Alteration of the crystal structure of Mulhacén antigorite caused by dry, vibration grinding was investigated by X-ray diffraction (XRD), infrared spectroscopy (IR), thermal analyses (TG), grain-size distribution, and transmission and analytical electron microscopy (TEM, AEM). Grinding for 1 min reduces particles to a size ideal for IR and TG. With prolonged grinding, XRD and electron diffraction patterns showed that the crystal structure was affected mainly along the c axis, causing a partial loss of crystallinity. TG analyses revealed that vibration grinding modified mineral dehydration, accelerating the dehydroxylation process and transforming the structural OH to adsorbed water in the resulting matrix. IR spectra and AEM showed that grinding affected the tetrahedral sheet to a lesser extent than the octahedral sheet. Partial release of Mg by preferential destruction of the octahedral sheet after 10 min grinding produced an increase in the Si/Mg ratio in semi-crystalline particles, whereas the amorphous material product after 120 min showed the same composition as the initial antigorite. TEM and grain-size distribution results revealed that grinding led to a general decrease in particle size at the beginning of the experiment followed by the agglomeration of ultrafine particles as grinding proceeded.

The Tazzeka Mountain, located approximately 20 km south of Taza, eastern Morocco, is composed of a Westphalian volcano-sedimentary complex. It contains rhyolitic ignimbrites with the following minerals: quartz, potassium feldspar, oligoclase-andesine, and biotite. The ignimbrites are extensively altered because of a dense network of fractures in the massif. Alteration has resulted in the formation of spheroidal rocks and saprolite, the thickness of which depends on local topography. The evolution of the biotites in the ignimbrites was investigated by microprobe analysis of the mica crystals. This technique provides data that are not accessible through classical analytical methods. Biotites are transformed into secondary clay minerals, mainly chlorites and illites; intermediate stages are related to the degree of alteration of biotite, the latter being expressed by the K2O content which decreases progressively from 7.3 to 1.3%. Next come protochlorites and chlorites sensu stricto, in which the K2O content is 0.3%. Several processes including retrodiagenesis, hydrothermal activity, fumarolic activity, and geochemical weathering contributed to the transformation of the biotites at Tazzeka.

Extensive hydrothermal alteration is observed around volcanogenic massive sulfide deposits. These deposits are related to Late Cretaceous volcanism in various parts of the Eastern Pontide province. Mineral assemblages resulting from alteration consist of mostly clay minerals and silica polymorphs, some sulfate minerals, and scarce zeolite minerals. The clay minerals are kaolinite, illite, and smectite. These minerals were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM)-energy dispersive spectrometry (EDS), X-ray fluorescence spectroscopy (XRF), and differential thermal analysis (DTA)-thermal gravimetry (TG) techniques. The illite and the toseki deposits are a result of hydrothermal alteration of dacitic-andesitic volcanites. Two groups of bentonite deposits occur; the first mainly formed by hydrothermal solution whereas the second group resulted from halmyrolysis.

The smectite in these alteration zones is generally montmorillonitic in composition and the interlayer cation is mostly Ca and lesser amounts of Na. The SiO2 and Fe2O3 contents of the hydrothermal bentonites are higher than those of the halmyrolysis smectites; however, the MgO content of both groups is similar. The Na2O and K2O contents of both groups are generally <0.5%. The hydrothermal bentonites are not plastic and have open honeycomb microtextures, although the halmyrolitic smectites are plastic with ultrafine and rod-shaped textures. Illite, which contains some smectite layers, is a 1M polymorph, and has an asymmetry to the low-angle side of the XRD peaks. The impure illite deposits contain various combinations of smectite, kaolinite and gypsum, galena, sphalerite, pyrite, goetite, and quartz. The illite has >35 wt. % Al2O3. The toseki raw material, which may be possibly useful as a porcelain raw material, is composed mainly of illite, kaolinite and quartz, or illite and quartz. The crystallinity of the kaolinite is poor.

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.

Palygorskite and sepiolite show a high sorption capacity for organic molecules. Adsorption of 2 organic cations, methylene blue (MB) and crystal violet (CV), by palygorskite and sepiolite were examined. The maximum sorption of MB and CV far exceeded the cation exchange capacity (CEC) of these minerals. This shows that, besides the contribution of free negative sorption sites (P-), the sites satisfied with sorption of single cations (PXi0) and neutral sorption sites (N) on clay surfaces may contribute to the sorption of organic cations. The number of neutral sites was determined by examining the sorption of 2 neutral organic molecules, triton-X 100 (TX100) and 15 crown ether 5 (15C5), and by application of the Langmuir isotherm.

