Evidence for the Formation of Trioctahedral Clay upon Sorption of Co(2+) on Quartz

The sorption mechanism of Co on quartz at room temperature has been investigated by an in-depth analysis of published extended X-ray absorption fine structure (EXAFS) spectroscopy and solution chemistry data. In particular, the 3.5-5 ? mid-range atomic environment of Co has been determined with unprecedented precision by combining ad initio FEFF7.02 calculations and results obtained by polarized EXAFS on the mid-distance structure of sheet silicate minerals. The local atomic environment around sorbed Co atoms is identical to that of Co in trioctahedral clays and substantially different from that in the cobalt hydroxide Co(OH)(2(s)). Neoformation of a trioctahedral clay is consistent with calculated thermodynamic solubilities, which indicate that 2:1 and 1:1 Co-rich hydrous silicates, similar to kerolite and chrysotile, are less soluble than Co(OH)(2(s)). Consequently, precipitation of Co-rich clay is favored over that of Co(OH)(2(s)) at pH values below 9 and for a dissolved Si concentration equal to quartz solubility. New experimental data show that dissolved Si concentrations can approach, and even exceed, that of quartz solubility during the short times of sorption experiments. Based on the available data, it is not possible to conclude unequivocally if the Co layer silicate grew epitaxially on the quartz surface, topotactically in a surface amorphous layer, or independently of the quartz framework structure. The structural and chemical interpretation is supported by recent published studies in which sorption of a hydrolyzable cation leads to the neoformation of a mixed layer phase formed from the sorbate species and the sorbent metal. This surface-induced precipitation mechanism is a general phenomenon that may account for the formation of secondary clays as coatings on silicates. Copyright 1999 Academic Press.     

Sorption of Metal Ions on Clay Minerals: II. Mechanism of Co Sorption on Hectorite at High and Low Ionic Strength and Impact on the Sorbent Stability

The mechanism of Co uptake from aqueous solution onto hectorite (a magnesian smectite) and its impact on the stability of this clay mineral were investigated as a function of Co concentration (TotCo = 20 to 200 μM, 0.3 M NaNO₃) and ionic strength (0.3 and 0.01 M NaNO₃, TotCo = 100 μM) by combining kinetics measurements and Co K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The morphology of the sorbent phase was characterized by atomic force microscopy (AFM) and consists of lath-type particles bounded by large basal planes and layer edges.At low ionic strength (0.01 M NaNO₃), important Co uptake occurred within the first 5 min of reaction, consistent with Co adsorption on exchange sites of hectorite basal planes. Thereafter, the sorption rate dramatically decreased. In contrast, at high ionic strength (0.3 M NaNO₃), Co uptake rate was much slower within the first 5 min and afterward higher than at 0.01 M NaNO₃, consistent with Co adsorption on specific surface sites located on the edges of hectorite. Time-dependent isotherms for Co uptake at high ionic strength indicated the existence of several sorption mechanisms having distinct equilibration times. The dissolution of hectorite was monitored before and after Co addition. A congruent dissolution regime was observed prior to Co addition. Just after Co addition, an excess release of Mg relatively to congruent dissolution rates occurred at both high and low ionic strengths. At high ionic strength, this excess release nearly equaled the amount of sorbed Co. The dissolution rate of hectorite then decreased at longer Co sorption times.EXAFS spectra of hectorite reacted with Co at high and low ionic strengths and for reaction times longer than 6 h, exhibited similar features, suggesting that the local structural environments of Co atoms are similar. Spectral simulations revealed the occurrence of 2 Mg and 2 Si neighboring cations at interatomic distances characteristic of edge-sharing linkages between Co and Mg octahedra and corner-sharing linkages between Co octahedra and Si tetrahedra, respectively. This local structure is characteristic of inner sphere mononuclear surface complexes at layer edges of hectorite platelets. The occurrence of these complexes even at low ionic strength apparently conflicts with kinetics results, as exchangeable divalent cations are known to form outer sphere surface complexes. To clarify this issue, the amount of Co adsorbed on exchange sites was calculated from the solute Co concentration, assuming that cation exchange was always at equilibrium. These calculations showed that sorbed Co was transferred within 48 h from exchange sites to edge sorption sites.     

