The thermal reaction sequence of a synthetic hectorite (Laponite CP) was studied by X-ray diffraction, i.r. spectroscopy and thermal analysis. Although most of the interlayer water is removed at 200°C, a smally steady weight loss occurs until dehydroxylation is complete at about 700°C, indicating that an anhydrous intermediate phase is not formed prior to dehydroxylation. Immediately after dehydroxylation, enstatite and cristobalite can be identified, but lithium silicates are formed only from lithium-saturated hectorite. Around 1200°C a glass is formed by reaction of the alkalis with cristobalite, and removal of silica from the enstatite produces some forsterite. An inhomogeneous mechanism of dehydroxylation is postulated by analogy with that proposed for talc.

The structure of a lepidolite-2M1 from Biskupice, Czechoslovakia, has been redetermined. Violations of systematic extinctions and of monoclinic equivalences plus the results of a second harmonic generation test indicate that the true symmetry most likely is C1̄. The deviation of the data set from C2/c symmetry, however, proved to be too small to permit a statistically significant refinement in C1̄. Refinement in C2/c symmetry indicated no ordering of tetrahedral cations but ordering of octahedral cations so that M(1) = Li0.93R2+0.06Fe3+0.01 and M(2) = Al0.58Li0.35□0.07. The tetrahedra are elongated to form trigonal pyramids with a rotation angle of 6.2°. The anomalous orientation of the thermal ellipsoid for the F,OH anion plus the large equivalent isotropic B value of 2.58 for F,OH and of 1.74 for the interlayer K cation, whose position is partly restricted in C2/c symmetry, suggest a lower symmetry than C2/c.

The compositions of this sample and of a second lepidolite-2M1 from Western Australia fall outside the stability field of lepidolite-2M1 in the synthetic system. Structural control of the stacking sequence is discounted on the basis of the structural similarity of the lepidolite unit layers. Crystallization parameters are considered more important than composition or the structure of the unit layer in determining the stability and occurrence of different layer-stacking sequences in lepidolite.

The surface charge characteristics of a range of synthetic amorphous aluminosilicates, hydrous alumina, hydrous silica and two allophanic soil clays were determined by the retention of Na+ and Cl− as counter-ions from 0.1 M NaCl solution. In the pH range investigated (3–9), only negative charges could be detected in the hydrous silica and the most siliceous aluminosilicate [Al/(Al + Si) = 0.29], and only positive charges were detected in the hydrous alumina; whereas both positive and negative charges were detected in the more aluminous aluminosilicates and the soil allo-phanes. In all cases, the surface charges were pH-dependent and in the aluminosilicate series negative charge decreased and positive charge increased with Al/(Al + Si). Consequently, the point of zero charge increased with Al/(Al + Si).

The charge characteristics of the amorphous aluminosilicates could be explained by current models of their structure. Negative charge can be attributed to isomorphous substitution of Al for Si in the silicate structure and to the dissociation of silanol groups in structural and adsorbed silicate. Positive charge is attributed to protonation of hydroxy-aluminum species occupying cation exchange sites.

Two diagenetic stages of zeolitic alteration were recognized in a study of a thin bed of rhyolitic ash that was deposited in Eocene Lake Gosiute (Laney Member of the Green River Formation). The ash bed can be traced for 30 km along strike and represents a single volcanic event. The bed was not buried deeply (<100°C), and originally it was compositionally homogeneous. Initially, the bed altered to clino-ptilolite, heulandite, an intermediate phase between these two zeolites, and mordenite. These early reactions involved the hydration and solution of glass by saline, alkaline solutions and the subsequent precipitation of zeolites. The variation in zeolite mineralogy is due to differences in interstitial fluid chemistry that resulted from either fluctuations in lake-water chemistry or the proximity of spring discharge. These reactions, exclusive of the addition of H2O, involved only minor amounts of mass transfer over very small distances. Later, after burial, the early-formed zeolites reacted with upward moving sodium carbonate brines that were produced by dewatering of underlying evaporite deposits. The sodium carbonate brines, in equilibrium with trona and nahcolite, elevated the activity of Na+ and produced analcime. These later dehydration reactions involved significant mass transfer.

