Transmission electron microscopy has been used to characterize coexisting pyrophyllite and muscovite in low-grade metamorphosed pelites from Witwatersrand and northeastern Pennsylvania. The Witwatersrand sample consisted largely of porphyroblasts of interlayered muscovite and pyrophyllite in a fine-grained matrix of the same phases. In both textures, muscovite and pyrophyllite occurred as interlayered packets (with apparently coherent interfaces) from about 300 Å to a few micrometers in thickness, with no mixed layering. Their compositions were determined with a scanning transmission electron microscope to be

$$(\Box{_{{\rm{0}}{\rm{.11}}}}{\rm{ }}{{\rm{K}}_{{\rm{1}}{\rm{.72}}}}{\rm{Na}_{{\rm{0}}{\rm{.17}}})(A}{{\rm{l}}_{{\rm{3}}{\rm{.91}}}}{\rm{ F}}{{\rm{e}}_{{\rm{0}}{\rm{.03}}}}{\rm{M}}{{\rm{g}}_{{\rm{0}}{\rm{.05}}}}{\rm{T}}{{\rm{i}}_{{\rm{0}}{\rm{.01}}}}{\rm{)(S}}{{\rm{i}}_{{\rm{6}}{\rm{.11}}}}{\rm{ Al}}{{\rm{l}}_{{\rm{1}}{\rm{.89}}}}{\rm{)}}{{\rm{O}}_{{\rm{20}}}}{{\rm{(OH)}}_{\rm{4}}}$$

$$(\Box_{{\rm{1}}{\rm{.90}}}{\rm{N}}{{\rm{a}}_{{\rm{0.06}}}}{{\rm{K}}_{{\rm{0}}{\rm{.04}}}}{\rm{)(A}}{{\rm{l}}_{{\rm{3}}{\rm{.94}}}}{\rm{F}}{{\rm{e}}_{{\rm{0}}{\rm{.01}}}}{\rm{M}}{{\rm{g}}_{{\rm{0}}{\rm{.05}}}}{\rm{)(S}}{{\rm{i}}_{{\rm{7}}{\rm{.94}}}}{\rm{A}}{{\rm{l}}_{{\rm{0}}{\rm{.06}}}}{\rm{)}}{{\rm{O}}_{{\rm{20}}}}{{\rm{(OH)}}_{\rm{4}}},$$

The pyrophyllite and muscovite in the Pennsylvania shale likewise occurred only as coexisting coherent to sub-parallel packets as thin as 200 Å, with compositions of

$$(\Box_{{\rm{1}}{\rm{.89}}}{\rm{N}}{{\rm{a}}_{{\rm{0.04}}}}{\rm{C}}{{\rm{a}}_{{\rm{0}}{\rm{.02}}}}{{\rm{K}}_{{\rm{0}}{\rm{.05}}}}{\rm{)(A}}{{\rm{l}}_{{\rm{3}}{\rm{.93}}}}{\rm{F}}{{\rm{e}}_{{\rm{0}}{\rm{.04}}}}{\rm{M}}{{\rm{g}}_{{\rm{0}}{\rm{.02}}}}{\rm{T}}{{\rm{i}}_{{\rm{0}}{\rm{.01}}}}{\rm{)(S}}{{\rm{i}}_{{\rm{7}}{\rm{.92}}}}{\rm{A}}{{\rm{l}}_{{\rm{0}}{\rm{.08}}}}{\rm{)}}{{\rm{O}}_{{\rm{20}}}}{{\rm{(OH)}}_{\rm{4}}}$$

