Paul Giesting | University of Tennessee Knoxville (original) (raw)

Papers by Paul Giesting

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Agu Fall Meeting Abstracts, Dec 1, 2001

The thermal conductivity (k) of garnet phases is calculated from a formula originating with Debye... more The thermal conductivity (k) of garnet phases is calculated from a formula originating with Debye, adapted to treat the vibrations in a solid as a collection of damped harmonic oscillators. Our model utilizes phonon lifetimes obtained from Kramers-Kronig analyses of existing IR reflectivity spectra, as well as new measurements presented here, and calculates k at ambient conditions. Two series of

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Carbon Capture and Storage (CCS) from large stationary CO2 point sources is considered a promisin... more Carbon Capture and Storage (CCS) from large stationary CO2 point sources is considered a promising option to reduce anthropogenic CO2 emissions in short- to medium time scales. Besides a storage reservoir allowing for large storage capacity at reasonable injection rates, an impermeable caprock overlying the reservoir is indispensable to guarantee safe long-term storage. In this context, understanding the behavior of

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The strong magnetic field detected around Ganymede by the Galileo probe has caused many to conclu... more The strong magnetic field detected around Ganymede by the Galileo probe has caused many to conclude that Ganymede possesses a working dynamo, despite the inherent difficulties in keeping the core of Ganymede partly molten over >4 Ga and other problems. This paper explores the possibility of remanent magnetism of the outer solid portion of Ganymede as a major component of the observed field by examining and correcting the mathematical treatments of magnetization of exterior shells by past interior dynamos by Runcorn (1975) and Crary and Bagenal (1998). Although errors and hidden assumptions were present in both derivations, the conclusion of Crary and Bagenal that an exterior remanent field would remain after shutdown of an interior dynamo given an adequately high magnetizability of the shell remains valid.

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Impurities were revealed in four high-pressure, high-temperature synthetic polycrystalline garnet... more Impurities were revealed in four high-pressure, high-temperature synthetic polycrystalline garnets along the pyrope [Mg3Al2Si3O12] - majorite [Mg3(MgSi)Si3O12] join by infrared absorbance, Raman scattering spectroscopy, and detailed electron microprobe analyses (EMPA). Close examination of slight differences in the backscatter-electron images of one sample of Mj40 and subsequent X-ray imaging and spot analyses documented the presence of Mj95 interstitial impurities and a silica rich phase near the 5% level. These phases would not have been observed in a typical traverse. Spectroscopic measurements show that all samples contain the narrow bands of OH-, broad bands of fluid water, hydrocarbons, and disordered graphite. Hydroxyl is expected in either structural sites or as defects, whereas the other impurities are most likely on grain boundaries or as microscopic inclusions. Whereas infrared spectroscopy is needed to ascertain OH- and H2O contents, and is more sensitive to hydrocarbons...

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Meteoritics & Planetary Science, 2015

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ABSTRACT We report the first occurrence of Cl-scapolite in a martian meteorite and use terrestria... more ABSTRACT We report the first occurrence of Cl-scapolite in a martian meteorite and use terrestrial metamorphic analogs to constrain its origin.

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Infrared reflectance, thin-film absorbance, and polarized Raman spectra were acquired from ∼100 t... more Infrared reflectance, thin-film absorbance, and polarized Raman spectra were acquired from ∼100 to ∼4000 cm -1 from polycrystalline garnets along the pyrope (Py = Mg3Al2Si3O12)-majorite (Mj = Mg3(MgSi)Si3O12) join. We measured Py100, Mj39, Mj45, Mj80, and natural single-crystal, nearly end- member pyrope. Consistency is obtained between measured absorption spectra and absorption coef- ficients calculated through Kramers-Kronig analysis of reflectivity ( R) data, if R-values are scaled to account for losses through scattering. The widths of the lattice modes double from each end-member toward the middle of the binary, whereas frequencies are nearly independent of composition. Strong polarization of Raman peaks of all our samples except pyrope shows that the space group is reduced from cubic, even for the Al-rich majorites. The largest number of IR or Raman peaks is observed for Mj80. The number of peaks for Al-rich majorites lies between those seen for cubic pyrope and I41/a majorite...