Previous studies of diffraction band profiles of montmorillonite are extended to the 13, 20 band which, for reasons discussed, is more sensitive to structural details than the diffraction bands considered previously. Hydration of Na-montmorillonite produces appreciable sharpening of this band, indicating, contrary to previous results, that the water layers have at least a partially ordered arrangement. For Cs-montmorillonite, the single water layer hydrate shows only a small sharpening of the band profile, possibly attributable to the water layer, but which clearly indicates that the Cs ions cannot be significantly displaced from their positions in the anhydrous material. For Ba-montmorillonite, the two-layer hydrate shows a small broadening of the diffraction band, which is possibly the result of a partial ordering of the water layers together with a movement of the Ba ions away from the hexagonal holes.

Nine synthetic Na-saponites with charge densities varying between 0.33 and 1.0 have been prepared. Their swelling properties and structural organization in water, ethylene glycol and glycerol show discontinuities in the physico-chemical behaviour of these samples. The layer charge densities caused changes in swelling properties and structural organization of the minerals. These changes also depended upon the nature of the solvation liquid and the interlayer cation involved.

Electron diffraction patterns of the Ba-saponites showed no abnormal diffusion making honeycomblike patterns between Bragg reflections.

The results indicate criteria for estimating the layer charge of tetrahedrally substituted trioctahedral 2/1 phyllosilicates.

There is no upper limit until x = 1 for the layer charge x which is specific to the smectite-group. Consequently, the changes in the swelling properties observed when x = 0.5-0.6 and x = 0.8-0.9 come from the modifications of the interlayer structure, which are mainly a function of cation-liquid and silicate layer-liquid interactions. Consequently, there is an overlap between the saponite and the vermi-culite mineral groups.

A systematic study of the influence of salinity and clay content on the electrical conductivity of sodium-illite clay gels shows that the geometry or “formation resistivity factors” of such systems can adequately be described by the model of oblate ellipsoids, used to simulate the shape of the clay particles. This conclusion is in agreement with the results previously obtained on kaolinite and montmorillonite clays. An axial ratio of 16 was found for the illite clay particles.

On the basis of Burger’s and Maxwell’s equations for electric flow through porous media, formulae are derived for calculating the electrical conductivity of mixed systems, i.e. “clay 1 + clay 2 + electrolyte solution” and “clay + spherical particles + electrolyte solution”. The electrical conductivity of these systems is expressed in terms of the shape parameters, surface conductances, specific surfaces and volume concentrations of the constituents. The type of equation can eventually lead to an explanation (in terms of a non-uniform particle shape distribution) of the anomalous geometry effects in some clays.

Experimental results conform fairly well to the equations. Glass powder at volume fraction between 0.18 and 0.60 added to a 17.4% montmorillonite gel acts as an inert diluent on the specific electrical conductivity of the mixture. For a mixture of 1 part montmorillonite to 9 parts kaolinite, the measured specific electrical conductivity agrees within about 10% with the predicted over the range studied (volume fraction of montmorillonite: 0.035 to 0.039; mixture porosity: 0.61 to 0.660; salt concentration range: 0.5 n to 2 n NaCl).

Empirical reaction progress diagrams showing the trends of major element oxide concentrations (in g/cm3) as functions of bulk density for a diabase saprolite reveal discontinuities in the trends of Al2O3, MgO, H2O+, and nonextractable Fe2O3. The discontinuities coincide with discontinuities in the trends of (1) the kaolinite-smectite 001 peak-intensity ratio, (2) the smectite 002-001 peak intensity ratio, and (3) the smectite basal spacing as functions of bulk density. The discontinuities are apparently related to redox conditions in the weathering profile because they occur at a depth where siderite veins first appear in the saprolite. Oxidizing conditions in the upper part of the profile appear to have favored the formation of Ferich smectite over kaolinite, whereas reducing conditions deeper in the profile favored the formation of kaolinite over Al-rich smectite. These results indicate that where geochemical conditions favor retention of Fe over Al, smectites can form in preference to kaolinite or gibbsite even under conditions of strong leaching.

