Showing papers in "Clays and Clay Minerals in 1975"

The Syntheses of Hydrotalcite-Like Compounds and Their Structures and Physico-Chemical Properties I: The Systems Mg2+-Al3+-NO3-, Mg2+-Al3+-Cl-, Mg2+-Al3+-ClO4-, Ni2+-Al3+-Cl- and Zn2+-Al3+-Cl-

Abstract: The basic salts of this system were prepared and their structures and physico-chemical properties were studies by electron microscopy, chemical analysis, X-ray powder diffraction, thermal analysis, i.r. absorption spectra, BET absorption, and acidity-basicity measurements. The salts were found to be new compounds analogous to hydrotalcite. They can be expressed by the formula; [M 2+ M 3+ (OH)2(x+y))]y+ [A 1 − , Az2- · mH2O]-(z1 + 2z2) where M2+ and M3+ denote di- and trivalent cations, A− and A2− denote mono- and divalent anions, respectively, and y = z1 + 2z2; z1 ≫ z2. The structures consist of positively charged Cd(OH)2-like basic layers and intermediate layers formed from anions and water molecules with the solid solution of divalent cation (M2+) and trivalent cation (M3+) being formed in the range of 0.6 > x/(x + y) > 0.9. The anions of Cl−, NO 3 − and ClO 4 − are easily substituted by CO 3 2− . A large part of the NO 3 − makes a monodentate-type bond and the ClO 4 − a bridge-type bond.

The Formation of Hematite from Amorphous Iron(III)Hydroxide

Abstract: The formation of hematite from amorphous Fe(III)hydroxide in aqueous systems at pH 6 and 70°C, both with and without oxalate, was followed by kinetic measurements, electron microscopy, i.r. spectroscopy and thermal analysis. In the absence of oxalate, small amorphous particles coalesce into aggregates which eventually become single crystals of hematite. When oxalate is present, crystal growth is much faster and does not proceed through the intermediate stage of aggregation. Aggregates, when formed, consist of groups of single crystals. It is suggested that oxalate accelerates the nucleation of hematite crystals by acting as a template, the Fe-Fe distance in Fe-oxalate ions being similar to that in hematite.

Swelling and Structural Organization of Saponite

Abstract: The structural formula of Kozfikov saponite (Czechoslovakia) is as follows: $$N{a_{0.005}}C{a_{0.22}}{K_{0.01}}[S{i_{3.30}}A{l_{0.68}}F{e^{3 + }}{}_{0.02}][M{g_{2.50}}F{e^{2 + }}{}_{0.26}F{e^{3 + }}{}_{0.24}]{O_{10}}{(OH)_2}.$$ Saturated with 6 different cations (Li, Na, K, Ca, Mg, Ba) its swelling in ethylene glycol, glycerol and water and its homogeneous hydration extents according to the relative humidity have been studied. Our results were compared with those found for montmorillonites, beidellites and vermiculites in order to estimate the respective influence of the surface charge density and the charge localization on the swelling properties. The three-dimensional organization of the saponite is more or less affected by random stacking faults and by multiple b/3 translations according to the exchangeable cation, the swelling state and the nature of the solvation liquid. Our experimental results indicate that the three-dimensional order met in the hydrated saponites can be explained by an anchoring of the layers towards each other by chains made up of cation -dipole interactions and of hydrogen bonds between negatively charged surface oxygens and the interlayer water. This type of interlayer link is relatively weak. It is therefore easy to introduce stacking faults in these edifices in particular by grinding of the samples.

Folding in sepiolite crystals

Abstract: Fibrous sepiolite crystals derive much of their commercial value from their molecular size channels and grooves. The crystals fold upon drying and these channels and grooves are lost. A model for the folding and unfolding of the crystals is presented. Extensive i.r., X-ray and thermogravi- metric evidence shows that folding occurs when approximately half of the water of hydration, which is coordinated to the edge magnesium atoms inside of the channels, is removed. This occurs near 175~ under vacuum and near 300~ in air. When the crystals fold, all remaining water molecules enter a new environment, that of the hexagonal holes of the neighboring silica surface. A true anhydride is produced at about 500~ under vacuum when the final water is lost, but this final dehydration produces no important structural change. Rehydration of the anhydride to the normal hydrated sepiolite does not occur at room temperatures in 100% r.h. However, above, 60~ rehydration does occur. not after the high temperature treatment. Nagata et al. (1974) consider that the folded stage produced at half dehydration will rehydrate, but the true anhy- dride does not rehydrate even under hydrothermal conditions, Our study is designed to clarify the conditions un- der which sepiolite folds and unfolds and the involve- ment of the water of coordination in the folding. In- terpretation of TGA-DTGA. X-ray powder diffrac- tion patterns and, especially, careful study of the major changes observable in the i.r. spectra of the struc- tural OH during the dehydration and folding process will be used to explain a folding model.

