Physics and Chemistry of Minerals最新文献

Complex mixtures of sulfates, silicates, and ice have been observed in a variety of planetary environments on Earth, Mars and the icy satellites of the solar system. Characterizing the properties of the corresponding compositional endmembers is important for understanding the interiors of a range of planetary bodies in which these phases are observed. To measure the electronic and vibrational properties of the pure ferrous iron endmember of the kieserite group, szomolnokite, (FeSO₄⋅H₂O), we have performed synchrotron ⁵⁷Fe nuclear resonant inelastic and forward scattering experiments in the diamond-anvil cell up to 14.5 GPa. This pressure range covers depths within Earth’s interior relevant to sulfur cycling in subduction zones and the range of pressures expected within icy satellite interiors. We find evidence of crystal lattice softening, changes in elastic properties, and changes in the electric field gradients of iron atoms associated with two structural transitions occurring within the experimental pressure range. We apply these findings to icy satellite interiors, including discussion of elastic properties, modeling of ice-sulfate aggregates, and implications for tidal observations.

The interplay between crystal–melt and grain boundary interfaces in partially melted polycrystalline aggregates controls many physical properties of mantle rocks. To understand this process at the fundamental level requires improved knowledge about the interfacial structures and energetics. Here, we report the results of first-principles molecular dynamics simulations of two grain boundaries of (0l1)/[100] type for tilt angles of 30.4° and 49.6° and the corresponding solid–liquid interfaces in Mg₂SiO₄ forsterite at the conditions of the upper mantle. Our analysis of the simulated position time series shows that structural distortions at the solid–liquid interfacial region are stronger than intergranular interfacial distortions. The calculated formation enthalpy of the solid–solid interfaces increases nearly linearly from 1.0 to 1.4 J/m² for the 30.4° tilt and from 0.8 to 1.0 J/m² for the 49.6° tilt with pressure from 0 to 16 GPa at 1500 K, being consistent with the experimental data. The solid–liquid interfacial enthalpy takes comparable values in the range 0.9 to 1.5 J/m² over similar pressure interval. The dihedral angle of the forsterite–melt system estimated using these interfacial enthalpies takes values in the range of 67° to 146°, showing a decreasing trend with pressure. The predicted dihedral angle is found to be generally larger than the measured data for silicate systems, probably caused by compositional differences between the simulation and the measurements.

Crystal structures of Ca₂SiO₄, Na₂SO₄–K₂SO₄ sulfates, and related minerals bubnovaite K₂Na₈Ca(SO₄)₆ and dobrovolskyite Na₄Ca(SO₄)₃ were described as consisting of microblocks for the first time. A microblock [M(TO₄)₆] that consisted of an octahedron interlinked by six vertices with six adjacent tetrahedra was considered a structural unit inherited upon cooling from a high-temperature disordered parent unit. The relationship between the parent and inherited microblocks was established. Based on this relationship, 15 possible types of microblocks maintaining a trigonal symmetry were derived. The minerals and compounds structurally related to α-Na₂SO₄-derived superstructures were formed as a result of the cooling of the high-temperature phases containing the disordered parent microblock. Here, the inheritance driving force was the tendency of the structure to become ordered upon cooling. The reasons for the formation of a microblock from the parent microblock were mainly determined by the ionic radius and type of cation occupying the octahedral site. The identification of minerals with the described structural features could be a promising tool for the synthesis of novel compounds with useful properties.

The infrared hydroxyl bands and first hydroxyl combination bands of glaucophane are characterized under pressure. In this weakly hydrogen-bonded mineral, the anharmonicity parameter, as determined from the difference between combinations and the fundamentals, is nearly constant with pressure to 15 GPa, indicating that the ambient pressure value of hydroxyl-bond anharmonicity closely reflects its value at high pressures. Given this near-constancy, the Grüneisen parameters of the hydroxyl stretching vibrations of a wide range of minerals, as derived from the pressure dependence of their O–H stretching frequencies, are correlated with the anharmonic parameter of each vibration, as determined from the ambient pressure offset of the summed frequencies of the fundamental n = 0 to 1 transitions and the frequency of the hydroxyl combination or overtone band corresponding to the n = 0 to 2 transition. This correlation is motivated by (1) the anharmonic origin of the Grüneisen parameter; and (2) the grossly similar form of the interatomic potential governing weak- and medium-strength hydrogen bonding in many minerals. This possible correlation provides a means through which the likely pressure-induced hydroxyl mode shifts of phases might be estimated from ambient pressure near-infrared measurements and emphasizes the importance of near-infrared combination/overtone band measurements. In this context, the combination/overtone bands of high-pressure hydrous phases are almost completely uncharacterized, and thus one probe of their anharmonicity has been neglected. Such information directly constrains the nature of hydrogen bonding in these phases, and hence provides possible insights into both their retention of hydrogen and its mobility. Deviations from the anharmonicity-Grüneisen parameter correlation, when observed (as may be the case in prehnite), could provide insights into anomalous effects on the hydroxyl potential well induced by bifurcated H-bonds, pressure-dependent Davydov splitting, or the influence of neighboring cations.

