Paul A. Schroeder

The nature of organic phosphorus in marine sediments: New insights from 31P NMR

Abstract Different classes of organic phosphorus compounds have been identified in marine sediment samples taken at depth in cores from pelagic, lower slope, and continental shelf depositional environments using solution and solid-state magic angle spinning (MAS) 31 P nuclear magnetic resonance (NMR) techniques. Phosphate esters have been identified as the major form of organic phosphorus in all sediment extracts and in separated bulk organic matter. Phosphonates, a form of organic P previously unreported in marine sediments, were identified in all but one of the samples. The persistence of both phosphate esters and phosphonates at depth in sediment cores suggests that these compound classes include undegradable forms of organic phosphorus that represent an important sink for phosphorus in the ocean.

New mineral occurrences and mineralization processes: Wuda coal-fire gas vents of Inner Mongolia

Abstract Five unique mineral assemblages that include the sulfates millosevichite, alunogen, anhydrite, tschermigite, coquimbite, voltaite, and godovikovite, as well as the halide salammoniac and an unidentified phase, according to X-ray diffraction and EDS data, were found as encrustations on quartzofeldspathic sand and sandstone adjacent to coal-fire gas vents associated with underground coal fires in the Wuda coalfield of Inner Mongolia. The mineral assemblage of alunogen, coquimbite, voltaite, and the unidentified phase collected from the same gas vent, is documented for the first time. Coquimbite also occurs as rosettes secondarily nucleated on a cryptocrystalline mass of alunogen, coquimbite, voltaite, and the unidentified phase during storage in a sealed container at room temperature. Field observations, analyses of vent gases, SEM images, and mineral compositions suggest that the sulfates millosevichite, alunogen, coquimbite, voltaite, godovikovite, and the unidentified phase, crystallized in response to a complex sequence of processes that include condensation, hydrothermal alteration, crystallization from solution, fluctuating vent temperatures, boiling, and dehydration reactions, whereas the halide salammoniac crystallized during the sublimation of coal-fire gas. Tschermigite and anhydrite formed by the reaction of coal-fire gas with quartzofeldspathic rock or by hydrothermal alteration of this rock and crystallization from an acid-rich aqueous solution. Variations in the mineral assemblages found at five gas vents are possibly due to differences in coal-bed chemistry, exchange reactions involving coal-fire gas, and the composition of sediment, rock, and aqueous solutions prior to the exhalation of gas at the surface, as well as the temperature and cooling rate at a vent. Few studies have addressed the interaction of coal-fire gas with sediment, rock, and aqueous solutions and the subsequent mineralization processes. Coal fires present opportunities for discovering rare and new mineral occurrences. These minerals have potentially important environmental significance and may be vectors for the transmission of toxins. Coal fires also provide insight for the recognition in the geologic record of preserved mineral assemblages that are diagnostic of ancient fires.

Accurate quantification of quartz and other phases by powder X-ray diffractometry

Abstract The 33 parameters that affect accuracy of quantitative analysis by X-ray powder diffractometry can be grouped as 1. (1) Instrumental or systematic, 2. (2) Inherent properties of the analyte, or 3. (3) Parameters related to preparation and mounting of powders. The effect of each on diffraction intensity is summarized. An optimal value or range is given for instrumental parameters. Evaluation of inherent parameters of the analyte and optimization of those related to preparation and mounting of powders are discussed. Published methods are briefly reviewed. Their reported detection limits for crystalline silica are well below what can be reliably determined in natural and industrial products if one or more critical parameters are neglected, as the size and shape of coherent diffraction domains. An addendum illustrates practical consideration of major parameters during routine analysis for quartz.

