Wyoming bentonite, Fithian illite, and basalt from the Umtanum Formation, Washington, were treated hydrothermally at 200° to 460°C and 260 to 500 bars for 71 to 584 days. No change was detected for the bentonite and basalt, except for the loss of calcite and exchange of Ca for K in the smectite and the growth of a small amount of smectite (presumably from a glass phase) in the basalt. Calcite in the initial bentonite may have stabilized the smectite by Ca/K exchange; thus, if the latter is used as a packing material in a nuclear waste repository, limestone should be added. No change was detected in the illite samples treated <300°C; however, at 360°C, euhedral crystals of berthierine and illite grew at the expense of original illite/smectite, apparently by a solution-crystallization process. Significant changes involving the dissolution of starting phases and the formation of illite and chlorite were also detected in mixtures of basalt and bentonite at 400°C; at temperatures <400°C, no changes were observed.

The newly formed mineral phases (berthierine, illite, and chlorite) observed by transmission electron microscopy showed euhedral to subhedral shapes. These shapes are the same as those observed in hydrothermally altered sediments from the Salton Sea field and different from those from burial metamorphic environments, such as Gulf Coast sediments. The reaction mechanism is apparently the dissolution of reactants followed by the crystallization of products from solution, without conservation of structural elements of the reactants. Reactions apparently required temperatures greater than those for analogous changes in nature, suggesting that the degree of reaction was controlled by kinetics. The lack of dissolution in experimental runs at low temperatures, however, does not necessarily imply long-term stabilities of these clay minerals.

Beidellite was synthesized hydrothermally from a noncrystalline gel at 320°C and 130 bar pressure. The beidellitic character of the product was verified by infrared spectroscopy on the NH4+-exchanged form. Intercalation was achieved with hydroxy-aluminum solutions having different OH/Al molar ratios. The solutions were investigated by several methods, including 27Al nuclear magnetic resonance. Essentially, two Al species were detected: monomelic Al and a polymerized form containing Al in four-fold coordination. This latter species was found to be selectively fixed in the interlamellar region, which resulted in a stable spacing of 18 Å at 110°C and 16.2 Å at 700°C. The pillared beidellites had specific surface areas of > 300 m2/g, mainly due to micropores. Both Brönsted and Lewis acid sites were evidenced by infrared spectroscopy using pyridine as a probe molecule.

The Excello Shale is one of the best exposed and most laterally continuous of the Pennsylvanian cyclothemic black shales in the midcontinent region of the United States. Its petrology and paleoenvi-ronmental significance were studied to understand the nature of cyclic black shales in general and how they relate to the habitat of hydrocarbon source beds. The Excello is thinly laminated, fissile where weathered, and rich in organic matter and phosphate nodules; it is 90–120 cm thick. Its thin laminations, fine particle size, and high total organic carbon (TOC) content suggest that it was deposited in a quiet water environment of an epeiric sea having anaerobic bottom water. The Excello Shale consists of two lithofacies: non-bioturbated black shale and bioturbated yellow-brown shale. Petrographic studies show that the black shale contains wavy to straight laminations and that the yellow-brown shale contains discontinuous and random laminae and mottled stratification. The close association of organic matter and phosphate-controlled nodule morphology (spherical, elongated, bladed, and platy) appear to be related to progressive decreases in nutrient supply of the sea water from the ancient ocean (Panthalassa).

Clay-mineral assemblages consist mainly of detrital illite, kaolinite, chlorite, and illite/smectite (I/S). Grain size and amount of these clays increase and TOC decreases shoreward towards the probable source areas of the clay minerals in the northern Ouachita region and northern Iowa. Quartz, carbonate-fluor-apatite, carbonate fossil fragments, and minor feldspar and pyrite are the principal minerals in the Excello Shale. Minor amounts of fine-silt-size carbonate minerals are present in some samples. Limestone concretions, 90–150 cm in diameter and 30 cm thick, were found at only one locality in Missouri where the Excello is a maximum of about 3 m thick. Fissility increases with weathering along the bedding plane, and laminae are separated by a limonite film. Four petrographically distinct microfabric variations of the Excello Shale appear to be related to the TOC content and bioturbation. Textural and structural properties of the shale are more developed with increasing organic matter content.

