Nine hematites and 22 goethites were synthesized by a variety of methods to obtain monomineralic samples having a range of Al substitutions and particle sizes. The second derivative of absorbance and Munsell color designations were calculated from visible reflectance spectra obtained from the dry powders. Unit-cell dimensions, Al substitution, infrared band positions, mean crystallite dimensions (MCD) from X-ray powder diffraction, and particle size from fiber-optic Doppler anemometry (FODA) were determined. Previously reported correlations between Al substitution, goethite unit-cell dimensions, and OH-stretching and -bending band positions were confirmed. For hematite, the position of the second derivative peak at ∼600 nm was negatively correlated with Al substitution (r = −.86). Munsell value and chroma were positively correlated with Al substitution (r =.94 for both), but hue was not related to Al substitution. Hue appeared to become redder, however, as particle size measured either by FODA or MCD increased. For goethite, the position of the second derivative minimum at ∼485 nm was negatively correlated with Al substitution (r = −.99). Munsell hue appeared to be related to both Al substitution and MCD perpendicular to (110), MCD110, with hues becoming redder with increasing Al substitution and yellower with increasing MCD110. Correlations between Munsell value and chroma and parameters such as Al substitution, particle size, and OH-stretching and -bending band positions were poor, but goethites synthesized by oxidation of Fe2+ solutions at room temperature had higher chromas than goethites synthesized hydrothermally from an Fe3+ system. Visually determined colors agreed well with calculated ones. Second-derivative spectra and color designations calculated from visible spectra appear to be potentially useful for quickly estimating other properties of goethite and hematite, such as Al substitution and particle size.

An extensive survey of clay mineral relationships in the subsurface Wilcox formation (Eocene) has shown progressive diagenetic conversions with depth. Montmorillonite, a common constituent of Wilcox outcrop material, becomes loss evident below 3000 ft and is not normally found in an unmixed state below the 9000—10,000 ft overburden level. At depths between 3000 and 14,000 ft, montmorillonite lattices are commonly interpersed with illite components, the frequency of which increases with depth to a virtual elimination of montmorillonite swelling characteristics below 14,000 ft.

Chlorite is present at all stratigraphic levels including surface exposures. It appears to be a more dominant constituent at depth; however, observed increases in basal intensities in samples that had been more deeply buried may result from more perfect crystal development rather than quantitative differences.

The diagenetic conversion of montmorillonite to illite and possibly to chlorite has resulted in a distribution of the last two minerals that is related to estimated depositional environments as reconstructed from micro-paleontological criteria in at least one well in southern Louisiana. It is inferred, therefore, that different chemical characteristics in the ancient Wilcox seas are responsible for the distribution coincidence even though the mineral groups defining the distribution were not necessarily indigenous to the ancient Wilcox sea.

Correlations between clay minerals and environment are not particularly noted in the investigation of analogous environmental situations in Recent sediments, and it is thus concluded that the environment indicators which appear as minerals in lithified sediments such as the Wilcox are present in freshly deposited sediments in the form of submineralic chemical constituents such as absorbed ions, molecular groups or subcrystalline lattice configurations which are not detected by the ordinary clay mineral identification procedures. The change to mineralic form is aided by the natural “bombing” resulting from normal increases in temperature and pressure due to burial. The process is apparently a continuum through the entire subsurface residence of the sediment and the results are seemingly in accordance with phase equilibria.

The acid dissolution of 8 chlorites in 2N Si-saturated HCl showed that there was no preferential dissolution of Al in octahedral positions and that the octahedral and tetrahedral sheets in the chlorite structure were equally attacked. An analysis of chemical data suggested a simple two-dimensional diffusion model in which the acid attack on the chlorite particles proceeded from the edges inward leaving a reacted layer which formed a diffusion barrier. Microscopic examination showed, however, that the acid attack was not simply an edge attack but started at any point where cracks, structural defects and weaknesses apparently predisposed sites to acid attack. It was also clear from the formation of etch figures and solution channels that the product layer at least partially dissolved or disintegrated during the progress of acid attack. The residue which remained after acid attack appeared to be an opaline amorphous hydrated silica as was indicated by index of refraction measurements. The orderly arrangement of etch figures on flakes of some chlorites reflected certain crystal symmetry elements. The results indicate that the acid dissolution technique to determine the ratio of Al in octahedral and tetrahedral positions can not be used as an aid in the calculation of structural formulae for chlorites.

