Showing papers on "Silicate minerals published in 1988"
TL;DR: In this paper, a theoretical model for the weathering rate of silicate minerals in the laboratory and the natural soil environment has been developed where the rate is assumed to be proportional to the exposed surface area of the mineral, the soil moisture saturation and the chemical driving force, given as a kinetic expression.
Abstract: A theoretical model for the weathering rate of silicate minerals in the laboratory and the natural soil environment has been developed where the rate is assumed to be proportional to the exposed surface area of the mineral, the soil moisture saturation and the chemical driving force, given as a kinetic expression The kinetic expression describes the dependency of the rate on the solution concentration of reactants and has the general form of a sum forward rates minus a sum backward rates Data from the Gardsjon watershed in Southern Sweden were used to estimate weathering rate of several silicate minerals, and the result is in good agreement with laboratory values The weathering model developed by the authors was applied to the watershed to predict the present day weathering in the area, and the predicted values coincide with the observed weathering rates
196 citations
TL;DR: In this article, high-resolution proton magic-angle NMR spectra of minerals containing stoichiometric hydroxyl groups as the only hydrous species are obtained, provided that the hydrogen density in the sample is less than about 15 atoms/nm^3.
Abstract: Proton magic-angle spinning (MAS) NMR at 200 and 500 MHz and at high spinning speeds (ca. 8 kHz) has been used to characterize hydrous species, both stoichiometric and nonstoichiometric, in a variety of minerals. High-resolution
^1H MAS-NMR spectra of minerals containing stoichiometric hydroxyl groups as the only hydrous species are obtainable provided that the hydrogen density in the sample is less than about 15 atoms/nm^3. Structurally isolated water molecules in analcite, NaAlSi_2O_6•H_2O, and gypsum, CaSO_4•2H_2O, yield characteristic ^1H MAS-NMR spectra with numerous spinning sidebands extending over a range of about 100 kHz, reflecting the strong, largely inhomogeneous character of the homonuclear dipolar coupling. The field dependence of both line widths and spinning sideband patterns provides evidence about the nature of the
broadening interactions. Lawsonite and hemimorphite, minerals containing stoichiometric amounts of both OH and H_2O groups, yield spectra with numerous intense spinning sidebands; strong dipolar interactions preclude discrimination of OH and H_2O.
Nonstoichiometric hydrogen in nominally anhydrous minerals (feldspars, nepheline, quartz, and grossular garnet) is found to occur in a variety of forms: mobile H_2O in fluid inclusions, anisotropically constrained, isolated H_2O molecules, and clustered species consistent with H_4O_4^(4-) groups in a hydrogarnet substitution.
183 citations
TL;DR: In this article, the effect of temperature on the structures of three silicate liquids has been studied by 29Si NMR spectroscopy on glass samples prepared with different glass transition temperatures.
139 citations
TL;DR: In this paper, the relative partitioning behavior of REE in high-silica rhyolites is dominated by crystal-chemical controls and not by liquid structural effects, and the true REE partition coefficients of La Primavera and Bishop Tuff pyroxenes obtained by microprobe are only slightly higher than they are in lower silica rhymes, and are not as variable as previously thought.
114 citations
TL;DR: In this article, the suitability of various covalent potentials in mimicking the topography of the ab-initio potential surfaces was explored and the use of such quantum-derived potentials was extended in generating the structures of hydroxyacid dimers, trimers, and pentamers of silicate tetrahedra and in studying the structure and dynamical properties of minerals and glasses.
Abstract: Recently, ab-initio quantum mechanical potential surfaces calculated for silicate hydroxyacid molecules were used to extract covalent potentials for use in mineral physics calculations (Lasaga and Gibbs 1987). The calculations showed that these potentials are capable of generating the structure and physical properties of silicate minerals. In this paper we explore in more detail the suitability of various covalent potentials in mimicking the topography of the ab-initio potential surfaces. We also extend the use of such quantum-derived potentials in generating the structures of hydroxyacid dimers, trimers, and pentamers of silicate tetrahedra and in studying the structure and the dynamical properties of minerals and glasses.