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$Research paper thumbnail of X-ray Diffraction Study of K- and Ca-Exchanged Montmorillonites in CO 2 Atmospheres$

Environmental Science & Technology, 2012

Powder X-ray diffraction shows that K- and Ca-exchanged montmorillonites swell upon interacting w... more Powder X-ray diffraction shows that K- and Ca-exchanged montmorillonites swell upon interacting with CO(2) at ambient temperatures, depending on their initial hydration state. K-exchanged montmorillonite swells rapidly to a maximum d(001) of ∼12.2 Å. In contrast, Ca-exchanged montmorillonite swells more slowly, but reaches a maximum d(001) of ∼15.1 Å. Reaction kinetics differ significantly between the K- and Ca-exchanged montmorillonite complexes. Expansion of K-exchanged montmorillonite samples was rapid, occurring on time scales of tens of minutes or less. The Ca-exchanged montmorillonite samples continued to expand over periods up to 42 h. Aging of both K- and Ca-exchanged montmorillonite complexes at elevated CO(2) pressure for 1-2 days resulted in greater stability when CO(2) pressure was released. The observed intercalation reactions have important consequences for carbon sequestration: (1) CO(2) absorption by swelling clays may represent a significant pathway for storage of CO(2). (2) The swelling of smectites under CO(2) pressure may have a significant impact on the permeability of caprock formations.

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Earth and Planetary Science Letters, 2004

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Uranyl-organic complexation in geologic fluids can have a profound impact upon uranium solubility... more Uranyl-organic complexation in geologic fluids can have a profound impact upon uranium solubility and transport. Studies of uranyl organometallic crystal structures provide a basis for understanding complexation of the uranyl ion in solution.The crystal structures of several novel uranyl oxalates, synthesized under mild hydrothermal conditions, have been determined. These structures demonstrate new features little seen or not previously known in this chemical system, in particular polymerization into infinite sheets and direct linkage of uranyl polyhedra. Further work on the chemistry of this and other systems of hexavalent uranium and low molecular weight carboxylic acids, especially formic acid, is likely to turn up new insights.Although a hierarchical scheme exists for classifying inorganic uranyl compounds [1], no similar work has been done for organic compounds. Such a hierarchy would have practical benefits, in particular making structural information more accessible and understandable to workers studying related problems such as the environmental transport of hexavalent uranium as dissolved organic complexes. We offer a simple scheme that classifies uranyl oxalate structures by analyzing the long-range structural features and the coordination environments of uranyl ions, which leads to a structural symbol that can be used to easily identify uranyl oxalates with common structural features. This system is equally applicable to other carboxylate complexes with the uranyl ion, and could be extended to apply to any organic complex of the uranyl ion.

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American Mineralogist, 2014

ABSTRACT Minerals of the amphibole group are found in igneous rocks on Earth and other rocky bodi... more ABSTRACT Minerals of the amphibole group are found in igneous rocks on Earth and other rocky bodies. Since the O(3) site of amphibole can contain OH, O 2– , F, and Cl, amphibole composition provides important information about water and halogen contents, oxidation state, and other features of its formation and alteration environments. However, the complexity of amphibole crystal chemistry means this informa- tion is difficult to extract. Furthermore, it has been regular practice in the era of the electron microprobe to neglect H and Fe 3+ analyses for amphibole, critically reducing the amount of information available in amphibole analyses in the literature. We have assembled models and insights from previous work to create a methodology that allows the estimation of magmatic H 2 O and Cl contents from existing amphibole analyses. Since the methodology requires use of a cation norm, we begin with a deeper investigation of the consequences of different cation normalization schemes for amphibole analyses, and provide grounds for deciding which scheme best fits a given amphibole analysis. We then show how the existing model of Popp and coworkers can be reversed to estimate the OH and [O(3)] O 2– contents of amphiboles in synthesis experiments. Using a synthetic data set collected from the literature (39 amphibole analyses), we calibrate a partitioning model for the OH/Cl competition on the O(3) site of igneous amphiboles K Cl = (X Cl /X OH ) amphibole /([Cl]/[OH]) melt ln K Cl = 6.59 K/(Na + [A] o) – 0.679 Mg + 0.487 [6] Fe where X signifies a mole fraction of an anion on the O(3) site; [Cl] and [OH] signify melt mole fractions of the anion in question on a one-oxygen (Stolper-Zhang) basis; K, Na, [A] o, Mg, and [6] Fe signify the amount of each component in the amphibole in atoms per amphibole formula unit, with [A] o denoting vacancies on the amphibole A site. We then combine the Popp et al. model with our new model to link the occupancy of the amphibole O(3) site and other crystal chemical parameters to the Cl and H 2 O content of melts crystallizing amphi- bole. The competition between OH and Cl for this site can be used to calculate the melt and amphibole OH/H 2 O contents, as well as the speciation of Fe in amphibole, provided that the Cl content of both the amphibole and its coexisting melt is known, without analyzing either phase for H or Fe 3+ /Fe 2+ . While the models in this paper should be recalibrated using future experimental data, this work shows that considerably more information about the volatile contents of magmas can be gleaned from amphibole than previously shown and provides additional information about the crystal chemistry of amphibole and how it affects Cl partitioning into minerals of this group.

