Clay mineralogy and whole-rock chemistry of the borate-bearing layers of the Hisarcik and Esbey mines were examined. The Hisarcik clays occur as laminated or unlaminated clay layers with sharp contacts. Unlaminated layers contain quartz derived from metamorphic rocks and carbonate fragments in a clay matrix, and are interpreted as reworked tuffs deposited in playa-lake environments. An important feature is that the unlaminated clays contain little MgO (3–15 wt. %) as compared with the laminated clays (15–30 wt. %). As previous studies have shown, the clay fraction of the studied profile contains predominantly Li-bearing saponite, and accounts for 60–90 wt. % of the clay fraction (<2 μm). Illite in the clay fraction varies from 0 to 67 wt. % and the average illite percentage never exceeds 40 wt. %. Chlorite is scarce (2–5 wt. %). Illite-smectite interstratified clays (illite at 70%, smectite at 30%) were only found in low concentrations in the laminated clay layers of the upper limestone unit (above the borate zone), where illite-2M of detrital origin is also present. The Esbey clays occur interstratified with colemanite layers and envelope colemanite nodules. Calcite is the major mineral of the clays whereas quartz, plagioclase, feldspar, colemanite, and cahnite are minor components. The MgO contents vary between 4.70–13.95 wt. % in the clays interstratified with colemanite layers, between 7.24–11.89 wt. % in the enveloping clays, and between 10.27–21.25 wt. % in clays located above the colemanite zone. The composition of the clay fraction (<2 μm) in all samples is similar. Smectite represents between 40–90 wt. % of the clay fraction in the upper portion of the stratigraphic profile and decreases towards the lower part of the stratigraphic profile. Smectite always occurs with illite which may vary from 20 to 90 wt. % of the clay fraction, and a small amount of kaolinite and chlorite. Illite-2M polytype is abundant. The d(060)-reflection position suggests that the smectite minerals from the Hisarcik and Esbey colemanite mines contain both dioctahedral and trioctahedral smectites to form a transitional zone. These smectites are a product of a magnesium-rich alkaline playa-lake environment.

A commercial bentonite (primarily smectite) from Fischer Scientific Company (F bentonite) and a natural bentonite from Peru (P bentonite) were used in the preparation of pillared clays with polyoxymetal cations of Al that were subsequently modified with Ce and La. Several Al/metal ratios (5 and 9) were used to investigate the effects on the thermal and hydrothermal stability of these synthetic clays. The structure of these materials was studied by X-ray diffraction. Isotherms were determined by N2 adsorption. Thermal stability was determined using thermogravimetric (TG) measurements and ara-monia-TPD (temperature programmed desorption) was used to obtain acidity data. These materials exhibited basal spacings from 16 to 20 Å, with surface areas from 239 to 347 m2g−1, with microporosity contributing from 50 to 80% of the total surface area. Pillared clays prepared from F bentonite generally showed larger basal spacings and surface areas than those prepared from P bentonite. Pillared clays modified with Ce or La did not show any apparent structural changes relative to the Al-pillared clays. Pillared clays modified with Ce and La had similar acid properties as Al-pillared clays. In contrast, the thermal and hydrothermal stabilities of these materials were greater than Al-pillared clays. However, Ce-pillared clay appears to be more effective than La-pillared clay in delaying the dehydroxylation of pillared clays with increasing temperature. The intercalation of Ce and La into Al-pillared clays improved the thermal stability, which may increase the utility of these materials as catalysts.

To assign far infrared (FIR) absorption bands of K+ in muscovite, dichroic experiments were performed. For a muscovite crystal rotated about a crystallographic axis, c*, a, or b, two bands corresponding to vibration modes of K+ appear, respectively, at 107 and 110 cm−1 (rotation about c*), 107 and 143 cm−1 (rotation about a), and 110 and 143 cm−1 (rotation about b). Two in-plane modes at 107 and 110 cm−1 and one out-of-plane mode at 143 cm−1 are identified for the vibrations of K+ in muscovite. Each of these transition moments are near the crystallographic axes b, a, and c, respectively. These observations match well predictions based on the approximate C3i symmetric environment of K+, although the site symmetry in the space group of muscovite is only C2.

A method is proposed to measure the absolute concentration of paramagnetic Fe3+ ions in kaolinite from various geochemical environments using powder X-band electron paramagnetic resonance (EPR) data. An Fe3+-doped corundum sample is used as a concentration standard. The Fe3+ signal is calibrated by calculating the powder EPR spectra of Fe3+ ions in corundum and low-defect kaolinite. The paramagnetic Fe3+ concentration in other samples is obtained by an extrapolation procedure. This study provides a direct assessment of the iron distribution between isolated structural Fe3+ ions and other iron species, such as Fe3+ concentrated phases and Fe2+ ions. The concentration of isolated structural Fe3+ ranges between 200–3000 ppm and represents less than half of the total iron within kaolinite crystals.

