The swelling of an n-butylammonium vermiculite in solutions of n-butylammonium chloride has been studied by neutron diffraction as a function of temperature and the concentration of the soaking solution. On heating a swollen sample a transition to the crystalline phase took place at a well-defined temperature, the c-axis spacing changing from 120 to 19.4 Å at 14°C in a 0.1 M solution and from 330 to 19.4 Å at 33°C in a 0.01 M solution. The phase transition was completely reversible, and a study of the temperature-concentration phase diagram was made as high as 50°C The swollen phase was studied in a range of concentrations of the external solution between 0.2 M and 5 × 10-4 M, for which the c-axis spacings were 85 and 910 Å, respectively. The reversibility, sharpness, and reproducibility of the phase change from crystalline to swollen gel suggest that the transition is truly thermodynamic, which is not in accord with DLVO theory. The concentration dependence of the observed d-values also could not be explained satisfactorily by DLVO theory.

Three methods were developed that allow for the imaging of any clay mineral in aqueous solutions with atomic force microscopy (AFM). The methods involve fixing the particles onto special substrates that do not complicate the imaging process, but hold the particles sufficiently so that they do not move laterally or float away during imaging. Two techniques depend on electrostatic attraction under circumneutral pH conditions, between the negatively charged clay particles and the high point of zero charge substrate (either aluminum oxide or polyethyleneimine-coated mica) whereas the third technique depends on adhesion to a thermoplastic film. The first electrostatic technique involves a polished single crystal α-Al2O3 (sapphire) substrate. This was used successfully as a substrate for clay-sized minerals with high permanent layer charge localized on the basal planes (phlogopite and vermiculite) and when the AFM was operated in TappingMode to limit the lateral forces between the probe tip and the particles. However, electrostatic attraction between the sapphire surface and clay minerals such as smectite and kaolinite (low or no permanent layer charge) is not sufficiently strong to adequately fix the particles for imaging. The second electrostatic technique involves a polyethyleneimine-coated mica surface designed to immobilize a larger variety of clay minerals (phlogopite, vermiculite, montmorillonite, and kaolinite), and in this technique weak bonding between the clay and the organic film is also a factor. The third technique, which does not depend on electrostatic attraction, fixes clay particles into the surface of a thermoplastic adhesive called Tempfix. This has proven useful for fixing and imaging relatively large clay particles with well-defined morphology. The Tempfix mount also requires imaging in TappingMode because the Tempfix is relatively soft.

The chemical composition and the thermal behavior of sodium and hydrogen octosilicate was studied by chemical and thermal analysis, infrared (IR), magic-angle-spinning nuclear magnetic resonance (MAS-NMR) spectroscopy, and X-ray diffractometry. Both compounds are layer silicates with basal spacings of 11.10 and 7.38 Å, respectively. In both forms the ratio of Q4 silicon (connected via oxygen bridges with four silicon atoms) to Q3 silicon (connected with only three other Si atoms) is 1. At least a small part of the Q4 silicon can be substituted by aluminum. Elimination of water coordinated to the cations in sodium octosilicate results in a concomitant structural collapse. Replacement of the sodium ions by protons affects the atomic arrangement in the sheets only to a minor degree, but results in a decrease of the periodicity along the crystallographic c axis. Upon heat treatment an endothermal structural rearrangement occurs at about 360 K as revealed by significant changes of the IR and 29Si MAS-NMR spectra. Reexchange with Na ions largely, but not completely, restores the structure of the parent octosilicate.

The X-ray diffraction pattern of sodium octosilicate was indexed in the monoclinic system with a = 7.345 Å, b = 12.74 Å, c = 11.25 Å and β = 99.3°. Based on conclusions drawn from the results of the present study, the X-ray pattern of hydrogen octosilicate was tentatively indexed in the monoclinic system with a = 7.345 Å, b = 12.74 Å, c = 8.51 Å and β = 119.8°.

