To interpret the erratic conditions, rates, and extent of gibbsite crystallization from partially neutralized A1C13 solution, the following hypothesis is proposed: The initial OH-A1 polymers in the freshly prepared solutions were probably unstable and transformed into either gibbsite or stable OH-A1 polymers via two different reaction paths. In the presence of nuclei, the OH-A1 polymers dissociated into monomeric ions, which then deposited onto nuclei to form gibbsite. In the absence of nuclei, the unstable polymers slowly converted to stable polymers. The erratic stability of OH-Al solutions and gibbsite crystallization are therefore attributed to the relative magnitudes of these two reaction paths which, in turn, are attributed to two key factors: (1) the distribution of unstable vs. stable OH-Al polymers; and (2) the presence or absence of nuclei. The duration of aging of the parent solution governed the distribution of unstable vs. stable polymers. The rate of neutralization resulted in varying localized high alkalinity in OH-Al solution preparation and thus varying development of nuclei.

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.

A mineralogical investigation of the highly kaolinized Chanon granite and albite-muscovite granite of the Montebras cupola, Creuse, France, indicates that the magmatic stage was followed by two hydrothermal events related to successive cooling stages and by late weathering. The hydrothermal alteration was accompanied first by greisen formation and then a broad kaolinization process, which pervasively affected the granitic bodies. In the Chanon granite, the greisens are characterized by a trilithionite-lepidolite-quartz-tourmaline assemblage and are surrounded by concentric alteration zones. From the greisen to the fresh granite three zones were distinguished: (1) a zone characterized by secondary brown biotite (<400°C), (2) a zone characterized by secondary green biotite and phengite (300–350°C), and (3) a zone characterized by the presence of corrensite (180°–200°C) located around greisen veinlets. In the albite-muscovite granite the greisen is composed of lepidolite and quartz. This mineral assemblage was followed locally by Li-tosudite crystallization. During the second hydrothermal event (<100°C) an assemblage of kaolinite, mixed-layer illite/smectite (I/S), and illite formed pervasively and in crack fillings; the smectite layers of the US are potassic. Weathering produced Fe oxide and kaolinite. This kind of alteration developed mainly in the overlying Chanon granite. Here, Ca-Mg-montmorillonite formed in subvertical cracks, which transect the two granitic bodies, and hydrothermal I/S was obliterated by Ca-Mg-montmorillonite.

The hydrothermal parageneses were apparently controlled by magmatic albitization and the bulk chemistry of the two granitic bodies. The albitization, the formation of large micaceous greisens, and the successive recrystallizations of biotite (which was the most susceptible phase to alteration) provide information on the temperature range and chemical mobility during successive cooling stages. Si and Mg activities increased as the temperature of alteration decreased, and secondary Mg-biotite and Mg-phengite crystallized as long as the K activity was sufficient. The crystallizations of secondary biotite and phengite were followed by the crystallization of I/S during stages of low K activity. Secondary hydrothermal phases in the Chanon granite contain substantial Fe and Mg. Secondary hydrothermal phases in the albite-muscovite granite contain only small amounts of Fe and Mg, suggesting a lack of chemical exchange between the enclosing Chanon granite and the albite-muscovite granite, which is depleted in Fe-Mg-rich primary phases, such as biotite.

Several clay organic complexes were prepared by placing organic cations on the exchange sites of smectite clays and studied as sorbents for pentachlorophenol (PCP). The organic cations used ranged from very hydrophobic in nature (e.g., dioctadecyldimethyl+ (DODMA+)- and hexadecyltrimethyl+ (HDTMA+)-ammonium) to those having minimal hydrophobic properties, such as tetramethylammonium+ (TMA+). In general, the more hydrophobic the cation on the smectite the greater the uptake of PCP from water. For the very hydrophobic clays (DODMA+- and HDTMA+-smectite) the uptake of PCP was via non-polar interactions between the alkyl (e.g., -C18) groups on the organic cation and PCP. In a mechanistic sense, this interaction appeared to be similar to a partitioning process between water and the organic phase of the clay-organic complex. The organic phases of DODMA+-smectite were about 10 times more effective than the organic matter of natural sediments for removing PCP from water. For those organo-clays containing small organic cations (e.g., TMA+), the organic phase consisted of separate small organic moieties, such as the methyl group. This phase did not act as an effective partitioning medium despite a significant carbon content, and very little PCP was taken up. Results from this study suggest the possibility of treating soils and subsurface materials with large hydrophobic organic cations to enhance the sorptive properties of these natural materials.

