The alteration or transformation of impact melt rock to clay minerals, particularly smectite, has been recognized in several impact structures (e.g., Ries, Chicxulub, Mjølnir). We studied the experimental alteration of two natural impact melt rocks from suevite clasts that were recovered from drill cores into the Chesapeake Bay impact structure and two synthetic glasses. These experiments were conducted at hydrothermal temperature (265 °C) in order to reproduce conditions found in melt-bearing deposits in the first thousand years after deposition. The experimental results were compared to geochemical modeling (PHREEQC) of the same alteration and to original mineral assemblages in the natural melt rock samples. In the alteration experiments, clay minerals formed on the surfaces of the melt particles and as fine-grained suspended material. Authigenic expanding clay minerals (saponite and Ca-smectite) and vermiculite/chlorite (clinochlore) were identified in addition to analcime. Ferripyrophyllite was formed in three of four experiments. Comparable minerals were predicted in the PHREEQC modeling. A comparison between the phases formed in our experiments and those in the cores suggests that the natural alteration occurred under hydrothermal conditions similar to those reproduced in the experiment.

Core descriptions, thin-section analyses, and X-ray powder diffraction analyses of whole-rock samples and clay-sized fractions were employed to interpret the sedimentology and mineralogy of synimpact Exmore beds and the overlying Chickahominy Formation. This study attempts to explain the origin and postdepositional alteration of materials in the Eyreville core from the central zone of the Chesapeake Bay impact crater. Samples were obtained from eight zones extending from core depths of 435 to 1471 m, with emphasis on the interval from 435 to 455 m, representing the upper Exmore beds and the lower Chickahominy Formation. Qualitative clay mineral determinations were aided by peak decomposition procedures to unravel overlapping diffraction bands, and quantification was accomplished by least squares matching of actual and computed patterns. The major facies in approximate ascending order are suevite breccias, poorly sorted conglomerate and sandstone, and upward-fining glauconitic sandstone within the Exmore beds followed by parallel laminated sandy siltstone and claystone in the Chickahominy Formation. They all contain clay minerals (mica, smectites, and some serpentine, kaolinite, and chlorite) plus quartz and feldspar. Heulandite, pyrite, calcite, and disordered silica (partly representing nanofossils and microfossils) are present in the Chickahominy Formation. The boundary beds (upper 7 m) of the Exmore beds have higher clay contents but fewer varieties of expandable clay minerals than in the Chickahominy Formation. The Exmore beds are enriched in reworked glauconite, but there are no indications of heulandite, calcite, disordered silica, or pyrite, except in the very top of the 7-m-thick boundary bed interval. The clay fractions of the Eyreville materials are dominated by different species of expanding clay minerals (smectite, fine and coarsely crystalline nontronite, and fine and coarsely crystalline smectite-illite mixed-layered clay minerals), but dioctahedral mica and illite are also present. Amorphous material and minor amounts of quartz, chlorite, and mixed-layered smectite (0.95)/iron-rich illite (0.05) are common. The abundance of the clays in most intervals is highly variable due to the chaotic assemblage of sediments and crystalline materials from diverse sources. The boundary beds are dominated by a single smectitic mineral, nontronite, which is assumed to be the principal product of melt glass alteration. Amorphous material (melt glass) and nontronite are calculated to represent 13 vol% and 13–19 vol% of the sediments in this interval, respectively. Grain size, or clast size, has a major influence on mineralogical variability, i.e., when grain size (clast size) is large, the mineral content of adjacent samples is highly variable.

Abstract This paper illustrates the use of multimedia, digital still images and PowerPoint slide shows (other presentation applications may be used), to guide the student through one of the most common tasks in the clay mineralogy laboratory, extracting the less-than-two micrometer fraction. A second activity to be demonstrated employs a digital video clip to enhance instruction in the smear-slide technique for the preparation of oriented aggregates for XRD analysis. Each provides a stand-alone introduction to basic laboratory methods and equipment that frees the instructor to devote more time to more challenging topics. Both PowerPoint presentations are available on the senior author's website and The Clay Minerals Society website and may be freely downloaded for non-commercial use. The increased availability of the personal computer in the last decade has made it possible for educators to provide desktop access for every student to a multitude of applications. They generally result in an improved presentation of subject matter and procedures to enhance the learning process. In this environment, “multimedia” has taken on a special connotation to imply that the latest computer-based audio and visual technologies are being employed. It has become one of the terms associated with progress in education today. However, multimedia simply means more than one method of communication. Computer-based multimedia should not replace individual instruction and should only be used when they clearly enhance instruction. These new approaches are particularly suitable for repetitive tasks such as those associated with laboratory procedures. A good introduction to the general use of multimedia in education

