This thesis presents ab-initio quantum mechanical calculations at the density functional theory (DFT) level on defect centers hosted by crystalline systems of geologic importance (i.e. fluorite, quartz, stishovite). The research brings new, complementary data to the current understanding of defect structures in minerals and explores the advantages of a theoretical approach in the field of mineral spectroscopy. This present research presents the first ab-initio calculations of the O23- type defects in crystalline solids. New data on the electronic properties and structural characteristics of O23--Y3+ defect in fluorite-type structures (CaF2 and SrF2) were obtained at the DFT level. These results confirm the stability and the molecular character of the O23--Y3+ center, revealing a spin density that is equally distributed between the two oxygen atoms. Our results report an O-O bond distance of 2.47 Å in CaF2 and 2.57 Å in SrF2. The calculated 17O and 19F hyperfine constants for of the O23--Y3+ center are in good agreement with their corresponding experimental values reported by previous electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) studies, while discrepancies are notable for the 89Y hyperfine constants and are probably attributable to an inadequate basis set for Y.<p> The present study provides a more complete picture of the coupled Al-M substitution for Si in quartz, while investigating the characteristics and electronic properties of the diamagnetic [AlO4/M+]0 (where M = H, Li, Na and K) defects. The diamagnetic [AlO4/M+(a<)]0 defects with M = H, Li and Na have been shown to be more stable than their [AlO4/M+(a>)]0 structural analogues (where a> and a< denote the location of the charge compensating ion on the long-bond and short-bond side, respectively), correctly predicting the common occurrence of paramagnetic [AlO4/M+(a>)]+ centers. The present study confirms previous suggestions that incorporation of the [AlO4/M+]0 defects results in significant structural relaxations that extend at least to the nearest Si atoms. The [AlO4/K+]0 defects have been investigated for the first time and are shown to be stable in quartz. The results of this study have implications for the uptake of Al in quartz.<p> The present research evaluates the structural models of [AlO4/Li] paramagnetic defects in α-quartz. The results confirm the previous experimental findings and propose an additional paramagnetic defect [AlO4/Li+(csmall)]+, with the unpaired electron located on a short-bonded O atom and the Li compensator just off the edge of the small channel. Accordingly we suggest that three distinct Al-Li paramagnetic defects can be can be found in quartz, two of them having the hole located on a short-bonded O and one trapping the hole on a long-bonded O atom. However the structural similarities with the [AlO4/Li+(a>)]+ defect would require detection and measurement of the 17O hyperfine structure for an unequivocal EPR identification.<p> The present work also reports on first-principles quantum-mechanical calculations on the previously proposed [O23--Al3+] defect in stishovite. Our results show that the unpaired spin is 85% localised on one of the six oxygen atoms at an AlO6 octahedron, while the calculated 27Al hyperfine constants are similar to those determined by EPR experiments. Accordingly we propose the Al center to represent an [AlO6]0 defect, and hole hoping among equivalent oxygen atoms is responsible for its detection only at cryogenic temperatures. Theoretical calculations also show that diamagnetic precursors [AlO6/H+]0, [AlO6/Li+]0 and [AlO6/Na+]0 are stable in stishovite. The calculated OH bond distance and orientation are in excellent agreement with those inferred from FTIR spectra and previous theoretical calculations. The calculated [AlO6/Li+]0 and [AlO6/Na+]0 defects suggest that monovalent cations such as Li+ and Na+ are potentially important in accommodating Al in stishovite in the lower mantle.

