The 16-8-, 8-5-, 5-2-, 2-1-, 1-0.5-, 0.5-0.3-, 0.3-0.1-, and <0.1-μm size fractions were centrifuged from a Georgia (U.S.A.) sedimentary kaolin and a hydrothermal kaolin from the Sasso mine (Italy) and analyzed by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), infrared spectroscopy (IR), differential thermal analysis (DTA) and thermogravimetry (TGA) together with the corresponding whole rocks. All size fractions of the Georgia sample consisted dominantly of well-crystallized, fine-grained kaolinite, associated with minor quantities of smectite. Some halloysite-like elongate particles were noted by SEM in the intermediate size fractions, minor amounts of quartz were identified in the coarsest size fractions, and < 1% noncrystalline material and traces of organic material were suspected in the finest size fraction. The crystallinity of the kaolinite as measured by XRD and IR varied moderately with size. IR suggested that nacrite-like stacking disorder increased with decreasing size for particles < 5 μm in size.

In the Sasso sample kaolinite dominated all size fractions and was accompanied by dickite in the coarse and by halloysite in the fine size fractions. Regular mixed-layer illite/smectite (I/S) was present in all size fractions and dominated in the finest. Abundant quartz and traces of alunite were identified in the whole rock and coarsest size fractions. The kaolinite in this sample showed marked variation in stacking order and crystallinity, as shown by changes in XRD, IR, and DTA patterns.

The observed compositional and structural variations in the size fractions of the Georgia sedimentary kaolin are small, as expected from formational environment, which was characterized by low temperatures and relative stable genetic conditions. The much more marked differences in composition within the size fractions of the Sasso hydrothermal kaolin are likely a result of the broad range of temperatures and fluid chemistry of its formational environment. The sequence dickite-well-crystallized kaolinite-kaolinite-halloysite is probably temperature-dependent.

The first stage of lateritic weathering of pyroxenes in the Niquelandia area, Brazil, leads either to Fe-rich products or to a phyllosilicate clay. In relatively unfractured parent rock the phyllosilicate clay contains Ni-rich smectites, the atomic ratio of Ni: octahedral cations ranging from 0.3 to 0.5. These smectites were studied by polarized light microscopy, X-ray powder diffraction (XRD), transmission electron microscopy, and electron microprobe, and infrared, optical absorption, Mössbauer, and extended X-ray absorption fine-structure (EXAFS) spectroscopy. The chemical composition of the smectite is constant on the optical microscope scale even to the smallest analyzed particles (3000 A in diameter and about 75 Å thick). From XRD data the mineral is principally a swelling, trioctahedral smectite; however, some kerolite-pimelite-like layers are present, and a weak 06,33 reflection indicates the presence of a small amount of a dioctahedral phase. Mössbauer results show that all Fe cations are Fe3+ in octahedral sites. The structural formula of the smectite is: (Ca0.01K0.05)(Al0.17Fe0.5Mg0.48Ni1.47Cr0.02)(Si3.92Al0.08)O10(OH)2

The results obtained from all the above methods suggest that in the smectites Ni, and, perhaps, a small amount of Mg are clustered in pimelite-like domains (or layers), whereas Fe and some Al are clustered in nontronite-like domains (or layers). Most selected-area electron diffraction patterns exhibit continuous or punctuated (hk) rings, indicating that particles contain several stacked layers. The patterns of some thin particles, however, suggest dioctahedral layers having trans-octahedral vacancies, such as in the Garfield, Washington, nontronite. Thus, the Ni-Fe-Mg-smectite, which seemingly is homogeneous, actually consists of mixed trioctahedral and dioctahedral layers or domains.

Pillaring of montmorillonite and beidellite with aluminum polyhydroxypolymer takes place first by the saturation of the cation-exchange capacity by monomeric and/or dimeric aluminum hydroxide species and then the intercalation of the so-called Al13-polyhydroxypolymer. The clay slurry must have a solid concentration greater than 0.01% (w/w) to produce a basal spacing of about 18 Å. Sizeable clay tactoids must therefore exist in the slurry in order to produce a turbostratic structure ordered along the c axis. The main difference between pillared montmorillonite and pillared beidellite seems to be a more ordered distribution of pillars within the interlamellar space of the clays that are rich in tetrahedral substitutions. Recent 27Al and 21Si high-resolution nuclear magnetic resonance data suggest that this higher degree of ordering results from the reaction of the aluminic pillars and the clay sheet near the sites of the tetrahedral substitutions.