In cases where the provenance of raw materials used in the manufacture of local archeological ceramics is of interest, a detailed study of thermal transformations of minerals may be useful. The purpose of this study was to measure mineralogical transformations of different types of clays obtained during experimental firing runs, carried out at different temperatures, with the main goal of establishing Algarve reference groups based on the composition of raw material and high-temperature mineralogy, which may be compared with ceramics in studies of provenance. Eleven samples of clay-rich raw materials from the Algarve Basin (southern Portugal) were fired to temperatures ranging from 300 to 1100°C in increments of 100°C under oxidizing conditions. These were chosen to have variable chemical and mineralogical compositions, representing the main compositional range of the clay deposits from the region. Mineralogical and geochemical characterizations of the original clays were carried out by X-ray diffraction (XRD) and X-ray fluorescence (XRF), respectively. Mineral transformations on the fired products were also studied by XRD.

Three groups of clays were distinguished according to the type of neoformed high-temperature minerals: (1) non-calcareous clays; (2) clays containing calcite as the only carbonate; and (3) clays with dolomite or dolomite + calcite. Firing of non-calcareous clays produced mullite at 1100–1200°C. Gehlenite and wollastonite formed by firing calcite-rich clays above 900°C, accompanied by anorthite or larnite in samples with small or large calcite contents, respectively. Firing of dolomite-rich clays at temperatures >900°C yielded a member of the gehlenite-åkermanite group and diopside. Anorthite, enstatite, periclase, forsterite, and monticellite may also form in the firing products.

An account is given of the interactions between clay minerals and organic polymers with particular reference to their applications in agriculture, foundation engineering and industry.

The discovery of phyllosilicates in terrains of Noachian age (>3.5 Ga) on Mars implies a period in the planet’s history that was characterized by wetter, warmer conditions that may have been more hospitable for life than the cold and dry conditions prevalent today. More specific information about the original locations and mechanisms of clay mineral formation on Mars is not as well constrained, however, in part because the origin of particular clay minerals is often non-unique. For example, Fe and Mg smectite-bearing deposits on Mars may have formed in various environments, including the weathering profiles of basic volcanic rocks, impact-induced hydrothermal sites, or in bodies of standing water. The identification of lacustrine deposits on Mars is of great interest due to their potential for the preservation of organic material, but identifying any given suite of sedimentary rocks as such is difficult when limited to mineralogy and morphology derived from orbital data. Here, the processes and conditions leading to clay mineral formation in lakes and evaporative marine basins on Earth are reviewed, with a focus on the spatial and stratigraphic distribution of clays in these settings. The goal is to provide criteria to determine if certain Martian clay deposits are consistent with such an origin, which in turn will aid in the identification of possible ancient habitable environments on Mars.

Reaction of a Mg-Al carbonate layered double hydroxide (LDH) with boric acid leads to a borate-pillared LDH with the stoichiometry [Mg0.65Al0.35(OH)2][B3O5]0.35.0.65H2O and an interlayer spacing of 1.07 nm. Infrared and 11B magic angle spinning nuclear magnetic resonance data are consistent with the presence of polymeric triborate anions of the type [B3O4(OH)2]nn- in the interlayer galleries so that the material can be formulated as [Mg0.65Al0.35(OH)2][B3O4(OH)2]0.35.0.30H2O. The flame-retardant properties of the borate-pillared material and the carbonate precursor in composites with ethylene vinyl acetate copolymer were compared. Introduction of the borate anion leads to a significant enhancement in smoke suppression during combustion without compromising the flammability of the material. This is related to the synergistic effect between the host layers of the LDH and the borate anions uniformly distributed in the interlayer region.