The Hançılı bentonite from Turkey shows significant changes in surface area, micro- and mesoporosity, surface acidity and acid strength with heating from 100 to 900°C for 2 h. The specific surface area (S) and specific micro-mesopore volume (V) of the original and heated samples were evaluated from N2 adsorption and desorption data, respectively, by standard methods. The adsorption of n-butylamine from the solution in cyclohexane on the samples was used to determine the total surface acidity (nm) and the adsorption equilibrium constant (K) was taken as a measure of the acid strength. S, V and nm having initial values of 98 m2g−1, 0.080 cm3g−1 and 4.8 × 10−4 mol g−1, respectively, stayed approximately constant as the temperature increased to 450°C and then decreased almost in parallel with each other, reaching their minimum or zero at 900°C. The total surface acidity, in general, declines with increasing temperature. The most acidic sites, however, increase with heating, and especially at dehydration and dehydroxylation. Acid strength reaches its maximum during the dehydroxylation phase at ∼600°C. It was concluded that the total surface acidity does not necessarily parallel the strength of the most acid sites.

Trioctahedral smectite and regularly interstratified chlorite/smectite in strata of the East Berlin Formation of the Connecticut Valley are largely restricted to black shale and gray mudstone deposited in alkaline, perennial lakes. The precursor of the mixed-layer clay appears to have been a smectite. Alkaline lake waters and inherited pore waters rich in magnesium favored the transformation of smectite to mixed-layer chlorite/smectite by fixation of brucitic interlayers into the smectite unit structure. Gray mudstones containing the mixed-layer chlorite/smectite are invariably underlain by magnesium-rich black shale—a possible source of Mg for the clay mineral transformations. The black shale is composed predominantly of Mg-rich trioctahedral smectite of probable authigenic origin.

Raman and Fourier-transform-infrared (FTIR) spectroscopic methods and X-ray powder diffraction (XRD) techniques have been used to study the influence of hydrazine on the vibrational modes of kaolinite. Strong vibrational perturbations of the OH-stretching and -deformation bands were observed in the Raman and FTIR spectra on intercalation. The intensities of the Raman- and IR-active OH-stretching bands decreased significantly upon intercalation; the intensities of the Raman bands were reduced to a greater extent than the IR bands. The deformation bands were also strongly perturbed by the presence of hydrazine in the interlamellar region. Upon evacuation of the intercalate, two new bands at 3628 and 912 cm−1 were noted, indicating the presence of a different structural conformation of the complex under vacuum. Similar results were obtained using XRD, on evacuation of the kaolinite-hy-drazine (KH) complex the d(001) value decreased from 10.4 to 9.6 Å. Partial collapse of the intercalate from 10.4 to 9.6 Å was probably due to keying of the -NH2 moiety of hydrazine into the siloxane ditrigonal cavity, as indicated by a blue-shift of the inner-OH band from 3620 to 3628 cm-1. Structural OH vibrational modes may therefore be useful probes of amine interactions with clay mineral surfaces.

Upper Cretaceous-Tertiary marine clayey-calcareous rocks of the Hekimhan basin contain fibrous clay minerals in significant amounts. Ophiolitic rocks in the provenance area have contributed the elements to form the clay minerals. XRD, SEM, major, trace and REE analyses were applied to samples taken from several stratigraphic sections. Diagenetic minerals such as smectite, dolomite, calcite, gypsum, celestite and quartz/chalcedony are associated with sepiolite-palygorskite group clays. Trace and rare earth elements (REE) are more abundant in palygorskite than sepiolite. REE abundances in the sepiolite-palygorskite are characterized by negative Eu and positive Nd anomalies when normalized with respect to chondrite and shale. Sepiolites with sharp XRD peaks are formed by diagenetic replacement of dolomite and diagenetic transformation of palygorskite, or by direct crystallization from solution. The average structural formula of the sepiolite is:

(Mg7.15Al0.13Fe0.31Cr0.06Ni0.04)(Si11.98Al0.02)O30(OH)4(OH2)4Ca0.03Na0.02K0.02.8H2O

Palygorskite appears to be authigenic by direct precipitation from solution. It exists in both monoclinic and orthorhombic forms with the mean structural formula given below

(Mg2.22Al1.00Ti0.04Fe0.77Cr0.01Ni0.02)(Si7.68Al0.32)O20(OH)2(OH2)4Ca0.07Na0.05K0.10.4H2O