Several new minerals, structurally and chemically similar to the hydrotalcite-manasseite group, have been found in the saline deposits of the central pre-Caspian depression and in those of Middle Asia. Their structures consist of layers of (Mg1-xAlx)(OH)2 plus interlayers of anions and molecular water. In addition to manasseite itself, [(Mg4Al2)(OH)12][(CO3)-3H2O], having unit-cell parameters of a = 3.042, c = 2 × 7.56= 15.12 Å and a calculated density of Dc = 2.15 g/cm3, other varieties were identified whose interlayers contain alternately SO42− or SO42− and CO32− anions. The following new phases were recognized: (1) an 8.85-Å phase having the composition [(Mg4Al2)(OH)12][(SO4)·3H2O], subcell dimensions of a' = 3.04, c' = 8.85 Å, and Dc = 1.96 g/cm3; (2) an 11-Å phase having the composition [(Mg3.96Fe0.06Al1.98)(OH)12][Na0.56(SO4)1.30·7.3H2O], hexagonal unit-cell parameters of a = √3 · 3.042 = 5.28 Å, c = 11.16 Å, and Dc = 1.90 g/cm3; (3) a 16.5-Å mixed-layer phase having the composition [(Mg4Al2)(OH)12][(SO4)0.5(CO3)0.5·3H2O] and an ordered ABAB... alternation of 7.56-Å layers (i.e., a brucite-like layer + a CO32−-containing interlayer) and 8.94-Å layers containing SO42− anions in interlayers; this phase has unit-cell dimensions of a' = 3.05, c' = 16.5 Å and Dc = 2.06 g/cm3; and (4) an 18.5-Å ordered mixed-layer phase having the ideal composition [(Mg8Al4)(OH)24][M+0.5(SO4)1.25(CO3)1.0·9H2O] and an alternation of 7.56-Å, CO3-containing layers and 11-Å layers having SO42− anions and Na and Mg cations in interlayers (M+0.5 corresponds to interlayer cations). This last phase has unit-cell dimensions of a = 3.046, c = 3 × 18.54 = 55.62 Å and Dc = 1.99 g/cm3. Some of the varieties containing SO42− in the interlayers swelled with ethylene glycol or glycerol.

For this diverse family of minerals whose structures are based on brucite-like layers of the composition (R2+1-xR3+x)(OH)2, a unifying system of nomenclature is offered for consideration. In describing these brucite-like structures intercalated with anion- and cation-containing interlayers, the composition of the hydroxide sheet and the interlayers, the periodicity of the layers, and the mixed-layer nature of the material should be described. By means of symbols, a single term might be used to describe the crystal chemistry of any member of the group having a given cation composition for the brucite-like layers, for example, manasseite, a 2H polytype of hydrotalcite that has a repeat distance of 7.56 Å and CO3-containing interlayers, might be designated as 7.56-Å CO3-hydrotalcite-2H.

The weathering of eastern Australian basalts, sampled from the rounded, hard, core-stone to the rind of softer weathered material, has been examined by bulk chemical analyses, thin section petrography, electron microprobe, and X-ray powder diffraction analyses. Using density as a measure of weathering intensity, data from four core-stones show that at a stage of weathering in which the total loss due to dissolution is – (i.e., at the core-stone rim), the percentages lost of the following major elements are: Ca, 85; Mg, 80; Na, 70; K, 50–80; P, 55; Si, 45; Mn, 40; Al, 5; Fe, 0; and Ti, 0. With more intense weathering, deposition of some elements, particularly rare earths and Ba, and mobilization and deposition of Al and Fe make quantification impossible. The rate of weathering of individual minerals is consistent with the well-known susceptibility series: glass ∼ olivine > plagioclase > pyroxene > opaque minerals. Clay minerals in the core-stones are dominated by smectites, whereas those in the surrounding more intensely weathered rinds are dominated by halloysite and goethite.