Water Vapor Isotherms and Heat of Immersion of Na/Ca-Montmorillonite Systems—I: Homoionic Clay

Abstract: Adsorption isotherms for water vapor, c-spacing and heat of immersion in water of Na- and Ca-montmorillonite were measured at 25°C at various r.h. The amount of water adsorbed as a function of the r.h. increased gradually, whereas the c-spacing increased, and the heat of immersion (per mole of adsorbed water) decreased in steps. There was good agreement between the calorimetric data, the heat calculated from the isotherms by use of BET equation, and the calculations from the ion-dipole model. A model is presented to describe the hydration of sodium and calcium montmorillonite.

Structural Hydroxyls in Sepiolites

Abstract: Three sepiolite clays studied showed evidence for the presence of structural hydroxyl groups in three to five different environments depending on the composition of the clay. A 3720 cm-l i.r. frequency is shown to be characteristic of SiOH at crystal edges which are very abundant in sepiolites. This band has not been seen by most workers because the Nujol, fluorolube or KBr used in sample preparation perturb it sufficiently to obscure it under other OH stretching bands. The 3680 cm-1 band is confirmed as being from the (Mg)aOH and evidence of a very small band near 3640 cm 1 is suggested to arise from limited trioctahedral substitution. The very crystalline Ampandrandava sepiolite shows only the above three bands. The intermediately crystalline Vallecas shows a 3620 cm-1 band in addition which is characteristic of dioctahedral systems and is due to either some vacancy sites or to the presence of attapulgite. This dioetahedral band is greater in the less crystalline Salinelles sepiolite; in addition, it has a smaller 3585 cm-1 band. Mg-Al-vacancy and Mg-Fe'"-vacancy are suggested as the source of the 3620 cm- 1 and 3585 cm- 1 bands.

The Mineralogy of Glauconite

Abstract: The mineral in monomineralic glauconite pellets is an iron-rich mixed-layer illite-smectite (here called glauconite), often composed almost entirely of illite layers. The nature of the interlayering is closely analagous to that of aluminous illite smectite and varies with the proportions of the layer types: >30 per cent smectite, randomly interstratified; 15 30 per cent smectite, allevardite-like ordering; < 15 per cent smectite, 'IMII' ordering. Glauconite is analagous to aluminous illit~smectite chemically as well as structurally. A good corre- lation has been found between the number of potassium atoms per O~0(OH)2 in structural formulas calculated from the chemical analyses and the proportion of illite layers as determined by X-ray powder diffraction methods. This relationship indicates a remarkably systematic increase in the potassium content of the illite layers with an increasing proportion of illite layers. This feature and the existence of ordered interlayering at high proportions of illite layers can be explained by crystal-chemical effects of illite layers on neighboring smectite layers. Glauconite differs from aluminous illite-smectite in that glauconite contains significantly less potassium per illite layer than does aluminous illite-smectite with the same proportion of illite layers except near the pure illite composition. The strength with which the interlayer potassium is held and the ease of conversion of smectite to illite layers in glauconite may be attributed to its 1M structure and, perhaps, to its high octahedral iron content, which lead to stronger bonding of potassium by allowing a higher tilt angle of the O-H axis of hydroxyls adjacent to the potassium ion. The apparent octahedral cation occupancy in excess of two-thirds of the octahedral positions in many glauconites appears largely attributable to the presence of significant amounts of interlayer hyd- roxy-iron, aluminum and magnesium complexes in the smectite layers.

