Hydrothermal alteration of andesitic and dacitic rocks in the Goldfield District, Nevada, has produced regularly interstratified chlorite-vermiculite and tobermorite. X-ray diffraction and oscillating-heating data indicate the regular interstratification of the chlorite-vermiculite. This mineral is found in the zone of least alteration and was formed by the alteration of hornblende phenocrysts. Penninite is an intermediate stage in this reaction. Increased intensity of alteration resulted in the disappearance of chlorite-vermiculite and the development of montmorillonite. Tobermorite, found only in the dacite, is associated with alunite as pseudomorphs after plagioclase phenocrysts in the most intense zone of alteration. The intermediate stage of hydration for tobermorite is indicated by the 11 Å spacing of the 002 diffraction peak. Oscillating-heating X-ray data at atmospheric pressure show that tobermorite decomposes thermally in two stages. The (00l) planes collapse at approximately 520 °C and crystal planes having an 8 Å periodicity collapse at about 760 °C. Wollastonite develops from tobermorite above 700 °C under static heating conditions.

An association between clay minerals and rock type is recognized in the rocks of an interlayered sequence of fossiliferous shaly, sandy bioclastic, and cherty limestone, dolomitic limestone, calcareous and dolomitic quartzite, and quartzite that form a portion of the lower part (Pennsylvanian age) of the Oquirrh formation in the northern Oquirrh Range, Utah. These sedimentary rocks are largely of clastic origin and range from fine- to coarse-grained. In part they are cross-bedded, and fossils are locally abundant. Calcite-rich rocks predominate (78 percent) over dolomite- and quartz-rich rocks (17 and 5 percent, respectively). Clay minerals constitute less than one percent in quartzite and range from one to five percent in some limestones.

Clay minerals and rock types are commonly observed in the following associations: Illite and chlorite occur in limestone; illite, chlorite, and mixed-layer clay occur in cherty, bioclastic, and sandy limestone and in calcareous quartzite; chlorite and illite commonly are present in dolomitic quartzite; chlorite, illite, and mixed-layer clay are found in dolomitic limestone; and kaolinite, illite and chlorite are typically present in quartzite. The mixed-layer clay has a lattice spacing of 29.4 Å that expands to 31.0 Å when glycolated and contracts irregularly to 13.2 Å when heated to 500 °C; the clay is assumed to consist of 14 Å chloritic and 15 Å montmorillonitic material. Chlorite or mixed-layer clay, or both, generally are associated with rocks containing dolomite.

A carbonate rock silicification reaction has been defined and shown to be dependent on the presence of clay in the host rock. Introduction of silica in soluble form(s) serves to polymerize the clay fraction, forming a continuous three-dimensional network. This siliceous network (polymer) can be separated from the rock by leaching away the carbonate minerals. Laboratory silicification of argillaceous carbonate rocks under controlled conditions has served to define critical variables.

Early studies were limited to argillaceous carbonate rocks from the Devonian Cedar Valley formation in eastern Iowa. Similar results have been obtained with carbonate rocks from the Devonian Chaffee formation in south-central Colorado. Some of the rocks in the latter formation have been silicified in nature, and yield siliceous polymers on acid leaching identical to those formed by silicification in the laboratory.

The reaction defined is suggested to be common in natural diagenesis of argillaceous rocks, clay-rich sedimentary material, and soils.

In the case of argillaceous carbonates this reaction affects physical properties of the rock which control processes involved in petroleum migration, ore-metal transfer, rock leaching and all diagenetic reactions that involve solution transfer.

The changes occurring in fully hydrated halloysite during dehydration have been studied by X-ray diffraction at relative humidities that ranged from 0 to 100 percent. From the results of this study it has been concluded that: (1) layers dehydrate randomly, but instantaneously; (2) the diffraction from an individual crystallite is governed by the ratio of hydrated to dehydrated layers present; and (3) halloysite dehydrated to any degree shows no detectable rehydration when exposed to 100 percent relative humidity for 2 months.

On the basis of mineralogical studies on many kinds of clay minerals found in Japan, the writers attach great importance to subtle variations in clay minerals and discuss them in the light of the concept of intermediate minerals. An intermediate mineral behaves partly as one mineral (say A) with certain treatments, and as mineral B under other conditions. There are two types of intermediate minerals: the deviation type and the mixed-layer type. The deviation type is homogeneous enough in its structure that we can describe it as composed of a combination of clearly different layer groups. The mixed-layer type has an interstratified structure of two or more kinds of layers. Furthermore it is suggested that each component layer of the mixed-layer type, in general, shows the properties of the deviation type. As an example of a mineral that can be discussed in light of the intermediate mineral concept, the writers describe the properties of very complex mixed-layer minerals related to mica clay minerals associated with epithermal ore deposits in Japan. Normally the mixed-layer minerals are found where there has been successive attack under different conditions of chemical environment or in an area that is transitional between two different chemical environments.

