The basic outlines of most of the hydrous layer silicate structures were determined during the 1930’s. Present escalating interest in obtaining additional detail is indicated by (a) publication of over twenty structural refinements (2-D or 3-D) during 1954-64, (b) publication of at least nine structures in 1965 or early 1966, and (c) personal communication that at least fifteen additional refinements are in progress. Points of especial interest in these recent studies follow.

1. 1. Octahedral cation order is common, but tetrahedral cation order is confirmed in only three cases. Because ordering of Si, Al does not significantly affect the statistical tests for centrosymmetry, centrosymmetric space groups that do not permit order should be avoided during refinement.

2. 2. Oversize tetrahedral sheets articulate with smaller octahedral sheets by tetrahedral rotation and, for dioctahedral species, by tetrahedral tilting around vacant octahedra. The latter mechanism influences the type and regularity of layer sequences. Undersize tetrahedral sheets articulate with larger octahedral sheets by tilting plus octahedral contraction or by inversion of some tetrahedra.

3. 3. The amount and direction of tetrahedral rotation and tilt, length of T—O, M—O, and O—O bonds, sheet thicknesses, and relation of cell dimensions to composition can now be predicted with some confidence.

4. 4. Variation in layer stacking (polytypism) is common. In some cases the stabilities of different polytypes can be explained by the relative amounts of repulsion and attraction between the ions in the structures. The stabilities can be correlated with the energy available in the environment of crystallization.

Attempts to find a generally acceptable scheme of classification and nomenclature for clay minerals by the nomenclature committees of The Clay Minerals Society (C.M.S.), the Comité International pour l’Étude des Argiles (C.I.P.E.A.), and the International Mineralogical Association (I.M.A.) are summarized. The C.M.S. committee has been working on this problem continuously since 1961 and has transmitted its views to C.I.P.E.A., first at the time of the Stockholm meeting, 1963, and subsequently, in more detail, after receiving the first draft of the C.I.P.E.A. proposals. The C.I.P.E.A. committee held discussions in Stockholm, 1963, and subsequently submitted a first draft to 32 nations; from the replies received, a final draft of the C.I.P.E.A. proposals was prepared and submitted to the I.M.A. in 1964. The report from the I.M.A. was made available in August, 1965.

The objective of this paper is to present flow sheets for a system of quantitative minera-logical analysis of clays of soils and sediments and to show representative results. Selective dissolution analysis by the Na2S2O7-HCl-NaOH procedure yields the quartz and feldspar contents (0 to 63%) and differentiates feldspar K from mica K. The NaOH-thermal system of selective dissolution yields the allophane plus gibbsite, kaolinite plus halloysite, and dickite contents (0 to 84% for the sediments; 1 to 25% for soil clays) Mica contents (0 to 92% for the rock specimens, 7 to 43% for soil clays) are determined by nonfeldspathic K (and Na). Vermiculite contents (1 to 97% of specimens; 3 to 21% for soil clays) are measured by blocking of interlayer CEC by drying at 110°C while K saturated and replacing with NH4Cl. Montmorillonite (and palygorskite) contents (0 to 85% of specimens; 3 to 36% of soil clays) are determined by the CEC not blocked by the K and NH4 sequence for vermiculite. Chlorite contents (0 to 85% for specimens; 0 to 37% for soil clays) are determined by thermal gravimetric analysis, after allocation of OH water lost between 300 and 950°C to other hydrous minerals determined.

The best evidence of the accuracy of the system of analysis lies in the consistent total recovery of 24 standard mineral samples averaging 100.4 ± 1.3 (± standard error of means) and of 22 soil clay samples averaging 99.5 ± 0.8. The different constituents were present in widely different proportions in the various samples, and were determined by independent methods. The complementary total of near 100% (maximum range 95 to 105% for specimens; 95 to 103% for soil clays) for the analyses is a significant measure of the specificity of the several determinations.

Micaceous clays (“illites”) of a number of sediments, subjected to quantitative mineralogical analysis, ranged in different samples from 58 to 65% of a dioctahedral mica of muscovite type, from 3 to 8% vermiculite, from 0 to 10% montmorillonite, from 2 to 12% quartz, from 0 to 4% feldspars, from 1 to 2% rutile and anatase, from 0.3 to 1.2% free iron oxides, and from 16 to 30% chlorite. The soil clays contained less mica (13 to 35%) but more vermiculite (13 to 16%), montmorillonite (6 to 14%) and chlorite (30 to 33%), besides kaolinite (3 to 8%) and amorphous material (6 to 15%). The presence of the various minerals was verified by X-ray diffraction. When the interlayer K of these micaceous clays was replaced by hydrated Na ions through treatment with 0.2 n sodium tetraphenylboron in 1 n NaCl, the analytically determined vermiculite and montmorillonite contents increased. The freshly produced vermiculites had an interlayer charge of 177 to 198 me/100 g. During this replacement of interlayer K in a 1 N salt solution, the pH of the equilibrium matrix solution was observed to increase instead of decreasing as would be expected if oxonium (OH3+) ions were associated with K in the interlayer space, thus precluding the possibility of interlayer ONz+. The calculated stoichiometric equivalent of the pH rise established a significant uptake of protons by the lattice as K was released.