An assemblage of clay minerals, Na-zeolites, Fe- and Sb-sulfides, and borates occurs in cavities in the basalt flow that underlies the main borax ore body exposed by the U.S. Borax open pit at Boron, Kern County, California. Analcime and saponite are widespread in cavities and fractures near the top of the basalt. Part of the basalt recently exposed, although restricted in distribution, contains a much more diverse assemblage of diagenetic minerals. Although only a few different minerals occur in each cavity, the composite order of deposition is: ferroan saponite, pyrrhotite, saponite, phillipsite, gmelinite, clinop-tilolite, herschelite, analcime, greigite, rhodochrosite, searlesite, borax, calcite, and colemanite. In some cavities early-formed zeolites appear to have dissolved as later ones crystallized.

Microprobe analyses of the zeolites yielded the following compositions: phillipsite, Na4.28K0.08(Al4.36-Si11.64O32)·xH2O (Si/Al = 2.67); gmelinite, Na6.64K0.10(Al6.80Si17.22O48· xH2O (Si/Al = 2.53); herschelite, Na2.96K0.24(Al3.21Si8.79O24)· xH2O (Si/Al = 2.75); clinoptilolite, Na6.48K0.56(Al7.15Si28.77O72) · xH2O (Si/Al = 4.02); analcime, Na14.02K0.09(Al13.33Si34.44O96)· xH2O (Si/Al = 2.58).

These zeolites formed by reactions between the basalt and evolving fluids, which were controlled by the development of an overlying, Na-borate lake. The wide distribution of saponite, analcime, and searlesite suggests that these minerals formed by the diagenetic reaction between basaltic glass and Na- borate water. The localized occurrence of the complex mineral assemblage, including some of the saponitic clay and the zeolites, phillipsite, gmelinite, and clinoptilolite, formed through a different process, perhaps deuteric or hydrothermal alteration of the basalt, before the lake developed. Because these zeolites are extraordinarily rich in Na, cation exchange may have taken place as the pore fluids became increasingly Na rich. In the latest stages of mineral growth, each of these zeolites was apparently partially dissolved and epitaxially overgrown by a second generation crystal, phillipsite on phillipsite, herschelite on gmelinite, and sodian heulandite on clinoptilolite.

Chromate (CrO42−) adsorption was investigated on kaolinite (0.2–2 μm) saturated with NaClO4 over a range of pH. Adsorption increased with decreasing pH because of protonation of chromate and/or variable charge sites on kaolinite. Chemical pretreatment to remove noncrystalline and crystalline oxide contaminants affected the magnitude of CrO42− adsorption, but not the pH range over which CrO42− adsorbed. Chromate adsorption at different sorbate and sorbent concentrations increased below the pHzpc for the kaolinite edge, suggesting the formation of weak surface complexes. If CrO42− and SO42− were present at equal concentration (5.0 × 10−7 M), the two solutes sorbed independently, suggesting binding to separate sites. The presence of excess SO42− (5.0 × 10−4 M), however, unexplainably enhanced CrO42− adsorption. The adsorption of both Chromate and sulfate can be described in terms of a site-binding model of the kaolinite edge, in which the edge is viewed as composite layers of Al and Si oxide. Surface complexation constants for CrO42− on kaolinite were similar to those for alumina, pointing to the importance of Al-OH edge sites in Chromate adsorption.

Atmospheric acidic deposition introduces hydrogen ions to terrestrial and aquatic ecosystems, which become partially neutralized by chemical weathering. In the southern Alps of Switzerland, small catchments containing little or no soil and lacking carbonate minerals represent sensitive hydrological settings in which the relationship between alteration of granitic gneiss by acid deposition and the resulting composition of lake waters can be studied. Transmission and scanning electron microscopy, coupled with X-ray powder diffraction of lake sediments from such areas showed mainly unaltered minerals from parent rocks and no secondary silicate minerals. Element mapping indicated noncrystalline aluminum hydroxide as a product of the chemical weathering of silicates. Noncrystalline iron hydroxide was also observed. Mass balance calculations and the stoichiometry of suitable chemical reactions representing the weathering processes were used to derive a plausible reaction sequence on the interaction of the predominant reactive rock minerals with acid precipitation that accounted for the measured chemical composition of the acid lakes.