To determine the contribution of different sites, an adsorption model that applies the Gouy-Chapman equation and takes into account the formation of different clay-organic complexes in a closed system was employed. Application of this model to sorption data provided the calculation of binding coefficients for neutral sites, as well as the surface potential of the minerals at different sorbate concentrations.

At sorption maxima, for both palygorskite and sepiolite, the contribution of neutral sites for sorption of organic cations was the highest, followed by the PXi0 sites in case of CV sorption, while in sorption of MB the contribution of P- sites was the second highest. The Fourier transform infrared (FTIR) patterns of clay-organic cation complexes compared with pure clays confirm that the sorption of organic cations is by silanol groups located at the edge of fibrous crystals, which account for neutral sorption sites.

Previous investigations of goethite revealed a substantial variation of color and diffuse reflectance spectra (DRS) in the extended visible range (350–2200 nm). To better understand the causes of this variability and to assess the potential of DRS as a mineralogical tool, we investigated the DRS of pure and Al-substituted goethite, α-Fe1−xAlxOOH with x from 0 to 0.33, and mean crystal lengths (MCL) from 170 to 1800 nm. The strongly overlapping ligand field bands were extracted by fitting the single-electron transitions 6A1 → 4T1, 6A1 → 4T2, 6A1 → (4E; 4A1), and 6A1 → 4E(4D) as functions of the ligand field splitting energy, 10 Dq, and the interelectronic repulsion parameters, Racah-B and -C. With x increasing from 0 to 0.33, 6A1 → 4T1 decreased from 10,590 to 10,150 cm−1 (944 to 958 nm), and 6A1 → 4T2 decreased from 15,310 to 14,880 cm−1 (653 to 672 nm), while 10 Dq increased from 15,770 to 16,220 cm−1. From the change of 10 Dq we calculated a decrease of the Fe-(O,OH) distances from 202.0 to 200.9 pm (−0.5%). This decrease is smaller than the average decrease of all (Al,Fe)-(O,OH) distances (−1.8%) calculated from the change of the unit-cell lengths (UCL). That is, there remains a substantial difference in size between the larger Fe- and the smaller Al-occupied octahedra in the solid solution which may indicate the existence of diaspore clusters within the goethite structure. The increasing strain in the crystal structure due to the size mismatch and limited contractibility of the oxygen cage around Fe may be the primary reason for Al substitution being restricted to x < 0.33. The bands 6A1 → (4E; 4A1) and 6A1 → 4E(4D) did not shift, indicating a constant covalency of the Fe-(O,OH) bonds with B = 628 cm−1 and C = 5.5B. Whereas variation of band energies could be explained in terms of the Fe-(O,OH) ligand field, the variation of color and band intensities was mainly determined by crystal size. Although our study confirmed the potential of DRS for mineralogical investigations, there is still a gap between the fundamental theory and the explanation of some spectral features.

Double hydroxide solids precipitated homogeneously from three laboratory-synthesized aqueous solutions that simulated mildly contaminated surface or groundwater. Over a limited pH range, precipitates formed rapidly from dissolved ions, and more slowly by incorporating ions dissolving from other solids, including highly soluble aluminous solids. The precipitates were characterized by size and shape via transmission electron microscopy (TEM), by composition via inductively coupled plasma-mass spectrometry (ICP-MS) of mother solutions and analytical electron microscopy (AEM) of precipitates, and by structure via powder X-ray diffraction (XRD), TEM, and extended X-ray absorption fine structure (EXAFS) spectroscopy. They were identified as nanocrystalline cobalt hydrotalcite (CoHT) of the form [Co(II)1-xAl(III)x(OH)2]x+(An−x/n)·mH2O, with x = 0.17–0.25, A = CO32−, NO3−, or H3SiO4−n = anion charge and m undetermined. Complete solid solution may exist at the macroscopic level for the range of stoichiometrics reported, but clustering of Co atoms within hydroxide layers indicates a degree of immiscibility at the molecular scale. Composition evolved toward the Co-rich endmember with time for at least one precipitate. The small layer charge in the x = 0.17 precipitate caused anionic interlayers to be incomplete, producing interstratification of hydrotalcite and brucite-like layers. Solubility products estimated from solution measurements for the observed final CoHT stoichiometries suggest that CoHT is less soluble than the inactive forms of Co(OH)2 and CoCO3 near neutral pH. Low solubility and rapid formation suggest that CoHT solids may be important sinks for Co in contact with near neutral pH waters. Because hydrotalcite can incorporate a range of transition metals, precipitation of hydrotalcite may be similarly effective for removing other trace metals from natural waters.

