Physics and Chemistry of Minerals最新文献

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.

The single-crystal elastic moduli of three natural aragonites, CaCO₃, have been determined at ambient conditions by Brillouin spectroscopy. The samples contain different amounts of Sr ranging from 0.1 mol% to 1.5 mol% and cover the majority of the compositional range of natural aragonites. Brillouin spectroscopy can resolve changes in elasticity produced by small differences in the Sr content in aragonite, however, these changes are at the limit of the resolving power of our measurements. Our results are in good agreement with the full tensor of a Sr-bearing natural aragonite determined by Brillouin spectroscopy and with the tensor obtained by DFT calculations. The decrease we measured of the aggregate adiabatic bulk modulus, (K_S), with increasing Sr content is qualitatively in good agreement with the softening observed in previously measured isothermal bulk modulus, (K_T), of synthetic CaCO₃-SrCO₃ solid solutions and with the value of (K_S) determined for SrCO₃. Our study provides the first full tensor on nominally pure (end-member) aragonite and places contraints on its dependence on Ca/Sr substitutions at levels observed in natural samples. Furthermore, we compare the elastic tensor of aragonite and calcite, the two main CaCO₃ polymorphs observed at ambient conditions, and describe their differences based on the arrangement of the polyhedral structural units of the two polymorphs. In particular, the different arrangement of the Ca-O polyhedra leads to a smaller compressibility of aragonite along the c-axis, higher compressibilities along the a- and b-axes and an overall lower bulk modulus ((-)9.7%) with respect to that of the less dense calcite.

Quartz is one of the most abundant minerals in the Earth crust and therefore quartz inclusions in garnet are of great interest for elastic geobarometry, an approach that exploits the elastic properties of the mineral pair to back-calculate the conditions of inclusion entrapment. However, the high-temperature behavior of quartz inclusions close to the (alpha)–(beta) transition boundary has not been studied experimentally. We have therefore performed in situ high-temperature Raman spectroscopy on a quartz-in-garnet system up to 1000 K, and have also collected an improved reference data set for the temperature dependence of the Raman scattering of free quartz. Our results show that the (alpha)-to-(beta) phase transition is hindered by the stress imposed by the host on the quartz inclusion, resulting in a thermosalient effect of the whole host-inclusion system or a mechanical cracking of the host mineral.

The pioneering hydrothermal synthesis of the compound Be₂[(Si_1−xGe_x)O₄] with a phenakite structure (the size of individual crystals up to 1 mm) was carried out in acidic alkaline-containing fluoride solutions at a temperature of 625 °C and a pressure of ~ 150 MPa. Uniform (x = 0, 0.80 and 1) and zonal (x = 0.04 − 0.025) Be₂[(Si_1−xGe_x)O₄] crystals synthesized in the Li-containing mineralizer were obtained. The possibility of formation of intermediate compounds under hydrothermal conditions remains an open question. In the Na-containing mineralizer, only Be₂SiO₄ crystallizes due to the formation of insoluble sodium germanates. The fading of formation of Be₂[(Si_1−xGe_x)O₄] was determined with the use of technique of temperature-induced zoning and can be explained by the fact that newly formed crystals screen the surface of the initial BeO. The instantaneous growth rates of the prismatic faces of Ge-substituted phenakite crystals, decreasing from 18 microns/day to 2, were determined using the technique of temperature-induced zonality. The crystal structures of Be₂[(Si_1−xGe_x)O₄] samples with x = 0, 0.80 and 1 were refined by direct X-ray diffraction methods, and the linear dependence of the unit cell parameters and bond lengths on the germanium content has been quantitively described. First Raman spectroscopy study of Be₂[(Si_1−xGe_x)O₄] on zonal crystals indicated the linear shift of vibration bands in Raman spectra to a lower frequencies with an increase in germanium concentration (x up to 0.25). A new Raman band of Ge–O stretching vibrations at ~ 1115 cm⁻¹, which is not common for natural and synthetic germanium-free phenakites, was observed.