X-ray powder diffraction (XRD), transmission electron microscopy, infrared spectroscopy, differential thermal analysis, and surface area (BET) measurements were employed to investigate the transformation of microcrystalline maghemite to hematite. At 500°C pure maghemite was completely altered to hematite in 3 hr, whereas maghemites containing small amounts (≤1%) of Co, Ni, Zn, Cu, Mn, Al, V, and Cr required much longer heating times. The maghemite-to-hematite transformation temperature varied from 540° to 650°C. XRD line widths suggest that each particle of maghemite and hematite may have been a mosaic of many independent, coherently diffracting crystals. The transformation of maghemite to hematite at 650°C was accompanied by a reduction in surface area due to sintering of particles.

Hypothetical model structures for magadiite and sodium octosilicate, based on the structure of the zeolite dachiardite, are proposed that consist of layers of 6-member rings of tetrahedra and blocks containing 5-member rings attached to both sides of the layers. The infrared (IR) and nuclear magnetic resonance spectra of magadiite and sodium octosilicate have features in common with spectra of zeolites in the ZSM-5 and mordenite groups. A peak at 1225 cm-1 in the IR spectra of magadiite and sodium octosilicate is characteristic of zeolites containing 5-member rings, such as ZSM-5- and mordenite-type zeolites. The defect structures of pentasil zeolites may therefore be akin to layered alkali metal silicates containing zeolite-like domains, in which part of the silanol groups from adjacent silicate layers are condensed (cross-linked) forming siloxane linkages.

The wetting contact angle was measured for water drops settled on the surface of pressed discs of kaolinite, alumina, bentonite, marble, montmorillonite, and quartzite immersed in hexane, octane, dodecane, cis-decalin, and air. Minimum and maximum values of the contact angle were obtained for the given systems of solid-water drop-hydrocarbon, depending on the manner of disc preparation. Using both minimum (θmin) and maximum (θmax) values of the contact angle, values of the dispersion component (γsd) of surface free energy of these solids were calculated from the equation which was derived on the basis of an equilibrium state of the system solid-water drop-hycrocarbon for two different hydrocarbons. The values of γsd for kaolinite, alumina, bentonite, marble, montmorillonite, and quartzite obtained from θmin are 83.5, 98.1, 98.9, 80.2, 95.9, and 89.7 mJ/m2, and from θmax are 73.1, 85.0, 84.4, 75.8, 85.5, and 75.5 mJ/m2. These values for marble and quartzite are similar to those in the literature (marble = 67.7 mJ/m2; quartzite = 71.3 and 76.0 mJ/m2). The values of the dispersion components of surface free energy for marble and quartzite covered with a water film (γsfd) were found to be: 41.8, 36.9; 49.2, 42.5; 49.6, 42.2; 40.2, 38.1; 48.1, 42.8; and 44.9, 38.0 mJ/m2, respectively. Values of γsfd for kaolinite, bentonite, and montmorillonite agreed well with those obtained from hydrocarbon adsorption isotherms determined by differential thermal analysis (35.5, 36.5, and 37.4 mJ/m2).

Using values of γsfd and contact angles measured in the system solid-water drop-air, the nondispersion component of the surface free energy of solids with adsorbed water film (γsfn) was calculated from the modified Young equation. The values of γsfn for kaolinite and quartzite are as follows: 55.8, 69.0; 85.6, 94.0; 52.1, 75.0; 64.7, 68.9; 54.9,71.3; and 59.2,74.4 mJ/m2. The values of the nondispersion components determined for kaolinite, bentonite, and montmorillonite agreed well with those obtained by differential thermal analysis (67.6, 78.3, and 65.5 mJ/m2, respectively). Further, based on the assumption that the adsorbed water film decreased the surface free energy of these solids by the value of the work of spreading wetting, the nondispersion component (γsn) of the surface free energy of the solids was calculated to be: 86.9,129.6; 169.5, 187.7; 67.1, 144.8; 117.5, 129.3; 83.0, 135.7 and 100.2, 143.4 mJ/m2. These calculated values of the nondispersion component of marble and quartzite surface free energy agree with those obtained from adsorption isotherms determined by chromatographic and differential thermal analysis (marble = 103.8, 106.4; quartzite = 112, 115, 153.6 mJ/m2).

Euhedral, pseudohexagonal nacrite was discovered as a thin layer coating a carbonaceous shale in the Sherwood Tunnel in Durban, Republic of South Africa. The nacrite apparently formed authigenically within a few weeks at ambient temperature by precipitation from pore solutions, probably as a result of evaporation. This observation suggests that nacrite can no longer be considered to indicate a high-temperature genetic environment. Precipitation from saturated pore solution may have been the mechanism of formation for this kaolin-mineral polymorph.