Investigations were conducted to determine the hydrothermal transformations of synthetic birnessite exchanged with different metal ions. Autoclaving in a Teflon-lined stainless steel pressure vessel at 155°C for 24 hr of Mg-, Ca-, La-, and Co-saturated birnessite yielded manganese minerals having 10-Å X-ray powder diffraction (XRD) spacings. The autoclaved Mg-birnessite yielded a mineral identical to natural todorokite in its infrared (IR) spectrum and XRD patterns. High-resolution transmission electron microscopy (HRTEM) provided images having 10-, 12.5-, 15-, and 20-Å wide fringes indicating heterogeneous channel widths in the crystallographic a direction, and IR spectroscopy produced bands at 757, 635, 552, 515, 460, and 435 cm-1, confirming the product obtained by autoclaving Mg-birnessite to be todorokite. Prolonged autoclaving of Mg-birnessite yielded manganite (γ-MnOOH) as a by-product; manganite did not form when the autoclaving time was shortened to 8 hr. Also, when Ca-saturated samples were autoclaved, the product gave d-values of 10 Å, but the XRD lines were broad and heterogeneity of the channel sizes was evident from HRTEM observations. The Ca-derivative had an IR spectrum similar to that of natural todorokite. Images showing 10-Å lattice fringes were observed by HRTEM for the Ni-saturated sample, which also produced an XRD pattern similar to that of the Mg-saturated sample. Co- and Lasaturated samples did not form todorokite, although HRTEM of La-saturated samples indicated some 10-Å lattice fringes that were unstable in the electron beam. Birnessite saturated with Na, K, NH4, Cs, Ba, or Mn(II) gave products having 7-Å spacings upon autoclaving.

The mineralogy of partially kaolinized strata interbedded with lignite at the San Miguel mine, Atascosa County, Texas, was investigated by X-ray powder diffraction and optical and scanning electron microscopy. The San Miguel lignite occurs in the lower Jackson Group (late Eocene) of southern Texas. Based on mineralogical and micromorphological data, some of these clay partings are probably volcanic in origin and were exposed to variable degrees of in situ kaolinization in a swamp environment. Coexistence of kaolinite, clinoptilolite, and opal-CT in several of these strata suggests that the partially kaolinized volcanic layers were subjected to a subsequent resilication process following burial. Kaolinite is the dominant mineral in the oldest and most kaolinized volcanic layer (underclay) below the lowest lignite bed (seam D). The kaolinite exhibits a well-developed vermicular morphology. The youngest volcanic layer, which occurs stratigraphically above the uppermost lignite seam, is characterized by pseudomorphs of volcanic glass shards and consists mainly of clinoptilolite. Movement of siliceous ground water from this layer to the underlying strata apparently provided silica-rich solutions from which opal-CT and large (as long as 300 μm) euhedral crystals of clinoptilolite precipitated in the fossilized plant roots, veinlets, and fractures within the underlying strata. Micromorphological relationships between the Sirich (opal-CT and clinoptilolite) and sulfide (marcasite and pyrite) minerals in the fossil roots and fractures suggest that the marcasite formed before and pyrite after the resilication process.

Core cuttings from numerous wells traversing Oligocene through Recent sediments of the Texas Gulf Coast were examined with a scanning electron microscope using the back-scattered electron imaging mode (BSE) to ascertain diagenetic changes in clays and associated minerals of mudrocks and of adjacent sandstones. Several occurrences of authigenic kaolinite and chlorite were noted, each characterized by a specific texture and a specific diagenetic microenvironment. In all occurrences kaolinite appears to have formed before chlorite, and in some the kaolinite appears to have precipitated directly from solution. Chlorite, ubiquitously an iron-rich variety, appears to have precipitated in some places directly from solution. It has also been noted pseudomorphous after kaolinite. A progressive decrease in the iron content of mixed-layer illite/smectite with increasing depth is believed to have released the necessary iron and to have driven the kaolinite-to-chlorite reaction.