In the absence of oxygen, Fe(II) chloride, sulfate, and carbonate solutions react at pH 6.5 to 7 with aluminum hydroxide suspensions to form new Fe(II)-Al(III) hydroxy anion compounds of the pyroaurite group. The Fe(II)-Al(III) hydroxy-chloride and -sulfate compounds are isostructural with Fe(II)- Fe(III) “green rust” compounds with A1 essentially substituting for Fe(III). Where CO32- is the only anion in the system, an Fe(II)-Al(III) compound isostructural with hydrotalcite is formed. Either in the dried or wet state, these compounds are unstable in air due to oxidation of Fe(II). Oxidation of the dried sample in air yields akaganeite or aluminous ferrihydrite, whereas, if the sample is maintained in a moist condition and oxidized by air under water, lepidocrocite or aluminous goethite is produced along with small amounts of ferrihydrite. On X-ray powder diffraction, the lepidocrocite so formed commonly shows no diagnostic (020) basal reflection, or one with a markedly reduced intensity. The products of oxidation, and the rapidity of their formation, appear to be dependent on the composition of the initial double hydroxy compound and the conditions under which the oxidation is carried out.

The green colored compounds commonly observed in gleyed soils also rapidly become yellow brown on exposure to air, and difficulty arises in the identification of the Fe oxide phases assumed to be present. Similar conditions and reactants to those involved in the formation of the compounds described above are expected in these soils, and it is suggested that Fe(II)-Al(III) members of the pyroaurite group may form in such an environment.

Most detrital ilmenite grains in sandstones of the Chaswood Formation are completely altered to pseudorutile, leucoxene and rutile. The textural, chemical and mineralogical changes involved in alteration were tracked using electron microprobe analyses, backscattered electron images, and elemental maps. Ilmenite grains (Ti/(Ti+Fe) ≈ 0.48) alter patchily to pseudorutile (Ti/(Ti+Fe) 0.5–0.7) with volume loss, forming a porous structure and this process continues with the development of leucoxene (Ti/(Ti+Fe) 0.7–0.9). Within the pseudorutile and leucoxene, stubby prismatic rutile crystals have been precipitated. Si and A1 occur in the altered ilmenite, either (1) inherited from original quartz and muscovite inclusions in the parent crystal or (2) as kaolinite altered from muscovite inclusions or precipitated in the pore space, under pedogenic or early diagenetic conditions. Distribution of alteration phases has been related to facies and diagenetic variations. With increasing amounts of leaching in different types of paleosols, there was increasing alteration of pseudorutile to leucoxene. In light gray mudstones and interbedded sandstones with diagenetic kaolinite that formed beneath the water table from percolating meteoric water, most leucoxene was converted to rutile. Burial diagenesis (to vitrinite reflectance values >0.4%) also promoted the change from leucoxene to rutile. The alteration of ilmenite is an important source of Fe for diagenetic minerals in the Chaswood Formation and correlative offshore deltaic and marine facies of the Scotian basin.

Samples of nacrite, dickite, kaolinite, and halloysite were investigated using X-band electron paramagnetic resonance (EPR) and Mössbauer spectroscopy. Fe3+ gave rise to EPR signals at g ≃ 4 which differed with the individual polytype. Only nacrite had no resonance in this region of the spectrum, but it had one at g ≃ 2. Dickite had a quadruple line, kaolinite a triple line, and halloysite a single line in this region. The EPR spectra of these minerals are apparently dependent also on the orientation of adjacent layers in the structures. Other resonances were attributed to (1) clusters of ferric ions giving rise to broad resonance near g ≃ 2, (2) trapped holes, and (3) free radicals linked with organic matter. The Mössbauer spectroscopic results suggest that iron occurs in the ferric state (except in nacrite where Fe2+ is present also) as an ionic substitution (IS) in octahedral layers. This suggestion follows from the difference is the IS values between octahedral and tetrahedral symmetry sites occupied by Fe3+ equal to ∼0.4 mm/sec. Linewidths depend mainly on the way the layers stack; for monoclinic modifications represented by nacrite and dickite, the linewidths are narrow (Γ = 0.45 mm/sec and 0.56 mm/sec, respectively); pseudomonoclinic halloysites also gave narrow linewidths (Γ = 0.39 mm/sec and 0.48 mm/sec). The widest line was observed for triclinic kaolinite (Γ = 0.62 mm/sec and 0.71 mm/sec).