Clay distributions in Recent estuarine sediments

Abstract: The distribution of clay minerals in Recent sediments can be explained by the relative stability of the clays. The rates of particle aggregation for three clays were determined in the laboratory in synthetic estuarine solutions; from the kinetic studies stability values were calculated. The results indicate that illite is more stable than kaolinite which is more stable than montmorillonite. The distribution of the clays in the Pamlico River Estuary can be explained on the basis of relative clay stability where kaolinite which aggregates rapidly (relatively unstable clay) is found upstream of illite.

The Definition and Nomenclature of Halloysites

Abstract: This review of the literature shows that there have been many attempts to modify or revise the original definition of halloysites as distinguished from kaolinites, which was based on the greater water content of the halloysites. In general, these various attempts have arrived at definitions of halloysites as distinguished from kaolinites that are based on one or more particular instrumental or chemical techniques. Further investigations with almost all of these techniques have shown the apparently clear distinctions of this kind to be misleading. All such instrumentally—or chemically—based definitions were shown to either complicate and confuse the distinction between halloysites and kaolinites or to provide only empirical and subtle distinctions. It is concluded that only the original definition, with slight adaptations, enables clear and unambiguous distinctions to be made between halloysites and kaolinites. It is noted, however, that a distinctive structure for halloysite has been postulated as a result of electron diffraction studies. Further studies of this kind could well establish such a structure as being definitive of the mineral species. The literature also reveals a long-standing disagreement over the nomenclature of different forms of halloysite and particularly over the nomenclature of and distinction between the two forms of halloysite at the extreme ends of the hydration series. An analysis of experimental studies of the relationship between these two and other hydration states of halloysite reveals that forms of halloysite with all possible interlayer water contents between 0 and 2 molecules H2O per Al2Si2O5(OH)4 unit cell may exist and that the two end members of the hydration series may not be seen as distinct phases. The fully dehydrated halloysite is the only thermodynamically stable form of the mineral. A nomenclature system which was proposed by MacEwan in 1947 is consistent with these results. This system, amended only by the exclusion of the unnecessary term ‘metahalloysite’ should therefore be adopted in all studies of halloysites.

The composition of kaolinite; an electron microscope microprobe study

Abstract: Electron microscope microprobe analysis (EMMA) has been applied to the determination of the elemental compositions of the kaolinite particles (Mg, A1, Si, K, Ti and Fe) contained in the 0.~0-3 Izm e.s.d., the 0.9-1.0/~m e.s.d, and the 1.9-2.0/am e.s.d, fractions of an English kaolin and an American kaolin. Particles with masses as small as 10-13 g were analysed. An EMMA-4 instrument (A.E.I. Ltd.) equipped with linear fully focussing spectrometers was used. The ratio method of analysis was employed. The operating procedures used to obtain the required high experimental precision in the measurement of AI:Si atom ratio are discussed. Statistical analysis of the results gives the estimated mean and spread of the AI:Si atom ratios. In the English kaolin the mean AI: Si atom ratio differs from the ideal 1:1 at the 0.05 significance level. There is evidence for a variation in composition from kaolinite particle to kaolinite particle in the 1.9-2.0~m fraction of each kaolin. In the 0.9-l.0#m fractions, the mean Fe:Si atom ratio was close to 0.002 showing the presence of iron in the kaolinite structure. The mean K:Si ratio was about 0.002 which would be equivalent to 1 unit muscovite layer associated with a 0.175 #m thick kaolinite particle. In the American clay the Ti:Si atom ratio was 0.002 suggesting that some 12 per cent of the 'titania' found by conventional chemical analysis was associated with the kaolinite particles either as titania itself or as an isomorphous substituent.

Micaceous Occlusions in Kaolinite Observed by Ultramicrotomy and High Resolution Electron Microscopy