ON THE ADSORPTION OF HYDROPHOBIC POLLUTANTS ON SURFACTANT/CLAY COMPLEXES: COMPARISON OF THE INFLUENCE OF A CATIONIC AND A NONIONIC SURFACTANT

The adsorption of the cationic surfactant dodecyl trimethyl ammonium bromide (DTAB) and of the nonionic surfactant dodecyl octaethylene glycol ether (C₁₂E₈) on four different layer silicates and their influence on the sorption processes of the fungizide biphenyl were studied. Unexpectedly, no great differences were found in comparing the adsorption of the two surfactants on the basis of physicochemical investigations, although the adsorption mechanism up to monolayer formation is fundamentally different (ion exchange and physisorption). Thus, the plateau values of the adsorption isotherms and the molar enthalpies of displacement Δ ₂₁h are of the same order of magnitude for both surfactants and the same basal spacing by intercalation is observed in the case of swelling clays. The isotherms of the hydrophobic contaminant biphenyl are of the linear Cl-type at all layer silicates and very low adsorption takes place approximately proportionally to the BET (N₂) surface area. If the surface is weakly hydrophobized by surfactants (c_surfactant<< critical;micelle concentration (CMC)), biphenyl adsorption is clearly increased. These processes can be adequately described using the distribution coefficients K and K_OC (Henry coefficient related to the organic carbon content). K_OC is hardly influenced by the type of layer silicate for DTA⁺-layer silicates, whereas the C₁₂E₈ layer silicate complexes generally show higher, but also different K_OC values. If the surfactant concentrations are above the CMC, solubilization and adsorption compete for the pollutant molecules, which leads to a significant decrease in biphenyl adsorption.     

Sorption of Metal Ions on Clay Minerals

The mechanism of Co uptake from aqueous solution onto hectorite (a magnesian smectite) and its impact on the stability of this clay mineral were investigated as a function of Co concentration (TotCo = 20 to 200 μM, 0.3 M NaNO(3)) and ionic strength (0.3 and 0.01 M NaNO(3), TotCo = 100 μM) by combining kinetics measurements and Co K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The morphology of the sorbent phase was characterized by atomic force microscopy (AFM) and consists of lath-type particles bounded by large basal planes and layer edges. At low ionic strength (0.01 M NaNO(3)), important Co uptake occurred within the first 5 min of reaction, consistent with Co adsorption on exchange sites of hectorite basal planes. Thereafter, the sorption rate dramatically decreased. In contrast, at high ionic strength (0.3 M NaNO(3)), Co uptake rate was much slower within the first 5 min and afterward higher than at 0.01 M NaNO(3), consistent with Co adsorption on specific surface sites located on the edges of hectorite. Time-dependent isotherms for Co uptake at high ionic strength indicated the existence of several sorption mechanisms having distinct equilibration times. The dissolution of hectorite was monitored before and after Co addition. A congruent dissolution regime was observed prior to Co addition. Just after Co addition, an excess release of Mg relatively to congruent dissolution rates occurred at both high and low ionic strengths. At high ionic strength, this excess release nearly equaled the amount of sorbed Co. The dissolution rate of hectorite then decreased at longer Co sorption times. EXAFS spectra of hectorite reacted with Co at high and low ionic strengths and for reaction times longer than 6 h, exhibited similar features, suggesting that the local structural environments of Co atoms are similar. Spectral simulations revealed the occurrence of approximately 2 Mg and approximately 2 Si neighboring cations at interatomic distances characteristic of edge-sharing linkages between Co and Mg octahedra and corner-sharing linkages between Co octahedra and Si tetrahedra, respectively. This local structure is characteristic of inner sphere mononuclear surface complexes at layer edges of hectorite platelets. The occurrence of these complexes even at low ionic strength apparently conflicts with kinetics results, as exchangeable divalent cations are known to form outer sphere surface complexes. To clarify this issue, the amount of Co adsorbed on exchange sites was calculated from the solute Co concentration, assuming that cation exchange was always at equilibrium. These calculations showed that sorbed Co was transferred within 48 h from exchange sites to edge sorption sites. Copyright 1999 Academic Press.     

