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SummaryKerolites from Goles Mountain (Yugoslavia), Wiry (Poland), Madison Co. (North Carolina), and Kremze (Czechoslovakia) are compared with talc and stevensite. Chemical analyses give a composition for kerolite near R3Si4O10(OH)2.nH2O with R mainly Mg and n about 0·8–1·2. Infra-red data and dehydration-rehydration experiments suggest that the additional water is partly surface-held hydrogen-bonded molecular water, lost up to about 300 °C and easily recoverable, and ‘water’ held as surface hydroxyls, lost at temperatures up to about 650 °C and less easily recoverable. The surface area of kerolite from North Carolina by nitrogen absorption measurements is 196 m2/g.X-ray data show broad basal reflections, a basal spacing (after Lorentz-polarization correction) of about 9·6 Å and a crystallite size of about five structural layers, which is consistent with the large surface area. Two-dimensional hk bands indicate a randomly stacked layer structure with b ≈ 9·14 Å and a crystallite ‘diameter’ of about 150 Å. The basal spacing shows no expansion in water and no thermal contraction up to 500°C. A partial and irregular swelling with ethylene glycol is obtained only after prolonged cxposure (several weeks). In both respects, kerolites differ from stevensite. Kerolites come close to talc in structure and composition but differ in having a highly random layer arrangement, a slightly enlarged basal spacing, which could be due to misfit of layers caused by random stacking, and weaker interlayer bonding.Kerolite is considered to be a useful varietal name for this talc-like mineral in agreement with the views of D'yakonov and of Maksimovic. It cannot be defined as serpentine + stevensite.

SummaryAn X-ray and chemical examination of deweylites reveals that they are intimate mixtures of very poorly ordered trioctahedral 2:1 and 1:1 layer silicates. The 2:1 mineral exhibits no swelling in the presence of ethylene glycol or water and is best described as an extremely fine-grained and highly disordered form of talc, for which the term kerolite is often used. Stevensite is not a component of deweylites. The 1:1 component most closely resembles a disordered chrysotile.Evaluation of the chemical data, including values for H2O +, shows that both end-members are hydrated to various degrees. This hydration is most probably attributable to the presence of water molecules and hydroxyls associated with the large surface areas and unbalanced surface bonds. Formulae for the end-members are approximately R3Si4O10(OH)2·0·3 0·7 H2O and R3Si2O3(OH)4·0·3–0·7 H2O where R is principally Mg, but samples with more or less H2O are entirely possible due to variations in crystallinity. No specific formula can be given to deweylites as they are mixtures with variable proportions of the components. The name is useful, however, as a field or ‘box’ term, similar to the use of garnierite and limonite.

Progress in science is not a linear function of time but resembles more closely a sigmoidal process in which new trends depend on the nucleation of new ideas and the re-activation of older studies. New and improved instruments, particularly electron microscopes and microprobes, infrared spectrometers and atomic absorption analysers have been the nucleating agents for many new lines of investigation. The interdisciplinary nature of clay mineralogy makes communication between different areas of study very important and the clay mineral societies have an important part to play in this respect.In the future, renewed efforts to obtain a convenient and reliable method of quantitative mineral analysis are likely to be made. Crystal structure analysis will be directed increasingly towards the study of order and disorder in cation distributions, layer charges, and layer stacking arrangements. Studies of domain structures in layer silicates will continue, and further refinements in mixed-layer structure analysis can be expected. Infrared spectroscopic analysis will increasingly become a major tool. The study of clay mineral synthesis and alteration in nature and in the laboratory shows signs of important re-activation. Clay-organic studies are developing in many directions.

Hydroxy-aluminium beidellites are prepared by treating Na-saturated beidellites from Taiwan, with compositions intermediate between end-member beidellite and end-member montmorillonite, with hydroxy-aluminium solutions having OH/Al ratios mainly between 2·00 and 2·50. Chemical analyses show that hydroxy-aluminium ions have compositions near Al6(OH,O)16 and charges near 1·0 in two cases, and near 2·2 in a third case. The basal spacing of the prepared clays is near 17 Å and remains without collapse up to 500°C. Argon adsorption measurements at liquid nitrogen temperatures, after heat-treatment up to 325°C in vacuo overnight, give surface areas near 500 m2/g when the exchangeable Na ions are about one-third replaced by hydroxy-aluminium, but near 200 m2/g when wholly replaced by hydroxy-aluminium. In the latter case the hydroxy-aluminium covers the internal surfaces of the clay almost completely prior to the heat-treatment.