Abstract: The layer structure of kaolinite from Twiggs, Georgia and fire-clay type kaolinite (Frantex B, from France), particle size separates 2–0·2 μm was studied by high resolution electron microscopy after embedment in Spurr low-viscosity Epoxy media and thin sectioning normal to the (001) planes by an ultramicrotome. Images of the (001) planes (viewed edge-on) of both kaolinites were spaced at 7 A and generally aligned in parallel, with occasional bending into more widely spaced images of about 10 A interval. Some of the 10 A images converged to 7 A at one or both ends, forming ellipse-shaped islands 80 to 130 A thick and 300 to 500 A long. The island areas and interleaved 10 A layers between 7 A layers may represent a residue of incomplete weathering of mica to kaolinite. The proportions of micaccous occlusions were too small and the layer sequences too irregular to be detected by X-ray diffraction. The lateral continuity of the layers through the 7-10-7 A sequence in a kaolinite particle would partially interrupt or prevent expansion in dimethyl sulfoxide (DMSO) and other kaolinite intercalating media. Discrete mica particles were also observed with parallel images at 10 A, as impurities in both kaolinites. The small K content of the chemical analyses of the kaolinite samples is accounted for as interlayer K, not only in discrete mica particles but also in the micaceous occlusions.

Fabric of Consolidated Kaolinite

Abstract: Fabric refers to the spacial arrangement of clay particles in a sample relative to a reference plane. X-ray diffraction data yield an 'amount of orientation' (AO) that varies from zero for ideal random to 100 for ideally oriented fabric. The AO has been related to the average angle of inclination of clay par- ticles to the reference plane. Fabric data from 50 samples involving 2000 determinations are presented on the effects of: the method of sample preparation prior to one-dimensional consolidation; the magnitude of consolidation stress from 0.1 to over 1000 kg/cm2; changes in direction of consolidation stress; isotropie consolidation; and distur- bance during removal of samples from oedometer cells. The single most important variable was the method of sample preparation, as illustrated by the following data on samples consolidated one-dimen- sionally to 1.5 kg/cm 2 :clay initially moist, AO = 27 per cent; air-dry clay, AO = 44 per cent; clay slurries, AO = 76-95 per cent. The change in fabric with increasing consolidation stress was most pronounced with samples at very low stresses, the changes in fabric were small for consolidation stress increments usually encountered in engineering practice. Fabric data provide a very sensitive measure of sample disturbance. Extrusion causes significant distur- bance at the center of a 24 cm dia. sample cylinder.

Kaolinite Synthesis: The Role of the Si/Al and (Alkali)/(H +) Ratio in Hydrothermal Systems

Abstract: The Si/A1 ratio of an hydrothermal system plays an important role in kaolinite synthesis. If the atomic Si/A1 ratio of a system is greater than 2-0, kaolinite will disappear at 345 _+ 5~ and 2 kbars water pressure according to the reaction kaolinite + 2 quartz -~ pyrophyllite + H20. If the atomic Si/A1 ratio is less than 2.0, however, kaolinite will persist until 405~ where it will react according to the equation 2 kaolinite---* pyrophyllite + 2 boehmite + 2 H20. The Si/A1 ratio of the system and temperature are also factors in determining whether b-axis ordered or disordered kaolinite will crystallize. The ordered variety is favored by a lower Si/Al ratio and a higher temperature than is the disordered form. Hydrothermal experiments also show that kaolinite can be synthesized at 150~ and 5 bars pressure in distilled water from amorphous starting materials. Previous investigators were unsuccessful in form- ing kaolinite under these conditions because their systems were contaminated with alkalis. Attempts to synthesize halloysite and dickite failed, but halloysite was converted to kaolinite at 150~ suggesting that balloysite can be synthesized only at low temperatures.

The crystallinity of minerals; a new variable in pedogenetic processes; a study of goethite and associated silicates in laterites

Abstract: The crystallinity of minerals in terms of crystallite size distribution and lattice perfection is quantified by means of statistical measures derived from X-ray line profiles (2 cr values). A low degree of crystallinity facilitates the non-stoichiometric incorporation of foreign elements in the crystal lattice. Crystallinity is affected by a number of factors and in natural profiles it may vary laterally as well as vertically. For instance, goethite in laterite deposits shows decreasing crystallinity with increasing depth. Serpen- tine type minerals, on the other hand, show the lowest crystallinity at the surface where the degree of weathering is the most advanced. The presence of silica in migrating solutions prevents crystal growth and results in a low degree of crystallinity of minerals such as goethite. This has been observed in natural profiles and has been confirmed by laboratory experiments on the synthesis of goethite and sodium-birnessite. The crystallinity of minerals affects their response to extractive procedures. It could also be an important parameter in soil science.

