In the nearly 2000 occurrences of zeolites in sedimentary rocks of volcanic origin about 15 zeolite minerals have been identified. The mode of occurrence of six of these, clinoptilolite, erionite, chabazite, phillipsite, analcime, and mordenite, is described, and their morphology is illustrated with scanning electron micrographs.

SEM, TEM, and electron probe studies indicate that the anatase in Georgia kaolins, and probably anatase in general, consists of subspherical particles (TiO2 pellets) 0.05–0.1 µm dia. Some pure anatase aggregates may be pseudomorphic after ilmenite and have a tabular shape, but much of the anatase is formed from Ti that occurs as scattered ions in the octahedral sheets of biotite. When removed from the biotite this material forms TiO2 pellets. These pellets can occur as: single pellets; irregular aggregates; layered aggregates; spherical aggregates; mixed aggregates (with kaolinite); coated aggregates (with kaolinite). Physical energy can be used to break TiO2—kaolinite aggregates, separate single TiO2 pellets from kaolinite plates and remove kaolinite coatings from TiO2 aggregates.

Al and Si are present in all TiO2 aggregates and the Si—Al ratio is lower in the aggregates than in the kaolinite. An amorphous Si—Al compound may be present and act as a cement.

The anatase apparently is formed from Ti that is released from the parent mineral as Ti (OH)4. The Ti (OH)4 precipitates to form an amorphous hydrous oxide gel which dehydrates to form a granular aggregate of small anatase crystals.

Scan electron micrographs are shown of (1) kaolinite and dickite which crystallized from solution within cavities, (2) kaolinite weathered from clastic primary silicate material, (3) residual kaolinite from primary silicate rock, (4) kaolinite above and below a basal unconformity on granitic rock, and (5) hydrothermally altered kaolinite. The texture of kaolin reflects the environment in which the clay was formed.

Euhedral crystals of kaolin minerals characterize cavity fillings. The weathering environment produces large crystal flakes of kaolinite, expanded books, mats of elongates, high porosity, and low bulk density (less than 2.0). The hydrothermal environment produces smaller crystals, singles, sheaves and packets of crystals, low porosity and high bulk density (2.0 and above).

The interrelationships of genetic environment of kaolin minerals and accompanying texture are discussed in light of available geochemical information.

Mössbauer and i.r. spectra of a series of nontronites show that Fe3+ and Al3+ are distributed between tetrahedral and octahedral sites. The Mössbauer results have reaffirmed the occupation by Fe3+ of octahedral sites at which these ions are coordinated to pairs of OH groups in both cis and trans configurations. The distribution of Fe3+ between these two sites varies considerably but in all of the nontronites some Fe3+ occurs in the trans site in contrast to the all cis occupancy of the centro-symmetric structure proposed by Mering and Oberlin (1967). In one of the nontronites the distribution of Fe3+ between these two sites approaches that in the ideal non-centrosymmetric structure proposed for montmorillonite.

Hydrazine and dithionite, both of which are strong reducing agents, react differently with various dioctahedral smectites. Both the nature of the reducing agent and the structure of the clay affect the course of the reaction. Hydrazine reduces octahedral Fe3+ efficiently if the mineral has a low tetrahedral charge. The reducing action of dithionite does not depend upon the charge.

The results obtained by different physical methods of investigation suggest that reduction of iron is associated with protonation of an adjacent OH group. The Fe2+ formed is readily re-oxidised but the structural changes occurring on reduction are reversible only when Al-OH-Fe, but not when Fe-OH-Fe associations are involved. Reaction mechanisms are proposed and changes in the distribution of iron in the octahedral sites are discussed.

The stability of smectite separated from a Houston Black clay soil was studied by solubility methods in an acid environment. High Silicon levels (supersaturated with respect to amorphous Si) probably were due to dissolution of the smectite and slow precipitation of amorphous Silicon. Also, mica and vermiculite impurities may have contributed to high solution Si values. Solubility data from equilibrium solutions of various treatments and chemical structural analyses permitted the formulation of a solubility equation. The ΔG°f for the Houston Black smectite computed from pK values was —2433.9 ± 0.8 kcal/mole. The stability of this clay could then be determined by calculations for any desired solution environment. It was found that under some conditions this soil smectite could be more stable than Belle Fourche and Aberdeen montmorillonites. Therefore, it appears that this soil clay has the required stability area in which it can form in nature.

Micas are described from the kaolin type Tertiary weathering crusts formed on granites and gneisses of Lower Silesia, Poland. In the weathering crust, large scale processes of transformation of micas (muscovite, biotite) take place. Weathering of micas is a gradual transformation of their structures by removal of the mobile cations Mg2+ Fe2+ Fe3+ and finally K +. Muscovite transforms into kaolinite through the intergrowths of two phases, mica and kaolinite. A degradation series, muscovite → mica/montmorillonite → montmorillonite → kaolinite also is observed. Biotite passes directly into kaolinite, but at higher concentrations of K and Al one observes the following sequence of biotite degradation: biotite → dioctahedral mica rich in Fe → dioctahedral mica poor in Fe → kaolinite. This process involves the exchange of Mg2+ and then Fe2+ of octahedral layers by Al3+ less mobile under weathering conditions. In the next stage of degradation, K + removal and kaolinite formation takes place. The micas representing different stages of this transformation, dark green, light-green, and silver-white, have been separated and investigated.