Kinetics of carbon dioxide mechanosorption by Ca-containing silicates

Kinetics of mechanically induced CO₂ extensive sorption by silicate minerals (labradorite, diopside, okermanite, ghelenite and wollastonite) was considered. Mechanical activation of the silicates was carried out in a planetary mill in CO₂ at atmospheric pressure. Carbon dioxide was consumed by the silicates in the form of carbonate ions and its content in the samples after 30 min of mechanical treatment reached 3–12 mass% CO₂ depending on mineral composition. Equations that reasonably good represent kinetics of CO₂ mechanosorption by silicates were proposed. These equations enable to calculate mechanosorption coefficients that characterize the diffusivity of CO₂ into disordered silicate matrix under intensive mechanical impact. Thermal analysis of the mechanically activated silicates showed that there was positive correlation between temperature of complete carbonate decomposition and mechanosorption coefficient.     

Designed organo‐layered silicates as nanoreactors for 1,3‐butadiene stereospecific polymerization toward rubber nanocomposites synthesis

Organo‐modified layered silicates were synthesized and used as inorganic carriers for CoCl₂(P^tBu₂Me)₂‐MAO catalyst in the polymerization of 1,3‐butadiene, yielding cis‐1,4‐enriched polybutadiene. The organoclays were prepared by: (i) intercalation of (ar‐vinyl‐benzyl)trimethyl ammonium chloride salt through an ion exchange reaction, and (ii) the edge‐surface grafting by trimethylchlorosilane. The ammonium modifier acts as “spacer” increasing the layer d‐spacing and as “filler” favoring the silylation of the edge‐surface clay hydroxyls. The grafted silane prevents the MAO cocatalyst from reacting with the edge‐OHs, by forcing it to react within the interlayer clay region. MAO lead to methylation of the cobalt complex and carbanion abstraction to give a cobalt‐methyl cation that is stabilized by the MAO anion. The nanoconfined cationic alkylated species insert the butadiene on the Co‐Me bond affording the growth of the polymer chains within the clay layers. The growing of the macromolecular chains fills the interlayer silicate region giving an intercalated polybutadiene rubber nanocomposite. The role of the silicate organo modification on the heterogeneous catalyst structural features, the polymerization behavior and the nanocomposite structures are discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Comparison of surface properties between kaolin and metakaolin in concentrated lime solutions

The surface adsorption of calcium hydroxide onto kaolin and metakaolin was investigated by monitoring with atomic emission spectroscopy and pH measurements the amounts of ions left in solution after exposing clays to calcium hydroxide solutions of various concentrations. Both clays adsorb calcium and hydroxyl ions but differently. Kaolin adsorbs calcium hydroxide not only at the edges of the clay particles but also onto the basal faces. The adsorbed hydrated calcium ions form a layer on the clay particle surfaces, preventing further dissolution of the clay mineral platelet. Metakaolin shows high pozzolanic activity, which provides the quick formation of hydrated phases at the interfaces between metakaolin and lime solutions. The nature of the hydration products has been investigated using X-ray diffraction (XRD) and differential thermal analysis (DTA). The most important hydrated phases like CSH (hydrated calcium silicate) and C₂ASH₈ (gehlenite) have been identified.     

Sorption and transport mechanism of gases in polycarbonate membranes

The transport phenomena of oxygen and nitrogen across a pure polycarbonate (PC) and a cobalt(III) acetylactonate (Co(acac)₃) containing PC membrane was studied. Co(acac)₃ was added into a polycarbonate membrane to enhance its oxygen solubility. The oxygen sorption isotherms was measured. It was found that the oxygen solubility decreased sharply as pressure increased, especially at low pressure region. On the contrary, the oxygen permeability increased slightly with respect to pressure. Both the solution-diffusion model and traditional dual mobility model were unable to explain the inconsistent pressure dependency between solubility and permeability. Instead of adopting Langmuir-Henry sorption model, a modified dual mobility model which incorporates BET-type isotherm to describe oxygen sorption. The diffusivity of molecules moving at the first adsorbed layer was assumed to be different from those moving at higher layers. This modified dual mobility model satisfactorily described both the pressure dependency of oxygen solubility and permeability. It was also found that the increase of oxygen/nitrogen selectivity was not due to the elevation of oxygen to nitrogen solubility ratio but due to the mobility ratio of oxygen to nitrogen at the higher adsorption layers.     