Abstract Twenty years ago, three electron-beam analytical systems were available to scientists studying clay minerals. Numerous scientific reports illustrated the morphological detail and electron diffraction patterns of clay minerals in soils, sediments, and rocks, as revealed by the transmission electron microscope (TEM); electron microprobe analyzers (EMPA) were employed to provide chemical analyses of micrometer-size volumes of minerals in rocks; and the newly introduced scanning electron microscope (SEM) was enthusiastically received. Clay mineralogists quickly recognized the value of the SEM's large depth of focus and the minimal specimen preparation required to view clay minerals in rocks, and it soon became an essential instrument in many laboratories. In recent years, improvements to energy-dispersive X-ray analysis systems (EDX) have greatly increased the microchemical analysis capabilities of all electron microscopes and microprobes. The result has been a loss of identity for individual systems and a trend towards hybridization. Modern laboratories now employ TEMS with scanning coils and EDX systems to analyze thin rock and clay films (Hughes et al., 1990). SEMs are equipped, almost routinely, with X-ray"detectors, and some have optical viewing systems and petrographic stages. Electron microprobes now employ the same high-quality beam rastering systems, back-scattered electron detectors, and secondary electron detectors utilized in high-resolution scanning electron microscopes. The new generation instruments offer advantages of great value in the study of clay minerals. In geological studies, as in other related fields, the basic solutions to problems involve knowledge of the crystal identity, the crystal structure, the chemical composition, the particle morpholagy, and the spatial

Abstract A detailed palynologic, sedimentologic, and mineralogic investigation of the Robulus L No. 2 and the Robulus L No. 5 sands in cores from Texaco well No. 6 of Vermilion Block 31, offshore Louisiana, confirms that the units were deposited in the middle to outer part of the continental shelf during the early Miocene Epoch. The co-occurrence of the dinocysts, Hystrichosphaeropsis obscura and Lejeunecysta hyalina , further restricts the cored intervals to the Burdigalian Age. Variations in the abundances of Polysphaeridium zoharyi , Lingulodinium machareophorum, Tuberculodinium vancampoae , and terrestrial organic matter indicate the sediments are mixtures of marine and estuarine debris accumulating in the neritic zone.Five lithofacies and seven palynofacies are recognized. Current-structured, medium-grained sandstone containing abundant terrestrial organic matter and shell fragments (lithofacies B) forms the best potential reservoirs. Original high clay content and bioturbation restrict the permeability of other lithofacies and, hence, their producing potential. The Robulus L No. 2 is a better producer because lithofacies B is more abundant. Sandstones of this lithofacies often exhibit porosities between 15-28 percent and permeabilities as high as 2000 md because of their coarser grain size and the dissolution of shell fragments. In the Texaco No. 6 well, there is a clear relationship between original characteristics of the sediments, diagenesis, and hydrocarbon production.

Abstract Marine clays derived from glacial debris in the Bonnefjord, the most easterly portion of the Oslofjord, Norway, are characterized by distinctive microscopic textures that originated at the time of deposition and are similar to the particle-to-particle arrangements reported in studies of “quick clays.” Scanning electron micrographs show that these clays consist chiefly of flocculated domains of face-to-face particles arranged in an edge-to-face, card-house, random pattern. Pelletization by organisms has caused partial collapse of some of the floccules and has produced a rough parallelism of clay domains around silt-size particles. Other bioturbation structures, such as burrows, tubes, and feeding traces, are not associated with any changes in the microtexture of the sediment. The card-house structure is the characteristic textural arrangement of the clays deposited in this quiet, anoxic environment.