Reaction with Na2S solutions at high pH led to almost complete, reversible reduction of iron in montmorillonite, whereas the structural iron of nontronite persisted in the ferric form. Concentrated Na2S solutions caused severe corrosion of nontronite and extracted appreciable amounts of iron, which was precipitated as sulphides. In contrast the morphology of montmorillonite was preserved and only very minor amounts of iron were extracted. These differences were attributed to the high concentration of Fe-OH-Fe groups in nontronite, which are unstable on reduction. The difference between Na2S and other reducing agents is discussed.

Stable organomineral derivatives are formed by reaction of organochlorosilanes with certain phyllosilicates. Organosiloxyl functions are grafted on silanol groups present at external mineral surfaces.

Water molecules adsorbed on external mineral surfaces may cause hydrolysis of the reactant organosilicon products, with liberation of HCl. This, in turn, may react with the silicate: octahedral cations are extracted from the lattice and fresh Si-OH groups, capable of further grafting, are formed on the mineral surface.

On the other hand, when difunctional reagents such as methylvinyldichlorosilane are used and if the ratio of adsorbed water to added reactive is adequate, then polymeric species with polysiloxane chains are grafted on the mineral.

Because of its high content of silanol groups, sepiolite forms organomineral compounds having a relatively high organic matter content. With chrysotile, the amount of organic matter grafted to the silicate, is considerably smaller, but it increases appreciably if water is added to the reacting products. This is attributed to hydrolysis of the organic reactant and subsequent destruction of external “brucitic” layers by acid attack.

Complexes of 1,4-diazabicyclo [2.2.2] octane (triethylene diamine) with smectite and vermiculite were made for the purpose of exposing the internal surfaces of the clays for adsorption of gases and possible catalytic activity. When the diprotonated form of the amine saturated the exchange sites, internal surfaces of the clays were found to be available to nitrogen, ethane, and 2,4-dimethyl pentane. Proton lability in the smectites was studied with NH3, D2O, and C6D6 experiments. Catalytic function was demonstrated in the conversion of acetonitrile to acetamide in the smectite.

The possibility of recording the absorption band which is related to oscillations of free OH in a superficial plane of the octahedral sheet of kaolinite inspired the present authors to review the problem of cohesion forces in kaolinite. Structural and spectroscopic criteria as applied to kaolinite proved that the cohesion of adjacent kaolinite layers may be estimated in terms of bent hydrogen bonds. Energy calculations were performed with the aid of a Lennard-Jones function using a modified linear model of the hydrogen bonds. The entire energy is composed of four terms described by the general potential function, van der Waals repulsion and an electrostatic attraction. The energy values of the individual terms are within the limits characteristic of each of them.

Scan electron micrographs (SEM) show the textures of ball clay, plastic refractory clay, flint clay, and of kaolins from Cornwall, U.K., and Brittany, France. The texture of ball clay is a swirl and ragged-flake pattern. Plastic refractory clay shows a transition in texture from ball clay to plastic, semi-plastic, to semi-flint, and flint-clay. Flint-clay texture exhibits a matrix of tiny, compactly interlocked clay grains in which may be interspersed small, tight books and sheaves of kaolinite. The plastic to flint clays are interpreted to be sequential components of the flint-clay facies. In one sense they represent elements in clay diagenesis.

Kaolins from the Cornwall district, U.K., and Brittany, France, show more similarity than dissimilarity in texture. Evidence from texture suggests that while hydrothermal action at Cornwall initiated alteration of the granite, the last significant process of kaolinization there was weathering.

Quantitative analysis of clay minerals by X-ray powder diffraction requires oriented clays in order to increase detection limits of the analyses. This is achieved commonly either by smear or sedimentation techniques; however, these techniques can lead to poor analytical precision when used with an internal standard because they often produce non-homogeneous internal standard—clay mineral mixtures. Compaction of bulk shale material at 8000 psi in an hydraulic press produces preferred orientations comparable to that produced by smear or sedimentation. When used with a suitable platy internal standard which provides an estimate of clay mineral preferred orientation, excellent analytical precision is achieved routinely. Several lines of experimental evidence indicate that 1–5 µm MoS2 is an ideal orienting internal standard for use with compaction mounts.

Nontronite and biotite were analyzed by Electron Spectroscopy for Chemical Analysis (ESCA). Both minerals yielded ESCA spectra with well-defined peaks and the elements identified by the ESCA spectra were in good agreement with the molecular formulas. High resolution scans were made of the iron (2p3/2) and oxygen (1s) electron binding energies for oxidized and reduced forms of nontronite and biotite. Binding energies for Fe3+ were observed at 711.8 eV in dithionite-reduced nontronite and in oxidized biotite. Peaks for Fe2+ occurred at 710.0 eV for unaltered biotite, at 709 eV for oxidized biotite and at 708.6 eV for hydrazine-reduced and dithionite-reduced nontronite. The oxygen (1s) peak for unaltered nontronite was skewed to the high energy side of the 530.6 eV maximum, but became more symmetrical as the Fe2+ content increased.