Transmission electron microscopy (TEM) and analytical electron microscopy (AEM) methods were used to study the crystal chemistry of phyllosilicates occurring in green grains of Miocene sediments from the Congo continental shelf. Using diagrams based on wt. % K and the (Fe + Mg)/Al ratio, minerals were distinguished from mixed-layer phases. The most abundant detrital mineral is Fe-kaolinite. The morphology and composition identify this mineral as a component of ferralitic soils. This Fe-rich kaolinite has undergone a complex process of partial dissolution and recrystallization and further enrichment in Fe and, to a lesser extent, in Mg in the marine environment. The detrital mica observed with TEM retains the original morphology and chemistry of muscovite. Alteration processes resulted in the crystallization of 1:1 trioctahedral Fe2+ and Mg-rich minerals and interstratified phases with 1:1 and 2:1 layers in varying proportions observed with the aid of high-resolution transmission electron microscopy (HRTEM) imaging. Included among the newly formed 7-Å phases are those apparently containing excess Si. The smectites are apparently neoform, and chemical analyses showed that these marine K-smectites belong to the beidellite-nontronite series and have tetrahedral substitutions similar to muscovite. Their compositions are closer to beidellite than to nontronite, although the latter was observed in association with goethite. The TEM observations and crystallochemical data show that mineral alteration ceased after forming mixed-layer minerals, and alteration did not reach the glauconitization stage. Apparently, the Miocene assemblages experienced rapidly changing environmental conditions and high sedimentation rates that continue today.

The effect of freezing and thawing on the rheological behavior of illite suspensions was studied by examining viscosity and plasticity. Stability of suspensions was characterized by a hysteresis loop of thixotropy. Thermal gravimetric and differential scanning calorimetry analysis were also used. After initial freezing and thawing, the flow curves of the suspensions show an increased viscosity, an “irregular up line”, and a greater hysteresis loop of thixotropy. The ratios of mean viscosity of previously frozen (F) and control (O) samples (ηF/ηO) for non-expandable 2:1 phyllosilicates ranges from 1.3 to 2.1. Addition of monovalent (0.1% Na2SiO3) and divalent cations (0.3% CaCl2 or BaCl2) increase and decrease the shear-stress difference between F and O samples, respectively. Prior freezing of clay samples results in an increase of plasticity by ∼20–30%. The thermal analysis data of F samples show an increase in weight loss, and a decrease in enthalpy of dehydration. The changes of physico-chemical properties from cycles of freezing and thawing are long lasting. The freezing memory effect of illite-type clays is expected to play an important role in ceramic processing, i.e., casting processes, plastic formation, and sintering.

A new technique utilizing Raman microscopy and Fourier transform infrared (FTIR) microsacopy is described. This technique uses thin films of oriented clay aggregates on glass slides suitable also for X-ray diffraction (XRD). Raman microscopy proved the most useful technique providing both better resolution of the OH-stretching bands and greater spectral resolution. Kaolinites from Washington County, Georgia, with varying defect structures involving layer stacking were intercalated with formamide and additional Raman bands were observed at 3610 and 3627 cm−1. A concomitant decrease in the inner-surface OH band intensities at 3695 and 3685 cm−1 occurred. These bands are attributed to the inner-surface OH hydrogen bonded to the formamide molecule through the C=O group. The 3627 cm−1 band is sharp with a half width of 7.5 cm−1 and comprises 11% of the total normalized band area. When two additional OH bands are observed at 3610 and 3627 cm−1 two C=O bands at 1674 and 1658 cm−1 are observed also. The two additional Raman inner-surface OH bands were not observed in the IR spectra. However, a band of low intensity was observed at 3590 cm−1. Models for the intercalation of formamide in kaolinites are proposed.