The relationship between the I.R. spectra of serpentines and their structures

Abstract: Possible assignments are suggested for some of the absorption bands in the 1150-400 cm-I region of the i.r. spectra of serpentines. Polarized light was used to identify the out-of-plane vibrations in antigorites and platy lizardites and the vibrations parallel to the fibre axis in chrysotiles and fibrous lizardites. An attempt is made to correlate some known structural characteristics and the chemical composition of the serpentines with some features of the i.r. spectra.

Od-Interpretation of Kaolinite-Type Structures—I: Symmetry of Kaolinite Packets and their Stacking Possibilities

Abstract: The idealized symmetry of kaolinite-type minerals (1:1 phyllosilicates) is analysed in detail. They can be considered as OD-structures consisting of three kinds of OD-layers. Each of them, taken separately, possesses higher symmetry than their combination. This explains the well-known tendency of kaolinite-type minerals to form a wide variety of ordered and disordered polytypes as well as twins. The possible stacking sequences result from the different kinds of pairs of kaolinite layers which are derived for dioctahedral, trioctahedral as well as 'monoctahedral' kaolinite-type minerals, the latter being defined as those in which the three octahedral positions are occupied by three different cations or two different cations and a void. The analysis makes use of a simple symbolism and a simplified pictorial representation. A brief summary of the most important terms and definitions of the theory of OD-structures is given in an Appendix.

Heterogeneity of charge density distribution in montmorillonite as inferred from cobalt adsorption

Abstract: Abstraet--A comparison is made of the ion exchange behavior, towards the cobalt ion, of five sodium montmorillonite clays. The selectivity for the bivalent ion at low cobalt loading is correlated with the average dimensions of the particles in the various clays, as characterized by several methods. The data are interpreted in terms of a higher selectivity of the bivalent ions for the broken bonds located at the edges of the clay crystals. Using a model comprising two areas of different charge densities, the experimental differences in behavior can be predicted reasonably well.

Electron-microscopic and Mössbauer Spectroscopic Studies of Iron-Stained Kaolinite Minerals

Abstract: An electron-microscopic and Mossbauer spectroscopic study of a range of kaolinites has revealed three distinct types of iron contamination within these minerals: a) Ferric ion may substitute for aluminium and be evenly distributed throughout the lattice, b) Ferric ion may be present as a crystalline coating of goethite, as indicated by lattice-imaging studies, or c) as an amorphous coating. The distribution of the iron in the groups b and c is non-uniform and is highest at the flake surfaces. Ferrous ion, when detected, is thought to be evenly distributed throughout the lattice. The size of the contaminating goethite crystallites and the observed Mossbauer spectra of these samples suggest that such particles are super-paramagnetic. All kaolinites can be cleaned by acid treatment except those having iron substituting for Al3+.

Dielectric properties of montmorillonites saturated by bivalent cations

Abstract: This study deals with the analysis of dielectric measurements made on montmorillonites saturated by bivalent cations. These measurements are performed between -150~ and +30~ at frequencies ranging from 300 to 10,000 Hz. Their interpretation is based on a numerical analysis allowing determination of the dielectric losses due to free charge carriers conductivity phenomena and losses due to relaxation phenomena. The free charge carriers conductivity is due to the movement of protons. It depends very much on the nature of compensating cations and on the water content and seems to be closely related to the characteristics of the swelling. Two types of relaxation phenomenon are described: a Debye relaxation due to electric dipole rotations and a Maxwell-Wagner relaxation due to heterogeneity effects. The analysis of the first phenomenon leads to the examination of the values of the relaxation time. It appears that the rotations of water molecules are difficult with bivalent cations. This essentially is shown by the high activation energy of the phenomenon. The discussion of these parameters shows that the state of adsorbed water molecules are certainly different as compared to the state of water molecules in ice or in liquid water. The characteristics of the second relaxation phenomenon are closely dependent on the free carriers charge conductivity.