Changes in the infrared absorption spectrum of ammonium-saturated rectorite on heating suggest that the ammonium cations are hydrogen bonded to water molecules when the mineral is hydrated. Further spectral changes above 300°C indicate that lattice OH groups are perturbed by protons liberated from the decomposition of ammonium ions giving rise to an absorption doublet at 3500 and 3476 cm-1. The doublet attains maximal intensity when decomposition of ammonium cations and dehydroxylation of the mineral is complete at about 550°C.

The perturbation effect occurs only for swelling dioctahedral minerals which derive their layer charge from Al-for-Si substitution.

Nickel-chlorite has been obtained by the co-precipitation of nickelous hydrous oxide and montmorillonite at an OH/Ni ratio of 2.0. Chemical analysis shows that 16 me of Ni is fixed per gram of clay. System without any free nickelous hydrous oxide is quite stable up to an investigated period of 6 months, shows impedence to collapse on heating to 550°C, and no expansion of 001 spacing on glycerol treatment.

Different properties studied (X-ray diffraction analysis, thermal [D.T.A. and T.G.A.] data, i.r. absorption analysis, Polarographic reduction behavior and cation exchange capacity measurements) confirm the complete transformation of montmorillonite to nickel-chlorite.

“Seeding” of the hydroxide out of the “fixed” interlayer positions takes place on ageing the sample with free nickelous hydrous oxide. No montmorillonite could be detected by X-ray diffraction analysis in spite of this backward reaction.

Samples of smectites and vermiculites were evaluated to (1) determine the effects of source and amount of charge, (2) determine if a continuum of properties exists, and (3) improve the basis for differentiating criteria for identification.

The montmorillonites expanded to the equivalent two-layer complex upon solvation by condensation of ethylene glycol or glycerol vapor. Beidellite exhibited the one-layer complex with glycerol vapor and the two-layer complex with ethylene glycol. The vermiculite samples did not yield regular two-layer complexes regardless of saturating cation, prior moisture or solvating agent. A number of different complexes of vermiculite were obtained depending on conditions of solvation. These corresponded to spacings of approx 13·6, 14·0, 14·3, 15·0, and 15·3 Å. Two or more of the complexes may be present in the same sample.

Potassium-saturated vermiculites and smectites both exhibited collapsed layers in a dry atmosphere. Hydration of smectites occurred at humidities above 20 per cent and resulted in poorly ordered diffraction maxima of 11–12 Å. The K-saturated vermiculites tended to retain the collapsed lattice and exhibited diffraction maxima of 10–10·6 Å with integral higher orders. Some hydration occurred as evidenced by peak asymmetry or the appearance of a small 14·3 Å line at higher humidities, although the collapsed spacing predominated. The tendency of vermiculite to hydrate decreased as the exchange capacity increased.

Differences in properties can be related to both source and amount of charge. Nevertheless, a continuum in the properties of expansion and collapse between the smectites and vermiculites was not observed. The data indicate two discrete populations. These properties may be used as differentiating criteria for identification.

We examine provenance data collected from three types of geological resources recovered at Goat Spring Pueblo in central New Mexico. Our goal is to move beyond simply documenting patterns in compositional data; rather, we develop a narrative that explores how people's knowledge and preferences resulted in culturally and materially determined choices as revealed in those patterns. Our analyses provide evidence that residents of Goat Spring Pueblo did not rely primarily on local geological sources for the creation of their glaze paints or obsidian tools. They did, however, utilize a locally available blue-green mineral for creation of their ornaments. We argue that village artisans structured their use of raw materials at least in part according to multiple craft-specific and community-centered ethnomineralogies that likely constituted the sources of these materials as historically or cosmologically meaningful places through their persistent use. Consequently, the surviving material culture at Goat Spring Pueblo reflects day-to-day beliefs, practices, and social relationships that connected this village to a broader mosaic of interconnected Ancestral Pueblo taskscapes and knowledgescapes.