Correns and Lippmann have extended the work carried out in England on swelling chlorites by some investigations on Keuper clays.

Dietzel has succeeded in showing that the infrared absorption band of kaolinite at 2.7 μ has two peaks which can be correlated with two different kinds of (OH) groups in the structure.

The “fire-clay” type of clay mineral has been found in Grossalmeroder clay by Lippmann and in Frantex clay from Provins by von Engelhardt. In Frantex clay especially the layer sequence is highly disordered. Halloysite is distinguished from these minerals by its greater layer spacing and metahalloysite by its tubular morphology.

Winkler has studied the particle size distribution of numerous brick clays and has established that the mineral must have a certain proportion of fine and coarse clay and fine sand, but also a very smooth particle size distribution curve from the finest to the coarsest particles if the clay is to be suitable for thin-walled ware.

The clay mineral section of the Deutsche Keramische Gesellschaft tested various methods for quantitative clay mineral analysis. More than 20 laboratories used the following methods: x-ray analysis, dilatometer analysis, D.T.A., dehydration curves, microscopic analysis, and the determination of free silica by solution in phosphoric acid.

By the investigation of mixtures made up of the purest quartz, feldspar, halloysite, illite, kaolinite, montmorillonite and “fire-clay” mineral, the correct values were found for the most part within a few percent.

In the investigation of natural clays, greater differences were found, amounting to as much as 10 percent. Von Engelhardt especially investigated the errors arising with Geiger counter x-ray equipment.

This clay has been studied by Fourier transform methods, which show that it is a random interstratification of mica with montmorillonite, subject however to the limiting condition that montmorillonite layers are never contiguous. It is very similar to one of the mixed-layer clays from Kinnekulle, Sweden, described by Mrs. Byström. The “separation rule” is perhaps one of the factors conditioning the appearance of definite stages in the mixed-layer mica-montmorillonite sequence, as noted by Mrs. Byström.

It is suggested that the minerals of the palygorskite-sepiolite group occupy the region of discontinuity between dioctahedral and trioctahedral minerals. There is thus a series of minerals, the two extremes having a planar lattice, and the intermediate members a fibrous lattice. The lamellar-fibrous change in structure takes place as the number of vacancies increases progressively.

Among the minerals of fibrous structure, the structural change from sepiolite to atta-pulgite occurs in such a way as to allow no more than one vacancy per structural fiber, and per half cell, as if this vacancy were not distributed at random, but symmetrically among the octahedral positions. The greater the number of vacant octahedral positions, the smaller the extension of the octahedral layer. The margin of variation in the number of vacant octahedral positions per structural fiber is greater in sepiolite than in attapulgite, probably because of the greater width of the fiber in the former mineral.

A detailed study has been made of the dehydration of sepiolite. This work, together with other studies of dehydration in vacuo and over phosphoric anhydride, rehydration of samples heated to various temperatures, specific surface, water uptake, and x-ray examination of natural and heated samples (to be published later), lead us to certain conclusions regarding types of water in sepiolite. A comparison is made with attapulgite.

The smectic clay from Sierra de Gata, Cabo de Gata region, Almería, Spain, is montmor-illonoidal like the smectic clay from Serrata de Nijar in the same region. These clays are formed by alteration of calco-alkaline volcanic rocks by marine and/or hydrothermal action.

Studies on clays in Japan were begun about 1900. Modern clay mineralogical work began about 1940 and is being developed in the following scientific and industrial branches: geology, mineralogy, chemistry, ceramics, soil sciences, soil mechanics, etc. Recent important items are as follows: (a) Order-disorder problems of clay minerals, (b) Studies of clay minerals by electron micrographs and electron diffraction methods, (c) Mixed-layer minerals, (d) Studies on alteration products of volcanic glass, (e) Studies on sedimentary rocks and recent sediments, (f) Clay minerals associated with various kinds of ore deposits, and particularly wall-rock alterations, (g) Soil clay minerals, particularly of volcanic ash soils, paddy soils, etc. (h) Mineralogical and Bolioid-chemical studies of bentonites and acid clays. (i) Clay deposits for ceramic uses, (j) Studies of complexes between clay minerals and organic reagents, (k) X-ray studies on transformation of kaolin minerals.

The results emphasize certain general characters of Japanese clays such as a complex mode of association among clay minerals, or prevalent occurrence of minerals having a lower degree of crystallinity.

An account of recent progress and current work is given in a summarized form dealing mainly with clay investigations in C. S. I. R. O., an Australian government research organization.