Mineralogy and Origin of the Coalinga Asbestos Deposit

Abstract: Since 1960 asbestos production of the United States has more than tripled, a phenomenon due in large part to the development of the Coalinga asbestos deposit in western California. Although most asbestos ores contain 5–10 per cent chrysotile in the form of cross- or slip-fiber veins within massive serpentinite bodies, no such veins are to be found in the Coalinga deposit despite the fact that it contains more than 50 per cent recoverable chrysotile. The Coalinga ore consists of soft, powdery, pellet-like agglomerates of finely matted chrysotile surrounding blocks and fragments of serpentinite rock. The highly sheared and pulverized nature of the ore favors its exploitation by simple, open-pit mining, and high quality products can be prepared by either wet or dry milling processes. Four types of serpentine material are distinguishable: (1) hard, dense blocks of serpentinite rock, ranging from fractions of an inch to several tens of feet in diameter; (2) tough, leathery sheets, resembling mountain leather, up to several square feet in size; (3) brittle blades and plates of green serpentine, a few square inches in size; and (4) friable agglomerates of soft, powdery chrysotile containing appreciable amounts of the other three. Chrysotile is the principal component of all the above materials, with the exception of the serpentinite rock which consists mainly of lizardite and/or antigorite, with small amounts of brucite, magnetite, and very short fiber chrysotile. Although chrysotile fibers up to several microns in length are present in the leathery sheets, most Coalinga chrysotile is much shorter and arranged in a swirling mesh or disoriented, tangled fibers, much like cellulose fibers in paper. Fragments of serpentinite gangue are scattered throughout the ore and contain most of the lizardite, antigorite, and brucite. Chemical, electron probe, and X-ray analyses confirm the iron-rich nature of the brucite, a critical factor in the susceptibility of this phase to oxidation in the surface weathering zone. Here brucite either dissolves, leaving behind a residue of brown, amorphous iron oxides, or transforms in situ to pyroaurite or coalingite. Dissolved magnesium precipitates as hydromagnesite immediately above the water table throughout the deposit. The abnormally high chrysotile content of this deposit is probably a result of the intensive shearing that it underwent during or after emplacement. If the friable, chrysotile-rich ore was produced during this pulverization episode, (1) lizardite and/or antigorite in the serpentinite must have been transformed into chrysotile and (2) brucite must have been removed. It is likely that early-formed lizardite/antigorite dissolved in the ground waters which pervaded the highly sheared body and that chrysotile later precipitated from these waters, coating all available surfaces.

Variability in Exchange Ion Position in Smectite: Dependence on Interlayer Solvent

Abstract: Full and reduced charge smectite saturated with Na(I), Ca(II), Cu(II), or tetralkylammonium ions were s&ollen by a series of solvents of various bulk physical properties. In the full charge smectites, swelling occurred in all solvents regardless of the exchange ion or the initial water content. Charge differences did not usually result in differential swelling of the smectite. Little correlation was found between the degree of swelling and the Gutmann donor numbers, bulk dielectric constants, bulk surface tensions, or dipole moments of the solvents. The intensities of the high field Fe(III) resonance (9 = 3.6) in the esr spectra of full charge smectite swollen in various solvents reflected variability in exchange ion positions and depended upon the Gutmann donor number of the solvent. Considerable variety in the stereochemistry of Cu(II)-solvent complexes was revealed by esr spectra of the swollen systems.

Isomorphous substitution of iron for aluminium in some soil kaolinites

Abstract: Clay ( < 2 ttm) and fine silt (~20/~m) fractions of twenty seven soil samples from eight tropical ferruginous profiles of the Mysore Plateau (India) were analysed for kaolinite by dehydroxylation and selective dissolution. The considerable amounts of iron extracted by the procedure and the closeness of the SiO2/R203 molar ratios (2.00-2.18) to the ideal value of 2.00 indicated that iron was a structural constituent of the kaolinites, The calculated unit cell cation composition of the kaolinites showed a substitution of 0.114).82 atoms of Fe(III) for A1 in every four octahedral sites. The kaolinites in these soils appear to be products of crystallization from weathering solutions.