$$({\rm{N}}{{\rm{a}}_{{\rm{0}}{\rm{.04}}}}{\rm{C}}{{\rm{a}}_{{\rm{0}}{\rm{.02}}}}{{\rm{K}}_{{\rm{2}}{\rm{.03}}}}{\rm{)(A}}{{\rm{l}}_{{\rm{3}}{\rm{.54}}}}{\rm{F}}{{\rm{e}}_{{\rm{0}}{\rm{.24}}}}{\rm{M}}{{\rm{g}}_{{\rm{0}}{\rm{.16}}}}{\rm{T}}{{\rm{i}}_{{\rm{0}}{\rm{.06}}}}{\rm{)(S}}{{\rm{i}}_{{\rm{6}}{\rm{.09}}}}{\rm{A}}{{\rm{l}}_{{\rm{1}}{\rm{.91}}}}{\rm{)}}{{\rm{O}}_{{\rm{20}}}}{{\rm{(OH)}}_{\rm{4}}}.$$

The compositions of these coexisting pyrophyllite and muscovite define a solvus with steep limbs and extremely limited solid solution. Illite is a white mica, intermediate in composition between pyrophyllite and muscovite, formed at much lower temperatures than muscovite. These relations show that illite is metastable relative to pyrophyllite + muscovite in all of its diagenetic and low-grade metamorphic occurrences. This further implies that illite precursor phases, such as smectite, are also metastable. The prograde reactions involving smectite, illite, and muscovite are therefore inferred to represent Ostwald-step-rule-like advances through a series of metastable phases toward the equilibrium states attained in the greenschist facies. “Illite crystallinity” can therefore be a measure of reaction progress, for which temperature is only one of several determining factors.

Structure, morphology, and chemical composition of illite/smectite (I/S) containing 30–50% smectite layers (% S) from Kinnekulle bentonites, Sweden, of diagenetic origin were examined using X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Interlayer arrangements of I/S changed from random interstratification to short-range ordered at about 40% S. The transition from random to ordered structure proceeded continuously as reflected by the gradual decrease in probability of two smectite neighbors (Pss) towards zero. TEM observations of water-dispersed samples that had not been cation-exchanged showed that the I/S consisted dominantly of flakes coexisting with laths having a length/width ratio of about 4, regardless of % S. The thickness of the I/S particles ranged from 30 to 100 Å, and no systematic variation in thickness was detected with decreasing % S. The chemical composition of the I/S also changed continuously with decreasing % S. These observations suggest no dissolution of smectite layers and no recrystallization of illite layers during the formation of the I/S in these bentonites; rather, cationic substitutions occurred within a smectite precursor (termed a solid-state transformation mechanism). A comparison of interlayer order, particle texture, and chemistry of the I/S from various types of rocks suggests that the mechanism of smectite-to-illite conversion in the range 100% S-30% S was related to the porosity and permeability of original rocks. The solid-state transformation mechanism appears to have predominated in rocks of low porosity and permeability.

Pillared bentonites were found to be efficient catalysts for the O-methyl bond cleavage of anisoles (e.g., m-methylanisole, guaiacol, and creosol) under very mild, static conditions (150°C, a few hours, inert atmosphere). The O-methyl bond cleavage led to phenolic products. Gas chromatographymass spectrometry and solid-state 13C nuclear magnetic resonance (NMR) techniques used to probe 13C-labeled anisoles revealed that dealkylation and transalkylation reactions occurred to a large extent, and that conversion was efficient at >95% after two days. Ortho- and para-isomers were observed exclusively, without any evidence of meta-substitution. Volatile products were determined by mass spectrometry to be 13CH3OH and (13CH3)2O. Magic-angle spinning 13C NMR experiments showed that the molecules were fairly mobile in the clay micropores prior to catalysis. After catalysis, cross-polarization NMR showed that molecular motion had decreased markedly. Ultraviolet-visible spectroscopy of the colored complexes suggested some quinone formation. The trend of clay reactivity was found to be: pillared bentonite ≫ acid-washed montmorillonite > untreated bentonite > pillared fluorhectorite ≃ untreated fluorhectorite.