Although some emphasis is laid on the work designed to identify the nature and assess the properties of clays concerned with building-material manufacture, soils, and ceramics, there are several investigations which deal in a fundamental manner with the crystal structure and surface properties of clay minerals. These items of general interest include projects on the structure of vermiculite, the rehydration and surface properties of kaolinites, the nature and occurrence of Australian illites and attapulgites, and a regular exfoliation effect in montmorillonite suspensions.

Purified sodium bentonite suspensions in water display rigidity at concentrations as low as about 2 percent. On addition of NaCl the yield stress decreases, but beyond about 5 meq/ liter of NaCl it increases. The same is true for the relative viscosities and the sediment volumes of more dilute suspensions. This is interpreted as a flocculation-deflocculation-floccu-lation sequence. The paradoxical phenomenon of flocculation of the clean suspensions is explained by the concept of positive edge charge of the clay plates, allowing positive edge to negative flat-surface flocculation.

Both the purified and the salt-flocculated gels show Bingham flow behavior. When Good-eve’s analysis of Bingham flow is applied, the linking force between the clay plates in the pure gels is computed at about 10−4 dyne.

The salt-flocculated gels show thixotropic hysteresis, whereas the pure gels set immediately after stirring. This means that there is no energy barrier for gelation in the pure gels, which is in line with the proposed mechanism of association due to Coulomb attraction. In the salt-flocculated gels there must be an energy barrier causing thixotropic hysteresis. This might be expected from the summation of residual double-layer repulsion and van der Waals attraction. Considering thixotropic stiffening as slow coagulation, the height of the energy barrier could be calculated from the thixotropic increase of the modulus of elasticity with time after previous shear breakdown of the structure. The reasonable value of 7 kT was found for the height of the energy barrier of a gel containing 30 meq/liter of NaCl.

While the variations of the physical properties of colloidal suspensions of bentonite clays under various conditions of contamination have been the subject of extensive investigations, the role of the associated electrical phenomena in the impartation of these physical properties is virtually undefined. Successful techniques for the measurement of the electrical phenomena have been reported previously but they are applicable only to very dilute clay suspensions in which negligible electrical interference between clay particles exists. Apparatus and techniques applicable to concentrations of colloidal material normally used in bentonite oil-well drilling fluids were developed and are discussed.

Measurement of electrokinetic phenomena in concentrated suspensions was effected by application of the principle of electroosmosis by suitable modification of existing apparatus. The distinguishing modification was replacement of the conventional, consolidated diaphragm with a diaphragm of colloidal material supported by thin membranes.

The applicability of the apparatus and techniques is demonstrated by qualitative comparison with data of previous investigations wherein the comparable depression of the electro-kinetic potential by the addition of various contaminating ions is shown. In addition, the relation between the measured electrokinetic potential and the filtration rate is shown to be linear and independent of the valence or type of contaminant for a major portion of the investigated concentration range. This suggests that for ions which appreciably repress the electrokinetic potential the fluid-loss may be used as a means of approximating the changes of the electrokinetic potential.

A technique has been developed for obtaining reproducible viscometric data on dilute clay suspensions using the recently developed capillary viscometer of Maron, Krieger and Sisko. Aging and type of mixing have important effects on the viscosity of the dispersions. At-tapulgite, hectorite, and Wyoming bentonite exhibit non-Newtonian behavior at all concentrations studied. The effect of temperature on the reduced fluidities of suspensions of the three clays is negligible. In this respect they agree with the behavior predicted for suspensions of rigid, noninteracting particles.

An experimental technique was developed for studying the deformation properties of kaolinite-water mixtures, and a study was made of the effects of different wetting agents on the deformation behavior of these mixtures. Particular care was taken to minimize physical effects that could be attributed to preferred orientation of clay particles. Evaluation of different compositions was made in terms of stress-strain diagrams obtained by means of a simple compression plastometer test. Auxiliary studies included sedimentation and filtration experiments of kaolinite-water mixtures containing wetting agents.

The various classes of wetting agents investigated, viz., anionic, cationic and nonionic wetting agents, were found to affect the deformability of clay-liquid mixtures independently of the surface tension of the liquid phase. As compared with water alone, cationic and nonionic reagents decreased and anionic reagents increased the deformability of clay-liquid mixtures.

In general, the sedimentation and filtration properties of kaolinite-water mixtures containing various wetting agents were consistent with the results of the deformation experiments.