Fifteen iron oxide accumulations from the bottoms of two Finnish lakes (“lake ores”) were found to contain as much as 50% Fe. Differential X-ray powder diffraction and selective dissolution by oxalate showed that the samples consisted of poorly crystallized goethite and ferrihydrite. The crust ores of one lake had higher ferrihydrite to goethite ratios than the nodular ores of the other lake. The higher ferrihydrite proportion was attributed to a higher rate of Fe2+ supply from the ground water and/or a higher rate of oxidation as a function of water depth and bottom-sediment permeability.

Values of Al-for-Fe substitution of the goethites determined from unit-cell dimensions agreed with those obtained from chemical extraction if the unit-cell volume rather than the c dimension was used. In very small goethite crystals a slight expansion of the a unit-cell dimension is probaby compensated by a corresponding contraction of the c dimension, so that a contraction of the c dimension need not necessarily be caused by Al substitution.

The goethites of the two lakes differed significantly in their Al-for-Fe substitutions and hence in their unit-cell sizes, OH-bending characteristics, dehydroxylation temperatures, dissolution kinetics, and Möss-bauer parameters. The difference in Al substitution (0 vs. 7 mole %) is attributed to the Al-supplying power of the bottom sediments: the silty-clayey sediments in one lake appear to have supplied Al during goethite formation, whereas the gravelly-sandy sediments in the other lake did not. The compositions of the goethites thus reflect their environments of formation.

Changes in hydraulic conductivity of smectite-sand mixtures (using four reference smectites) as a function of the concentration (0.01, 0.003, 0.002, 0.001 M Cl- and distilled water) and potassium adsorption ratio (of 2, 4, and 6) of the percolating solution were measured. Swelling and dispersion of the clays were evaluated from the changes in hydraulic conductivity of the mixture and from the clay concentration in the effluent.

The effect of exchangeable potassium percentage (EPP) on the hydraulic conductivity of the smectites depended on the charge density of the clays. The effect of potassium at EPPs <20 on the hydraulic conductivity of smectites having high charge density was negligible. Conversely, the hydraulic conductivity of smectites having low charge density (smectites from Wyoming and Belle Fourche, South Dakota), changed markedly when leached with dilute solutions as the EPP of the clay increased. The dispersive effect of exchangeable potassium on low-charge smectites was similar to that of exchangeable sodium. The low hydration energy of the K+ cations, coupled with the strong electrostatic attraction forces between platelets of smectites with high charge density account for the “inefficiency” of K+ in dispersing these smectites.

Clay fractions of eight vertisols and vertisolic soils from Israel were found to consist principally of a Fe-rich beidellite. Sediment volumes of Na-clay suspensions, obtained in measuring cylinders and read every 24 hr for as long as 720 hr, ranged from 3.8 to 8.4 cm/l00 mg clay and were as much as 19 times larger than corresponding suspensions of Ca-clays. Optical density data for all clay suspensions showed absorption curves typical of smectite. The relative number of platelets per tactoid, calculated from optical density measurements, ranged between 1.4 and 5.4 for the Na-clays and between 7.4 and 14.1 for the Ca-clays. In the Ca-clays, the sediment volume decreased with an increase in the relative number of platelets per tactoid. With increase in the major dimension of particles (calculated also from optical density curves), sediment volume tended to increase for the Na-clays and decrease for the Ca-clays. These relationships can be explained on the basis of particle arrangement patterns: face-to-face arrangements dominated the Ca-clays and edge-to-edge and edge-to-face arrangements dominated the Na-clays. The amount of iron extractable in dithionite-citrate-bicarbonate (DCB) correlated positively with the relative number of plates per tactoid and with the major dimensions of the particles in the Ca-clay suspensions. This correlation suggests that DCB-extractable iron affects the tactoid dimensions of Ca-clays from vertisols and, therefore, may also affect structural properties of vertisols.