Three montmorillonite samples, from Wyoming (particle size <0.2 µm, 4.6 wt. % Fe2O3), Greece (<14 µm, 6.5 wt. % Fe2O3), and Poland (0.5 wt. % Fe2O3, two fractions <2 µm and 2–10 µm) were intercalated with hydroxy-Al species. The amount of hydroxy-Al cations exchanged by the clays depended on the particle size: it decreased from 31 wt. % Al2O3 for 0.2 µm in size to 22.6 wt. % for >2 µm. The X-ray powder diffraction (XRD) pattern showed that most of the material was not intercalated after refluxing at 80°C for 2 hr; several redispersions of the pillared clay in hot water were required to obtain a single sharp XRD line at 18.6 Å. The diffusion of the Al cations therefore limited the cation-exchange process. The addition of NH4+ to the pillaring solution decreased the amount of Al fixed by the clay from 31 (no NH4+ to 26 wt. % (NH4+/Al = 10), but increased slightly the microporous volume of the resulting pillared material from 0.13 to 0.14 ml/g. The competition between NH4+ and Al-hydroxy cations for ion-exchange sites forced the Al species into the interlayer space and increased the homogeneity of the resulting pillared material. The influence of particle size on the amount of Al exchanged was then reduced. After calcination in air at 700°C the pillared Wyoming clay retained a microporous volume of 0.09 ml/g if no NH4+ was added, compared with 0.11 ml/g for a NH4+/Al ratio of 10. The Fe content of the clay affected the thermal stability of pillared clays at 800°C: for two samples prepared by competitive ion exchange (NH4+/Al = 10) the microporous volume increased from 0.06 ml/g for 6.4 wt. % Fe2O3 to 0.08 ml/g for 0.5 wt. % Fe2O3. The acidity of the pillared clay was determined by calorimetric adsorption of ammonia at 150°C, on samples calcined at 500°C. Pillared montmorillonite prepared using noncompetitive intercalation showed a weak acid strength: most sites adsorbed ammonia with an enthalpy of 65 kJ/mole. The intercalation of the same original clay using competitive ion exchange yielded a solid that possessed both weak (heat = 60 kJ/mole) and strong (120 kJ/mole) acid sties. Competitive ion exchange appears to be a simple means of preparation of large quantities of pillared clays of reasonable thermal stability and higher acidity than those obtained by conventional methods.

Samples of underclays corresponding to nine different coal beds of the María Luisa coal seam in the Aller valley (Asturias, Spain) were collected to determine whether their mineralogy and geochemistry could be used for correlation. The underclays are dominated by illite, with an average abundance of 46%, and contain smaller amounts of chlorite, kaolinite (chlorite always more abundant), paragonite, pyrophyllite, mixed-layer illite/smectite (I/S), and mixed-layer muscovite/paragonite. This mineralogical association along with the illite “crystallinity” values (mean values of “crystallinity” in air-dried and ethylene glycol-solvated illite are 0.48° and 0.35°2θ, respectively) suggest that the samples have undergone very low-grade metamorphism. No consistent variation in the mineral components with increasing depth below the coal was noted. The presence of chlorite and K-feldspar precludes the development of the underclays by extensive leaching by acid swamp waters and thereby suggests that their mineral composition was determined largely by provenance.

Thirty-seven mineralogical and geochemical variables were treated by stepwise discriminant analysis. The variables that best served as discriminators between the underclays were: illite + I/S contents of both the whole rock and clay fraction, illite “crystallinity” of the clay fraction in both air-dried and glycolated patterns, pH of the samples, and the elements (in order of atomic number) Na, Al, K, Ca, Ti, V, Sr, Zr, Nb, Ba. The Molino underclay is clearly distinct from the other eight underclays, suggesting its potential use in regional correlation.