Preparation of Silicates Using HSi(OC2H5)3 and Their NO x -Adsorption Behavior

The preparation and NO-adsorption/desorption behavior of Li, Ca and Ba silicates were investigated aiming at the application to a NO_x-absorbent. Li silicate was prepared by reaction of HSi(OC₂H₅)₃ with aqueous lithium silicate solution (LSS). Ca and Ba silicates were prepared from gels obtained using CH₃Si(OC₂H₅)₃, Si(OC₂H₅)₄, HSi(OC₂H₅)₃ and alkaline-earth alkoxides. The surface of these silicates indicated the solid basicity of H₀ = 9 and adsorbed the acidic gas of NO. FT-IR spectra of the silicates adsorbing NO showed the absorption peaks in the range of 1300–1600 cm^{– 1} corresponding to ionic and covalent nitrate NO₃^–. The complete desorption of adsorbed NO species occurred above 500°C in the Li silicate, above 500°C in the Ca and Ba silicates prepared using CH₃Si(OC₂H₅)₃, and above 700°C in the Ba and Ca silicates prepared using Si(OC₂H₅)₄. Regarding the Ca and Ba silicates, the difference in siloxane structure is thought to cause the difference in adsorption state and desorption behavior of NO.     

Raman spectroscopic study of ancient South African domestic clay pottery

The technique of Raman spectroscopy was used to examine the composition of ancient African domestic clay pottery of South African origin. One sample from each of four archaeological sites including Rooiwal, Lydenburg, Makahane and Graskop was studied. Normal dispersive Raman spectroscopy was found to be the most effective analytical technique in this study. XRF, XRD and FT-IR spectroscopy were used as complementary techniques. All representative samples contained common features, which were characterised by kaolin (Al2Si2O5(OH)5), illite (KAl4(Si7AlO20)(OH)4), feldspar (K- and NaAlSi3O8), quartz (alpha-SiO2), hematite (alpha-Fe2O3), montmorillonite (Mg3(Si,Al)4(OH)2 x 4.5 5H(2)O[Mg]0.35), and calcium silicate (CaSiO3). Gypsum (CaSO4 x 2H2O) and calcium carbonates (most likely calcite, CaCO3) were detected by Raman spectroscopy in Lydenburg, Makahane and Graskop shards. Amorphous carbon (with accompanying phosphates) was observed in the Raman spectra of Lydenburg, Rooiwal and Makahane shards, while rutile (TiO(2)) appeared only in Makahane shard. The Raman spectra of Lydenburg and Rooiwal shards further showed the presence of anhydrite (CaSO4). The results showed that South African potters used a mixture of clays as raw materials. The firing temperature for most samples did not exceed 800 degrees C, which suggests the use of open fire. The reddish brown and grayish black colours were likely due to hematite and amorphous carbon, respectively.     

On the interaction of tetraethoxosilane with metal alkoxides: Sol-gel synthesis of alkaline-earth metal silicates

Physicochemical analyses (solubility method, conductometry, and IR spectroscopy) revealed no complex formation in M(OR)_n-Si(OR)₄-ROH systems (M = Na, Ba, Al; R = Et, Prⁱ), unlike in the systems containing alkoxides of two metals. IR and NMR spectroscopy showed that Si(OR)₄ became reactive only due to microhydrolysis, which is accompanied most likely by the formation of intermediates (asymmetric molecules [Si(OH)_n(OR)_{4 ? n} ]). The hydrolysis was studied for model systems M(OEt)₂ ? si(OEt)₄ (M = Ba, Ca), and conditions for the synthesis of silicates were optimized.     

Sorption of neptunium on clays

Batch sorption experiments with²³⁷Np using kaolinite and molasse clays were carried out under oxic conditions. The sorption kinetics and the effects of particle size of clay samples, concentration of neptunium in the solutions and the pH below and above the point of zero charge of the clays on the sorption coefficients were studied. The sorption coefficients of neptunium, on kaolinite were between 23 and 1100 ml/g at pH 1.5 and 7.6, respectively, whereas, sorption on the molasse clay was not affected significantly by pH (R_d600 ml/g).     