Wyoming bentonite, Fithian illite, and basalt from the Umtanum Formation, Washington, were treated hydrothermally at 200° to 460°C and 260 to 500 bars for 71 to 584 days. No change was detected for the bentonite and basalt, except for the loss of calcite and exchange of Ca for K in the smectite and the growth of a small amount of smectite (presumably from a glass phase) in the basalt. Calcite in the initial bentonite may have stabilized the smectite by Ca/K exchange; thus, if the latter is used as a packing material in a nuclear waste repository, limestone should be added. No change was detected in the illite samples treated <300°C; however, at 360°C, euhedral crystals of berthierine and illite grew at the expense of original illite/smectite, apparently by a solution-crystallization process. Significant changes involving the dissolution of starting phases and the formation of illite and chlorite were also detected in mixtures of basalt and bentonite at 400°C; at temperatures <400°C, no changes were observed.

The newly formed mineral phases (berthierine, illite, and chlorite) observed by transmission electron microscopy showed euhedral to subhedral shapes. These shapes are the same as those observed in hydrothermally altered sediments from the Salton Sea field and different from those from burial metamorphic environments, such as Gulf Coast sediments. The reaction mechanism is apparently the dissolution of reactants followed by the crystallization of products from solution, without conservation of structural elements of the reactants. Reactions apparently required temperatures greater than those for analogous changes in nature, suggesting that the degree of reaction was controlled by kinetics. The lack of dissolution in experimental runs at low temperatures, however, does not necessarily imply long-term stabilities of these clay minerals.

Beidellite was synthesized hydrothermally from a noncrystalline gel at 320°C and 130 bar pressure. The beidellitic character of the product was verified by infrared spectroscopy on the NH4+-exchanged form. Intercalation was achieved with hydroxy-aluminum solutions having different OH/Al molar ratios. The solutions were investigated by several methods, including 27Al nuclear magnetic resonance. Essentially, two Al species were detected: monomelic Al and a polymerized form containing Al in four-fold coordination. This latter species was found to be selectively fixed in the interlamellar region, which resulted in a stable spacing of 18 Å at 110°C and 16.2 Å at 700°C. The pillared beidellites had specific surface areas of > 300 m2/g, mainly due to micropores. Both Brönsted and Lewis acid sites were evidenced by infrared spectroscopy using pyridine as a probe molecule.

Yucca Mountain is being studied as a potential site in southern Nevada for an underground, high-level nuclear waste repository. A major consideration for selecting this site is the presence of abundant zeolites in Miocene ash-flow tuffs underlying the region. Beneath Yucca Mountain four diagenetic mineral zones have been recognized that become progressively less hydrous with depth.

Zone I, the shallowest zone, is 375–584 m thick in the central part of Yucca Mountain, but 170 m thick to the north. Zone I contains vitric tuffs that consist of unaltered volcanic glass and minor smectite, opal, heulandite, and Ca-rich clinoptilolite. Zone II thins south to north from 700 to 480 m and is characterized by complete replacement of volcanic glass by clinoptilolite with and without mordenite, and by lesser amounts of opal, K-feldspar, quartz, and smectite. Zone III thins south to north from 400 to 98 m thick and consists of analcime, K-feldspar, quartz, and minor calcite and smectite. Heulandite occurs locally at the top of zone III in the eastern part of Yucca Mountain. Zone IV occurs in the deepest structural levels of the volcanic pile and is characterized by albite, K-feldspar, quartz, and minor calcite and smectite.