Novel modified clay adsorbents were prepared by blocking cation-exchange sites of an expandable clay, such as montmorillonite, with polymeric or polyvalent inorganic ions and by using cationic surfactants as sources of surface organic carbon. Electrokinetic measurements demonstrated that the adsorbed polycations were essentially nonexchangeable. Adsorption and desorption experiments revealed that about 90% of the cationic surfactant was apparently irreversibly bound to the surface. Flocculation and peptization studies were performed to establish that the adsorbed surfactant moiety was oriented with its hydrocarbon tail towards the surface. Such a configuration of simultaneously adsorbed polycations and cationic surfactants was designated as an inorgano-organo-clay (IOC). As shown in an accompanying paper, these IOCs bind priority pollutants as strongly as granulated activated carbon.

Benzo(a)pyrene (B(a)P), and chlorophenols were sorbed from their respective aqueous solutions onto inorgano-organo-clays (IOCs). Cetyl pyridinium hydroxy-Al montmorillonite (CPC-hydroxy-Al montmorillonite), an IOC, containing only 11–12% surface organic carbon by weight, bound pentachlorophenol strongly, with an observed monolayer capacity of 0.08 mmole/g. The comparable value for granulated activated carbon (GAC) was found to be 0.12 mmole/g. On the other hand, cetyl pyridinium cation-exchanged montmorillonite (CPC-montmorillonite), containing 19.2% surface organic carbon by weight, did not bind pentachlorophenol as efficiently as did IOCs. For benzo(a)pyrene, CPC-hydroxy-Al montmorillonite was found to be a better adsorbent than GAC and CPC-montmorillonite. The significant difference in the sorption potential of the two types of surfactant-laden clays for pentachlorophenol and benzo(a)pyrene was probably due to the surface orientation of the adsorbed organic carbon. For 3,5-dichlorophenol, however, both types of organo-clays exhibited weak binding, which was probably due to the greater aqueous solubility of the dichlorophenol.

Ferrihydrite samples having Si/Fe molar ratios ranging from 0 to 1 were synthesized by the reaction of Fe2(SO4)3 and Na2SiO3 with NaOH to an equilibrium pH of 8.2. Hematite formed by incubating the ferrihydrite (Si/Fe molar ratios ≤0.05) at pH 12.5 and 91°C for 36 hr had a globular morphology. Hematite formed from Si-free ferrihydrite gave infrared (IR) bands at 548, 471, 397, and 337 cm−1, whereas, hematite formed from Si-containing ferrihydrite having 0.001 to 0.05 Si/Fe molar ratios gave broad IR bands at about 550, 450, and 330 cm−1. Ferrihydrite having Si/Fe molar ratios ≥0.10 did not transform to hematite following the aqueous-thermal treatment.

The ferrihydrite samples were thermally treated for 2 hr at consecutive 100°C intervals from 100° to 800°C. The Si-free ferrihydrite transformed at 300°C to poorly crystalline hematite. Transmission electron microscopic analyses indicated that the hematite consisted of aggregates of spheroidal particles of 20–80 Å cross sections. Broad IR bands were observed at 529 and 452 cm−1; however, after heating the sample to 800°C, the particle cross sections increased to about 150–600 Å, and additional IR bands were present at 378 and 325 cm−1. The differences in the IR patterns of hematite formed from ferrihydrite at 300° and 800°C were probably due to increases in particle size and aggregation and improved crystallinity of the hematite particles following the higher temperature treatment. The hematite formed by the thermal transformation of the ferrihydrite having a 0.01 Si/Fe molar ratio was also spheroidal, and IR vibrations were present at about 528 and 443 cm−1. An increase in the temperature of the thermal treatment, however, did not result in additional IR bands.

Differences in the IR vibrations of hematite formed during aqueous- and dry-thermal treatments of the ferrihydrite samples were probably due to differences in the particle size and morphology of the product. The Si content, due to its effect on particle size of the precursor and the prevention of sintering and particle growth of hematite, influenced the IR pattern of the product. Particle morphology and IR spectroscopy may therefore be useful indicators of the precursor of hematite and the conditions of hematite formation in soil.