Thermal analyses of vermiculites show 0.5 to 0.7% higher OH water content than the parent micas. Oxidation of ferrous iron in the silicate structure, suggested as a possible mechanism for lowering of layer charge during weathering of mica to vermiculite, accounted for about 66% of this in samples high in iron (16.0% FeO) and only 30% of this in samples fairly low in iron. The rate of extraction of K from muscovite with no ferrous iron was found to be pH dependent, increasing at lower pH values. The data indicate proton incorporation with structural oxygens of the silicate sheet to form OH as a charge reduction mechanism in weathering of mica, independent of and additional to that involving the oxidation of ferrous iron.

Interlayer K in muscovite, biotite, phlogopite, illite and vermiculite-hydrobiotite samples was replaced by cation exchange with Na. The rate and amount of exchange varied with the mineral and the level of K in solution.

Essentially, all the K in muscovite, biotite, phlogopite and vermiculite was exchangeable when the mass-action effect of the replaced KT was reduced by maintaining a very low level of K in solution. The time required for this exchange varied from < 10 hr with vermiculite to > 45 weeks with muscovite. Only 66% of the K in the illite was exchangeable under these conditions. When the replaced K was allowed to accumulate in the solution, the amount of exchange was determined by the level of K in solution required for equilibrium. These levels decreased with the degree of K-depletion and with the selectivity of the mica for K. The order of selectivity was muscovite > illite > biotite > phlogopite > vermiculite. Decreasing the K in solution from 10 to 7 ppm increased the exchangeable K in biotite from 30 to 100%. A K level of only 0.1 ppm restricted the exchange of K in muscovite to 17%.

A decrease in layer charge was not required for K exchange, but a decrease did occur in K-depleted biotite and vermiculite. Muscovite with the highest layer charge (247 meq/100 g), least expansion with Na (12.3Å), and least sensitivity to solution pH had the highest selectivity for K and the slowest rate of exchange. The K in vermiculite was the most readily exchangeable.

Clay fractions from four soils were analyzed for kaolinite and gibbsite by differential thermal analysis (DTA) and selective dissolution analysis (SDA). The kaolinite values by the two methods had a standard deviation of ±0.95 for the 2–0.2 μ clay of the three most highly weathered soils. Apparently some kaolinite was dissolved with amorphous material in the 0.2–0.08 μ kaolinite standard and probably in 0.2-0.08 μ soil clays. Accuracy of kaolinite determination for the 0.2–0.08 μ soil clays by DTA was reduced because of uncertainty of exact composition of the standard. Presence of montmorillonite in Sango soil clays, particularly the 0.2-0.08 μ fraction, apparently contributed to the error in kaolinite determination by SDA. More precise values for gibbsite were obtained by DTA than by SDA because of the dissolution of alumina from sources other than gibbsite.

A Solution containing fluoride (0.4 n NH4F, 0.1 n HCl, n NH4Cl), permits the concentration of dioctahedral mica and dioctahedral vermiculite in mixed clay systems. Allophane, halloysite, kaolinite, and in particular, Mg-rich montmorillonite, biotite, and vermiculite of clay size, are destroyed in 24–48 hr at room temperature. A salt-free, NH4-saturated sample, weighing 80 mg, is shaken in 80 ml of the fluoride solution. The residue is washed with water and X-ray diffraction patterns made.

The method has use in characterizing some of the 2:1 layer silicates in clays. Anatase, if present, is also concentrated and is more positively identified by X-ray diffraction.

Electrical double layer theory is used to analyze an idealized model unit of a clay particle system with the purpose of describing the mechanical stability in terms of an equilibrium of attractive and repulsive forces. Restricting the analysis to two dimensions, a symmetrical parallelogram formed by four typical clay mineral particles is taken as a representative unit of a flocculated clay and the interactions of mineral faces and associated electrolyte is investigated. The distortion energy of the system thus found is then directly related to the mechanical stability of the model unit’s structure as it varies from parallel to perpendicular orientation. The general pattern of behaviour of the model unit will be shown to be compatible with the mechanical behavior of the clay mass.

Equivalent conductivities of adsorbed cations were determined in clays saturated with Na+, Cs+, Ca++ and with mixtures of these cations. Measurements were also made on Ca++ clays which had been forced by previous drying into bundles of platelets or tac-toids. The average mobility of adsorbed Ca++ and Cs+ is much lower than that of adsorbed Na+.