CLAY MINERALOGY AND CHEMISTRY OF HALLOYSITE AND ALUNITE DEPOSITS IN THE TURPLU AREA, BALIKESIR, TURKEY

A field-mapping and crystal-chemical study of two alunite- and halloysite-rich deposits in the Turplu area, situated northwest of Balıkesir on the Biga Peninsula of northwest Turkey reveals a mineralogically diverse and a potentially economic clay deposit. The mineral assemblage along fault zones is dominated by halloysite and sometimes alunite. The alunite is nearly end-member in composition (a = 6.995 Å, c = 17.195 Å) often occurring with a minor Ca phosphate phase. Of the two deposits studied, the more northerly mine contains more alunite relative to halloysite. Geochemical alteration indices suggest that the northern mine has experienced a slightly greater degree of hydrothermal modification. Halloysite is found in both hydrated and dehydrated states and assumes a tubular morphology. Observations by transmission and scanning electron microscopy are consistent with a model of halloysite dehydration, where the shapes transform from an open-hole tubular morphology to a closed-hole unfurled morphology.Mineral paragenesis includes the effects of initial deposition of volcanic tuffs and andesite on top of karstic terrain. The contact between altered volcanics and underlying limestones is irregular and appears to have provided a mechanism to flush both hydrothermal and meteoric waters through the volcanics. Periods of hydrothermal alteration (hypogene) contemporaneous with extensional and strike-slip faulting have resulted in alunite and halloysite deposits. Hydrothermal alteration is concentrated near the fault zones. Because of subsequent weathering (supergene) away from the fault zones, much of the andesitic volcanic rocks have been altered to a more smectite-rich and kaolinite-bearing assemblage. The deposits continue to be both plastically deformed in the alunite/halloysite regions and to undergo brittle deformation in the saprolitized volcanics. Tectonic deformation has mixed the contacts, such that limestone blocks are entrained into parts of the alteration zones. Gibbsite and gypsum are common weathering products associated with limestone block inclusions. Genetic models for the origins of alunite-halloysite deposits in NW Turkey should consider as possible influencing factors the underlying lithologies, the extent of hydrothermal alteration, and recent weathering by meteoric fluids. In the case of the Turplu deposits, karstic limestones, hydrothermal circulation of sulfate-rich waters, and a post-alteration history of meteoric weathering were all important factors in their formation.

The Application of Vibrational Spectroscopy to Clay Minerals and Layered Double Hydroxides

It has been nearly 30 years since two of the most influential books were published on infrared spectroscopy on minerals by Farmer and on clay minerals in particular by van der Marel and Beutelspacher. Since then much has changed in terms of technology, such as the development of Fourier Transform infrared spectroscopy, and the development of new vibrational spectroscopic techniques for the study of minerals. Clays have formed and still form a very important part of our economy and it is thus not unreasonable to expect that this is reflected in the research applying vibrational spectroscopy to study clay minerals. However, all these developments are spread over a large amount of literature and a book reviewing these developments is lacking. I hope that this book will be able to fill this gap. Major developments in the use of mid- and near-infrared to study the structure of clays modified clays, the use of Raman spectroscopy to study clays and their intercalation and the use of infrared emission spectroscopy to study thermal processes have resulted in a CMS workshop lecture volume in which a unique set of overviews in this specialized field of research, on a level that can be appreciated by all to whom clay science is dear, is brought together.

Gas emissions, minerals, and tars associated with three coal fires, Powder River Basin, USA.

Ground-based surveys of three coal fires and airborne surveys of two of the fires were conducted near Sheridan, Wyoming. The fires occur in natural outcrops and in abandoned mines, all containing Paleocene-age subbituminous coals. Diffuse (carbon dioxide (CO(2)) only) and vent (CO(2), carbon monoxide (CO), methane, hydrogen sulfide (H(2)S), and elemental mercury) emission estimates were made for each of the fires. Additionally, gas samples were collected for volatile organic compound (VOC) analysis and showed a large range in variation between vents. The fires produce locally dangerous levels of CO, CO(2), H(2)S, and benzene, among other gases. At one fire in an abandoned coal mine, trends in gas and tar composition followed a change in topography. Total CO(2) fluxes for the fires from airborne, ground-based, and rate of fire advancement estimates ranged from 0.9 to 780mg/s/m(2) and are comparable to other coal fires worldwide. Samples of tar and coal-fire minerals collected from the mouth of vents provided insight into the behavior and formation of the coal fires.