Diffuse Reflectance Fourier Transform Infrared spectroscopy was used to monitor both molecular interactions and concentrations of volatile organic chemicals adsorbed on a commercial montmorillonite. Chemicals tested included propanoic acid, hexanal, heptanal, trimethylamine, dimethylsulfide and dimethyldisulfide. Diffuse Reflectance Fourier Transform Infrared spectroscopy had several advantages over other infrared techniques including ease of sample preparation, greater numbers of useful bands and the ability to detect both major and minor components from the same spectra. Evidence for the formation of organo-clay complexes was found for all chemicals except dimethylsulfide. Spectra of mixed chemicals on the clay showed numerous overlapping bands. Organic concentrations were determined by multicomponent analysis using a least squares curve fitting technique. Significant correlation (P < 0.01) between actual and determined concentrations of added organics was obtained for all except dimethylsulfide. Here the weak spectral contribution appeared to be overshadowed by the strongly adsorbing montmorillonite with consequent decrease in sensitivity. Diffuse Reflectance Fourier Transform Infrared spectroscopy of organo-montmorillonite complexes could be used both as a means of studying molecular interactions and for the determination of adsorbed organic concentrations.

We have investigated the adsorption of adenine, adenosine, ribose, and adenosine-5′-phosphate (5′-AMP) by allophane at pH 4, 6 and 8. Adenine, adenosine and ribose gave similar isotherms, i.e. adsorption increased regularly with solution concentration and decreased in the order: pH 8 > pH 6 > pH 4. Allophane had a greater affinity for 5′-AMP than for adenine, adenosine or ribose. Further, the extent of adsorption for 5′-AMP increased in the order: pH 8 ≪ pH 6 ≈ pH 4. The adsorption of 5′-AMP at pH 4 and pH 6 was about 60 times greater than at pH 8. The strong adsorption of 5′-AMP accords with the well known high phosphate-retention capacity of allophane and allophane-rich soils. The experimental data may be rationalized in terms of the pH-dependent charge characteristics of the organic solutes and allophane. The large propensity of allophane to retain 5′-AMP is ascribed to ligand exchange between the phosphate of 5′-AMP and the hydroxyl of (HO)Al(OH2) groups, exposed at perforations on the wall of allophane spherules, giving rise to a surface (chelation) complex. The high affinity of nucleotides for allophane has implications for the possible role of allophane in the abiotic formation of RNA-type polynucleotides although nucleotide ‘immobilization’ by surface complexation might hinder RNA oligomerization.

Stability determinations were made by solubility methods on two trioctahedral mica-derived vermiculites. The phlogopite-derived vermiculite was found to be unstable under acid solution conditions, where stabilities of montmorillonite, kaolinite and gibbsite had previously been determined. An attempt was next made to locate a possible montmorillonite-vermiculite-amorphous silica triple point. This triple point involved conditions of alkaline pH, high pH4SiO4 and high Mg2+. These are conditions where phlogopite and biotite-derived vermiculites are most likely to control equilibria if they are stable minerals. The montmorillonite-vermiculite-amorphous silica samples went to the montmorillonite-magnesite-amorphous silica triple point, leaving no stability area whatsoever for the vermiculites. These large particle-size, trioctahedral, mica-derived vermiculites appear to be unstable under all conditions of room T and P.

Arguments are presented indicating that micas are unstable in almost all weathering environments. A hypothesis is proposed that mica-derived vermiculites result from the unique way in which unstable micas degrade in these environments. It is proposed that vermiculite derives from a series of reactions whose relative rates often result in an abundance of vermiculite. These relative reaction rates are slow for mica dissolution, rapid for K removal and other reactions pursuant to vermiculite formation, and slow for vermiculite dissolution. In chemical terms, mica-derived vermiculites may be considered fast-forming unstable intermediates.

A new approach to the interpretation of Mössbauer spectra of Fe3+-phyllosilicates having vacant trans-octahedra is based on (1) crystal structure simulation methods that allow for the size and the shape of a Fe3+-octahedron as a function of the nearest surrounding cations; and (2) calculations of electric field gradients (EFG) on Fe3+ in terms of the ionic point-charge model. Calculations were performed by direct summation within the region of radius ≤50 Å. Coordinates for the anions in the coordination octahedra have been assigned to take into account the nearest cationic environment. Atomic coordinates for the rest of the summation volume are those for the average unit cell. EFG calculations for cation combinations responsible for the visible quadrupole splitting Δvis in the spectra of nontronite, “red” muscovite, and celadonite have led to good agreement between Δvis and Δcalc. Computer fitting of the nontronite and celadonite spectra based on EFG calculations for the rest of the possible cation combinations suggests that the distribution of tetrahedral cations in nontronite obeys the Loewenstein rule, and in celadonite, the distribution of R3+ and R2+ over cis-octahedra is predominantly ordered, in agreement with electron diffraction and infrared spectroscopy data. The Mössbauer spectrum of one of the glauconites suggested the presence of celadonite-like and muscovite-like domains in its 2:1 layers.

