboehmite) without Al(OH)3 polymorphs were found in solutions with a wide range of pH (from 6.0–11.0) in the presence of tartrate, citrate, tannate, malate, salicylate, sulfate, and phosphate after 7–15 years. The crystallinity of these samples was indeed very poor. On the contrary, gibbsite formation was observed in samples formed at pH 7.0 or 8.0 in the presence of oxalate (R = 0.1 or 1.0), aspartate (R = 0.1 and 0.5), malate (R = 0.03 or 0.17), salicylate (R = 0.05), and in samples containing very high concentrations of chloride (R = 700 or 1000). Finally, the formation of gibbsite was promoted in the presence of montmorillonite, but some samples at pH ≤ 6.0 in the presence of citrate (R = 0.1), tartrate (R = 0.1), or tannate (R = 0.02 or 0.1) showed after 6 years of aging interstratification of OH-Al species in the interlayers of the clay mineral and complete lack of Al(OH)3 polymorphs.

Ammonium-saponite is hydrothermally grown at temperatures below 300°C from a gel with an overall composition corresponding to (NH4)0.6Mg3Si3.4Al0.6O10(OH)2. The synthetic saponite and coexisting fluid have been characterized by means of X-ray powder diffraction, X-ray fluorescence, Induced Coupled Plasma-Atomic Emission Spectroscopy, thermogravimetric analysis, transmission electron microscopy, CEC determination using an ammonia selective electrode, and pH measurement. In the crystallization model developed, crystallization started with the growth of individual tetrahedral layers with an aluminum substitution not controlled by the A1IV/A1VI ratio in the gel and hydrothermal fluid, on which the octahedral Mg layers can grow. During the synthesis, individual sheets stacked to form thicker flakes while lateral growth also took place. The remaining A1VI partly replaced ammonium as the interlayer cation.

The destruction of the crystal structure of kaolinite caused by mechanical forces was investigated by X-ray diffraction, thermal analysis, infrared spectroscopy, and specific surface area determination. Attention was also directed to the change of thermal reactions of milled kaolinite. Grinding experiments for 5 min, 10 min, and 1, 2, 4, 6, and 10 h were carried out in an AGO I planetary mill. After 1 h of grinding, the crystalline order of kaolin is destroyed; but the amorphization continues in the course of prolonged grinding. Grinding for 1 h produces a favorable state for forming mullite-type crystals after heating even at 1000°C.

Hydrotalcite-like compounds (HT) with 24%–48% Al3+-substitution have been synthesized in the Mg2+-Al3+-Fe(CN)64- system. Conditioning of the synthesized and air-dried compound with K4Fe(CN)64- solution at 80°C was essential to obtain the 80%–90% pure ionic Fe(CN)64- form on an equivalent basis. A linear decrease in ao with an increase in the mole ratio of R = Al3+/(Mg2+ + Al3+) was extended to R = 0.48. The formation of highly Al3+-substituted HTs has been corroborated by the decrease in the hexagonal lattice constant ao down to 3.016 Å. The ao value was independent of the interlayer anions. The CO2 adsorption profiles were dependent upon both the Al3+-substitution and the interlayer distance. The isosteric heat of CO2 adsorption was 43.3 kJ mol-1 in the range of adsorption of 20 to 40 cm3 g-1 at 298 K and 0.1 MPa.

The Clay Minerals Society Source Clay kaolinites, Georgia KGa-1 and KGa-2, have been subjected to particle size determinations by 1) conventional sedimentation methods, 2) electron microscopy and image analysis, and 3) laser scattering using improved algorithms for the interaction of light with small particles. Particle shape, size distribution, and crystallinity vary considerably for each kaolinite. Replicate analyses of separated size fractions showed that in the <2 µm range, the sedimentation/centrifugation method of Tanner and Jackson (1947) is reproducible for different kaolinite types and that the calculated size ranges are in reasonable agreement with the size bins estimated from laser scattering. Particle sizes determined by laser scattering must be calculated using Mie theory when the dominant particle size is less than ∼5 µm. Based on this study of two well-known and structurally different kaolinites, laser scattering, with improved data reduction algorithms that include Mie theory, should be considered an internally consistent and rapid technique for clay particle sizing.