The Ayvacık bentonites, products of Miocene calc-alkaline volcanic rocks, are composed of smectite of the montmorillonite-beidellite series. Fault-related hydrothermal solutions have altered andesitic rocks to dioctahedral smectites. Differences in the micro-morphology of the two end-members are distinguished by scanning electron microscopy (SEM) studies. The beidellite particles are of delicate ribbons and rosette habits, whereas montmorillonite particles are very thin, curled sheets and flakes. Clay size (<2 µm) fractions contain (in wt. %) 54.90–56.80 SiO2, 19.65–28.54 Al2O3, 0.45–6.28 Fe2O3, 0.10–1.72 CaO, 0.80–4.15 MgO, 0.55–1.88 K2O, and 0.08–1.15 Na2O, which confirm that the beidellites are Fe-rich (5.06–6.28 wt. %), except for one sample (0.45 wt. % Fe2O3). The Greene-Kelly test (Li-saturation and heating) gave very good results for the measurement of the d(001) of the two end-members. Nickel, Ti, and Cr enrichment in smectite is related to the chemical composition of hydrothermal solutions that passed through the ophiolite complex.

The sorption of the uranyl oxo-cation (UO22+)at different types of binding sites on layer silicate mineral surfaces was investigated. Well-characterized samples of vermiculite and hydrobiotite were exposed to aqueous uranyl under conditions designed to promote surface sorption either at fixed charge ionexchange sites or at amphoteric surface hydroxyl sites. The local structure of uranium in the sorption samples was directly measured using uranium L3-edge extended X-ray absorption fine structure (EXAFS). Polarized L1- and L3-edge X-ray absorption near-edge structure (XANES) measurements were used to characterize the orientation of uranyl groups in layered samples. X-ray diffraction (XRD) measurements of interlayer spacings were used to assess the effects of ion-exchange and dehydration upon the mineral structure. The most significant findings are: (1) Under conditions which greatly favor ion-exchange sorption mechanisms, uranyl retains a symmetric local structure suggestive of an outer-sphere complex, with a preferred orientation of the uranyl axis parallel to the mineral layers; (2) Upon dehydration, the ionexchange complexes adopt a less symmetric structure, consistent with an inner-sphere complex, with less pronounced orientation of the uranyl axis; and (3) For conditions which favor sorption at surface hydroxyl sites, uranyl has a highly distorted equatorial shell, indicative of stronger equatorial ligation, and the detection of a neighboring U atom suggests the formation of surface precipitates and/or oligomeric complexes.

A new method is proposed for applying the chlorite geothermometer using X-ray diffraction (XRD) data. A linear correlation has been found between the (001) basal spacing of chlorite and its “crystallization” temperature. The basal spacing values were corrected for an increase of Al(IV) with Fe enrichment (Fe/Fe + Mg), when the Fe(II) value of chlorite is >2.6 in the formula unit. The regression coefficient of the best fit is r = 0.95. Only 2 Bragg lines need to be measured for application of the proposed technique: the (001) and (060) X-ray spacing. The proposed method is applied to 19 chlorite samples from 4 different geothermal fields. The temperatures of chlorite formation obtained with the present method and those calculated by the expressions formulated by Cathelineau (1988) and Kranidiotis and MacLean (1987) are presented. The method's validity was also tested on geothermal chlorites from the literature, and the results show good agreement with previous experimental trials.

We investigated the crystallization of ferrihydrite prepared by hydrolysis of Fe(NO3)3 solutions containing phosphate. Crystallization was studied at different pH (3–9), temperatures (298, 323, and 373 K), and initial P/Fe atomic ratios for periods to 730 d. Generally, crystallization was inhibited or only poorly crystallized lepidocrocite was formed at P/Fe > 2.5%. Phosphate favored the formation of hematite over goethite at all temperatures for most of the pH and P/Fe ranges investigated. This result is consistent with a model in which phosphate acts as a template for hematite formation, in analogy with other anions, such as oxalate. However, goethite was preferentially formed at alkaline pH and P/Fe > 1%, probably because high phosphate concentration resulted in a large increase in the negative charge of the ferrihydrite particles. This resulted in turn in less aggregation, a process that is known to precede dehydration to hematite. Phosphate greatly influenced the morphology of hematite and goethite. Hematite was often ellipsoidal or spindle-shaped. Twinned goethite crystals with a hematite core were formed at alkaline pH at P/Fe > 1%. Both hematite and goethite particles incorporated phosphate in an occluded form not desorbable by repeated alkali treatments.