It was concluded that the average mobility of adsorbed Ca++ is low because most of this Ca++ is on the internal surfaces of tactoids. Ca++ adsorbed between these internal surfaces appears to have a mobility much lower than Ca++ on the external surfaces which has a mobility of the same order of magnitude as Na+. Polarization of adsorbed Cs+ accounts at least partially for its low mobility in these clays.

Demixing of adsorbed cations (segregation with Na+ dominant between some platelets and Ca++ between others) is suggested as an initial step leading to breakup of a Na+-Ca++ clay mass into tactoids. The tactoid model, with Ca++ and Na+ preferentially on the internal and external surfaces respectively, furnishes an explanation of the instability of clay and soil aggregates with 15% exchangeable sodium.

A microscopic theory of the kaolinite-water system is presented, based upon the assumption that the clay-water interaction may be envisioned as partly hydration of the exchangeable cations and partly adsorption by the oxygen and hydroxyl surfaces. The theory treats exchangeable cation hydration quantum-mechanically as an ion-dipole phenomenon and considers water adsorption by the mineral surface as a problem in hydrogen bonding. A statistical mechanical model incorporating the quantum-theoretical results is then invoked to find the contribution of each component interaction to the initial portion of the adsorption isotherm for homoionic kaolinite. Good agreement between the theoretical calculations and available experimental data is achieved for water vapor adsorption by Li-, Na-, K-, and Mg-kaolinite, without the use of ad hoc empirical parameters. The concordance, in turn, is used to suggest that the basis for adsorption hysteresis in kaolinite-water vapor systems is the irreversible transition: mineral surface water → cation hydration water.

A systematic study of the influence of salinity and clay content on the electrical conductivity of sodium-illite clay gels shows that the geometry or “formation resistivity factors” of such systems can adequately be described by the model of oblate ellipsoids, used to simulate the shape of the clay particles. This conclusion is in agreement with the results previously obtained on kaolinite and montmorillonite clays. An axial ratio of 16 was found for the illite clay particles.

On the basis of Burger’s and Maxwell’s equations for electric flow through porous media, formulae are derived for calculating the electrical conductivity of mixed systems, i.e. “clay 1 + clay 2 + electrolyte solution” and “clay + spherical particles + electrolyte solution”. The electrical conductivity of these systems is expressed in terms of the shape parameters, surface conductances, specific surfaces and volume concentrations of the constituents. The type of equation can eventually lead to an explanation (in terms of a non-uniform particle shape distribution) of the anomalous geometry effects in some clays.

Experimental results conform fairly well to the equations. Glass powder at volume fraction between 0.18 and 0.60 added to a 17.4% montmorillonite gel acts as an inert diluent on the specific electrical conductivity of the mixture. For a mixture of 1 part montmorillonite to 9 parts kaolinite, the measured specific electrical conductivity agrees within about 10% with the predicted over the range studied (volume fraction of montmorillonite: 0.035 to 0.039; mixture porosity: 0.61 to 0.660; salt concentration range: 0.5 n to 2 n NaCl).

Montmorillonite may adsorb cobalt(III)hexammine and cobalt(III)chloropentammine cations, and the C.E.C. determined for these complex cations is of the order of magnitude of that obtained with ammonium. The infrared spectra of these coordination complexes adsorbed by the clay are similar to those observed for the corresponding chloride salts. However, when montmorillonite treated with these coordination complexes is dehydrated in vacuum or under moderate temperature conditions (<100°C) in a dry atmosphere, the infrared spectra are deeply modified. The complex cations decompose with NH3 evolution and ammonium formation. Cobalt(II)hydroxide is produced and ammonium cations balance the lattice electrical charge. The true decomposition rate was followed by IR absorbance of NH4 which showed that the complex decomposition followed that for the nomothetic decomposition of solid particles. The apparent activation energy of the decomposition was 20.5 and 43 kcal/mole for the CoCl(NH3)52+- and Co(NH3)68+-montmorillonite complexes respectively. An analysis of the combined chemical and IR data on the hexammine complex permitted calculation of the NH3 diffusion rate between collapsed montmorillonite sheets. When the interplanar gap approaches 1Å the diffusion coefficient is approximately 7 × 10-19 cm2/sec. In contradiction to their stability in solutions, the cobalt(III)hexammine cation is less stable than the cobalt(III)chloropentammine cation when absorbed on montmorillonite.

Changes in the infrared absorption spectrum of ammonium-saturated rectorite on heating suggest that the ammonium cations are hydrogen bonded to water molecules when the mineral is hydrated. Further spectral changes above 300°C indicate that lattice OH groups are perturbed by protons liberated from the decomposition of ammonium ions giving rise to an absorption doublet at 3500 and 3476 cm-1. The doublet attains maximal intensity when decomposition of ammonium cations and dehydroxylation of the mineral is complete at about 550°C.