Clinoptilolite and heulandites in zone I have uniform Ca-rich compositions (60–90 mole % Ca) and Si:Al ratios that are mainly between 4.0 and 4.6. In contrast, clinoptilolites deeper in the volcanic sequence have highly variable compositions that vary vertically and laterally. Deeper clinoptilolites in the eastern part of Yucca Mountain are calcic-potassic and tend to become more calcium-rich with depth. Clinoptilolites at equivalent stratigraphic levels on the western side of Yucca Mountain have sodic-potassic compositions and tend to become more sodium-rich with depth. Despite their differences in exchangeable cation compositions these two deeper compositional suites have similar Si:Al ratios, generally between 4.4 and 5.0. Analcimes have nearly pure end-member compositions, typical of these minerals formed by diagenetic alteration of siliceous volcanic glass; however, K-feldspars are Si-rich compared to the ideal feldspar formula.

Bulk-rock contents of Si, Na, K, Ca, and Mg of zeolitic tuffs generally differ significantly from stratigraphically equivalent vitric tuffs, suggesting that zeolite diagenesis took place in an open chemical system. Both the whole rock and the clinoptilolite are relatively rich in Ca and Mg in the eastern part of Yucca Mountain and rich in Na in the western part. The Ca- and Mg-rich compositions of the zeolitized tuffs in the eastern part of Yucca Mountain may be due to cation exchange by the sorptive minerals with ground water partially derived from underlying Paleozoic carbonate aquifers.

Diagenetic zones become thinner and occur at stratigraphically higher levels from south to north across Yucca Mountain, probably due to a higher geothermal gradient in the northern part of the area. The diagenetic zones were established when the geothermal gradient was greater than it is today, probably during the thermal event associated with the development of the Timber Mountain-Oasis Valley caldera complex north of Yucca Mountain.

The rate of sorption of methanol (MeOH), propan-2-ol (i-PrOH), and 2-methyl-propan-2-ol (t-BuOH) onto a Wyoming montmorillonite saturated with Al3+-, Cr3+-, or Fe3+-cations has been studied by isothermal gravimetry in the temperature range 18°–105°C using samples of differing weights and grain-size distributions. The rate of sorption for all the alcohols increased with decreasing sample and grain size, demonstrating that inter-, rather than intraparticle mass transfer was the rate-limiting process. Optimization of the sample parameters (2 mg sample of < 45-μm grain size, pretreated at 120°C yielded integral diffusion coefficients at 18°C of 1.1 × 10−4 m2/s for t-BuOH for the Cr3+-form and 2.0 × 10−14 m2/s for MeOH and i-PrOH for the Al3+-form. In general, the rate of alcohol sorption decreased as MeOH ≥ i-PrOH > t-BuOH, but no temperature dependence of the sorption rate was observed. The alcohol sorption rate was dependent on the cation present, with Fe3+ < Cr3+ < Al3+.

The formation of iddingsite by the oxidative weathering of Fo80 olivine begins by solution of Mg from planar fissures, 20 Å wide and spaced 200 Å apart, parallel to (001). Oxidation of Fe within the remaining olivine provides nuclei for the topotactic growth of goethite. Cleavage cracks < 50 Å in diameter allow Na, Al, and Ca from adjacent minerals, particularly plagioclase, to enter the altering olivine while Mg and Si diffuse away. In the early stages of weathering, strips of Fe-rich smectite (saponite), 20–50 Å wide and 1–7 layers thick, form bridges 50–100 Å long across the planar fissures. Dioctahedral smectite crystallizes on the margins of wider cleavage-controlled fissures; with further weathering halloysite is formed away from the fissure walls. In the ultimate stages of alteration, the saponite and dioctahedral smectite are lost, leaving a porous, oriented aggregate of goethite crystals each measuring about 50 × 100 × 200 Å (X, Y, Z, respectively), with sporadic veins of halloysite crossing the pseudomorph.

The 57Fe Mössbauer spectra of an iron-rich montmorillonite, an illite, and two glauconites were measured and computer-fitted with appropriate Fe3+ and Fe2+ doublet resonances. The broad experimental Fe3+ resonance of montmorillonite probably arises from Fe3+ in the octahedral sites and a trans-arrangement of OH groups; however, a large variation in the neighboring environment of these sites exists. In illite this Fe3+ resonance is similar but shows less broadening; it arises from Fe3+ located predominantly in trans-OH octahedral sites, with some Fe3+ being located in cis-OH octahedral sites. Because of the increased iron content less variation exists, compared with montmorillonite, in the neighboring octahedral sites. The Fe3+ resonance is narrower still for the glauconites and represents Fe3+ substituting primarily into cis-OH octahedral sites, similar to that previously reported for nontronite.