Gas barrier properties of poly(ε‐caprolactone)/clay nanocomposites: Influence of the morphology and polymer/clay interactions

Poly(ε‐caprolactone)/montmorillonite nanocomposites were prepared maintaining a constant inorganic content with three means: melt blending of poly(ε‐caprolactone) with natural or organomodified clays, in situ polymerization of ε‐caprolactone in the presence of organomodified clays, and initiation of ε‐caprolactone polymerization from the silicate layer with appropriate organomodified montmorillonites and activator. In this last case, the polymer chains were grafted to the silicate layers and it was possible to tune up the grafting density. The presence of clays did not modify the polymer crystallinity. It was shown that the in situ polymerization process from the clay surface improved the clay dispersion. The gas barrier properties of the different composite systems were discussed both as a function of the clay dispersion and of the matrix/clay interactions. The highest barrier properties were obtained for an exfoliated morphology and the highest grafting density. Similar evolution of the permeability and the diffusion coefficients was observed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 205–214, 2005     

Plasma Chemical Functionalisation of a Cameroonian Kaolinite Clay for a Greater Hydrophilicity

A Cameroonian kaolinite powder was treated with gliding arc plasma in order to increase the amount of hydroxyl functional groups present on its external surfaces. The functional changes that occurred were monitored by Fourier transform infrared spectroscopy. The crystalline changes were followed by the X-ray diffraction. The ionisation effect, acid effect, and water solubility of the treated samples were also evaluated. Results showed that there is breaking of the bonds in the Si–O–Si and Si–O–Al groups, followed by the formation of new aluminol (Al–OH) and silanol (Si–OH) groups at the external surface of kaolinite after exposing the clay to the gliding arc plasma. The increase in hydroxyl groups on the surface of kaolinite leads to the increase of its hydrophilicity. Moreover, new charges appear on its surfaces and no significant change in crystallinity has occurred. This study shows that clays in powder form being can effectively be functionalised by gliding arc plasma in spatial post discharge processing mode. Knowing that the treatment in spatial post discharge offers the possibility to process large amounts of clay, this work is of great interest to the industry.     

XRD study of the dehydration and rehydration behaviour of Al-pillared smectites differing in source of charge

The swelling properties of Al-pillared clays, obtained from five different smectites, were studied using X-ray diffraction. These clays, the dioctahedral beidellite and montmorillonite and the trioctahedral saponite, hectorite and laponite differ in source of isomorphic substitution and represent a series of decreasing basicity along the siloxane plane. An Al oxyhydroxy cation was inserted between the layers to form the respective pillared clays and these clays were heated incrementally to 600°C. The XRD peaks at each stage of heating were recorded as well as the same samples subsequently wetted. Basal spacings of each clay at each stage of dehydration d rehydration indicated that the swelling of tetrahedrally substituted saponite and beidellite was indeed restricted, compared with the other three clays. This was attributed to greater basicity of the oxygen plane of beidellite and saponite due to tetrahedral substitution of Si by Al, resulting in an increase in the strength of hydrogen bonds between either water or the interlayer polyhydroxy cation and the clay.The data from the XRD analyses helped in addition, to clarify the thermal transformations of the Keggin ion itself. According to the changes in thed-spacings of the pillared clays it was concluded that the Keggin ion lost its structural water at 200°C and dehydroxylated in a range beginning at 350°C. Between 500 to 600°C this polymer cation, which is thought to form the Al₂O₃ oxide, did not rehydrate.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthdayThe authors wish to thank Laporte Industries, Inc., U.K. for the laponite sample.     

Characterization and assessment of Saudi clays raw material at different area

The general characteristics of three types of clays obtained from the different locations in Saudi Arabia have been investigated. These clays were compared with those of pure kaolin samples. Clays were analyzed by DTA, TGA, SEM, X-ray diffraction, chemical composition (XRF) and optical properties. Three clays are white clay (WC), red clay (RC) from Jeddah area and grey clay (GC) from Elmadina area. The comparison made with Spain clay as pure kaoline (KA). The clays contain kaolinite, illite, montmorillonite and quartz. Quartz is present in every class and varies between 45% and 20%. Montmorillonite is found mainly in the WC (50%) and are lacking only in sample RC and GC. Another important aspect with respect to the chemical composition of the clays is the low amounts of Na₂O and K₂O. The clay deposits (WC, RC, and GC) are suitable for use in industrial ceramics due to the low whiteness, high yellowness and high content of impurities as montmorillonite and iron. This is an important technological aspect that renders possible use of clay RC and GC in the fabrication of products with a cream tonality, especially in roofing tiles and rustic floor tiles. The results also, showed that the studied clays have adequate characteristics for ceramics wall, floor, roof tiles, tableware, earthenware and brick fabrication.     