97 citations
TL;DR: In this article, the authors measured the leakage of radiogenic 222Rn and 40Ar and reactor-produced 39Ar and 37Ar in samples of granites, plagioclase, orthocase, cleavelandite and hornblende to assess the role of nanopores in gas transport through them.
85 citations
TL;DR: In this paper, a simple correlation has been found between 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) chemical shift and molecular geometry that is applicable to all silicate minerals.
Abstract: A simple correlation has been found between 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) chemical shift and molecular geometry that is applicable to all silicate minerals. It is based on the magnetic anisotropy and valence of the bond between the oxygen and the second-neighbour cation to the silicon. The equations can be used to calculate the chemical shift and hence can be applied to assess the validity of structural models.
83 citations
TL;DR: In this article, the authors argue that the temperature of fusion at low pressures is below the temperature range of the glass-liquid transition, and they extend an overlooked argument outlined by Jeanloz7 following the report by Mishima et al.8.
Abstract: A noteworthy feature of some high-pressure silicate minerals is their ready vitrification, either through moderate heating at 1 bar1–5, as for jadeite (NaAlSi2O6) or stishovite (SiO2), or through room-temperature decompression6, as for calcium silicate perovskite (CaSiO3). Little attention seems to have been paid to the actual significance of such transitions, and here I argue that these simply represent crystal fusion. The unusual aspect is that the temperature of fusion at low pressures is below the temperature range of the glass–liquid transition. Through a different, thermochemical line of evidence, this extends an overlooked argument outlined by Jeanloz7 following the report of the glass/ice I transition by Mishima et al.8. The similarities and differences with this transition will be pointed out, as will some theoretical and geophysical implications.
78 citations
TL;DR: In this article, the relationship between alteration of granitic gneiss by acid deposition and the resulting composition of lake waters can be studied in small catchments containing little or no soil and lacking carbonate minerals.
Abstract: Atmospheric acidic deposition introduces hydrogen ions to terrestrial and aquatic ecosystems, which become partially neutralized by chemical weathering. In the southern Alps of Switzerland, small catchments containing little or no soil and lacking carbonate minerals represent sensitive hydrological settings in which the relationship between alteration of granitic gneiss by acid deposition and the resulting composition of lake waters can be studied. Transmission and scanning electron microscopy, coupled with X-ray powder diffraction of lake sediments from such areas showed mainly unaltered minerals from parent rocks and no secondary silicate minerals. Element mapping indicated noncrystalline aluminum hydroxide as a product of the chemical weathering of silicates. Noncrystalline iron hydroxide was also observed. Mass balance calculations and the stoichiometry of suitable chemical reactions representing the weathering processes were used to derive a plausible reaction sequence on the interaction of the predominant reactive rock minerals with acid precipitation that accounted for the measured chemical composition of the acid lakes.
55 citations
01 Jan 1988
51 citations
TL;DR: In this paper, the average local environment and polarizability of oxygen in the near surface region of crystalline and amorphous SiO2, NaAlSi3O8, Na alSi2O6, NaalSiO4, and CaMgSiSiO6 were studied using X-ray photoelectron spectroscopy.
TL;DR: Oxygen self-diffusion coefficients have been determined in natural nepheline Na3(Na, K)[Al4Si4O16] and synthetic diopside CaMg(SiO3)2, at one atmosphere, by monitoring the rate of 18O exchange between CO2 gas and minerals of pre-determined grain size (10, 12.5, and 15 μm radius).
01 Jan 1988
TL;DR: In this article, the spin glass state in Garnet mixed-crystals was found to be a new Cubic polymorph with high density, and the phase transition in Ilvaite, a Mixed Valence Iron Silicate, was studied.