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Physical Review B - PHYS REV B, 2002

The thermal conductivity (k) of garnets is calculated from a formula originating with Debye, adap... more The thermal conductivity (k) of garnets is calculated from a formula originating with Debye, adapted to treat the vibrations in a solid as a collection of damped harmonic oscillators. Our model utilizes phonon lifetimes obtained from Kramers-Kronig analyses of existing IR reflectivity spectra, as well as new data presented here, and calculates k at ambient conditions within a nominal uncertainty of 6% of the experimental values for eight natural samples with well-constrained chemical compositions. Agreement is good for the remaining garnets with uncertain compositions. Two series of natural mixed crystals were studied: (1) X3Al2Si3O12, where the X site has varying amounts of Mg, Fe2+, and Ca and (2) Ca3Y2Si3O12, where the Y site has Al and/or Fe3+. The model predicts k at ambient conditions for the end members. The occurrence of a minimum in k near the midpoint of each compositional series correlates with the maximum widths of the IR peaks. Thus, disorder on crystallographic sites l...

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$Research paper thumbnail of X-ray diffraction study of K- and Ca-exchanged montmorillonites in CO2 atmospheres$

Powder X-ray diffraction shows that K- and Ca-exchanged montmorillonites swell upon interacting w... more Powder X-ray diffraction shows that K- and Ca-exchanged montmorillonites swell upon interacting with CO2 at ambient temperatures, depending on their initial hydration state. K-exchanged montmorillonite swells rapidly to a maximum d(001) of ∼12.2 Å. In contrast, Ca-exchanged montmorillonite swells more slowly, but reaches a maximum d(001) of ∼15.1 Å. Reaction kinetics differ significantly between the K- and Ca-exchanged montmorillonite complexes. Expansion of K-exchanged montmorillonite samples was rapid, occurring on time scales of tens of minutes or less. The Ca-exchanged montmorillonite samples continued to expand over periods up to 42 h. Aging of both K- and Ca-exchanged montmorillonite complexes at elevated CO2 pressure for 1–2 days resulted in greater stability when CO2 pressure was released. The observed intercalation reactions have important consequences for carbon sequestration: (1) CO2 absorption by swelling clays may represent a significant pathway for storage of CO2. (2) The swelling of smectites under CO2 pressure may have a significant impact on the permeability of caprock formations.

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Agu Fall Meeting Abstracts, Dec 1, 2001

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Meteoritics & Planetary Science, 2015

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$Research paper thumbnail of X-ray Diffraction Study of K- and Ca-Exchanged Montmorillonites in CO 2 Atmospheres$

Environmental Science & Technology, 2012

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Earth and Planetary Science Letters, 2004

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American Mineralogist, 2014

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Physical Review B - PHYS REV B, 2002

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$Research paper thumbnail of X-ray diffraction study of K- and Ca-exchanged montmorillonites in CO2 atmospheres$

Powder X-ray diffraction shows that K- and Ca-exchanged montmorillonites swell upon interacting w... more Powder X-ray diffraction shows that K- and Ca-exchanged montmorillonites swell upon interacting with CO2 at ambient temperatures, depending on their initial hydration state. K-exchanged montmorillonite swells rapidly to a maximum d(001) of ∼12.2 Å. In contrast, Ca-exchanged montmorillonite swells more slowly, but reaches a maximum d(001) of ∼15.1 Å. Reaction kinetics differ significantly between the K- and Ca-exchanged montmorillonite complexes. Expansion of K-exchanged montmorillonite samples was rapid, occurring on time scales of tens of minutes or less. The Ca-exchanged montmorillonite samples continued to expand over periods up to 42 h. Aging of both K- and Ca-exchanged montmorillonite complexes at elevated CO2 pressure for 1–2 days resulted in greater stability when CO2 pressure was released. The observed intercalation reactions have important consequences for carbon sequestration: (1) CO2 absorption by swelling clays may represent a significant pathway for storage of CO2. (2) The swelling of smectites under CO2 pressure may have a significant impact on the permeability of caprock formations.

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