Intermediate minerals in general are considered to be a mineral state (mineral configuration) modified in various degrees from an original mineral in response to successive changes of environmental conditions. The above viewpoints are supported by study of many clay specimens collected from alteration zones of epithermal ore deposits in Japan.

It is considered that formation of intermediate minerals may be originated because of a latent defect structure in the original mineral. Polar character that is due to unequal distribution or ratio of the tetrahedral cations in a silicate layer may be favorable for the formation of the regular mixed-layer structure. Finally, intermediate minerals may be arranged according to the following scheme: Mineral A—deviation type of mineral A—mixed-layer mineral A-B—deviation type of mineral B—mineral B.

The sorption of Co and Zn by layer silicates was studied in dilute mineral suspensions containing, in most cases, about 10-6 M Co or Zn. Electrostatic adsorption was eliminated by the presence of 0.1 N CaCl2. Co and Zn were determined by a radioisotopie technique.

Detailed studies on montmorillonite and to a lesser extent vermiculite, muscovite and biotite revealed the presence of at least two forms of specifically sorbed Co, one of which was exchangeable by certain ions such as Cu, Ni, Zn, Fe, Mn or more Co and the other, occurring in much smaller amounts, was not exchangeable by these cations. The latter form is considered to result from lattice penetration; the former is associated with surface groups. These forms may be separated quantitatively by several desorption procedures including successive extractions with dilute acetic acid.

The total amount and relative proportion of these forms of sorbed Co and Zn depend on the pH of the system, time of reaction, mineral species used, and amount of Co or Zn added. Equilibrium is not readily attained but tends to approach a slow steady state after several days. Isotherms indicate a variation in bonding energy with surface coverage. The sorption of Co and Zn from dilute solutions by any mineral is related to its stability.

These studies, considered in conjunction with published data, suggest that a common mechanism may be involved in the specific sorption of many heavy metal cations by many minerals.

Three techniques have been used to determine what clay mineral surfaces are involved in the selective bonding of Co: (a) polyphosphate ions were used to block edge surfaces of montmorillonite and vermiculite from Co, (b) collapse of the interlamellar spaces with potassium saturation was used to block internal basal surfaces of vermiculite from Co, and (c) autoradiographs were prepared of vermiculite and mica particles that had reacted with Co58. In each case Co in low concentration was allowed to combine with the mineral in the presence of high concentrations of CaCl2.

The preliminary sorption of polyphosphate ions had no appreciable effect on the sorption of Co by the minerals studied, indicating that the edge surfaces were not likely to be involved in the Co reaction. The blocking of internal basal areas had only a very slight effect suggesting that these surfaces were involved in the sorption of Co, but only to a limited extent. Autoradiographs of naturally occurring vermiculite particles revealed a somewhat uneven distribution of Co over the planar surface of the particles. Removal of the outer layers of the crystals, either before or after the material had combined with Co but before autoradiography, resulted in a concentration of the metal along edges and cracks.

Apparently the external basal surfaces are principally involved in the specific sorption of Co by layer silicates. It is suggested that chemical weathering and physical abrasion of the surfaces introduce defect structures which favor the chemical bonding of heavy metals.

The processes of dehydration and rehydration of montmorillonite and nontronite samples have been studied through infrared absorption spectra.

The changes observed in the intensity of the bands during dehydration show the analogy between absorption at 915 cm-1 (montmorillonite) and at 820 cm-1 (nontronite), their origin being a deformation vibration of OH groups.

During rehydration of the montmorillonite sample, the recovered OH groups occur in two different forms, in accordance with the results of differential thermal analysis.

The shadow lengths of dispersed flakes of the layer-lattice mineral, allevardite, were measured with the electron microscope. Details of the experimental technique are given, and the importance of using samples free from very small material is stressed. Measurements of flake thickness made in this way agree well with estimates of the basal spacing of the collapsed lattice obtained from X-ray diffraction, and dispersion of allevardite was found to produce suspended flakes 19 Å thick, corresponding in thickness to the basic structural unit of two 2:1 layers.