Analysis of Mossbauer effect in layer silicates provides a spectroscopic method for determining valences and coordination of iron. In this study Mossbauer spectra were obtained for amesite, cronstedtite, nontronite, two glauconites, biotite, lepidomelane, chlorite, minnesotaite, vermiculite. stilpnomelane, and chloritoid.

Trivalent iron was detected in tetrahedral coordination. Abundant trivalent iron in octahedral coordination apparently causes quadrupole splitting values of divalent iron in the same mineral to decrease. This phenomenon was noted in cronstedtite and glauconite. In cases where divalent iron predominates in the mineral, the quadrupole splitting is larger. It is generally accepted that ferrous iron is largely in octahedral coordination. This suggests that the octahedral sites may be more distorted when ferric iron is present in the octahedral sheet. In biotite, quadrupole splitting of divalent iron is decreased when trivalent iron is present in tetrahedral sheets. This suggests that there is also more distortion in the octahedral sheet because of iron in tetrahedral positions.

Clay samples of greenish colour were collected from submarine hydrothermal chimneys of the Galapagos Rift and Mariana Trough. Mineralogical and chemical investigations of the clay by scanning and transmission electron microscopy, X-ray diffraction, differential thermal analysis, infrared-spectros-copy, X-ray fluorescence, and determination of specific surface area, and oxygen isotope composition identify it as a well crystallized nontronite. This nontronite of hydrothermal origin has a nearly monomineralic character, a low Al-content, and a formation temperature of 21.5 to 67.3°C. The most remarkable characteristic, however, of the nontronite deposit is its microstructure, a network of microtubes composed of fine frequently folded clay sheets. These delicate filaments show close similarity in size and form to sheath forming bacteria. The correlation between clay mineral and chemical characteristics, as well as biological conditions at marine hydrothermal smoker chimneys, let us suggest that Fe oxidizing, sheath forming bacteria are playing a decisive role in nontronite formation at these sites.

The colloidal state (stable, coagulated, or gel-like) and the rheological properties of Na-rich montmorillonite (Wyoming) dispersions are strongly influenced by organic cations. This effect is shown for homologous organic cations: alkyl trimethylammonium ions, paraquat, diquat, alkyl bispyridinium ions, and the triphenylmethane dyes crystal violet, methyl green, and tris (tri-methylammonium phenyl) methane chloride. The critical coagulation concentrations, cK, are small (often < 1 mmol/L) because the cations are enriched in the Stern layer and influence the solvent structure near the surface. The strong adsorption of the counterions at the clay-mineral surface causes cK values to increase with the solid content. Charge reversal (recharging) of the particles was observed with the longer chain alkyl trimethyl-ammonium ions, dodecyl bispyridinium ions, and crystal violet. Other cations reduced the electrophoretic mobility to zero but positive particle charges were not observed.

The plastic viscosity increased sharply at the critical coagulation concentration and showed a minimum slightly below cK, which was caused by the electroviscous effect. Yield values were developed at concentrations above cK. In most cases, yield values reached a plateau where the amount of organic cations was ∼0.5 mmol/g, i.e., about half of the cation-exchange capacity. The cK values decreased with increasing hydrophobicity of homologous compounds, but the yield value showed maxima at intermediate chain lengths. The yield value of several 0.5% dispersions was high, e.g., dodecyl trimethylammonium ions, 71 Pa; paraquat, 100 Pa; diquat, 42 Pa; hexyl bispyridinium ions, 53 Pa (vs. Ca2+, 0.2 Pa; Al3+, 0.7 Pa). The storage modulus as a function of the number of organic cations changed in a similar way as the yield value, and high values were observed (e.g., dodecyl trimethylammonium ions, hexyl bispyridinium ions: 1000 Pa, paraquat: >4000 Pa). Thus, dispersions with high viscosity, yield value, and pronounced viscoelasticity are obtained by coagulating Na-rich montmorillonite dispersions with organic cations.