Synthesis details and solubility product for cobalt hydroxo salt Co(OH)<Subscript>1.8</Subscript>Cl<Subscript>0.2</Subscript>

The hydroxo salt Co(OH)_1.8Cl_0.2 is precipitated by a deficit of OH^? ions from dilute CoCl₂ solutions under the conditions that inhibit the appearance of local excesses of OH^? ions. The three-variable method is used to determine the solubility product for this compound. A linear correlation between the composition and solubility product is found for Co(OH)₂, Co(OH)_1.8Cl_0.2, and Co(OH)_1.5Cl_0.5.     

Spectroscopic characterization of some iron-containing pillared clays

Bentonites, when pillared with Al₂O₃-oxide clusters, can generate materials with BET surface area in the 290–310 m² g⁻¹ range having high cracking activity for gas oil conversion. The high coke make tendency of these catalysts has been attributed to their strong Lewis type acidity.Mössbauer and X-ray photoelectron spectroscopy have shown that iron in pillared clays can be found on the clay platelets, between the clay silicate layers or in the clay octahedral layer in substitution for Al. On heating, iron migration occurs. When iron is found near the pillars it can easily catalyze secondary cracking reactions and greatly enhances the already high coke make generation observed during gas oil conversion.     

Influence of compatibilizer degradation on formation and properties of PA6/organoclay nanocomposites

Nanocomposites based on polyamide 6 (PA6) and commercial layered silicates have been prepared by both in situ polymerization and melt compounding. The main aim of the present work has been centred on compatibilizer degradation, caused by the preparation conditions, in terms of nanocomposite end features. Two montmorillonite (MMT)-type, organically-modified clays (OMLS), namely Cloisite 30B^® and Nanofil 784^®, and a sodium MMT (Cloisite Na^®) have been studied. Thermal properties of the layered silicates have been evaluated by TGA, IR, WAXD and pyrolysis-gas-mass. In order to better assess the influence of high temperature processes on clay modifications, a thermal treatment which mimics the conditions used during the in situ polymerization (4 h at 250 °C) has been applied on layered silicates. The above treatment, besides the elimination of absorbed water from all the clays, turned out to prove noteworthy differences in compatibilizer modification for the two organoclays. Indeed, in the case of Closite 30B^® only a removal of organic molecules outside the silicate galleries and a likely reorganization of those present inside the galleries have been detected, while a relevant chemical modification of Nanofil 784^® compatibilizer has been conversely found.As far as nanocomposite characteristics are concerned, the latter have been found to depend on both the preparation method and clay type. In the case of in situ polymerization, also thermally-treated layered silicates, coded (T), have been used, in order to put more clearly in evidence the role of compatibilizer decomposition on nanocomposite formation and properties. Indeed, nanocomposite samples containing Closite 30B^®(T) have been found to be completely exfoliated, while the same thermal treatment seems to make worse the properties of those based on Nanofil 784^®(T). Furthermore, with respect to nanocomposites based on pristine clays, samples containing thermally-treated silicates turned out to be different in terms of both molecular mass and crystal structure of the polymer matrix. Namely, PA6 γ-form seems to be promoted for all nanocomposites prepared in such a way, probably because of water removal at high temperature, which makes -OH groups of the layered silicate more free to interact with polyamide chains, thus causing a restriction of their mobility.     

A new synthetic layered silicate of type metal silicate hydrate

A new layered silicate has been synthesized in the quaternary system Na₂O–SiO₂–H₂O-polymeric organic cation. The polymeric organic cation was intercalated into the silicate during crystallization. Composition, structure, and x-ray diffraction pattern of the new silicate do not fit with any known layered silicate [1–5]. Many similarities were found to hydrous alkali silicates (metal silicate hydrates, M-SH-type).The new silicate differs from M-SH by a high structural stability, against a wide range of different energetic influences. Due to the relatively high stability, high-resolution electron microscopy (HREM) can be applied to study the layer structure of this silicate as a representative of the M-SH silicates. All known M-SH, for example, magadiite and kenyaite are decomposed by the electronic beam.