Li+, Na+, Ca2+, Sr2+, Cu2+, or Zn2+-saturated samples of a cis-vacant montmorillonite from Linden, Bavaria, were heated to temperatures between 200–700°C. Half of each heated sample was subsequently autoelaved under steam at 200°C (∼1.5 MPa) to promote rehydroxylation. The smectites were characterized by cation-exchange capacity (CEC), determination of exchangeable cations, infrared (IR) spectroscopy, and thermoanalytical investigations of evolved water in a thermobalance linked with a mass spectrometer.

Changes in the montmorillonite structure and dehydroxylation behavior are related to three respective mechanisms: type of the interlayer cation, interlayer cation radius, and the movement of the interlayer cation. The migration of the smaller Li+, Cu2+, and Zn2+ ions after heating produces a strong reduction of CEC due to the Hofmann-Klemen effect before the initiation of dehydroxylation. Thereafter, the CEC of these smectites remains constant over a large temperature interval during dehydroxylation. After rehydroxylation, Cu2+ and Zn2+-rich samples release 16–23 meq/100 g of Mg2+ from the structure. No Mg2+ release is observed for the Li+-rich montmorillonite. Also the dehydroxylation behavior after rehydroxylation differs between the Cu2+, Zn2+, and Li+-rich samples. The mass curves of the evolved water during thermoanalysis of the rehydroxylated Cu2+ and Zn2+-rich smectites show a peak doublet between 480–700°C. For the Li+, Na+, Ca2+, and Sr2+-rich montmorillonites, the second peak disappeared and a third peak at ∼760°C developed after rehydroxylation. The resulting structure after rehydroxylation of all samples is celadonite-like.

A nickel hydroxide-vermiculite complex (NHVC) with csinβ = 1.41 nm and particle sizes from 0.075 to 0.15 mm was obtained hydrothermally by adding nickel nitrate solution to vermiculite from Transvaal, South Africa. The quantity of nickel hydroxide included in NHVC was controlled by adjusting the concentration of the nickel nitrate solution. The thermal behavior of NHVC at 450°C or above was independent of the Ni content. However, small differences exist in the dehydration behavior of NHVC below 450°C. One-dimensional Fourier electron density analysis of the NHVC structure containing 2.43 mol of Ni per half unit cell showed that Ni cations occupy the interlayer of NHVC, and 10% of the total Ni cations is in the ditrigonal cavity of the basal-oxygen plane of the tetrahedral sheet.

Because layered Fe(II)Fe(III)-hydroxides (Green rusts, GRs) are anion exchangers, they represent potential orthophosphate sorbents in anoxic soils and sediments. To evaluate this possibility, two types of experiments with synthetic sulphate-interlayered GRs (GRSO4 = Fe2+4Fe3+2(OH)12SO4 ×H2O) were studied. First, sorption of phosphate in GRSO4 was followed by reacting suspensions of pure GRSO4 synthesized by oxidation of Fe(II) with an excess of Na2HPO4 (pH 9.3). Second the possible incorporation of phosphate in GR during formation by Fe(II)-induced reductive dissolution of phosphate-containing ferrihydrites was examined in systems containing an excess of Fe(II) (pH 7). With excess phosphate in solution, GRSO4 initially sorbed phosphate in the interlayer producing a basal layer spacing of 1.04 nm, but only ~50% of the interlayer sulphate was exchanged with phosphate. This GR slowly transformed to vivianite within months. In the Fe(II)-rich systems, reaction with synthetic ferrihydrites produced GRSO4 similar to that produced by air oxidation. Reaction of Fe(II) with phosphate-containing ferrihydrites initially produced amorphous greenish phosphate containing precipitates which, after 3–4 h, crystallized to GRSO4 and vivianite. In these solutions, stable phosphate-free GRSO4 can form since precipitation of vivianite produced low phosphate activity. Consequently, in both systems GR or amorphous greenish precipitates act as reactive intermediates, but vivianite is the stable end-product limiting phosphate concentration in solution. It is also inferred that Fe(OH)2 is an unlikely phosphate sorbent in mixed Fe(II)-Fe(III) systems because GR phases are more stable (less soluble) than Fe(OH)2.