The structural formulas were determined of very pure specimens of montmorillonite, bei-dellite, saponite, nontronite, hectorite, wolchonskoite, vermiculite, and batavite. The lattice perfection of these minerals and the nature and variation of their crystalline swelling depend significantly on the surface density of the exchangeable cations between the silicate sheets.

In a neutral solution of NH4F, OH ions were replaced by F ions. The exchange capacity is smaller the greater the diameter of the silicate layers of the various montmorillonite minerals. Since the anion-exchange capacity of nontronite can be increased through oxidation of Fe2 it is probable that the exchangeable OH ions are located on the boundaries of the octahedral layers.

With kaolinite, the cation-exchange capacity decreases with increasing thickness of the crystal plates. The OH ions of the basal surface can be exchanged with F ions, which leads to the destruction of the lattice.

A one-dimensional Fourier synthesis of K-batavite, like the investigations of Walker on vermiculite and of Brown and also Méring on montmorillonite, provides confirmation of the structure and enables the lattice positions of the K ions to be determined.

The consequences of a nonhomogeneous charge distribution in clay systems are first examined. The mean ionic activity is shown to be a geometrical rather than an arithmetical average. Potentiometrie methods of measurement, with (quasithermodynamic), and without (thermodynamic) liquid junctions are compared. The latter give chemical potentials of soluble molecular species or ratios of mean activities; neither of these affords a characterization of single cations in relation to clay surfaces. The quasithermodynamic method, like conductance measurements, affords data which can be interpreted directly in terms of single ions. The two are compared for dilute and more concentrated clay systems by using the ratio: “Cation conductivity/total conductivity of clay systems.” For dilute systems this ratio varies slowly and smoothly with concentration and with degree of saturation. High concentrations give an abnormally high value. Cataphoresis results are shown to be in agreement with conductance and Potentiometric data for dilute clay systems.

Several montniorillonites and a nontronite were digested in hydrochloric acid at constant temperature for various periods of time. Soluble iron, aluminum, magnesium, and in two samples titanium, were determined for each digestion period. Rate of solution curves were obtained by plotting the logarithm of the percent of the residual ions against time. In general, the solution curves were straight lines or curves that could be resolved into two straight lines. From the interpretation of the dissolution curves, it was possible to determine the amount of the ions in octahedral and tetrahedral coordination. For some of the samples, the rate curves also gave the amount of iron and/or aluminum extraneous to the clay lattice. The amount of silicon in the clay lattice was calculated using the experimentally determined octahedral cations, substituted tetrahedral cations if any, and the exchangeable cations assuming 44 charges per unit cell. The distribution of cations in lattice layers indicates that the eight montniorillonites are substantially dioctahedral. Two of the samples showed the presence of iron in tetrahedral coordination while all the samples showed extraneous silicon. The presence of extraneous silicon, iron, and aluminum in purified samples indicates that formulas derived from bulk chemical analyses can be inaccurate.

The dissolution of the ions from the clay lattice determined at several different temperatures in one sample and at two acid concentrations in another sample is in agreement with chemical kinetic principles and is a first-order reaction. The rate constant for the acid dissolution reaction increased proportionately with the acid concentration.

The activation energies were determined for the solution of iron and aluminum in mont-morillonite from Polkville, Mississippi, and nontronite from Garfield, Washington, using Arrhenius’ Law. In both samples the activation energies (17 to 18 kilocalories per mole) were the same. In the nontronite sample the activation energies were identical for what have been interpreted as octahedral and tetrahedral ions.

Hydrogen hectorite-water sol was prepared using mixed-bed ion-exchange resins. At 25° C., the rate of change of concentration with respect to time was determined for (a) strong-and weak-acid hydrogen ions; (b) low molecular weight, unassociated silicates; and (c) soluble, unassociated magnesium ion.

The experimental data indicate that two consecutive first-order reactions are occurring: (1) strong acid is undergoing a rapid, spontaneous reaction to yield weak acid, and (2) the resulting weak acid is undergoing a slow, spontaneous reaction to yield a neutral clay. The equivalent weight of the strong acid is apparently one-half that of the weak acid. For each milliequivalent of strong-acid hydrogen ion undergoing reaction, one milliequivalent of magnesium ion is released from the crystal lattice. Thus, the acid clay is eventually converted to magnesium clay. In addition, for each milliequivalent of weak-acid hydrogen ion undergoing reaction, one millimole of silica is released from the lattice. Since the release of magnesium ion precedes the release of silica, proton attack is probably occurring at the edges of the crystals. The exact nature of the weak acid is unknown and detailed study would probably be difficult in view of its transitory existence.