The effect of heat treatments on the swelling, dispersion, particle charge and particle aggregation of Li-, Na-, K-, Mg-, Ca- and Al-Wyoming bentonite was investigated. Before thermal treatment, unheated (25 °C) Li-, Na- and K-clays showed increased d001 spacing on glycerol solvation and dispersed spontaneously in water. Mg-, Ca- and Al-clays did not disperse spontaneously in water, but the d001 spacing increased upon glycerol solvation. After heating at 300 °C or above, none of these clays dispersed spontaneously. However, swelling varied with the type of cation and the temperature of heating.

The results generally suggested that swelling and dispersion of homoionic Wyoming bentonite after heating at various temperatures depended upon the nature of bonding between clay particles and the cations. Enhanced swelling and dispersion of clays indicated the more ionic character of the cationic bonding than cases where heating resulted only in swelling, with polar covalent bonding of cations to clay surfaces allowing limited hydration. It is also suggested that, when both swelling and dispersion as a result of thermal treatment are absent, a covalent bond is formed between cation and clay surface.

Thermal treatment apparently affects the bonding in different ways. It appears that the smaller cations (ionic radius <0.7 Å) Li, Mg and Al migrate to octahedral vacant sites and form covalent bonds after heating at 400 °C; this drastically reduces the negative charge. This process for Li-clays occurred even at 200 °C. The larger cations (ionic radius > 0.9 Å) Na, K and Ca apparently did not migrate into the lattice sites after heating to 400 °C; a high proportion of them were exchangeable. The data for exchangeable cation, particle charge and clay particle size were consistent with the postulated effect of the nature of cationic bonding upon swelling and dispersion properties.

The Al-clay-rich rock units at Mawrth Vallis, Mars, have been identified as mixtures of multiple components based on their spectral reflectance properties and the known spectral character of pure clay minerals. In particular, the spectral characteristics associated with the ~2.2 μm feature in Martian reflectance spectra indicate that mixtures of AlOH- and SiOH-bearing minerals are present. The present study investigated the spectral reflectance properties of the following binary mixtures to aid in the interpretation of remotely acquired reflectance spectra of rocks at Mawrth Vallis: kaolinite-opal-A, kaolinite-montmorillonite, montmorillonite-obsidian, montmorillonite-hydrated silica (opal), and glass-illite-smectite (where glass was hydrothermally altered to mixed-layer illite-smectite). The best spectral matches with Martian data from the present study’s laboratory experiments are mixtures of montmorillonite and obsidian having ~50% montmorillonite or mixtures of kaolinite and montmorillonite with ~30% kaolinite. For both of these mixtures the maximum inflection point on the long wavelength side of the 2.21 μm absorption feature is shifted to longer wavelengths, and in the case of the kaolinite-montmorillonite mixtures the 2.17 μm absorption found in kaolinite is of similar relative magnitude to that feature as observed in CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) data. The reflectance spectra of clay mixed with opal and of hydrothermally altered glass-illite-smectite did not represent the Martian spectra observed in this region as well. A spectral comparison of linear vs. intimate mixtures of kaolinite and montmorillonite indicated that for these sieved samples, the intimate mixtures are very similar to the linear mixtures with the exception of the altered glass-illite-smectite samples. However, the 2.17 μm kaolinite absorption is stronger in the intimate mixtures than in the equivalent linear mixture. Modified Gaussian Modeling of absorption features observed in reflectance spectra of the kaolinite-montmorillonite mixtures indicated a strong correlation between percent kaolinite in the mixture and the ratio of the area of the 2.16 μm band found in kaolinite to the area of the 2.20 μm band found in montmorillonite.