The tetrahedral Fe3+ content is very low for montmorillonite and increases progressively for illite and glauconite, suggesting that a higher tetrahedral Fe3+ content directs Fe3+ in the octahedral layer into cis-OH sites. In montmorillonite, the Fe2+ is located only in trans-OH sites; in illite Fe2+ is largely in trans-OH sites and only slightly in cis-OH sites; and in glauconite, Fe2+ is located largely in cis-OH sites and only slightly in trans-OH sites. These assignments suggest that for Fe2-, the doublet with the larger quadrupole interaction arises from Fe2+ in trans-OH sites and the doublet with the smaller quadrupole interaction, from Fe2+ in cis-OH sites.

In the presence of Mn(II), ferrihydrite transforms into Mn-goethite and/or jacobsite. Chemical analysis showed that as much as 15 mole % Mn replaced Fe in the goethite structure. If Mn(III) replaced Mn(II), the formation of jacobsite was suppressed; ferrihydrite transformed into Mn-goethite, and, at high Mn(III) concentrations, a 7-Å phyllomanganate. Low levels of Mn(II) retarded the transformation of ferrihydrite only slightly, whereas in an Mn(III) system the nucleation and growth of Mn-goethite were both hindered. Mn-goethite nucleated in solution, whereas jacobsite appeared to form by interaction of dissolved Mn(II) species with ferrihydrite. Mn suppressed the formation of hematite in these systems; however, Mn-hematite containing as much as 5 mole % Mn was induced to form at pH 8 by adding oxalate to the system. Transmission electron micrographs showed that goethite crystals grown in the presence of Mn were long (≤2 μm) and thin and commonly contained etch pits. The presence of Mn appears to have promoted twinning.

The continuous conversion of smectite to illite in samples from the Shinzan hydrothermal alteration area of Japan has been examined by X-ray powder diffraction (XRD) and transmission (TEM) and analytical transmission electron microscopy (AEM). TEM shows that randomly interstratified illite/ smectite (I/S) containing 100-50% expandable layers exhibits a flakey shape, whereas regularly and partially ordered interstratified I/S having 50-0% expandable layers exhibits a lath-like habit. An early- formed lath of regularly interstratified I/S is typically <35 Å in thickness and 300–500 Å in width; these dimensions gradually increase with decreasing percentage of expandable layers. XRD shows that the lathshaped I/S has a 1M polytype mica structure. AEM shows that the interlayer K content of flakey I/S increases monotonously with decreasing percentage of expandable layers in the range 100-50% expandable layers, whereas the interlayer K content of lath-shaped I/S increases along a different trend from that for the flakey I/S in the range 50-0% expandable layers. These observations suggest that randomly interstratified I/S is fundamentally smectite that is undergoing K-fixation and dissolution and that regularly and partially ordered interstratified I/S are immature illite which is still growing. Consequently, they suggest a mechanism for the hydrothermal smectite-to-illite conversion that is based on the K-fixation in and dissolution of smectite and the precipitation and growth of thin illite particles. Furthermore, these data suggest that the kinetics of smectite dissolution and illite growth are the most important factors controlling the smectite-to-illite conversion.

Solutions containing hydroxy-SiAl (HSA) oligocations were prepared by two procedures: (1) treatment of a mixture of orthosilicic acid and AlCl3 with aqueous NaOH, followed by aging of the product; and (2) preliminary preparation and aging of hydroxy-Al13 oligocations followed by reaction of the latter with orthosilicic acid. Ion exchange of Na,Ca-montmorillonite with HSA oligocations yielded pillared, cross-linked montmorillonites (designated as HSA-CLM) showing a maximum d(001) value of 19.5 Å for air-dried samples, and maximum surface areas of ~500 m2/g after outgassing at 250°C/10−3 torr. Corresponding ion exchange of Li-fluorhectorite yielded HSA fluorhectorites (HSA-CLFH) showing a maximum d(001) value of 19.0 Å and a surface area of 355 m2/g. Calculated structural formulae for the HSA-CLM and HSA-CLFH products, based on elemental analysis, showed a gradual increase in the Si/Al ratio in the intercalated HSA oligocations with increasing Si/Al ratio in the pillaring solution. Optimum d(001) values and surface areas of HSA-CLM and HSA-CLFH products were obtained using method 2 and applying a ratio of 1.6–2.5 mmole (Si)Al/g smectite.