Cacoxenite having the composition (Al4.0Fe22.5O7.1(OH)14.3(PO4)17(H2O)23.7)·50.3H2O was identified in a bed of mature quartz sand in the Miocene Calvert Formation near Popes Creek, Maryland. This is the first reported occurrence of this mineral in Atlantic Coastal Plain sediments north of Florida. The cacoxenite occurs as silt-size to sand-size grains, both as irregularly shaped aggregates and as radiating arrays of delicate acicular crystals. The presence of discrete cores and overgrowths in some grains indicates at least two generations of crystal growth. Electron microprobe analyses reveal excess Si and Al (relative to the ideal composition), which is believed to reflect ultra-fine clay particles within the cacoxenite grains. Admixed clays probably served as a substrate for the formation of ferric oxyhydroxides, which were subsequently converted to cacoxenite through the addition of dissolved phosphorus.

To understand the genetic relationship between hisingerite material in the joints of an overlying grey basalt and nontronite and Fe-rich saponite in the joints and matrix of a more deuterically altered, underlying green basalt, the hisingerite material was treated in a series of hydrothermal experiments. No well-ordered clay mineral was produced at temperatures <340°C, although extended treatment for 445 days and at 110°C or 42 days at 180°C resulted in the formation of materials that gave broad, weak, basal X-ray powder diffraction (XRD) reflections characteristic of 2:1 phyllosilicates. Hematite did not form at 110°C, but it did form at 180°C in 1- and 6-week runs. Treatments at 340°C in Pt, Ag-Pd, and Au containers resulted in mixtures of Fe-rich saponite + hematite, but the same starting material treated at 340°C in stainless steel yielded, in addition, some chlorite, probably due to the more reducing conditions in the stainless steel container. Treatment of the unaltered grey basalt at 340°C and 50 MPa for 10 days resulted in complete alteration of olivine (and probably glass) to a trioctahedral smectite.

The Fe-rich saponite produced by the hydrothermal treatment of the hisingerite material has a composition and XRD pattern similar to the Fe-rich saponite found in the green basalt and an XRD pattern similar to that produced by the hydrothermal treatment of the grey basalt; thus these clays may have had a similar origin. The compositions and XRD patterns of these clays are not similar, however, to those of the nontronite in the joints of the green basalt. The nontronite probably formed during a subsequent low-temperature alteration.

The adsorption of tris(1,10-phenanthroline)-ruthenium(II) (Ru(phen)32+) by two kinds of colloidally dispersed clays, sodium montmorillonite and synthetic saponite, was studied by spectrophotometric and electron-optical methods. Montmorillonite adsorbed this complex stronger than saponite. The electronic spectrum measurements suggested that the electronic states of the complex were more perturbed on adsorption by montmorillonite than by saponite. High-performance liquid chromatography was attempted on an ion-exchanged adduct of optically active Ru(phen)32+ and these clays. 1,1′-Binaphthol was eluted with a 1:1 (v/v) water-methanol mixture as an eluent. The compound was resolved with a separation factor of 15 and 1.4 on the saponite and montmorillonite columns, respectively. If tris(acetylacetonato)-chromium(III) was eluted with water, the compound was resolved with separation factors of 1.9 and 11 on the saponite and montmorillonite columns, respectively. These separation tendencies were probably due to the difference in the external surface area and the density of the bound chelates.

The transformation of hausmannite (Mn3O4) into a K-bearing, 7-Å phyllomanganate (K-birnessite) in KOH was followed using X-ray powder diffraction and transmission electron microscopy. The transformation involved dissolution of Mn3O4 followed by reprecipitation of the 7-Å phase. The rate-determining step was the dissolution of Mn3O4. The reaction was accelerated by increasing the pH and/or the temperature of the system.

K-birnessite precipitated initially as thin, irregular plates and films that gradually recrystallized to thicker, more structured plates and laths. A pseudohexagonal unit cell with a0 = 2.87 Å and c0 = 7.09 Å was found for this phase. Synthetic K-birnessite was stable in KOH at 70°C for many months. In neutral to slightly acidic media it converted rapidly to Mn7O13•5H2O, and in more acid media, it dissolved and reprecipitated as γ-MnO2. The replacement of K+ by Na+ was not achieved. Jacobsite and magnetite also underwent a dissolution/reprecipitation transformation in KOH.