Abstract: 1. Toward a Thermodynamic Understanding of Feldspars: Order Parameters of Na-Feldspar and the I?-P? Phase Transition in Anorthite.- 2. Incommensurate Phase Transitions in Quartz and Berlinite.- 3. Phase Separation in Quadrilateral Pyroxenes and Olivines.- 4. Multicritical Phase Relations in Minerals.- 5. Equation of State and Possible Critical Phase Transitions in MgSiO3 Perovskite at Lower-Mantle Conditions.- 6. High-Spin to Low-Spin Transition of Iron(II) Oxides at High Pressures: Possible Effects on the Physics and Chemistry of the Lower Mantle.- 7. Molecular Dynamics Studies of Polymorphism of SiO2 at High Pressures: A Possible New Cubic Polymorph with High Density.- 8. Charge Localization and Associated Crystallographic and Magnetic Phase Transitions in Ilvaite, a Mixed Valence Iron Silicate.- 9. Magnetic Phase Transitions in Silicate Minerals.- 10. Magnetic Phase Transition in Olivines M2SiO4 (M = Mn, Fe, Co, FexMn1?x).- 11. The Spin Glass State in Garnet Mixed Crystals: New Evidence from Neutron Scattering and Macroscopic Measurements.- 12. Polytypism and Equilibrium Phase Transitions: In Situ Observation of the Polytypic Phase Transition 2H-12R in PbI2.
TL;DR: Several massifs of very old carbonatites have been discovered in the Archaean granulitic block of In'Ouzzal (Western Ahaggar, Algeria) as mentioned in this paper.
Abstract: Several massifs of very old carbonatites have been discovered in the Archaean granulitic block of In'Ouzzal (Western Ahaggar, Algeria). These carbonatites are original since they are associated with Silica — saturated syenitic magmatism and present, in the late stages of evolution, a very uncommon mineralogy, with silicate minerals, especially wollastonite, allanite, and quartz. The mineralogy, C and O isotopes and R.E.E. distributions indicate that the late stages of crystallization occurred under high SiO2 activities, and produced the uncommon mineralogy and extremely high R.E.E. concentrations in phosphate minerals apatite and britholite. Interaction with continental crust is a possible mechanism to explain the original features of these carbonatite complexes.
01 Jan 1988
TL;DR: In this paper, the main factors controlling the rates of the chemical weathering of silicate minerals were investigated and the end products of this process were predicted. But the main focus of this paper was not on the weathering process itself, but rather on predicting its end products.
Abstract: The present paper deals with the weathering mechanisms of silicate minerals from a fundamental point of view. The goal of such a study is to understand the main factors controlling the rates of this process and to predict its end products. The chemical weathering of silicates is one of the major processes responsible for the transfer of dissolved and eventually particulate components from land to sea.
TL;DR: In this article, the first report of boehmite as a major alteration mineral in a mid-ocean ridge hydrothermal environment was made, which constitutes the first reporting of BoEmite as an alteration mineral.
TL;DR: In this article, pyrochlore recovery with a secondary amine type reagent is much lower in recycle water than in the other waters, which suggests that the precipitation of Ca ++ (as Ca oxalate) present in recycle waters leads to improved recovery.
01 Jan 1988
TL;DR: In this article, the authors proposed a method to measure polarized spectra with areal resolution down to 3 μm of single crystals at normal and high pressures, which are the basis for determining the site geometry and crystal field stabilization energy of the 3dN-ion in the respective structural matrix.
Abstract: Microscope spectrometry, MISPE, allows to measure polarized spectra with areal resolution down to 3 μm of single crystals at normal and high pressures. Such spectra of synthetic single crystals, grown under controlled thermodynamic conditions to contain only one type of 3dN-ion, yield unambiguous band assignments which are the basis for determining the site geometry and crystal field stabilization energy of the 3dN-ion in the respective structural matrix.
Dissertation•
01 Jan 1988
TL;DR: In this article, the behavior of two amorphous and crystalline silicates (albite and olivine) toward aqueous dissolution has been investigated with emphasis on similarities and differences with silicate glasses, and influence of ion bombardment which transforms the initially crystalline structure to a glass-like one.
01 Jan 1988
TL;DR: In this article, a phase transition to a collective, magnetically ordered state at low temperatures was shown in natural silicates with small amounts of 3d transition metal ions in octahedral sites.
Abstract: Natural silicates often contain small amounts of 3d transition metal ions in octahedral sites, which possess a magnetic moment due to unpaired 3d electrons. When the concentration of 3d ions is sufficiently high for them to couple magnetically via exchange interactions, there may be a phase transition to a collective, magnetically ordered state at low temperatures.