Nickel ions play similar roles to magnesium ions in nickel-containing hydrous layer silicates. The extent of the replacement of Mg by Ni ranges from small proportions to complete, or almost complete, replacement. Particular interest attaches to the micro-crystalline, clay grade, minerals formed by processes of lateritic weathering. The multiplicity of names proposed in pre-X-ray-diffraction times must be re-evaluated in terms of modern identification procedures. Many of these minerals can now be placed in series such as:Garnierite is now used mainly as a field term, prior to more specific identification, and terms such as 7 Å- and 10 Å-garnierite are useful when identification can proceed no further than recognition of basal spacings. Further study is required of schuchardtite, and of nickel-containing smectites and sepiolites. Consideration also must be given to the composition ranges of the end-member names.

Beidellite clays near Chang-yuan, 80 km south of Hwalien, form vein-like bodies 5-10 m wide and 20-45 m deep. Andesitic rocks have been fractured by faulting permitting hydrothermal solutions to percolate and produce an altered mineral assemblage in which beidellite is associated with a mixed-layer illite-smectite, kaolinite, dusty pyrite, microquartz, cristobalite, calcite and dolomite, plagioclase, and gypsum. Ca-clay is common on outcrops and subsurface, where the clay is leached, Na-clay is found; some outcrops are partly kaolinized. Chemical analyses of the beidellite show that the structure is charged predominantly in the tetrahedral sheets. Exchange capacities are mainly in the range 120-140 mEq/100 g clay (110°C); exchangeable cations are Na ≫ Ca ≃ Mg > K. After K saturation and heating, ten samples still expand to near 17 A with ethylene glycol, but the two samples with the highest tetrahedral charge expand only to 14·6-15·0 Å although their total charge is similar to the other samples.

SummaryMotukoreaite resembles hydrotalcite and has positively charged brucite-like layers separated by carbonate and sulphate anions and water molecules. Four phases are recognized. Phase I, the normal mineral with an 11.1 Å basal spacing, readily changes to a mixture of phase I and a partially dehydrated phase II. Phase III with a basal spacing 8.7 Å persists from 50–170°C. Phase II is a pseudo-regular interstratification of phases I and III, with a spacing 11.1 + 8.7 = 19.8 Å; second- and third-order reflections are observed. Phase IV with a 7.5 Å spacing is obtained by treating motukoreaite with sodium carbonate solution to replace SO4 by CO3 anions. Motukoreaite itself shows only slight tendency to transform to a 7.5 Å phase by heat-treatment alone. Comparison is made with the mineral carrboydite, a NiAl sulphate carbonate hydrate. The possibility is considered that sulphate anions may substitute partially in the brucite-like layers to compensate for a deficiency of hydroxyl ions.

Basal X-ray peaks from normal and ethylene glycol-saturated tarasovite have been measured to 0.0.36 and 0.0.38, respectively; the mean basal spacings were 43·73 ± 0·44 and 46·05 ± 0·33 Å, with CV values of 1·31 and 0·97. The spacings indicate a near approach to a 3 : 1 illite-smectite but the CV values indicate a greater variability than is normally consistent with the allocation of a special name. Comparison of the observed spacings with those for illite showed that the more deviant values were always adjacent to positions of illite reflections. A modified Mering treatment of diffraction by mixed-layer sequences was used to estimate the proportion of illite layers; the average result was 79·9 ± 2·0%. The mineral is considered to have 3 : 1 illite-smectite units with randomly added illite layers, bringing the ratio from 75% for the ideally ordered sequence to near 80%.

SummaryThe composition of scarbroite, written in the form Al5(OH)13CO3·5H2O, suggests close crystal-chemical relations to gibbsite and to hydrotalcite and kindred minerals. Parametral relations a(S) ≃ 2b(G) and 3b(S) ≃ 5a(G), S = scarbroite, G = gibbsite, are obtained and are consistent with a hydroxy Al layer structure and interlayer carbonate anions and water molecules. Thermal transformations show two discrete hydrated phases with layer spacings near 8.5 and 7.65 Å and a third phase with initial spacing 6.65 Å which decreases progressively to 5.5 Å over the temperature range 100°–250 °C as decomposition proceeds. No clear break is observed between dehydroxylation and decarbonation.

Dickites with well-ordered crystal structures and with relatively high dehydroxylation temperatures develop a 14 Å phase when heated to temperatures in the range 550–800°C. The actual spacing is close to 13·7–13·8 Å. Dickites with less well-ordered structures and with lower dehydration temperatures give less development of this phase or none at all. Other kaolinite group minerals do not produce a similar phase. Thermal weight-change and differential thermal analysis data show that the 14 Å phase develops to a maximum as hydroxyl ions are eliminated from the dickite structure and infrared spectroscopic data are consistent with this result. AIKα fluorescence wavelength measurements indicate that the Al ions are in four-fold coordination in the 14 Å phase. Absence of other diffraction data makes structure analysis impossible. The description ‘chlorite-like’ for the 14 Å phase is of questionable validity.