Partial stabilization of Fe(II) in chemically reduced smectite, which normally readily undergoes reoxidation in air, was achieved. The purpose of this study was to determine if Fe(II) can be stabilized in reduced smectites by Li fixation upon heating. More than 80% of total Fe in ferruginous smectite SWa-1 was reduced to Fe(II) using the citrate-bicarbonate-dithionite (CBD) method while purging the clay dispersion with N2. The reduced smectite was Li-saturated, washed free of excess ions, freeze-dried, and heated in N2 atmosphere at 260°C for 24 h to produce Li-fixation. This treatment caused partial stabilization of Fe(II) in the clay structure. Chemical analysis, Mössbauer spectroscopy, and Fourier transform infrared (FTIR) spectroscopy proved that <20% of total Fe was Fe(II) after reoxidation with oxygen in a water dispersion, a treatment which causes complete reoxidation of Fe(II) in reduced Na-smectites. Decomposition of the OH-stretching band evident in the IR spectra indicated migration of Li into the vacant octahedra. Some of the OH groups in the reoxidized smectite were found in local trioctahedral configurations, associated with the AlFe(II)Li or Fe(III)Fe(II)Li groupings of central atoms in the octahedral sheet.

Samples of Silica Springs allophane from Tongariro National Park, New Zealand, having Al/Si atomic ratios in the range 1.1-1.9, were studied by 27Al nuclear magnetic resonance (NMR) spectroscopy with high field strength (9.4 and 11.7 T) and fast magic-angle spinning (MAS) (9-13 kHz). Spectra for all samples show peaks for 6- and 4-coordinate Al and also for 5-coordinate Al. For 1 sample, the peak for 5-coordinate Al is dominant. Use of 2 instruments and 2 field strengths allowed the integrity of the spectra and the assignment of 5-coordinate Al to be verified. The “true” chemical shift (after a small correction for quadrupolar shift) observed for 5-coordinate Al in Silica Springs allophane is 36 ± 1 ppm, which is consistent with shifts reported for 5-coordination in well-characterized crystalline structures. We suggest that 5-coordination in Silica Springs allophane is associated with the edges of fragments of incomplete octahedral sheets that are bonded to disordered, though more complete, curved tetrahedral sheets in the primary particles of this allophane. Other allophanes with Al/Si < 2, and which are poor in octahedra relative to tetrahedra, may also have significant Al in 5-coordinate sites.

The deintercalation of a low-defect kaolinite intercalated with hydrazine was studied by X-ray diffraction, diffuse reflectance infrared spectroscopy (DRIFT), and Raman microscopy over 30 d. X-ray diffraction showed that the kaolinite was fully intercalated. More than 120 h were required for the hydrazine-intercalate to decompose. The Raman spectra of the hydrazine intercalate showed only a single band at 3620 cm−1, which was attributed to the innerhydroxyl group. Upon deintercalation, additional Raman bands were observed at 3626 and 3613 cm−1. These bands decreased in intensity with further deintercalation. As deintercalation proceeded, the bands assigned to the inner-surface hydroxyl groups at 3695, 3682, 3670, and 3650 cm−1 occurred and increased in intensity. DRIFT spectra showed two bands at 3620 and 3626 cm−1 for the fully intercalated kaolinite only. Upon deintercalation, an additional band assigned to intercalated water was observed at 3599 cm−1 and increased in intensity at the expense of the 3626-cm−1 band. Bands attributed to the innersurface hydroxyl groups increased in intensity with deintercalation. Both the Raman and DRIFT spectra showed complexity in the NH-stretching region with two sets of NH-symmetric and antisymmetric stretching bands. Deintercalation was followed by the loss of intensity of these bands. Significant changes were also observed in the hydroxyl deformation and water-bending modes as a result of deintercalation. A model of hydrazine intercalation of kaolinite based on the insertion of a hydrazine-water unit is proposed. The hydrated end of the hydrazine molecule hydrogen bonds with the innersurface hydroxyl groups resulting in the formation of a band at 3626 cm−1 in the DRIFT spectra.