An electrooptic birefringence technique was employed to study the effect of particle size, saturating cation, and clay type on the rotational diffusion coefficient (a measure of the rate at which the particles rotate or relax within the solution) from a preferred orientation. These studies help elucidate the nature of the cation—water environment near the clay particles.

Previous work has shown that some clay particles orient at both low and high voltages due to a permanent dipole and an induced dipole, respectively, whereas other clays under similar short-duration pulses orient only at high voltages. The permanent dipole was attributed to the iron in the octahedral layer of the clay mineral, whereas the induced dipole was probably due to a redistribution of the diffuse double-layer cations. This study shows that smaller clay particles orient more readily at low voltages and have greater rotational diffusion coefficients at high voltages. The higher the rotational diffusion coefficient, the faster the particles move in their surrounding water-cation environment. The effect of the saturating cation on the rotational diffusion coefficients was Na > Li > K for the permanent dipole and K > Li > Na > Ca > Mg for the induced dipole orientation. Previous results (Schepers and Miller, 1974) are interpreted to mean that a particle in dilute suspension can rotate independently of its environment only when the salt concentration in the surrounding medium approaches zero. At higher salt concentrations, or if the particle environment is perturbed by an electric field, the particle rotates with a water shell. As the concentration of salt or strength of the electric field increases further, either the viscosity of the surrounding solution increases or the size of the rotating shell is greatly increased. Thus, the water around clay particles appears to be structurally different than normal, and this condition is probably caused by the nature of the clay—cation interaction.

A new magnetic separation technique combines high magnetic fields, extreme gradients, and controlled retention time to separate feebly magnetic mineral contaminants from kaolin.

Extraction of pyrite, siderite, hematite, iron stained anatase, and mica by magnetic filtration of kaolin significantly upgrades brightness of many sub-marginal deposits and reduces consumption of reagents in processing.

Chrome chlorite associated with the chromite deposits of the Nuggihalli schist belt has been investigated by detailed mineralogical, chemical, X-ray diffraction, differential thermal and i.r. spectral analyses. Following the nomenclature of Lapham (1958) it is inferred that the chromium of the chrome chlorite is in the tetrahedral position and therefore the mineral is kotschubeite and not kaemmererite as suggested by earlier workers.

An apparatus for consolidating fine grained materials under controlled conditions of total stress, pore fluid pressure and temperature is described and the variation in chemistry of pore fluid expelled during compaction from a montmorillonitic material at 40°C is reported. The decrease in concentration of dissolved salts in the pore fluid is related exponentially to the effective axial pressure.

Glauconite pellets in the Cambrian of the central U.S.A. frequently contain two textural forms of glauconite–aggregate and oriented—which differ in both mineralogy and chemistry. The aggregate glauconite composes the bulk of most pellets and consists of crystals in a nearly random arrangement. The oriented glauconite occurs primarily as rims on the periphery of pellets. It has a honeycomb-like structure—the crystals are oriented with their c-axes tangent to the aggregate-textured cores. Scanning electron photomicrographs show that the aggregate and oriented textures grade one into the other.

The aggregate glauconite has a 1 M structure and less than 5% expandable layers, whereas the oriented form has a 1 Md structure and ∼ 10% expandable layers. The aggregate glauconite contains 5–8% more total iron oxides and 2–3% less Al2O3 than the oriented glauconite. The b-cell dimension of individual samples increases nearly linearly with increasing octahedral Fe3+ + F2+ + Mg content. Chemical and crystallographic variations among various samples are, for the most part, related to the ratio of aggregate to oriented glauconite.

The transition between the texture of the aggregate and oriented glauconite suggests that some glauconite pellets may form by concretionary growth. It is proposed that Cambrian glauconite pellets grew through the repetitive development of a smectite-like clay at the margin of pellets. The smectite was later altered, both chemically and texturally, first to the oriented and then to the aggregate-textured glauconite.

Infrared spectra of nontronite reveal shifts to lower wave, number in peaks located at 3570, 1030, and 821 cm-1, which are assigned to vibrational modes for O-H stretching, Si-Ob (basal oxygens) tetrahedral vibrations, and FeO-H deformation, respectively, as the Fe2+ content increases upon reduction. A pleochroic shoulder at 1110 cm-1 resulting from Si-Oa (apical oxygens) interactions appears to be unchanged with reduction. The absorption band at 848 cm-1 shifts to higher energy with reduction of structural iron, and persists at 840 cm-1 after complete deuteration of structural hydroxyls. The band is assigned to a Fe-OH mode where the OH moves as a unit. The shift in the Si-Ob mode to lower vibrational energy with reduction may indicate a decrease in stress forces between the tetrahedral and octahedral sheets.