In a previous paper (Brindley, 1951) chamosites from a number of localities were examined, and their structure was shown to be of kaolin-type. Furthermore, it was shown that many of the variations in X-ray powder diagrams of chamosites can be accounted for by the existence of two kaolin-type structures, one hexagonal and one monoclinic, with simply related ceil dimensions.

A possible structure for kaolinite was first put forward by Pauling (1930) in a paper dealing generally with the structures of layer-type minerals, chlorites, micas, &c. He suggested that the structure consisted of a sheet of Si–O tetrahedra arranged in a hexagonal network with a superposed sheet of Al–(O,OH) octahedra, the two together forming a layer of composition Al2Si2O5(OH)4 (fig. 2). Ross and Kerr (1931), from a detailed microscopic study of the kaolin minerals, concluded that the symmetry of kaolinite is ‘probably monoclinic’. The first attempt at a detailed structure analysis was made by Gruner (1932a) from X-ray powder photographs. The reflections, some 40 altogether, were indexed on the basis of a monoclinic cell with a 5·14, b 8·90, c 14·51Å., β 100° 12′.

A 2–20 µ fraction of phlogopite has been converted to the sodium form by use of sodium tetraphenylboron-NaCl solutions. The cation exchange capacity of the treated material increases to a maximum of about 212 m-eq/100 g, which agrees well with the K2O + Na2O content of the initial mineral. Li-, Na-, Ca-, and Mg-saturated forms have been prepared and examined by X-ray diffraction and by thernogravimetric measurements in air, in vacuo, and at progressively elevated temperatures. Hydration states corresponding to double water layers are observed for the Mg- and Ca- forms, and to single water layers for the Mg-, Ca-, Na-, and Li- forms. The numbers of water molecules per unit cell and per interlayer cation are considered for the various hydration states.

Complexes are formed between a Ca-saturated fluorhectorite and organic molecules derived from propane by substituting benzene, pyridine, and piperidine rings in the 1,3 positions. The complexes are mainly of the A- and B-types described earlier by Greene-Kelly. Only one of the substances studied forms long-spacing complexes; in this case, the organic molecule is terminated at one end by a benzene ring and at the other by an active =NH group. Neutral forms of this molecule develop double-layer complexes, cationic forms develop single-layer complexes. The results are consistent with data for alcohols, alkyl chlorides and bromides, and alkyl amines.

Basal spacing data for neutral amine complexes with montmorillonite and vermiculite are explained on the basis of two layers of fully extended amine molecules inclined at about 65° to (001) with the NH2 groups closely associated with pairs of silicate oxygen atoms. The molecular orientation is shown to be favourable for good intermolecular packing and for possible NH..O bonding, but the results do not constitute proof of such bonding. Packing of the molecules on the silicate surfaces and with respect to each other may explain the formation of double layer complexes. The amine data are correlated with corresponding data for the low-temperature (or below melting point) series of alcohol-montmorillonite complexes and it is suggested that the molecular layers may have some solid-like characteristics.

This paper concludes the account of our experiments on halloysite and is to be read in conjunction with the two previous parts, to which frequent reference will be made.The effect of heat-treatment on metahalloysite was examined with the primary object of ascertaining if a recrystallization or ‘kaolinization’ of metahalloysite could be achieved.

SummaryForsterite formed from serpentine powders at various temperatures up to 800° C has been measured quantitatively by X-ray diffraction. The results are considered in relation to a reaction mechanism proposed by Ball and Taylor and are shown to be inconsistent with the details of this mechanism. An alternative mechanism is proposed by which all or nearly all the Mg ions together with some of the Si ions liberated in the reaction zones where water is formed migrate into regions where forsterite is formed. This mechanism is in closer accord with the experimental results. The retarded development of enstatite until temperatures above 1000° C are used is attributed to the nature of the reaction by which it is formed, namely a reaction between forsterite and silica.