Lithium-bearing donbassite and tosudite were found in veins in hydrothermally altered granite (Beauvoir granite) in the northern part of the Massif Central, France. The two minerals are characterized by their high Li contents and low Mg and Fe contents; their structural formulae are: $${\left( {S{i_{3.81}}A{l_{0.19}}} \right)_{\Sigma = 4.00}}{O_{10}}{\left( {A{l_{3.81}}L{i_{0.52}}Fe_{0.01}^{2 + }C{a_{0.02}}M{g_{0.01}}} \right)_{\Sigma - 4.38}}{\left( {OH} \right)_8}{\left( {N{a_{0.07}}{K_{0.04}}} \right)_{\Sigma = 0.11}}$$ for donbassite and $${\left( {S{i_{3.50}}A{l_{0.50}}} \right)_{\Sigma = 4.00}}{O_{10}}{\left( {A{l_{2.95}}L{i_{0.22}}Fe_{0.01}^{3 + }T{i_{0.01}}} \right)_{\Sigma = 3.19}}{\left( {OH} \right)_5}{\left( {C{a_{0.01}}N{a_{0.15}}{K_{0.18}}} \right)_{\Sigma = 0.34}}$$ for tosudite.

These chemical compositions indicate that the donbassite is an intermediate member of the donbassite-cookeite solid solution series and that the tosudite consists of interstratified Li-donbassite and beidellite. Both Li-bearing minerals show thermal behavior distinct from those previously reported for dioctahedral chlorite and tosudite.

Petrographie investigation of drill cuttings from the Echassières area indicates that the two minerals were formed in an intermediate stage of hydrothermal alteration following an early stage characterized by formation of muscovite (2M1) at >350°C and before the latest stage characterized by deposition of kaolinite and randomly interstratified illite/smectite at < 100°C. Moreover, tosudite occurs in the upper part of the granite, whereas donbassite is restricted to the lower part, suggesting the formation of tosudite at lower temperatures.

X-ray powder diffraction (XRD) patterns for many interstratified mica/glycolated smectites were calculated by changing combinations of probabilities and transition probabilities of two-component layers. Three basal XRD reflections, 5. l°–7.6°2θ (p1), 8.9°–10.2°2θ (p2), and 16.1°–17.2°2θ (p3) were selected for the quantification curves. A distinct relationship exists between Δ2θ, (p2–p1) and Δ2θ2 (p3–p2) which shows systematic changes with expandability at constant Reichweite values. The calculated values were plotted with Δ2θ1 and Δ2θ2 as the axes of coordinates, and quantification curves were calculated. The components and stacking parameters of mica/smectites were estimated easily using this diagram. Probabilities of existence of component layers and their transition probabilities for Reichweite (R=0) and (R=l) structures, and special cases of R=2 and R=3 structures were obtained.

Transmission electron microscopy suggests that biotite transforms to vermiculite primarily by direct structural modification, involving the replacement of K+ by hydrated interlayer cations, and only minor reorganization of the 2:1 layer. A second relatively uncommon mechanism appears to involve redistribution of components from two biotite sheets to form a single vermiculite layer. Distortion of the surrounding structure initially inhibits growth of vermiculite in the surrounding biotite, and promotes the propagation of vermiculite layers in opposite directions. This phenomenon may contribute to the development of relatively regular, widely spaced interstratifications of biotite and vermiculite. Additional components and space are provided by the dissolution of biotite where access of solutions is greater.

During weathering, biotite and vermiculite become increasingly replaced by kaolinite, which crystallizes epitactically onto existing layers, and goethite, which develops from a poorly crystalline iron oxyhydroxide precursor to form oriented laths. In areas parts of strongly weathered samples kaolinite and goethite appear to develop in proportions consistent with a reaction that conserves both Al and Fe.

Crystal growth theory was applied to describe edge sites of phyllosilicates. Three face configurations were found to exist. One face has one tetrahedral site per tetrahedral sheet and two octahedral one-coordinated sites per crystallographic area ac sin β, where a and c are layer dimensions and β is the angle between them. The other two faces are similar except that they have one less octahedral site which is replaced by one SiIV-O-AlVI site in this same ac sin β area. A transfer of bonding energy from the remaining octahedral site to the SiIV-O-AlVI site is believed to neutralize all edge charge on faces containing these latter sites at normally encountered pHs (pH 3–9). A similar charge rearrangement along the edges results in an apparent decrease in the permanent charge of the mineral with an increase in edge area.

On the basis of such an analysis, lath-shaped illite can be described as a very fine grained dioctahedral mica in which the apparent deficient occupancy of the octahedral sheet, presence of excess water, and measurable cation-exchange capacity may in part be the result of a large ratio of edge area to total volume, with no other chemical or structural change in the mica layers. The increasing importance of edge charge relative to layer charge produces erroneous formulae for 2:1 phyllosilicates in very fine grained samples containing fewer than 2 of 3 octahedral sites occupied by cations, on the basis of a 22-charge half cell.