The thermal stabilities of HSA-CLM and HSA-CLFH products were determined by heat treatment between 250° and 700°C and subsequent measurement of the d(001) values and surface areas. HSA-CLFH products showed the unusual behavior of increase of d(001) with increase in temperature from 400° to 500°C, and essential constancy of d(001) from 500° to 600°C. The HSA-CLM products showed a gradual decrease in surface area, whereas the HSA-CLFH products prepared with a Si/Al ratio of 1.04–2.18 in the pillaring solution showed constant surface areas with increasing temperature from 250° to 600°C. HSA-CLM and HSA-CLFH show sharply higher acidities compared with those of reference Al-CLM and Al-CLFH samples obtained by pillaring with hydroxy-Al13 oligocations. This increased acidity is probably due to the presence of acidic, surface silanol groups in the HSA oligocations.

The Excello Shale is one of the best exposed and most laterally continuous of the Pennsylvanian cyclothemic black shales in the midcontinent region of the United States. Its petrology and paleoenvi-ronmental significance were studied to understand the nature of cyclic black shales in general and how they relate to the habitat of hydrocarbon source beds. The Excello is thinly laminated, fissile where weathered, and rich in organic matter and phosphate nodules; it is 90–120 cm thick. Its thin laminations, fine particle size, and high total organic carbon (TOC) content suggest that it was deposited in a quiet water environment of an epeiric sea having anaerobic bottom water. The Excello Shale consists of two lithofacies: non-bioturbated black shale and bioturbated yellow-brown shale. Petrographic studies show that the black shale contains wavy to straight laminations and that the yellow-brown shale contains discontinuous and random laminae and mottled stratification. The close association of organic matter and phosphate-controlled nodule morphology (spherical, elongated, bladed, and platy) appear to be related to progressive decreases in nutrient supply of the sea water from the ancient ocean (Panthalassa).

Clay-mineral assemblages consist mainly of detrital illite, kaolinite, chlorite, and illite/smectite (I/S). Grain size and amount of these clays increase and TOC decreases shoreward towards the probable source areas of the clay minerals in the northern Ouachita region and northern Iowa. Quartz, carbonate-fluor-apatite, carbonate fossil fragments, and minor feldspar and pyrite are the principal minerals in the Excello Shale. Minor amounts of fine-silt-size carbonate minerals are present in some samples. Limestone concretions, 90–150 cm in diameter and 30 cm thick, were found at only one locality in Missouri where the Excello is a maximum of about 3 m thick. Fissility increases with weathering along the bedding plane, and laminae are separated by a limonite film. Four petrographically distinct microfabric variations of the Excello Shale appear to be related to the TOC content and bioturbation. Textural and structural properties of the shale are more developed with increasing organic matter content.

The transformation of ferrihydrite to goethite and/or hematite in alkaline media is strongly retarded by the presence of silicate species. These species probably stabilize ferrihydrite by adsorbing on the particles of ferrihydrite and linking them into an immobile network.

At concentrations low enough for the transformation to proceed, silicate species promote the formation of hematite and hinder the nucleation of goethite. The presence of silicate species modifies the morphology of both reaction products. Hematite forms ellipsoidal single crystals, commonly displaying outgrowths of goethite. Silicate species in solution appear to enhance the development of the (021) faces of goethite, probably by preferential adsorption on these faces; at high levels of silicate species, goethite crystals adopt a pseudohexagonal habit. This morphology has not been observed previously for goethite.