The experiments described below on the dehydration of halloysite were largely carried out in the laboratoire Central des Services Chimiques de l'État, Paris, where we enjoyed not only the excellent facilities of the laboratory but also the advice of Monsieur J. Méring and Mile R. Glaser who had made similar studies of montmorillonite. The use of a Guinier-type focusing camera with strictly monochromatic radiation was especially useful. These experiments were undertaken because little was known about the dehydration process beyond the recognition that it occurs very readily in dry atmospheres and at low temperatures. The main experimental difficulty lies in differentiating between water adsorbed oil external surfaces of the clay particles (adsorbed water) and water internally absorbed between the kaolin layers (interlayer water).

In X-ray studies of fireclays we have frequently observed the presence of anatase to the extent of 1 or 2% with little or no rutile, and no brookite. Chemical analyses of these clays usually record 1–2% of TiO2 and occasionally more (Ennos and Scott, 1924). The mineralogical form of the TiO2 is usually not stated, but a number of references to the observance of rutile needles give the impression that rutile is the form in which titania occurs in these deposits. Our own observations based on X-ray powder photographs lead us to conclude that anatase is commonly present and that rutile is either absent or present in smaller quantities. We have not detected brookite.

Nacrite is the rarest member of the kaolin group of minerals. The name was first applied by Brongniart in 1807 to a mineral (talc granuleux of Haüy, 1801) the properties of which were not then adequately described. In 1832 Breithaupt recorded a mineral from an ore vein near Freiberg in Saxony, which has since been called nacrite. In the past, however, 'nacrite' has been applied quite frequently to different nacreous and micaceous minerals, not necessarily of kaolin composition, and the authenticity of the species was not definitely established until 1931 when Ross and Kerr, on the basis of an X-ray study of nacrite from the locality Brand near Freiberg in Saxony, proved the mineral to be a distinct species of the kaolin group.

The water gained by two micas during a wet-grinding process (extra-water) has been evaluated. It was found to be proportional to the surface area and the amount was about 29 µmoles/m2 for a fluorphlogopite and about 16 µmoles/m2 for a muscovite. This estimation was made possible by eliminating the physically adsorbed water. The material contaminating the surfaces and the constitution water of muscovite were taken into account by the comparison of the two minerals and by the use of infrared spectroscopy in addition to thermovolumetric data. It is thought that the extra-water is related to a disordered and chemically modified surface layer of the particles. The bearing of these results on the nature of illite is indicated.

employed. The orientation of micaceous minerals is most easily investigated by considering the intensities of X-rays reflected from their basal (001) planes in different directions with respect to the bedding or cleavage plane of the material. With X-ray powder cameras of conventional type in which the reflected X-rays are recorded through an aperture on a strip of film, a series of photographs for different angular settings of the material will be required. If, however, a complete Debye-Scherrer diagram is recorded, then a single photograph taken with one angular setting of the material suffices to give the required information. Custers (i948) has analysed in detail this method for studying orientation with particular reference to rolled metal sheets. The practical problems are somewhat different with micaceous materials, since the fragility of many specimens makes the use of small blocks of material almost essential and these can be studied only by surface reflection methods. With thin sheets both surface reflection and transmission arrangements may be employed. With metals more penetrating radiations of shorter wave-length can be usefully used than are practicable

OR many years, a number of problems have persisted concerning the reactions which occur and the products which form when kaolinite and kaolin clays are heated to progressively higher temperatures. Between approximately 550 ~ and 900 ~ C., X-ray powder diagrams of kaolinite show mainly a broad band indicating either an amorphous, or a highly disordered, or a very finely dispersed state. The product is generally called metakaolin. At temperatures above 950 ~ C. y-alumina and mullite are formed. In some eases they appear together ; in others, the appearance of mullite is delayed. The relations of these products to each other and to the original kaolinite have received various interpretations and the course of the reaction is still disputed. Following an examination of nacrite from Hirvivaara, Finland (yon Knorring, Brindley, and ttunter, 1952), we considered that a single crystal study of its thermal reactions might throw further light on those of kaolinite. The two minerals have a similar lamellar morphology and are composed of silicate layers having the same structure and the same chemical composition; they differ only in the stacking arrangements of the layers and in crystal size. The dehydration of nacrite follows a similar course to that of kaolinite and the ultimate products of decomposition are the same for the two minerals. It seems reasonable to suppose that their thermal reactions will be closely similar, though tile particular temperatures at which reactions proceed may depend on crystal size.

The surface properties of wet-ground muscovite were studied by thermodynamics of water adsorption. The surface appears to be covered by contaminating material, probably organic, which is strongly held; it was not removed at 350° C and under a vacuum of 10−4 torr. Attention is directed to the difficulty of maintaining freshly made silicate surfaces without contamination and to the importance of surface conditions in the interpretation of silicate properties which involve surface phenomena.