A range of geochemical reactions are controlled by the interfacial characteristics of rocks and minerals. Many engineered and natural systems are affected by geochemical reactions that occur at interfaces. Asphalt-aggregate adhesion in road construction is influenced by the interfacial characteristics of the aggregate. Likewise, the remediation of nonaqueous-phase liquid contaminants, such as trichloroethylene or methyl tert-butyl ether, is controlled by the interactions between mineral surfaces and the organic liquid. Many natural systems are also influenced by reactions at interfaces. The migration of petroleum in sedimentary basins is influenced by the wettability of the surfaces of the basin pore space. Adhesion of organisms, such as bacteria or lichens, to rock surfaces is controlled by the interactions of proteins and mineral surfaces. Rock and mineral surfaces are described by surface energy. Surface energy is a thermodynamic construct defined as the amount of work required to form more of a surface. Surface energy can be divided into van der Waals, Lewis acid, and Lewis base components. The ability to predict the magnitude of surface energy components is valuable in understanding species behavior. Surface energy is controlled by three master variables: surface chemistry, surface morphology, and surface coatings. While the surface energy of a number of minerals and aggregates has been characterized, there has not yet been a comprehensive study of the surface energies of a variety of the most common minerals and aggregates using consistent methodology. In addition there has not yet been a study of the effect of these three master variables on surface energies of natural minerals and rocks. This study measured the surface energy of 22 common minerals and 7 aggregates. The samples’ bulk and surface chemistries were characterized with wavelength and energy dispersive spectra analyses on an electron microprobe and x-ray photoelectron spectroscopy. The XPS was also used to quantify the organic and inorganic coatings on the surfaces. Results showed that van der Waals surface energy is typically between 40 and 60 ergs/cm2. Polar surface energy varies by 1 to 3 orders of magnitude, and thus is likely the most important component in accounting for changes between natural minerals.

Growth and dissolution of the mineral calcite is important for prediction and control of surface and subsurface water quality, calculation of past sea-surface temperatures using paleoenvironmental proxies, and sequestration of contaminants through engineered calcite precipitation. At high concentrations of strontium, calcite growth is known to be inhibited, but the mechanism by which strontium inhibits growth is not well understood. Seeking to better understand this mechanism, atomic force microscopy is used with a flow-through fluid cell to measure real time growth rates of the obtuse and acute monomolecular step orientations on the calcite surface. Growth was measured at two saturation indices as a function of the ratio of the concentrations of aqueous calcium-to-carbonate and varying aqueous strontium concentration. It was found that the amount of strontium required to inhibit growth correlated with the aqueous calcium concentration, but did not correlate with carbonate concentration. This suggests that strontium inhibits attachment of calcium, but not carbonate, during growth. Analytical models of nucleation and propagation of steps are expanded from previous studies to capture multiple saturation indices.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (M.S.)--University of North Carolina at Wilmington, 2003. / Includes bibliographical references (leaves : [55]-[60]).

Thesis (M.A.)--University of Texas at Austin, 1984. / Vita. Includes bibliographical references (leaves 119-124).

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 206-210). Available also in a digital version from Dissertation Abstracts.

We present study of the synthesis and reactions of an analog of the meteoritic mineral schreibersite with formula (Fe,Ni)3P, believed to be a prebiotic source of reactive phosphorus that may have prompted the formation of phosphorylated biomolecules near the time of the origin of life (Pasek and Lauretta, 2005). The mineral was synthesized by mixing stoichiometric proportions of elemental iron, nickel and phosphorus and heating in a tube furnace at 820°C for approximately 235 hours under argon or under vacuum, a modification of the method of Skála and Drábek (2002). The mineral was characterized using X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), micro-raman spectroscopy and electron microprobe analysis (EMPA). Characterization indicates that both schreibersite, with approximate formula Fe2NiP and the mineral nickel-phosphide, FeNi2P were synthesized. In addition to characterization of the solid product, the reactions of the synthetic schreibersite were investigated to determine the similarity between these and prior work done with Fe3P. Synthetic schreibersite was corroded in several solutions: seawater and sulfidic water under both oxic and anoxic conditions. After corrosion, the solutions were analyzed using phosphorus nuclear magnetic resonance spectroscopy (31P NMR) and high performance liquid chromatography attached to an inductively coupled plasma mass spectrometer (HPLC-ICP-MS) to determine phosphorus speciation as well as concentrations of phosphorus present in solution. As expected from previous studies, the NMR and HPLC-ICP-MS results indicated the presence of orthophosphate, phosphite, pyrophosphate and hypophosphate in the corrosion solutions (Pasek and Lauretta, 2005). The HPLC-ICP-MS results indicate that the extent of corrosion of the mineral—measured by the concentration of phosphorus released—depends on the ionic strength of the solution, as well as the presence or absence of the chelating agent. Finally, we report the successful phosphorylation of a potentially prebiotic molecule—choline—using synthesized schreibersite.