Fe ordering in kaolinite; insights from 29 Si and 27 Al MAS NMR spectroscopy

Abstract Kaolinite-rich samples were selected for 27Al and 29Si MAS NMR study to explore the effect of Fe on their spectra and provide insight into the nature of Fe ordering in kaolinite. Initial characterization by Chemical analysis, TEM, X-ray diffraction, and magnetic mass susceptibility (x*) measurement was conducted to obtain five samples of high purity and with a range of Fe content. Secondary iron oxide and hydroxide phases were extracted using an HCl treatment. TEM study of the samples before and after treatment revealed the effective removal of secondary Fe phases and pristine kaolinite crystal habits. MAS NMR experiments included measurement of 29Si spin-lattice relaxation times (T1) at 6.36 T and quantitative 27Al measurements at 8.46 T. The 29Si T1 studies show a general increase in T1 with decreasing Fe content. It is probable that the relaxation mechanism occurs dominantly through the dipole-dipole interaction with unpaired electron spins in Fe Centers of the dioetahedral sheet. Data fitting indicates that spin relaxations are not best deseribed by a single T1. Improved fitting using double exponential or power-law behavior to describe 29Si spin-relaxation phenomena indicates a heterogeneous distribution of Fe centers. The relatively longer T1, values for two samples suggest their dioctahedral Fe domains may have a more clustered distribution within the kaolinite structure. Results from 27Al studies indicate very good eorrelation between Fe content, xg, and spinning sideband (SSB) intensity. There is very little eorrelation between total integrated27Al intensity and Fe content. When 27Al NMR intensity variations are compared with estimates of 27Al NMR signal loss predicted by a paramagnetic line-broadening wipeoutsphere model that uses an idealized kaolinite structure with regularly ordered dioetahedral Fe sites, the two samples appear to have a more clustered distribution of Fe. The relative increase in SSB intensity is consistent with an increase in the number of antiferromagnetic or ferrimagnetic domains.

Ti-BEARING PHASES IN THE HUBER FORMATION, AN EAST GEORGIA KAOLIN DEPOSIT

Six kaolin samples from the Lower Tertiary Huber Formation near Wrens, Georgia were analyzed using transmission electron microscopy (TEM), electron diffraction (ED), powder X-ray diffraction (XRD), chemical analysis, and magnetic susceptibility to characterize the Ti-bearing phases. Selected samples were treated with 5 M NaOH to remove kaolinite and concentrate the Ti-bearing phases for additional analysis. TiO2 content in the bulk fraction ranges from 1.2 to 5.4 wt. %. There are at least three Ti-bearing phases, including anatase, rutile, and a poorly defined nanocrystalline form. Anatase is most abundant and is commonly found with 010 faces in association with kaolinite edge and basal faces. The nanocrystalline form occurs at 0–1 wt. %, and rutile occurs in trace amounts. Bulk XRD analysis correlates well with the bulk TiO2 chemical measurements. Average anatase unit-cell parameters are a = 0.37908 ± 0.0002 nm and c = 0.951 ± 0.001 nm. These parameters indicate an approximate chemical formula of Fe3+0.05Ti4+0.95O1.95(OH)0.05.The distribution of TiO2 content as a function of depth may be useful to obtain original grain-size variations associated with relative sea-level changes responsible for the deposition of the Huber Formation. Evidence for original depositional sediment properties can be seen in the occurrence of pseudomorphic replacement of micas and fecal pellets by kaolinite. Additional evidence for post-depositional changes includes the sub-micrometer euhedral character and low Fe content of the anatase (relative to soil-derived anatase). These observations for the Huber Formation are consistent with a previously published theory for kaolin genesis that includes biomineralization of originally coarser-grained aluminosilicates into a kaolinite-rich ore body.