The complexes formed by ethylene glycol, HOCH2.CH2OH, and by glycerol, HOCH2.CHOH.CH2OH, with smectites (montmorillonite-saponite group), and vermiculites have received more attention than any other group of organo-silicate complexes. This interest arose in the first place from their use for identification purposes as proposed by MacEwan (1944, 1946) and by Bradley (1945b). Over the years, increasing attention has been given to the manner in which these complexes vary with the nature of the mineral, the magnitude and source of the charge on the silicate layers, and the number and kind of the exchangeable cations between the layers. The layer charge is determined most reliably from the full chemical analysis of a mineral, but more commonly is estimated from a measurement of cation exchange capacity.

Metahalloysite is one of the kaolin group of minerals with a composition approximating to the formuia Al2O3.2SiO2.2H2O, and its structure is generally considered to be built of composite layers of atoms of the kind found in other minerals of this group. It differs from them most strikingly in that it can be produced by the dehydration of the hydrated mineral halloysite, which has the approximate composition Al2O3.2SiO2.4H2O. Both minerals give comparatively poor X-ray diagranm showing relatively few lines attd bands. The lines correspond to reflections from a basal spacing of about 7·2 Å. in metahalloysite and 10·1 Å. in halloysite.

Chamosite is a commonly occurring hydrous ferrous silicate frequently found in close association with chalybite in marine mudstone deposits, the composition of different beds ranging from almost pure chamosite to pure chalybite. In oolitic ironstones chamosite is found both in the ooliths themselves and also in the groundmass. It occurs as a constituent in shales, as a cementing mineral in sandstones, and is occasionally found in lateritic and other deposits. Mineralogically it is usually regarded as a chlorite, or akin to the chlorites, but evidence has been accumulating which tends to show that some varieties may not be chlorites at all, but are probably closely related to the kaolin group of minerals (Brindley, 1949).

Water vapour atmospheres are known to raise the temperature of the endothermic reaction of clay minerals in differential thermal analyses. In isothermal kinetic studies of dehydroxylation, it is shown that a stationary state is attained depending on the operating temperature. The rate of dehydroxylation is a function of specimen size and shape, which suggests a controlling influence by entrapped water vapour. Even at constant reaction temperatures, the rate of dehydroxylation varies greatly between the interior and the exterior of a specimen. The bearing of these results on thermal analyses and on kinetic studies generally is discussed.

Summary. The layer structure of the kaolin mineral dickite has been shown to differ significantly from the idealized arrangement of regular tetrahedra and octahedra. Since the structure of kaolinite can be studied only by X-ray powder methods, it cannot be refined beyond the idealized arrangement. By applying the diekite type of layer structure to the ease of kaolinite, an explanation for the triclinic symmetry of kaolinite has been obtained, and also an improved agreement with the observed X-ray intensities. A DETAILED structure analysis of kaolinite was first attempted by Gruner (1932), based on X-ray powder diagrams of the mineral. He concluded that the unit cell was monoclinic, with probable space group C~-Cc, and contained two structural layers related by a c-glide plane. However, further examination of powder diagrams of various kaolinites by Brindley and Robinson (1946) revealed that there were reflections that could not be explained in terms of this monoclinic cell, and they put forward a triclinic cell containing only one structural layer. So far, it has been proved that this triclinie cell fits very well with the observed features of the X-ray powder patterns of the mineral as regards both spacings and intensities of reflections. The structure of the composite layer of Si-O and AI-OH was assumed to have the geometrically idealized arrangement first proposed by Pauling (1930). At that time, there were no means to establish a refined structure for the layer itself in the absence of suitable single crystals. In terms of this idealized layer, it is impossible to account in the actual structure of kaolinite for the s-angle and for a small departure of the fl-angle from an idealized displacement of --a/3. Recently, Newnham and Brindley (1956, 1957) have made a detailed analysis of the mineral dickite, a polymorphic form of kaolinite, and have shown that the actual layer structure is distorted to some extent from the idealized arrangement. This has opened the way to an interpretation of the triclinic nature of kaolinite, since there are good reasons for thinking that the structures of the layers in dickite and kaolinite

SummaryElectron micrographs of scarbroite show thin platy crystals of about 1 μ size, having rhombic outlines with angles 66° ± 1° and 113° ± 1°. Single-crystal electron-diffraction patterns show rectangular net patterns, with d100 = 9·90 Å., d010 = 14·67 Å., γ* = 90° ± 0·05°. Strong hk0 reflections show a pseudohexagonal arrangement, but true symmetry is probably orthorhombic or monoclinic. Faces outlining rhombic forms are of type {11l}, .