If anilinium ions are intercalated into Llano vermiculite, the stacking order of adjacent silicate layers is increased, resulting in a relatively sharp single crystal X-ray diffraction (XRD) pattern. The packing of intercalated organic members forms a superstructure and produces bonding from layer to layer which favors the stacking order. Superlattice reflections occur which, although sharp in the a*b* plane, are streaked along c*. Apparently there is little coherence between adjacent layers of ordered organic units.

A three-dimensional set of XRD reflections for a triclinic sub-cell having the following lattice parameters was measured: a = 5.326(3), b = 9.264(4), c = 14.82(5) Å, α = 90.31(7), β = 96.70(6), and γ = 89.55(5)°. In this unit cell (symmetry Cl), ditrigonal cavities in adjacent silicate layers are approximately opposite. Differential Fourier analyses and least-squares refinements showed that the principal axes of the anilinium ions, i.e., N-C(1)-C(4), are nearly perpendicular to the silicate layers. The planes of the aromatic rings, however, are about ±30° to X, neither parallel nor perpendicular to that direction, as indicated by earlier studies.

Inorganic cations and water molecules are also present in the interlayer; the former and some of the latter occupy sites near the middle of the layer. Anilinium-rich and anilinium-poor domains coexist. In the latter, the cation-water system predominates and apparently conforms to the superstructure. Although the cation-water structure could not be uniquely established from the reflections produced by the sub-cell, possible positional coordinates were obtained. From structural data for the silicate layers, no evidence was found for long-range Si/Al ordering in the tetrahedral sites.

The rate of vapor-phase sorption of tetrahydrofuran (THF), tetrahydropyran (THP), and 1,4-dioxan (DIOX) onto a Wyoming montmorillonite saturated with Al3+ or Cr3+ has been studied by isothermal gravimetry in the temperature range 18° to 105°C using samples of different weights and grain-size distributions. The rate of sorption for all the cyclic ethers increased with decreasing sample and grain size, demonstrating that inter-, rather than intraparticle mass transfer was rate-determining. Optimization of the sample parameters (2 mg sample of <45-μm grain size, pretreated at 120°C yielded integral diffusion coefficients at 18°C of 0.5 × 10−14 m2/s for DIOX for the Cr3+-clay to 3.5 × 10−4 m2/s for THF for the Al3+-clay; however, no temperature or cationic dependence of the cyclic ether uptake was observed. In general, the rate of sorption of the cyclic ethers increased as THF ≥ THP > DIOX indicating that the sorption rate of THF and THP was dependent on concentration or that DIOX sorption was retarded by bidentate coordination to aluminum ions at the edges of the clay platelets.

Dilute aqueous solutions of quinoline were contacted with Na-montmorillonite to elucidate the sorption process of the neutral and protonated species. Sorption occurs via a combination of ion exchange and molecular adsorption and yields S-type isotherms. Exchange between the quinolinium ion (QH+) and Na can be described by means of Vanselow selectivity coefficients and a thermodynamic exchange constant (Kex). Due to the apparent adsorption of the neutral species at high mole fractions (x) of the solid phase, the thermodynamic standard state was defined as 0.5 mole fraction. The selectivity at pH ~4.95 of the QH+ species over Na (at XQH+ = 0.5) was determined to be Kv = 340. At pH ≥ 5.5 surface mole fractions of 0.5 could not be obtained without adsorption of the neutral species. This study suggests that at dilute solution concentrations quinoline is sorbed preferentially as the cation even at pHs ≫ pKa. A critical surface-solution concentration is apparently necessary for adsorption of the neutral species.

High-resolution transmission electron microscopy of noncrystalline Fe-Si-Al-oxyhydroxide gels shows a common structure of hollow packed spheres having external diameters ranging from 50 to 1000 Å. Some sphere walls display a concentric structure, particularly if the gel composition is close to that of a crystalline clay mineral (e.g., smectite, kaolin). The spheres probably formed by expansion of void space (bubbles) as the surrounding gel contracted 5–10% because of partial ordering of the Fe-Si-Al-oxygen network. Much of the water contained in such noncrystalline minerals is incorporated within the bubbles.