Recent development of the intersalation method by which kaolinite (as well as dickite and halloysite) is expanded makes possible the application of X-ray diffraction to qualitative and semiquantitative determinations of these mineral species. It also permits their distinction from the X-ray-thermally similar intergradient 2:1–2:2 layer silicates which are not affected by the treatment. Intergradient 2:1–2:2 layer silicates are developed by interlayer precipitation of hydroxides of aluminum, iron, and magnesium during pedogeochemical weathering and probably also during burial in sediments. The quantitative determination of kaolinite-halloysite by NaOH differential dissolution is completely corroborated by the qualitative, semiquantitative X-ray diffraction intersalation technique with respect to their clear differentiation from chlorite and intergradient clays.

This paper reviews the present state of knowledge on clay mineral complexes and its theoretical and practical importance. It contains a plea for placing the study of these complexes in the more general context of interlamellar sorption in crystalline materials.

Cation exchange of dimethyldioctadecylammonium (DMDO) ion for dimethylbenzyllauryl-ammonium (DMBL) ion previously reacted with centrifuged homoionic Na+ bentonite has been demonstrated. The amount of DMBL ion removed from the clay was determined by ultraviolet spectroscopy.

In order to shift the exchange equilibrium toward removal of the DMBL cation, a large excess of DMDO cation was required. At the limit of these experiments, it was found that 16 percent of the DMBL cation was exchanged.

A green chloritelike material exfoliates on heating, and gives a series Of complexes with amines. Its structure is explained in terms of a 1:1 interstratitication of chlorite and swelling chlorite.

The adsorption of phenols from dilute aqueous solution by n-aliphatic amine and Ethomeen clays has been investigated and it is shown that dodecylammonium bentonite is the most active member of the series ethylammonium to octadecylammonium bentonite. On the basis of spatial considerations, thermodynamic data, and electron density measurements a theory of adsorption has been proposed in which it is envisaged that condensation of adsorbate molecules on the organo-clay surface occurs through electrostatic/hydrogen bond forces at the hydrophilic sites and van der Waals forces at the organophilic sites.

The adsorption of quinoline by Na+- and Ca2+-montmorillonite, illite, and kaolinite in water suspensions was studied for varying physico-chemical conditions. The shapes of the adsorption isotherms depended upon these imposed environmental conditions, which were quinoline concentration, pH, salinity, time, and temperature.

In order to be in the range of concentrations of organic materials in natural waters, these studies covered the concentration range, from 0 to several hundred ppm. Of the variables studied, pH was critical. Throughout the pH range 8.5–6.0, adsorption increased as pH decreased. The change in adsorption as salinity increased depended on pH, clay mineral, and quinoline concentration. In our experiments, samples reached equilibrium within 2–3 hr, and moderate temperature changes made little difference in adsorption amounts.

Under the same conditions, Na+-montmorillonite adsorbed the most quinoline, kaolinite the least, and Ca2+-montmorillonite and illite intermediate amounts.

Two mechanisms seem to control this adsorption: ion exchange and molecular adsorption. This paper attempts to explain the effects of the physico-chemical environment on adsorption by these two mechanisms.

Adsorption isotherms of 1-n-alkyl pyridinium bromides on Na-montmorillomte, and in addition of cetyl pyridinium bromide on Ca-montmorillonite, have been determined. For up to eight carbon atoms in the alkyl chain adsorption has a limit close to the exchange capacity of the clay. With larger ions adsorption occurs beyond this and is accompanied by adsorption of the bromide ion. Adsorption of the cetyl pyridinium ion beyond the exchange capacity is greater on Na- than on Ca-montmorillonite. Replacement of the cation initially present is incomplete. X-ray diffraction analysis shows that the adsorbed ions normally lie flat on the clay surface, but cetyl pyridinium ions may stand up in a plane at right angles to the surface. Interlamellar separations somewhat less than the minimum molecular thicknesses, found for the methyl and ethyl pyridinium ions, are attributed to a combination of (1) “keying” of the alkyl groups into the clay surface, and (2) the effect of the attractive forces between the clay and the pyridinium ring. It is concluded that adsorption is due to ionic and dispersion forces between the pyridinium ions and the clay. For the cetyl compound the dispersion forces are larger than ionic forces. The exchangeable cation initially present influences the adsorption by its effect on the exchange reaction and probably also by its influence on the domain structure of the clay and hence the accessibility of external surfaces of the crystallites.

Some montmorillonites may be differentiated by complexing them with polyalcohols having a CH2 group that is not connected to an oxygen atom. Montmorillonites with a low layer charge and high valence interlayer cations have larger basal spacings for their complexes than do those with a high layer charge and low valence interlayer cations. The basal spacings of these complexes are relatively larger if the clay has a large initial water content. The spacings for some complexes which are initially equilibrated at very low humidities are small, indicative of little penetration by polyalcohol molecules. Polyalcohol molecules may have difficulty replacing water molecules that are associated with the interlayer cations. The spacings of complexes with ethylene glycol and glycerol do not depend upon the initial interlayer water content. Water molecules may be an essential component of mont-morillonite-polyalcohol complexes.