The adsorption behavior of quaternary ammonium cationic surfactants with different hydrocarbon chain lengths, i.e. HDTMA (hexadecyltrimethylammonium), TDTMA (tetradecyltrimethylammonium) and DDTMA (dodecyltrimethylammonium), onto clinoptilolite has been investigated. The adsorption isotherms of these surfactants are correlated with the ζ potential curves of clinoptilolite. Accordingly, the applicability of the hemimicelle hypothesis to the adsorption of cationic surfactants at the clinoptilolite/water interface considering in the electrical double layer (EDL) of clinoptilolite is discussed. Even though the adsorption occurs in the EDL of clinoptilolite, the adsorption of HDTMA, TDTMA and DDTMA onto clinoptilolite is not conveniently described by the hemimicelle hypothesis. The absence of all expected marked increase in the ζ potential curves at the hemimicelle concentration is ascribed to the large external cation exchange capacity of clinoptilolite. The hydrocarbon chain length of surfactant molecules is found to have a significant effect on the ion exchange as well as hydrophobic interaction mechanisms. The effectiveness of both ion exchange and hydrophobic interactions increases with increasing chain length, and so the greatest surfactant adsorption onto clinoptilolite was obtained by HDTMA.

A new method has been developed for quantifying smectite abundance by sorbing polyvinylpyrrolidone (PVP) on smectite particles dispersed in aqueous solution. The sorption density of PVP-55K on a wide range of smectites, illites and kaolinites is ∼0.99 mg/m2, which corresponds to ∼0.72 g of PVP-55K per gram of montmorillonite. Polyvinylpyrrolidone sorption on smectites is independent of layer charge and solution pH. PVP sorption on SiO2, Fe2O3 and ZnO normalized to the BET surface area is similar to the sorption densities on smectites. γ-Al2O3, amorphous Al(OH)3 and gibbsite have no PVP sorption over a wide range of pH, and sorption of PVP by organics is minimal. The insensitivity of PVP sorption densities to mineral layer charge, solution pH and mineral surface charge indicates that PVP sorption is not localized at charged sites, but is controlled by more broadly distributed sorption mechanisms such as Van der Waals’ interactions and/or hydrogen bonding. Smectites have very large surface areas when dispersed as single unit-cell-thick particles (∼725 m2/g) and usually dominate the total surface areas of natural samples in which smectites are present. In this case, smectite abundance is directly proportional to PVP sorption. In some cases, however, the accurate quantification of smectite abundance by PVP sorption may require minor corrections for PVP uptake by other phases, principally illite and kaolinite. Quantitative XRD can be combined with PVP uptake measurements to uniquely determine the smectite concentration in such samples.

The octahedral composition of palygorskite in more than 300 samples from the Pefkaki deposit, W. Macedonia, Greece, has been studied by near-infrared (NIR) and X-ray diffraction (XRD), and evaluated according to the formula $y{\text{Mg}}_5{\text{Si}}_8{\text{O}}_{20}{\left(\text{OH}\right)}_2\cdot x{\text{Mg}}_2{\text{Fe}}_{\text{2}}^{\text{III}}{\text{Si}}_8{\text{O}}_{20}{\left(\text{OH}\right)}_2\cdot \left(1-x-y\right)$ Mg2Al2Si8O20(OH)2. Included in the study were PFl-1 and several commercial palygorskites. Our analysis of 2nd derivative NIR spectra shows that the dioctahedral composition is adequately described by three sharp overtone bands representing AlAlOH, AlFeIIIOH and FeIIIFeIIIOH in M2 dioctahedral sites, and that the summed intensity of these bands is proportional to the amount of dioctahedral component present (1−y). The samples show large variations in the degree of dioctahedral FeIII-for-Al substitution with FeIII occupying up to 70% of the dioctahedral M2 sites. Ternary analysis shows that the distribution of dioctahedral Al and FeIII is not random, but displays a tendency towards homoionic pairing. An overtone band at 7214 cm−1 and several combination bands are indicative of a trioctahedral Mg3OH component (y), and their appearance correlates with a distinct palygorskite signature in thermogravimetric analysis. Nevertheless, these bands cannot be used reliably for the quantification of a trioctahedral palygorskite component due to their close similarity to those of sepiolite. To circumvent this problem, we have evaluated y indirectly by calculating the difference between 1−y and the total concentration of palygorskite determined by the normalized intensity of the d110 XRD peak of palygorskite at 10.4 Å. Using this methodology, we have found that the samples conform to a trioctahedral limit of y ≈ 0.55, although within this limit they display large variations in octahedral character. Finally, we extend the above methodology to PLS chemometrics and show how NIR can be used to determine palygorskite content routinely in multimineralic geological samples.