The perturbation effect occurs only for swelling dioctahedral minerals which derive their layer charge from Al-for-Si substitution.

H-ion was added to Na or Ca bentonite suspensions. The H-ion was added either in solution, as HCl, or adsorbed on a cation exchange resin. The variation with time of the quantities of H and Al in various phases of the system was determined.

In the first stage of the reaction both exchangeable H and exchangeable Al on the clay increased rapidly. Several facts showed that the exchangeable Al was not liberated by crystal structure decomposition. It is postulated that its appearance is the result of a rapid dehydroxylation, of hydroxy Al groups located at plate edges or adsorbed on basal planes, producing water and trivalent Al ions.

During the second stage of the reaction, spontaneous self-decomposition of the clay structure takes place. It was found that when the H-clay in alone in suspension or with low concentration of acid, the decomposition stops after the liberation of a limited quantity of Al. Most of this Al is adsorbed on the clay and it becomes the prevailing exchangeable ion. On the contrary, when the H-clay is aging in the presence of H-resin, a system of consecutive reactions is operating. In this system, Al liberated from the structure is transferred to the adsorbed state in the clay and from there to the resin. As a result the decomposition reaction does not stop as in the absence of the resin, but is carried further.

Clay mineral compositions in specimens of Recent marine sediments in the neighbourhood of Japan and sedimentary rocks from Japan were studied. Identification of the clay minerals was made chiefly by X-ray, differential thermal and infrared analyses. Their relative amounts were determined by comparing the intensities of their basal X-ray reflections.

Recent marine sediments: Specimens from the bottom of the Northwestern Pacific Ocean contain montmorillonite, illite, chlorite and kaolinite. The amount of mont-morillonite varies locally, but that of kaolinite is generally small. Clay mineral compositions of the Eastern Sea specimens are different from those of the Northwestern Pacific Ocean and the crystallinity of clay minerals seems to be better in the Kastern Sea. It is most likely that the clay minerals in the Eastern Sea sediments were supplied from the continent. Specimens of the bottom sediments at the entrance of Tokyo Bay contain montmorillonite, illite, chlorite and a lesser amount of kaolinite. The amount of montmorillonite varies markedly with locality and tends to be low where the movement of sea water is relatively intense. This may be due to a finer particle size of montmorillonite in comparison with the other clay minerals.

Sedimentary rocks: The relationship between sedimentary formations and clay mineral compositions shows that the compositions are characteristic of the depositional environments. For example, kaolinite is abundant in the formations deposited in fresh water but its content is low in the formations deposited under marine environment. The Paleozoic formations from the Tohoku region contain chlorite and illite without exception; however, the Mesozoic formations contain them in various proportions according to localities.

Recent sediments of the Niger delta contain the detrital clay minerals kaolinite, mont-morillonite and a small amount of illite. The montmorillonite content increases with water depth and distance from the shore, and the results of laboratory experiments on natural Niger delta clay support the assumption that this is due to differential floc-culation and sedimentation.

The easterly Guinea Current, transporting montmorillonite-rich floccules in suspension, may cause an increase in the montmorillonite content of the clays in the ©cistern part of the delta.

Mineralized faecal pellets are present in most marine sediment samples. Chamosite occurs authigenically in coastal water shallower than 35 fathoms, as brown and dark-green pellets. Green pellets, composed of highly expandable, montmorillonite-type glauconite, are particularly common around the 100 fathom isobath. Both chamosite and glauconite have a high magnesium content, which seems to be usual during their early stages of formation.

The formation of chamosite and glauconite is governed by redox potential and the availability of iron. If no reduction takes place, the pellets remain grey and their composition is similar to that of the clay matrix. Grey pellets are less restricted to a particular depth than are the chamosite and glauconite pellets, but distinct maxima occur around the 250 fathom isobath.

A suite of granodiorite samples was collected by dredging from depths of about 1000 m from the walls of Carmel and Monterey submarine canyons, Monterey Bay, California. One surface of each of the various granodiorite slabs was weathered and encrusted with marine organisms. The weathering is maximum at the surface and penetrates to a depth of about 20 cm and selectively alters the feldspars to clay. Potassium feldspars are most severely altered. Mineral selective attack, shallow depth of weathering, restriction of biological growth to weathered surfaces, and regional geological setting are interpreted to mean that the samples were broken from bedrock and that this granodiorite probably weathered in the marine environment.

Authigenic clays formed as a result of the submarine weathering of the granodiorite are kaolinite, K-mica, montmorillonite, and halloysite.

These data suggest that the assemblage K-mica, montmorillonite, and kaolinite have a phase join that may lie on or close to the composition of sea water. Furthermore, kaolinite may be unstable in sea water and gradually break up to form halloysite tubes. The possible influence of biologie agents is suggested in the formation of marine halloysite.