The polyalcohol molecules probably are associated with the clay surface through weak C-H···O interactions although virtually no shortening of this bond distance occurs. The C-H···O interaction is enhanced by the presence of higher valence interlayer cations. OH groups increase the thermal stability of complexes probably by interacting with the exchangeable cations. Longer chain molecules are held more tightly between the silicate sheets. One layer of polyalcohol molecules between silicate sheets is more stable than two layers. One layer of organic molecules is more stable with higher valence interlayer cations. Small molecules such as those of ethylene glycol may pack down somewhat into the “hexagonal holes” in the silicate surface.

Proteins interact with montmorillonite forming mono- and poly-layer complexes. About 20 percent of the protein in a monolayer complex undergoes microbial decomposition and the X-ray pattern remains unchanged, whereas in polylayer complexes the protein undergoes extensive decomposition and the c-spacings of these complexes shrink from approximately 30 Å to 12 Å+. Urease is adsorbed completely by H-montmorillonite and only partially by basic montmorillonite. Initial release of urease from the clay is attributed to urea acting as a cation. Subsequently the ammonia evolved by the hydrolysis of urea becomes the active cation. Antibiotic-montmorillonite complexes are classified into three groups. Group I contains strongly basic antibiotics, II amphoteric, and III acid or neutral. The average adsorption of antibiotic in mg per g of clay for each group is: I, 186; II, 307; and III, 9. X-ray diffraction data for groups I and II showed expansion of the c-spacing of 4.4 and 7.6 Å, respectively. Bioassays showed no activity for I and appreciable activity for II. The complexes are incapable of diffusing through agar, but the antibiotics must be released first by cationic exchange and then diffuse through the agar.

Adsorption experiments were conducted by mixing homoionic kaolinite and C14-labeled hydrolyzed polyacrylonitrile (HPAN) in water and solutions of electrolytes. Langmuir type adsorption isotherms resulted. Exchange cations on kaolinite increased adsorption in approximately the same order as such cations reduce zeta potential, i.e. Th4+ > Ca2+ > Ba2+ > H+ > NH4+ > K+ > Na+. The anomalous increase in adsorption in the presence of polyvalent exchange cations suggested adsorption at the site of base exchange salt formation. Sorbed anions increased adsorption of HPAN in the order of electronegativity, i.e. F- > OH- > H2PO4- > Cl- > CH3COO- > NO3-.

An increase in the concentration of electrolyte and acidity of the adsorbate medium increased adsorption of HPAN. This effect was apparently due to the reduction of electrostatic repulsion between HPAN and kaolinite and a reduction in size of the polymer coil. Divalent cations, especially the transition metals capable of being complexed by HPAN, were more effective than univalent cations. Dissolution of the clay lattice caused desorption of HPAN.

HPAN adsorption reduced the intensity of the OH and O—Al—OH bands in infrared absorption spectra of the kaolinite. Preadsorption of aurintricarboxylic acid blocked adsorption of HPAN, suggesting that “positive spots” due to exposed lattice aluminum on edges of the clay platelets were adsorption sites.

Aliphatic chain molecules may be adsorbed on montmorillonite surfaces with the zigzag of their carbon chain either parallel or perpendicular to the surface. These orientations are designated αII and αI, respectively. Fourier syntheses have too few terms to distinguish clearly between these orientations. The problem is studied therefore by consideration of the basal spacings. These spacings are appreciably less than the sum of the van der Waals cross-section of the molecules plus the thickness of the montmorillonite layer. Chemical bonding or geometrical packing, or both, appear as possible explanations.

Previous studies have shown that CH activity influences the shape of the adsorption isotherms, but infrared studies of the adsorbed molecules have shown no appreciable change in the CH-stretching frequencies. This suggests the importance of the CH activity for organic—organic interaction on the clay surface rather than for clay-organic interaction itself.

The possibility of geometrical packing is studied by means of molecular models and it is shown that an appreciable contraction can occur at a clay-organic interlace owing to a keying of the molecules into the surface structure. This is possible equally well for the αII and the αI orientations.

From the information available, it appears that the αII arrangement is adopted by aliphatic chain molecules containing strongly polar groups in order to place the dipole parallel to the silicate surface, while the αI arrangement is favored by other aliphatic chain molecules possibly because this provides a favorable organic-organic interaction.