Clay mineralogy and petrography of the Early to Middle Eocene succession of the Dammam dome, Saudi Arabia, comprising the Rus and Dammam Formations, were studied using X-ray powder diffraction, light microscopy, and scanning electron microscopy. These formations consist of alternations of dolomite, dolomitic marl, claystone, and shale. The rocks were deposited and subjected to early diagenetic dolomitization in a shallow, coastal marginal basin characterized by rapid changes in salinity. Palygorskite occurs as interwoven fibrous mats forming fine laminae in shales and as coatings and pore-filling and pore-bridging cements in dolomitic marls. This textural evidence suggests a direct chemical precipitation, mostly post-dating dolomitization. Magnesium concentrations in presence of dolomite was sufficient for palygorskite precipitation; the necessary Si and Al were derived by dissolution of silicates under alkaline conditions. The maximum development of palygorskite was near the top of the Dammam Formation, which was deposited during a marine transgression in the Lutetian. The formation of palygorskite in marginal restricted basins in eastern Saudi Arabia took place during Paleocene-Middle Eocene time and was contemporaneous with similar occurrences in the Tertiary basins of West Africa.

The dissolution behavior of five noncrystalline oxides, montmorillonite, kaolinite, chlorite, and sepiolite in a basic tiron solution was studied at pH 10.5 and 80°C. The results show that for montmorillonite the concentrations of Al and Fe ions dissolved in the treating solution were diminished because of cation-exchange reactions of the sample in the suspension. To explain these observations, a mass-balance equation for the specified cation in solution was formulated, which consisted of both a dissolution term and an ion-exchange term. The several parameters of this differential equation were fitted to allow the calculated results to represent the experimental findings. Using these values, an equation lacking an ion-exchange term was also solved numerically. Thus, a dissolution curve was described, which would have been obtained had no cation exchange taken place. From these equations, the error resulted from the cation-exchange capacity of samples in chemical dissolution methods can be evaluated. According to this estimation, and assuming the value for a 1-hr treatment, an error of about 15% was determined for the amount of noncrystalline components contained in the specimen in this investigation.

Samples of cuttings from the Borchard A-2 well, Imperial Valley, California, were collected over a measured borehole temperature interval 135° to 275°C. The <0.5-µm (e.s.d.) fraction was separated using high-gradient magnetic separation (HGMS) to create a nonmagnetic fraction rich in illite and a magnetic fraction rich in chlorite. Chlorite was less easily separated from illite in lower temperature samples (<200°C), presumably due to the presence of polymineralic grains of chlorite and illite. Grains in higher temperature samples were more nearly monomineralic and more easily separated.

The chlorite is the IIb polytype. The thickness of coherent scattering domains of chlorite increased until 220°C and then remained constant. The amount of 7-Å interstratified material increased downhole until 195°C and then decreased. Over the same temperature interval, the illite polytypes varied systematically from 1Md (135° to 175°C) to 1M + 2M1 (230° to 275°C) and coherent scattering domains in the mineral became thicker to about 200°C and then remained constant in thickness. The percentage of illite in mixed-layer illite/smectite (I/S) increased from 40% at 135°C to 100% at temperature >205°C; ordering in the I/S changes from R0 to R1 between 135° and 155°C, and from R1 to R ≥ 3 at temperatures >155°C.

The concurrent structural changes in chlorite and illite indicate a general improvement in the overall structural order of the clay minerals with increasing temperature. Differences between chlorite and illite suggest that the minerals may have reacted differently to changing conditions or that they may have formed by different mechanisms. The exclusive occurrence of IIb chlorite at temperatures as low as 135°C extends the limit of IIb chlorite stability to temperatures lower than previous estimates.

The enthalpy of freezing of methyl salicylate sorbed by four commercial montmorillonite clays was used to estimate the absorption/adsorption capacity of the clay. Differential thermal analysis was therefore employed to give a quantitative estimate of the sorption capacity of the clay for methyl salicylate. The absorption capacity of the clay depended on the state of hydration and ranged from 30.4% for an 8% water content to 9.7% for a montmorillonite containing 24% water.