01 Jan 1988
TL;DR: In this article, the compositional information available from interplanetary dust particles (IDPs) and the recent Halley flybys was incorporated into a coherent model to account for cometary infrared emission.
TL;DR: In this article, the relationship between hydrated layer formation during aqueous corrosion of silicates and retention of heavy elements (Fe, REE, actinides) was investigated based on the comparison of the dissolution behaviour of silicate glasses, silicate minerals implanted with increasing doses of lead ions (1×E+12 to 1×E +15 ions/cm2), sorption experiments on silica surfaces and direct precipitation of hydrosilicates.
Abstract: We have investigated the relationship between hydrated layer formation during aqueous corrosion of silicates and retention of heavy elements (Fe, REE, actinides). Our approach is based on the comparison of the dissolution behaviour of silicate glasses, silicate minerals implanted with increasing doses of lead ions (1×E+12 to 1×E+15 ions/cm2), sorption experiments on silica surfaces and direct precipitation of hydrosilicates. The characterization of reacted surfaces was performed by combining Rutherford backscattering spectrometry (RBS) for profiling heavy elements with Resonant Nuclear Reaction Analysis (RNRA) for hydrogen profilimetry. The accumulation of these elements does not necessarily imply a selective dissolution and can be explained by the “precipitation” of hydroxides or hydrosilicates.
TL;DR: In this article, the authors investigated the cracking behavior of an allophanic material by sedimenting an aqueous suspension of the material onto a filter paper in a Buchner funnel, and allowing the filter pad to dry out at ambient humidity and temperature.
01 Jan 1988
TL;DR: In this paper, a survey of the collective magnetic order of end-member iron minerals belonging to the garnet, pyroxene, amphibole, serpentine, mica and olivine families is presented.
Abstract: An elementary account is given of the properties of the magnetic ions most commonly found in silicate minerals, Fe2+ and Fe3+, including the effect of the crystal field on the former. Collective magnetic behaviour is discussed, mainly in term of molecular field theory, and the influence of cation disorder is considered. There follows a survey of collective magnetic order of end-member iron minerals belonging to the garnet, pyroxene, amphibole, serpentine, mica and olivine families. They usually have complex antiferromangetic structures with Neel points in the range 1–100 K, but disorder may induce spin glass states. Finally, the thermodynamic consequences of magnetic order are considered, in relation to the enthalpy and entropy of iron minerals.
TL;DR: Rb-Sr and O isotopic data for mid-Tertiary alkalic rocks from the Trans-Pecos magmatic province of west Texas demonstrate that hydrothermal alteration and fluid/rock (cation exchange) interactions have affected the isotope geochemistry of these rocks.
TL;DR: In this article, a chemical model for extrapolating laboratory data on mineral/alakli reactions to reservoir time scales is presented, which may help operators predict when significant dissolution of the formation will occur and where precipitates will deposit.
Abstract: A chemical model is presented for extrapolating laboratory data on mineral/alakli reactions to reservoir time scales. Minerals in sandstone and ions in caustic solution that control sodium hydroxide consumption during alkaline flooding were identified. This work may help operators predict when significant dissolution of the formation will occur and where precipitates will deposit. The dissolution of eight silicate minerals in caustic solution at 24 and 70C (75 and 158F) was determined. The minerals studied were quartz, two feldspars (microline and albite), two micas (muscovite and biotite), and three clays (kaolinite, montmorillonite, and chlorite). The concentrations of sodium, silicate, aluminate, and hydroxide were measured periodically during bottle tests. Balanced chemical reactions are written for quartz, kaolinite, and phillipsite, and the corresponding equilibrium quotients are defined. A kinetic model is presented that includes rate constants, solid/liquid ratios, and equilibrium quotients to account for the effect of solution composition. The model was tested for kaolinite. The equilibrium quotient for kaolinite was found to be three times higher at 70C (158F) than at 24C (75F). Dissolution-rate data were fitted successfully with the kinetic model. The reaction of Kern River reservoir sand with sodium hydroxide was studied to test the model. Consumption of sodium hydroxidemore » occurred as predicted. However, caustic consumption was delayed in a slim tube packed with 99% quartz and 1% kaolinite, probably because of reduced nucleation of new minerals.« less
01 Jan 1988