A montmorillonite exchanged with large hydroxy-Al cations was thermally treated to convert the hydroxy cations to oxide pillars and to generate permanent microporosity in the interlayers. The pillared clay products were characterized by X-ray powder diffraction (XRD) and water-sorption measurements to delineate the effect of aging of the pillaring solutions, the methods of drying and concentration of clay-water suspensions, and the temperatures of calcination on micropore volumes. Although samples prepared at different conditions gave d(001) reflections of 17–17.5 Å, at least to 500°C, the concentrations of clay-water suspensions and the temperatures of calcination significantly changed the pore-size distribution and the volume of micropores present in the sample, as calculated from the water-sorption isotherms. A narrow pore-size distribution having little or no macroporosity or external surface condensation was observed in samples prepared by the addition of the pillaring solution directly to the clay (solid) without first making a clay-water suspension and calcining the sample at ≥400°C. About 87% of the total volume was found to be micropores of ≤14–17 Å in the sample calcined at 600°C. Aging the pillaring solution, however, did not influence either the water-sorption isotherms or the XRD patterns significantly under the conditions specified. Essentially the same results were obtained for samples prepared from both hydroxy-Al polymer (OH/Al = 2) and aluminum chlorohydrol (ACH) solutions.

Although alumina-pillared clays exhibited an extreme type-I isotherm (Langmuir type) for nitrogen adsorption, the sorption of water vapor gave an isotherm of unusual shape that fit neither a BET nor a Langmuir equation. This latter behavior has previously been attributed to a unique pore size and hydrophobicity and is apparently common to all pillared montmorillonite materials. The hydrophobicity of the pillared clay apparently developed on calcination by the migration of protons from the interlayers to the octahedral sheets, in which sites of cationic substitution (negative charge) were located. Protons migrated back to the interlayers by treatment with NH3, which subsequently converted to NH4+ in the interlayers. The exchange of the NH4+ by Ca2+ introduced hydrophilicity to the alumina-pillared clay, which was reflected both in the shape of the water isotherm (close to moderate Brunauer type I), the heat of sorption, and the total sorption capacity.

Thermogravimetric analysis combined with mass spectrometry was used to study H2O bound to samples of illite-1M, illite-2M2 and leucophyllite-1M. Samples were heated in a helium atmosphere at different temperatures and after heating at each given temperature were cooled to 35°C. Each cycle in the mass 18 spectrum of each illite sample contains a low-temperature peak at 60–80°C, a medium-temperature peak at 340–360°C, and a high-temperature peak at a temperature that is very close to the maximum temperature of sample heating of a given cycle. Within each heating-cooling cycle, the sample weight at the beginning of cooling is lower than that at the end of the same cooling stage because of H2O resorption. However, the number of H2O molecules released during each medium-temperature heating cycle is equal to the number of H2O molecules resorbed during the corresponding cooling stages.

The weight losses, under medium-temperature heating, of the illite samples are related to dehydration when H2O molecules located in K-free sites of the illite interlayers are removed. The medium-temperature peak is reproducible for each cycle because during each cooling stage the illite interlayers resorb the same number of H2O molecules that were lost during the preceding dehydration.

Two distinct features are characteristic of leucophyllite during heating-cooling treatments. First, the number of H2O molecules resorbed during cooling is significantly greater than the number of H2O molecules lost during dehydration. Second, the medium-temperature peaks in the spectrum appear only in the last five cycles and the maximum-peak temperature is 450–460°C. These data indicate that the heating-cooling treatments are accompanied by partial rehydroxylation. This rehydroxylation occurs during each coolingstage when a small number of resorbed H2O molecules are trapped in the interlayers, although most migrate into the octahedral sheet of the 2:1 layers and reform as OH groups. The crystal chemical factors responsible for the dehydration and rehydration as well as for the rehydroxylation reactions are discussed and speculation about the origin of the low- and medium-temperature H2O losses is presented.