Fe–Ni–S–Si alloy is considered to be one of the plausible candidates of Mercury core material. Elastic properties of Fe–Ni–S–Si liquid are important to reveal the density profile of the Mercury core. In this study, we measured the P-wave velocity (V_P) of Fe–Ni–S–Si (Fe₇₃Ni₁₀S₁₀Si₇, Fe₇₂Ni₁₀S₅Si₁₃, and Fe₆₇Ni₁₀S₁₀Si₁₃) liquids up to 17 GPa and 2000 K to study the effects of pressure, temperature, and multiple light elements (S and Si) on the V_P and elastic properties.

The V_P of Fe–Ni–S–Si liquids are less sensitive to temperature. The effect of pressure on the V_P are close to that of liquid Fe and smaller than those of Fe–Ni–S and Fe–Ni–Si liquids. Obtained elastic properties are K_S0 = 99.1(9.4) GPa, K_S’ = 3.8(0.1) and ρ₀ =6.48 g/cm³ for S-rich Fe₇₃Ni₁₀S₁₀Si₇ liquid and K_S0 = 112.1(1.5) GPa, K_S’ = 4.0(0.1) and ρ₀=6.64 g/cm³ for Si-rich Fe₇₂Ni₁₀S₅Si₁₃ liquid. The V_P of Fe–Ni–S–Si liquids locate in between those of Fe–Ni–S and Fe–Ni–Si liquids. This suggests that the effect of multiple light element (S and Si) on the V_P is suppressed and cancel out the effects of single light elements (S and Si) on the V_P. The effect of composition on the EOS in the Fe–Ni–S–Si system is indispensable to estimate the core composition combined with the geodesy data of upcoming Mercury mission.

In the first two papers of this series [Behrens, Phys Chem Minerals 48:8, 2021a; Behrens, Phys Chem Minerals 48:27, 2021b], incorporation of hydrogen in the feldspar structure, partitioning of hydrogen between feldspars and gases/fluids and self-diffusion of hydrogen in feldspars have been discussed, with particular focus on sanidine. Here, the results of reactions between sanidine containing strongly bonded hydrogen defects and (Na,K)Cl are presented. Experiments were performed at ambient pressure at temperatures of 605–1000 °C, and hydrogen profiles were measured by IR microspectroscopy. Profiles can be interpreted by an incomplete dehydrogenation at the crystal surface or a strong concentration dependence of hydrogen diffusivity. Both are consistent with hydrogen located on interstitial sites and difficult to substitute by the larger alkali ions. Chemical diffusivities of hydrogen derived from fitting of the profiles or Boltzmann–Matano analysis are similar to self-diffusivities determined by D/H exchange experiments. Activation energies are also comparable. Comparison to sodium and potassium diffusion data for sanidine (Wilangowski et al. in Defect Diffus Forum 363: 79–84, 2015; Hergemöller et al. in Phys Chem Minerals 44:345–351, 2017) supports a mechanism of proton diffusion charge-compensated by Na⁺ diffusion for hydrogen removal in the sanidines under dry conditions.

Turquoise is a well-known gemstone that has been used in artefacts across many cultures throughout history. However, due to its porosity it is often treated to enhance its color and beauty. One appreciated treatment is the patented Zachery process, although its details remain publicly undisclosed. Previous studies indicated that only a high K content distinguishes Zachery-treated from natural turquoises. In this study, natural and Zachery-treated turquoise samples from the famous Kingman mine, Arizona, USA, were analysed by means a multi-methodological approach, including standard gemological testing, electron microprobe (EMPA), scanning electron microscope with energy dispersive spectrometer (SEM–EDS) and X-ray diffraction (XRD), Fourier-Transform InfraRed (FTIR), non-destructive External Reflection-Fourier-Transform InfraRed (ER-FTIR) spectroscopy and X-ray computed microtomography (μCT). The results revealed new chemical–mineralogical and microstructural features that distinguish the Zackery-treated from the natural turquoise: higher specific gravity and lower porosity, associated with high and uneven concentrations of Cu, K and Na, the occurrence of tenorite (CuO), the presence and extension of reaction edges in the entire volume are distinctive of treated samples. Moreover, Cu-rich seeds and feldspar crystals may be interpreted as additional components used during the treatment. The hypothesis is that the Zachery treatment induces the re-crystallization of a new turquoise-like phase, which differs from the natural one from a chemical and microstructural point of view.