Since the initial studies of chlorite polytypes, it has been suggested that the stability of the various polytypes may be a function of the temperature at which the mineral formed; however, few studies have been performed in which polytypes of chlorite in a specific suite of samples have been determined and correlated with temperature. A review of the reported occurrences of type I chlorite indicates that other factors, including grain size of the host rock, may be at least as important as temperature in controlling the stability of these polytypes. Results of systematic studies in areas of diagenesis and very low-grade metamorphism suggest that type-II chlorite is stable at temperatures well below 200°C and that it can form as the initial chlorite phase without passing through any intermediate polytypic stages. The conditions under which type-I polytypes occur are somewhat restricted, and cognizance of those restrictions will help to direct future studies of chlorite polytype transformations. These studies should focus on the structural details of polytype transformations; on the relationship of polytype stability to pressure, composition and kinetics; and on experimental calibration of the transformations.

Structural Fe in ferruginous smectite (sample SWa-1, Source Clays Repository of the Clay Minerals Society) was reduced by a mixture of five Pseudomonas species of bacteria in a defined Fe-free medium to determine the effect of microbial reduction on clay swelling. Iron(II), total Fe, and gravimetric water content (mw/mc) were determined in clay gels equilibrated at applied pressures of 0.1, 0.3, and 0.5 MPa. The water content of microbially reduced SWa-1 decreased at all three applied pressures as the Fe(II) content approached about 0.8 mmol Fe(II)/g-clay. As Fe(II) increased from 0.8 mmol/g-clay, however, further change in mw/mc was negligible. Concurrent with microbial reduction of structural Fe was a significant decrease in the swelling pressure (PI) of SWa-1: for example, when mw/mc = 1.2 (g/g), PI changed from 0.47 MPa at Fe(II) = 0.2, to 0.19 MPa at Fe(II) = 0.9 mmol/g-clay. Both biologically and chemically reduced smectites displayed lower values of mw/mc and a concurrent decrease in II as Fe(II) content increased, but the effect of Fe(II) on mw/mc was greater for the microbially reduced smectites at all applied pressures.

The crystal structure of Keokuk kaolinite, including all H atoms, was refined in space group C1 using low-temperature (1.5 K) neutron powder diffraction data (λ = 1.9102 Å) and Rietveld refinement/difference-Fourier methods to Rwp = 1.78%, reduced χ2 = 3.32. Unit-cell parameters are: a = 5.1535(3) Å, b = 8.9419(5) Å, c = 7.3906(4) Å, α = 91.926(2)°, β = 105.046(2)°, γ = 89.797(2)°, and V = 328.70(5) Å3. Unit-cell parameters show that most of the thermal contraction occurred along the [001] direction, apparently due to a decrease in the interlayer distance. The non-H structure is very similar to published C1 structures, considering the low temperature of data collection, but the H atom positions are distinct. The inner OH group is essentially in the plane of the layers, and the inner-surface OH groups make angles of 60°–73° with the (001) plane. Difference-Fourier maps show minor anisotropy of the inner-OH group in the [001] direction, but the inner-surface OH groups appear to have their largest vibrational (or positional disorder) component parallel to the layers. Although no data indicate a split position of any of the H sites in kaolinite, there is support for limited random positional disorder of the H atoms. However, these data provided no support for a space group symmetry lower than C1.

Batch reactor experiments were performed at 150°C, 175°C, and 200°C to determine the effect of high pH KOH solutions on the mineralogy of the Opalinus shale. In these experiments, the change in solution quench pH at 25°C, solution composition, and mineralogy were monitored as a function of time for up to ≈ 50 days. Runs were performed in 50 ml titanium hydrothermal reactor vessels. Each reactor was charged with 0.5–5.0 grams of the 80–200 mesh size fraction of Opalinus shale, and 25 ml of solution (0.08 and 0.008 m KOH). Under these high pH conditions, the general sequence of reaction products observed is the formation of phillipsite, followed by K-feldspar ± K-rectorite. Phillipsite is a metastable intermediate that eventually transforms to K-feldspar. This sequence of mineral reaction products is very different from that found in the NaOH system.

Weathering of spodumene in a lateritized pegmatite in Western Australia was studied by investigating in situ samples by electron-beam techniques. The spodumene had mostly altered to smectite. However, some non-crystalline material adjacent to smectite and intermixed with smectite was also observed. No crystallographic orientation between spodumene and smectite was observed by high resolution techniques. The spodumene dissolved to produce etch pits similar to those observed on hornblende grains. The etch pits were almost completely filled with smectite. Most of the Li in the spodumene was lost during its weathering to smectite.