CRYSTAL-CHEMICAL CHANGES IN AN OXIDATIVE WEATHERING FRONT IN A GEORGIA KAOLIN DEPOSIT

The Eocene Huber Formation, exposed in the CFI Hall mine south of Irwinton, in Wilkinson County, Georgia, displays colored zones that are a consequence of an oxidative weathering front. These zones vary from very light gray (gray) to pinkish white (pink) to very pale yellow (cream) (Munsell N8, 5YR 8/2 and 2.5Y 8/2, respectively) with increasing degree of oxidation. A representative sample from each zone was collected and analyzed for its chemical, crystallographic and Raman spectroscopic properties. The comparison of these genetically related samples allowed for a quantitatively accurate assessment of anatase’s contribution to the total TiO2 content. All samples contain ∼1.5 wt.% TiO2. Progressing from gray to pink to cream, anatase contents range from half to nearly all the TiO2. The a lattice parameter for anatase is constant in all three kaolins (3.7916 Å), suggesting a constant 4.6 mol.% isomorphous substitution of Fe for Ti.Phase characterization and mass-balance considerations of the gray, pink and cream kaolins indicate that ilmenite and pyrite are precursor Ti- and Fe-bearing phases in the gray kaolin that undergo oxidation. Pseudorutile is a proposed intermediate phase resulting from the anodic corrosion of ilmenite. Hematite, goethite and anatase are the dominant end-products via dissolution-precipitation from the reactants pyrite and pseudorutile. The removal of Fe sulfides and organic matter and addition of hematite and goethite causes kaolin colors to change from gray to pink. Oxygen diffusing from groundwater in permeable overlying and underlying formations facilitates a process that probably involves aerobic and anaerobic bacteria that utilize Fe from pyrite, hematite and goethite. We postulate that the end result is the mobilization of Fe by siderophores and a kaolin color change from pink to cream.

Quantitative analysis of anatase in Georgia kaolins using Raman spectroscopy

Raman spectroscopy of Georgia kaolins ubiquitously show a strong Eg frequency near 144 cm � 1 . Analysis of the band intensity shows that under specific source, sample, and optical conditions, peak area measurements are predictable and reproducible. Using standard additions, successful quantitative techniques have been developed that allow analysis of 25% solids water slurries, which achieve anatase detection limits down to 0.3% with a standard error of F0.1%. Anatase was also studied with X-ray powder diffraction to examine the extent of crystal chemical variation. The a lattice dimensions of anatase from Georgia kaolins range from 0.3786 to 0.3796 nm. The mean coherent scattering length in the (100) direction range from 80 to 160 nm. Given the range of anatase particle sizes previously observed in Georgia kaolins (8000-150,000 nm), these parameters indicate an average defect density of 100 domains per crystal and structural formulae that range from Fe0.03Ti0.97O1.97(OH)0.03 to Fe0.06Ti0.93O1.93(OH)0.06. Quantitative estimates of anatase abundance using Raman require careful attention to background fluorescence effects due to the presence of hematite, goethite, and organic matter. Background fluorescence intensity in the regions of 400 and 600 cm � 1 correlate with known additions of hematite and goethite, respectively. The removal of organic matter from gray clays by H2O2 treatment significantly reduced background fluorescence. The small variations in anatase crystal chemistry do not appear to have any first-order effects on Raman intensity of the 144 cm � 1 band. The comparison of total TiO2 using X-ray fluorescence techniques with anatase content reveals that, in many instances, there is a significant non-anatase TiO2 component present in Georgia kaolins. The discrimination of Ti-phases has the potential to provide new insights into strategies for mineral separation techniques, kaolin reserve estimates, and understanding of the geologic history of the Georgia kaolin deposits. D 2003 Elsevier B.V. All rights reserved.