Solutions containing AlCl3 and Si(OH)4 (concentrations ≤ 1.5 mM with molar Si:Al ratios of 1:2, 1:1 and 3:1) and FeCl2 (0, 0.5 and 1.0 mM) were adjusted to pH 8 with Ca(OH)2, and incubated at 23°C and 89°C without exclusion of air in the presence of CaCO3 for 8–12 weeks. The products were characterized by infrared spectroscopy and X-ray diffraction. Systems with 3:1 and 1:1 Si:Al ratios without Fe gave hydrous feldspathoids at 23° and 89°C. Systems with 3:1 Si:Al ratios containing Fe gave aluminous nontronites at 89°C and noncrystalline, nontronite-like products at 23°C. Systems with 1:1 Si:Al ratios with added Fe gave Fe(III)-substituted hydrous feldspathoids at 23°C. At 89°C, the system with 1:1 Si:Al ratios and 0.5 mM Fe produced a “protohalloysite,” while that with 1.0 mM Fe gave a poorly ordered nontronite-like layer silicate. In systems with 1:2 Si:Al ratios, the formation of “protoimogolite” at 23°C was little affected by additions of Fe. At 89°C, the “protoimogolite” decomposed to boehmite and poorly-ordered layer silicate phases. Inclusion of 1 mM MgCl2 in the above systems had no effect on the products at 23°C, but at 89°C produced saponites and a mixed layer saponite-chlorite in the 3:1 Si:Al systems, and saponite-like layer structures in the 1:1 and 1:2 Si:Al systems.

The instability of palygorskite and sepiolite under soil conditions was investigated to determine if these fibrous minerals transform directly to smectite under laboratory conditions. The treatment of 100 mg (0.12 mmole) of palygorskite with 1 mmole of NaOH solution (17 ml) at 150°C for 24 hr yielded a smectite. Analcime and smectite were formed when ≥ 3 mmole of NaOH was used. The addition of ≤ 6 mmole NaOH to sepiolite destroyed it gradually. On addition of ≥ 8 mmole NaOH, sepiolite altered to an X-ray amorphous material. In the presence of Al and Si, however, it transformed to smectite and analcime. Transmission electron microscopy, cation-exchange capacity, and X-ray powder diffraction studies of the products suggest that alteration wa. (1) via solution, o. (2) by a structural reorganization wherein the basic 2:1 silicate structural units were unchanged.

Montmorillonite, kaolinite, illite, and chlorite were found to adsorb bitumen and its pentane-soluble and pentane-insoluble fractions. The formation of clay-bitumen complexes is influenced by the nature of the exchangeable cation on the clay and by the solvent carrier which stabilizes the bituminous compounds. Ca-clays adsorb organic compounds more strongly than sodium forms except in the presence of nitrobenzene. Solvents of high dielectric constant, such as nitrobenzene, promote ionization so that the ion-exchange mechanism of adsorption is favored, whereas solvents of lower dielectric constant, such as chloroform, tend to solvate rather than to dissociate bitumens. The behavior of the montmorillonite-bi- tumen complex in variable relative humidity indicates that organic molecules adsorb primarily on external surfaces and cause the clay to become less hydrophilic than prior to treatment. Clay-organic complexes are sufficiently stable to resist powerful organic solvents. The clay-organic complex separated from the Athabasca oil sand behaves similarly during chemical treatment to complexes formed between bitumen and the four reference clay minerals.