Clay mineralogy (including illite crystallinity) was studied in Pennsylvanian synorogenic sediments (Atoka Formation) in the subsurface of the Arkoma Basin and the adjacent Ouachita thrust belt. Vitrinite reflectance values range from ≥0.8% at the surface up to as high as 4.7% Ro at the base of the Atoka Formation. The mineralogy of the <2 µm fraction of the mudrocks is fairly monotonous and composed of illite (<10% interstratified smectite), Fe-chlorite, kaolinite, quartz, and traces of feldspars. Kaolinite is common at shallow levels and “disappears” in most wells at a thermal maturity of 1.9–2.1% Ro, suggesting its possible use as an independent paleothermal indicator in this basin. Illite crystallinity (IC) values are fairly high (0.3–0.5° 2θ) and show little variation throughout the entire maturity range. In addition, no relation was observed between vitrinite reflectance and illite crystallinity, indicating that IC is not a useful paleothermal indicator in these rocks. Illite is almost exclusively of the 2M1 polytype, suggesting a predominantly detrital origin. Incipient metamorphic and low-grade metamorphic mudrocks in the Ouachita thrust belt to the east of the Arkoma Basin are regarded as the source rocks for the clays of the Atoka Formation. Rapid transportation and deposition by turbidity currents probably played a key role in protecting these unweathered micas from pervasive alteration in the terrestrial environment.

The porosities of flocs formed from a used drilling mud were determined by measuring sizes and settling speeds of individual flocs. These flocs were produced in a Couette-type flocculator under a variety of combinations of fluid shear and solid concentrations. In the calculation of floc porosities, a floc settling model was employed that can consider the effects of creeping flow through a floc on its settling speed. Results show that floc structure can be well described as a fractal with a fractal dimension of 1.53–1.64 for the floc size range tested. The effects of flocculation conditions, such as fluid shear and solid concentration, on floc porosity and structure were examined. It was found that floc porosity and fractal dimension were not influenced by solid concentration, but they increased as fluid shear decreased. Empirical expressions for the porosity of drilling mud flocs are obtained from both the floc settling model and Stokes’ law. For solid volume fraction in flocs, the relative difference between these two expressions could be as much as 38%. However, the fractal dimensions estimated based on the two settling models are nearly the same.

Mica domains have received less attention in the literature than smectite quasi-crystals. This study was conducted to determine whether mica crystals form domains in suspension, the conditions in which those domains exist, and the distribution of adsorbed Na and Ca ions in the domains. Particle size distributions and electrophoretic mobilities (EM) of Silver Hill illite in suspension densities of 0.5 g liter−1 were determined by photon correlation spectroscopy (PCS). Solutions at salt concentration from 2 to 10 mmolc liter−1, sodium adsorption ratio (SAR) from 0 to ∞ (mmol liter−1)0.5, and pH values 5, 7, and 9 were used to prepare the clay suspensions. The particle size of Silver Hill illite suspensions showed a bimodal distribution. Through PCS measurements at low angles, the second peak of the bimodal distribution of the illite was found to be associated with the rotational movement of the b-dimension of the particles. Illite domains broke down in the range of SAR 10 to 15 (mmol liter−1)0.5 equivalent to exchangeable sodium percentages (ESP) of 13 to 18. Illite thus demonstrates a similar stability to smectites that require ESP ≈ 15 to disaggregate quasi-crystals. The EM of the illite particles increased drastically when the SAR increased from 2 to 10 (mmol liter−1)0.5. This increase in EM could not be explained exclusively by the change in the particle size. Cation demixing is required to explain the increase of the zeta potential at the shear plane. The EM of the Silver Hill illite was doubled when the pH increased from 5 to 9 at SAR > 15, but no pH effect was found when SAR < 15. The effect of pH on the EM at SAR values > 15 can be understood if we consider that at SAR > 15 most of the particles are single platelets. The relative importance of variable charge on single platelets or crystals is apparently greater than on domains because the pH affected the mobility of the individual crystals but not the mobility of the domains. The combination of particle size distribution and EM data gives additional information about the zero point of charge of the variable charge, also called point of zero net proton charge (PZNPC) of the clay. For Silver Hill illite, we estimate a PZNPC value between 5 and 7.