Area-weighted thickness distributions of fundamental illite particles for samples of illite and illite-smectite from seven locations (including bentonites and hydrothermally altered pyroclastics) were measured by Pt-shadowing technique, by transmission electron microscopy. Most thickness distributions are described by lognormal distributions, which suggest a unique crystallization process. The shapes of lognormal distributions of fundamental illite particles can be calculated from the distribution mean because the shape parameters α and β2 are interrelated: β2= 0.107α − 0.03. This growth process was simulated by the mathematical Law of Proportionate Effect that generates lognormal distributions. Simulations indicated that illite particles grow from 2-nm thick illite nuclei by surface-controlled growth, i.e., the rate of growth is restricted by how rapid crystallization proceeds given a near infinite supply of reactants, and not by the rate of supply of reactants to the crystal surface. Initially formed, 2-nm thick crystals may nucleate and grow within smectite interlayers from material produced by dissolution of single smectite 2:1 layers, thereby transforming the clay from randomly interstratified (Reichweite, R = 0) to ordered (R = 1) illite-smectite after the smectite single layers dissolve. In this initial period of illite nucleation and growth, during which expandable layers range from 100 to 20%, illite crystals grow parallel to [001]* direction, and the dimensions of the (001) plane are confined to the size of the original smectite 2:1 layers. After nucleation ceases, illite crystals may continue to grow by surface-controlled growth, and the expandable-layer content ranges from 20 to 0%. This latter period of illitization is characterized by three-dimensional growth. Other crystal-growth mechanisms, such as Ostwald ripening, supply-controlled growth, and the coalescence of smectite layers, do not produce the observed evolution of α and β2and the observed shapes of crystal thickness distributions.

A new method for the prediction of Gibbs free energies of formation for hydrated clay minerals is proposed based on the parameter ΔGO= Mz+(clay) characterizing the oxygen affinity of the cation Mz+. The Gibbs free energy of formation from constituent oxides is considered as the sum of the products of the molar fraction of an oxygen atom bound to any two cations multiplied by the electronegativity difference defined by the ΔGO= Mz+(clay) between any two consecutive cations. The ΔGO= Mz+(clay) value, using a weighting scheme involving the electronegativity of a cation in a specific site (interlayer, octahedral, or tetrahedral) is assumed to be constant and can be calculated by minimization of the difference between experimental Gibbs free energies (determined from solubility measurements) and calculated Gibbs free energies of formation from constituent oxides. Results indicate that this prediction method compared to other determinations, gives values within 0.5% of the experimentally estimated values. The relationships between ΔGO= Mz+(clay) corresponding to the electronegativity of a cation in either interlayer or octahedral sites and known ΔGO= Mz+(aq) were determined, thereby allowing the prediction of the electronegativity of transition metal ions and trivalent ions in hydrated interlayer sites and octahedral sites. Prediction of Gibbs free energies of formation of any clay mineral with various ions located in the interlayer and with different cations in octahedral sites is possible. Examples are given for Al-rich montmorillonite from Aberdeen, transition element-exchanged montmorillonite, and Ni-rich stevensite, and the results appear excellent when compared to experimental values.

Chlorite and illite are commonly associated with ubiquitous secondary K-rich feldspar in the rocks located immediately above and below the Precambrian-Paleozoic unconformity in southwestern Ontario, and elsewhere in the mid-continent of North America. This alteration assemblage is attributed to long-distance migration of hot brines driven westward by orogenic processes originating along the eastern seaboard of North America. The δD and δ18O values of chlorite and illite, plus K-Ar dates for secondary K-rich feldspar and illite, were used to determine the nature, origin, and timing of the fluids that altered Precambrian granites and their overlying rocks in southwestern Ontario. The δ18O values of the chlorite-forming fluids are best explained by initial hot brines (≥50°C) evolved mostly from seawater. Secondary K-rich feldspar formation followed shortly thereafter, as the fluids cooled and perhaps mixed with meteoric water. Regional migration of the brines was induced by Taconic orogenic events to the east. The hydrogen and oxygen isotopic compositions for the secondary illite of the early to mid-Carboniferous indicate its crystallization from local meteoric water at low temperatures (40–55°C). Infiltration of local meteoric water into the Paleozoic and uppermost altered Precambrian rocks occurred during uplift, erosion, and subaerial exposure of local arches in southern Ontario. The local basement reactivation and associated secondary illite formation in this portion of the North American hinterland was likely a distal expression of east-coast Acadian and Alleghanian orogenic activity.