High-resolution transmission electron microscope images of dioctahedral mixed-layer clay structures (illite/smectite) having various substitutional and polytypic schemes were modeled using computer simulation methods. Both one- and two-dimensional calculations were performed using parameters characteristic of a typical range of imaging conditions. One-dimensional images formed by imaging only 00/ diffractions show three important results: (1) The 20-Å periodicity resulting from rigorously ordered R1 illite/smectite can be imaged, but unconventional focus conditions may be necessary. (2) For crystals oriented with the electron beam perfectly parallel to the layers, the brightest fringes in the image correspond to either the octahedral sheets or the interlayer sites, depending on focus conditions. Misorientation of the crystal, however, by only 1° or 2° shifts the positions of the fringes by 1 to 3 Å. Furthermore, in tilted specimens, some defocus values produce images suggesting that smectite layers have a 11–13-Å periodicity, despite the uniform 10-Å periodicity present in the model structure. Thus, direct correlations between image and structure generally should not be made. (3) Two-layer polytypes of pure illite or pure smectite can also produce images with a 20-Å periodicity.

Two-dimensional images additionally showed that the cross fringes produced by some hkl diffractions can be imaged. The simulations showed that these cross fringes ideally might permit the determination of both layer stacking and compositional periodicity, but the fringes are lost by misorientations of a few degrees. These image simulations demonstrated, therefore, that mixed layering of illite and smectite theoretically can be directly imaged by transmission electron microscopy of chemically untreated specimens, but ambiguities may exist in the detailed intepretation of the images.

The surface microtopography of hematite over the course of dissolution in oxalic and citric acids was examined by in-situ and ex-situ atomic-force microscopy. In-situ imaging of the basal-plane surface of a centimeter-scale natural hematite sample immersed in 2 mM citric acid demonstrated that the basal-plane surface was relatively unreactive; rather, dissolution occurred along step edges and via etch-pit formation. Ex-situ imaging of synthetic hematite particles following batch dissolution in 1 mM oxalic acid showed similar dissolution features on basal-plane surfaces; in addition, etching along particle edges was apparent. The presence of etch features is consistent with a surface-controlled dissolution reaction. The results are in agreement with previous investigations suggesting that the basal-plane surface is relatively unreactive with respect to ligand exchange. Both in-situ and ex-situ imaging of particle surfaces can provide valuable information on the roles of surface structures and microtopographic features in mineral dissolution.

The clay and bulk mineralogy of soil and till from 26 Adirondack watersheds was studied. The materials consist typically of quartz, K-feldspar, plagioclase, mica, vermiculite, and kaolinite. Talc, smectite, halloysite, and hornblende are present in some samples. The clay fraction of the soils is composed predominantly of vermiculite, likely derived from the transformation of a mica precursor, and kaolinite. The soil vermiculite commonly contains hydroxy-Al interlayers which are especially prevalent in the B-horizon samples. Despite significant variation in the type of bedrock and the composition of heavy mineral assemblages in these watersheds, the clay mineralogy is remarkably uniform. This finding supports earlier suggestions that the occurrence of vermiculite in soils is more dependent on climate than on the nature of the parent material.

The Clay Minerals Society published a complete characterization scheme for its ‘Source Clays’ but not for its ‘Special Clays’. To address this issue, the specific surface areas (SSAs) of the 16 special clays from The Clay Minerals Society were determined using the Brunauer, Emmett and Teller (BET) method of adsorption of an inert gas. Two BET measurements were performed for each of the 16 special clays, and the average BET SSA of each of the special clays was determined. The BET SSA of cookeite is reported for the first time. In the present study, special clays from The Clay Minerals Society are classified under three groups based on their BET special surface area values as Group-I special clays, with BET values of 0.1–10 m2/g, Group-II special clays, with BET values of 10–100 m2/g, and Group-III special clays, with BET values >100 m2/g. Comparisons which proved interesting were the those involving the mixed-layer clays and the synthetic clays. The systematic approach employed in this paper will allow for better comparisons to be made between different clays and will provide a comprehensive database for future applications of such material (e.g. as catalyst carriers, as adsorbents in waste treatments, etc.).