Freshly prepared acid hectorite contains approximately 40 meq of hydrogen ion per 100 g clay. Therefore, only 3 percent of the total magnesium is released from the lattice. The lattice structure of the resulting magnesium clay is identical with that of natural hectorite as shown by x-ray diffraction.

Studies have been made of the alteration of pure albite single crystals and powders. No structural modification of the feldspar itself has been detected. No evidence has been obtained for any preferential orientation of an alteration product in relation to the initial feldspar. Under hydrothermal conditions at 280° C and 430° C., albite flakes and powders have been subjected to attack by 0.1 N HCl for periods ranging from a few hours to 52 days. The flakes changed mainly to boehmite, the powders to a variety of products, including a well-defined kaolinite. This difference of behavior is interpreted in terms of Correns’ ideas on the weathering of silicates.

Types of clay minerals have been determined in samples from three profiles in Indiana: (1) a residual soil from limestone; (2) a Pleistocene till of Illinoian age; (3) a Pleistocene till of Wisconsin, age. The type of clay minerals varies with depth from the surface because of degree of weathering. In the residual soil from limestone, montmorillonite is the dominant clay mineral; the entire profile is highly weathered. Likewise montmorillonite is dominant in the highly weathered portion of both the Illinoian till and the Wisconsin till. The relatively unweathered portion of both tills contains illite and chlorite as dominant clay minerals. The factors of the weathering process in central and southern Indiana evidently favor the development of the clay minerals having expanding lattices. The mechanism for changing chlorite and illite to montmorillonite seems to include oxidation of the iron in the lattice and subsequent leaching of magnesium and potassium.

When surface clays are eroded and transported by streams into a marine environment, the expanding-lattice clay minerals may revert readily to the original type, either chlorite or illite.

Wall-rock alteration along veins in the Central City-Idaho Springs region, Gilpin and Clear Creek Counties, Colorado, superficially resembles alteration around similar base-metal sulfide deposits, but differs in some details. Meso thermal-type veins of early Tertiary age cut deformed Precambrian metasedimentary, igneous, and metamorphosed igneous rocks; the veins contain pyrite, galena, sphalerite, chalcopyrite, and tennantite as principal constituents and minor gold, silver, and uranium minerals. A spatial zonation of ore minerals relates to distinct stages of ore deposition.

Detailed studies show that three of the wall rocks in the area—granodiorite, biotite-mus-covite granite, and biotite-quartz-plagioclase gneiss—are altered to varying degrees and in varying amounts. Clay-mineral formation was a major feature of the process. The alteration sheath around fractures and veins is divided into four gradational but regular zones: (1) Least altered (fresh) rock; (2) weakly altered, hard rock; (3) moderately altered, soft clay-mineral rock—(a) montmorillonite-rich, (b) kaolimte-rich, and (c) illite-sericite-rich; and (4) strongly altered, hard (silicified) rock. The sequence of silicate alteration is believed to relate first to the relative stability of primary mineral structures in the alteration environment, but ultimately to the chemistry of the environment.

The host rocks are significant factors in localization of altered mineral assemblages as they supply the requisite elements for argillic-type alteration. Structures of the host rocks and veins play a prominent role in localization of altered rocks and the zoned ore deposits. Coincidence of alteration and mineralization processes may have more spatial than temporal significance.

A working hypothesis explaining the geological evidence proposes that most alteration was accomplished by meteoric and/or hypogene solutions before ore minerals were deposited. Later solutions of the pyrite stage may have intensified the early zone 4 alteration assemblage close to the source channels, but base-metal sulfide stage solutions were not competent to impress additional alteration effects. Most supergene alteration occurs close to the surface. Therefore, in these areas alteration zonation does not afford a reliable guide to ore.

Quantitative estimation of mineral concentrations was made for the clay fractions of Omega loamy sand (Brown Podzolic) and Ahmeek loam (Brown Forest). These soils are relatively young and have developed from Pleistocene (late Wisconsin) outwash and till, respectively, in northern Wisconsin. A mineral weathering depth function was found, in which iliite and chlorite present at depth have weathered to vermiculite and montmorillonite nearer the surface, particularly in the clay fractions of Ahmeek loam. In the fine clay, the montmorillonite content increases from 5 percent in the C1 horizon to 44 percent in the A1 horizon. Conversely, chlorite decreases from 11 percent in the C1 to virtually none in the A1 horizon. Weathering in these soils is also reflected by distribution of minerals as a function of particle size. The occurrence of mineral-weathering depth and size functions in these young soils is attributed to accelerated leaching made possible by the coarse texture of the soils.