In this study, zeolite Y was synthesized from sodium silicate, aluminum hydroxide, sodium hydroxide and distilled water under hydrothermal method. The Box–Behnken design was used as a response surface method considering seven factors affecting the crystallization of zeolite to determine the number of experiments. The linear, square and interaction effects of the factors were investigated. The factors consist of four factors for the gel composition, including the molar value of Si, Al, Na and H₂O and three factors for the synthesis conditions, including aging time, crystallization time and temperature. The XRD patterns of the synthesized samples were compared with the XRD pattern of standard zeolite Y. Among the samples, sample 50 with the highest intensity and maximum total area of 14 peaks, was selected as the reference sample and it was used to determine the relative crystallinity percentage of the remaining samples. Based on the results of the experiments, it was concluded that changes in the gel composition have a more significant effect on the response in comparison with changes in the synthesis conditions. In addition, optimization of the obtained model was carried out and a zeolite with higher relative crystallinity than the standard zeolite Y was synthesized. At the optimal point, zeolite Y was synthesized with a relative crystallinity of 117.5%. The composition of the gel was 0.59 SiO₂: 0.0563 Al₂O₃: 0.4266 Na₂O: 12.376 H₂O. The total synthesis time was 30 h.

Muscovite (Ms) and phlogopite (Phl) series mineral is studied in the 2M₁ polytype and modeled by the substitution of three Mg²⁺ cations in the three octahedral sites of Phl [KMg₃(Si₃Al)O₁₀(OH)₂] by two Al³⁺ and one vacancy, increasing the substitution up to reach the Ms [KAl₂□(Si₃Al)O₁₀(OH)₂]. The series was computationally examined at DFT using Quantum ESPRESSO, as a function of pressure from − 3 to 9 GPa. Crystal structure is calculated, and cell parameters, and geometry of atomic groups agree with experimental values. OH in the Mg²⁺ octahedrons are approximately perpendicular to the (001) plane, meanwhile when they are in Al³⁺, octahedral groups are approximately parallel to this plane. From Quantum Theory of Atoms in Molecules, the atomic basins are calculated as a function of the pressure, K⁺ and basal O show the largest volumes. The bulk excess volume (Vxs) and the excess atomic volumes are analyzed as a function of the composition and the pressure. K⁺, basal and apical O Vxs show a behavior similar to the bulk Vxs as a function of the composition, keeping qualitatively this behavior as a function of pressure; substituent atoms do not show a Vxs behavior similar to the bulk and their effect consequently is mostly translated to atoms in the interlayer space. Atomic compressibilities are also calculated. Atomic compressibilities are separated in the different sheets of the crystal cell. Atomic moduli of K and basal O are the lowest and the ones behaving as the bulk modulus of the series. The atomic bulk modulus of the H’s is different depending of their position with respect to the (001) plane.

In this work, we investigated the thermodynamic properties of synthetic schafarzikite (FeSb₂O(_4)) and tripuhyite (FeSbO(_4)). Low-temperature heat capacity ((C_p)) was determined by relaxation calorimetry. From these data, third-law entropy was calculated as (110.7pm 1.3) J mol(^{-1})K(^{-1}) for tripuhyite and (187.1pm 2.2) J mol(^{-1}) K(^{-1}) for schafarzikite. Using previously published (Delta _fG^o) values for both phases, we calculated their (Delta _fH^o) as (-947.8pm 2.2) for tripuhyite and (-1061.2pm 4.4) for schafarzikite. The accuracy of the data sets was tested by entropy estimates and calculation of (Delta _fH^o) from estimated lattice energies (via Kapustinskii equation). Measurements of (C_p) above (T = 300) K were augmented by extrapolation to (T = 700) K with the frequencies of acoustic and optic modes, using the Kieffer (C_p) model. A set of equilibrium constants ((log K)) for tripuhyite, schafarzikite, and several related phases was calculated and presented in a format that can be employed in commonly used geochemical codes. Calculations suggest that tripuhyite has a stability field that extends over a wide range of pH-p(epsilon) conditions at (T = 298.15) K. Schafarzikite and hydrothermal oxides of antimony (valentinite, kermesite, and senarmontite) can form by oxidative dissolution and remobilization of pre-existing stibnite ores.

Phase relations for dissociation of spinel-structured Fe₂SiO₄ ahrensite to FeO wüstite + SiO₂ stishovite have been determined up to 20 GPa and 1400 °C under the iron-wüstite buffer conditions by multianvil high-pressure and high-temperature experiments. The dissociation boundary determined is expressed by P (GPa) = 19.6 (± 1.0) – 3.0 (± 0.8) × 10⁻³ T (°C). The boundary with the negative dP/dT slope is placed by ~ 1–4 GPa at lower pressure at 1000–1200 °C than the previously determined boundaries whose slopes ranged from strongly positive to weakly negative. Thermodynamic calculation based on available thermodynamic data of ahrensite, wüstite and stishovite has provided the dissociation boundary which is in good agreement within the errors with that experimentally determined in this study. By combining the post-spinel phase relations in Fe₂SiO₄ determined in this study with available phase relations in the Fe₂SiO₄-Mg₂SiO₄ system, it is suggested that natural Fe₂SiO₄-rich ahrensite crystals found in the shocked Umbarger L6 chondrite crystallized in shock-induced melt pockets of the FeO- and SiO₂-rich composition at pressures below ~ 13–16 GPa and above ~ 9–12 GPa in the shock process.