Further information related to the origin of glauconite

Abstract: Glauconite-smectite and illite-smectite interlayered minerals are compared by various means in an attempt to establish the mineralogical relations between the two groups. Experiments at 2 Kb pressure and 200–350°C are reported as well as microprobe scans of pelletal glauconites. This new information is used along with published chemical data in order to establish that

Hisingerite Occurring as a Weathering Product of Iron-Rich Saponite

Abstract: Hisingerite occurs as a weathering product of iron-rich saponite in rhyolitic tuff of Oya, Tochigi Prefecture. The chemical composition: SiO2, 40·68%; Al2O3, 4·44%; Fe2O3, 28·54%; MgO, 1·85%; CaO, 1·42%; Na2O, 1·50%; K2O, 0·33%; H2O+, 6·43%; H2O−, 13·70%; total 98·89%. Very broad and weak X-ray powder reflections occur at 16, 4·5, 2·5, 1·7 and 1·5 A, which correspond to the main peaks of nontronite. It is considered that trioctahedral iron-rich saponite was altered to hisingerite, a very poorly crystalline form of nontronite, by oxidation of iron and advanced leaching of octahedral Mg ions.

Kink Block Structures in Clay Organic Complexes

Abstract: Complexes of n-tetradecylammonium-beidellite with n-alkanols $${\rm{(n - }}{{\rm{C}}_{{\rm{14}}}}{{\rm{H}}_{{\rm{29}}}}{\rm{N}}{{\rm{H}}_{\rm{3}}}^{\rm{+}}{\rm{)_{{\rm{0,44}}}(n - C_{{\rm{x}}}}}{{\rm{H}}_{{\rm{2x}}}}{\rm{+}}{}_{\rm{1}}{\rm{OH) }}{}_{{\rm{1,56}}}{{\rm{\{ M}}{{\rm{g}}_{{\rm{0,28}}}}{\rm{A}}{{\rm{l}}_{{\rm{1,81}}}}{{\rm{(OH)}}_{\rm{2}}}{\rm{S}}{{\rm{i}}_{{\rm{3,56}}}}{\rm{Al}}{}_{{\rm{0,44}}}{\rm{O_{{10\}} }}}^{{\rm{0,44 - }}}}$$ (x = 8–22) have been prepared and characterized by their basal spacings and by measurements of the specific heat cp. The compounds undergo a series of reversible phase transitions $${\beta _1} \rightleftharpoons...\rightleftharpoons{\beta_i}\rightleftharpoons...\rightleftharpoons{\beta_\omega}\rightleftharpoons{\alpha_1}...\rightleftharpoons{\alpha_j}$$ with rising temperature. The maximum number ω of β-phases depends upon the chain lengths and increases from 1 with decanol to 6 with docosanol. Due to the evaporation of alkanol the number of χ-phases is not yet established in all details. The β-transitions correspond to conformational changes of the alkyl chains via rotational isomerisation, especially kink formation. The β-phases become unstable if the kink concentration exceeds 0,14 kinks/-CH2-. The β/α-transition is probably caused by a rearrangement into special gauche-block structures.

Perturbation of Structural Fe3+ in Smectites by Exchange Ions

Abstract: The electron spin resonance of some structural Fe 3+ for montmorillonites having low Fe 3+ content, is perturbed by electrostatic interaction between exchange cations and structural charge sites. The position of charge centers of organic and inorganic cations in the interlayer can thus be determined at various levels of solvation. Dielectric media between the silicate layers lower the electrostatic attraction between the silicate and the exchange cations. The silicate charge appears to be partially delocalized on structural oxygen atoms as shown by electron spin resonance and i.r. spectroscopy. There is also evidence that divalent exchange cations on dehydrated montmorillonites cause hydrolysis of water; the protons so produced migrate to structural charge sites.

Dissimilar Fabrics by Scan Electron Microscopy of Sedimentary Versus Hydrothermal Kaolins in Mexico

Abstract: Dissimilar fabrics, observed by scan electron micrography (SEM) on freshly broken surfaces of kaolins from weathered, water-laid material vs hydrothermally altered material in Mexico are illustrated, contrasted, and tentatively related to their respective environments of genesis. Coarse, open-textured, well-preserved books and vermiforms of kaolinite characterize the kaolin from water-laid material at Jacal, Mexico. Hydrothermal kaolins tend to have more tightly compacted crystals of either kaolinite flakes (individuals or in packets) or elongates (halloysite morphology) or mixtures of both in the same deposit. Variations in porosity of parent rock whether sedimentary or igneous, and dissimilar permeation by meteoric water and by vapor and liquids of hydrothermal fluids are deemed to be significant in the processes producing distinctive fabrics. The question is raised as to the fundamental distinction between kaolinite and halloysite and their nomenclature.