Physics and Chemistry of Minerals最新文献

Understanding the impacts of cation disorder (characterized by the inversion parameter x, the Mg fraction on the tetrahedral site) on the structural, and physical–chemical properties of Mg₂SiO₄-ringwoodite (Rw) is very important. In this study, first-principles method combined with quasi-harmonic approximation theory has been used to obtain the microstructures, thermodynamic properties, and elastic properties of Rw at six different cation disorder states, from normal spinel configuration (x = 0) to inverse spinel configuration (x = 1). By the cation configurations with the lowest enthalpies for the investigated x values, we have established quantitative relations between x and physical–chemical properties like zero-pressure volume (V₀), isothermal bulk modulus (K_T), the first pressure derivative of K_T (({{K}}_{{T}}^{prime})), the temperature derivative of K_T (∂K_T/∂T), thermal expansion coefficients (α), isobaric heat capacity (C_P), vibrational entropy (S), adiabatic bulk modulus (K_S), shear modulus(G), compressional wave velocity (V_P), and shear wave velocity (V_S). Our results show that all investigated physical–chemical properties of Rw are likely quadratically correlated to x, with the extremums of the quadratic functions presumably corresponding to the state of full cation disorder (x = 2/3). Therefore, any simplified linear extrapolation or interpolation of the properties of Rw with different cation disorders should be viewed with great caution.

Hončova hůrka Hill represents an Early Cretaceous strongly altered picritic effusive body. In the low-temperature hydrothermal mineralisation of both amygdales and rock fissures, a calcite-dominated mineral association including zeolites (harmotome, ferrierite-Mg, and heulandite-clinoptilolite series), chlorite, baryte, various clay minerals, quartz, and some accessories are known. Up to this moment, the only published analysis of the heulandite-clinoptilolite series mineral was a single wet analysis proving the existence of a Ca-dominant extra-framework cation. Two hundred twenty-three new energy-dispersive (EDS) microanalyses of 11 samples revealed a much more complicated picture. Two hundred spots are classified as clinoptilolites, with a continuous transition from more common barium-rich clinoptilolite-Ca to the Ba-dominant member (4 spot analyses). Twenty-three analyses correspond to the heulandite subgroup, with a continuous transition from barium-rich heulandite-Ca to the Ba-dominant member (5 spot analyses). The electron microscope backscattered electron images revealed the lamellar structure of the crystal aggregates of the heulandite-clinoptilolite series minerals and strong zoning, with the cores richest in barium and the outer parts enriched in calcium. We believe that originally the mineral aggregates were dominantly barian, while at the end of the hydrothermal solution precipitation resulting in carbonate crystallisation (calcite, minor dolomite), there was an extra-framework cation exchange of Ba²⁺ for Ca²⁺. The excess of barium at that moment stimulated baryte deposition in minute cracks of the heulandite-clinoptilolite series minerals. Four microanalyses revealing the presence of yet undescribed and unapproved clinoptilolite-Ba are not sufficient for a new phase description at this time but clearly indicate its presence in nature.

The equation of state of ilmenite (FeTiO₃) and geikielite (MgTiO₃) have been investigated using in situ synchrotron X-ray diffraction at high pressures up to ~ 21.8 GPa and ~ 23.0 GPa, respectively. No phase transitions were observed within the experimental pressure ranges for both samples. The pressure-volume data were fitted using the third-order Birch-Murnaghan equation of state (EoS), yielding the following results: for FeTiO₃, the zero-pressure unit-cell volume V₀ = 312.2(1) ų, the zero-pressure bulk modulus K₀ = 165(4) GPa, and its pressure derivative K′₀ = 6.6(6); for MgTiO₃, V₀ = 304.17(8) ų, K₀ = 157(3) GPa, and K′₀ = 7.3(4). Additionally, the axial compressional behavior of FeTiO₃ and MgTiO₃ were also fitted with a linearized third-order Birch-Murnaghan EoS. The axial compressibility coefficients for FeTiO₃ along the a- and c-axes are β_a = 1.43(4) × 10^− 3 GPa^-1 and β_c = 3.17(11) × 10^− 3 GPa^-1, respectively, with an anisotropic ratio of β_a: β_c = 0.45: 1.00, while β_a = 1.76 (7) × 10^− 3 GPa^-1 and β_c = 2.61(7) × 10^− 3 GPa^-1 with an anisotropic ratio of β_a: β_c = 0.67: 1.00 for MgTiO₃. Both FeTiO₃ and MgTiO₃ exhibit the axial compression anisotropy, of which FeTiO₃ shows stronger axial compressibility anisotropy than MgTiO₃. Moreover, the potential influencing factors (e.g., cation radius, crystal structure, and chemical bond strength) on the bulk moduli and the anisotropic linear compressibilities of FeTiO₃ and MgTiO₃ were further discussed.

This study investigates the thermal annealing kinetics of induced fission tracks in ZAD zircon from the Serra Geral Volcanic Complex, Brazil, and compares results with previously studied ZPC zircon. Both samples underwent identical pre-annealing treatment (1100 °C for 1 h) to remove fossil fission tracks before neutron irradiation and heating experiments at temperatures between 500 and 800 °C for durations of 1–100 h. Comprehensive statistical analysis, including Kolmogorov–Smirnov tests and effect size calculations, confirmed that observed differences between samples reflect genuine material properties rather than measurement bias. ZAD exhibited significantly higher annealing rates and lower activation energy (62 ± 14 kcal/mol) compared to ZPC (80 ± 20 kcal/mol), despite both samples undergoing identical laboratory procedures. This differential behavior is attributed to ZAD’s 20% higher accumulated α-recoil damage (3.34 × 10¹⁶ vs. 2.67 × 10¹⁶ decays/g), which persists as residual damage even after pre-annealing treatment. Calculations of displacements per atom (dpa) further quantified this difference (1.07 × 10⁻³ for ZAD vs. 8.5 × ⁻⁴ for ZPC). The study demonstrates how radiation damage accumulated over different timescales (134 Ma for ZAD vs. 80 Ma for ZPC) creates distinct microstructural defect patterns that significantly influence fission track annealing kinetics, with important implications for zircon thermochronology interpretations and geological thermal history reconstruction.

To investigate the impact of γ irradiation on bentonite, the natural bentonite from GaoMiaoZi (GMZ), located in Inner Mongolia, China, and foreseen as an engineering barrier in geological disposal facilities, was selected as the subject of this study. The sample underwent exposure to a Co-60 source followed by comprehensive analysis utilizing various techniques, including mass spectrometer, swelling pressure testing system, X-ray diffraction, simultaneous thermal analysis, infrared spectrometer, and Mössbauer spectroscopy. The findings indicated that γ irradiation detrimentally altered the microstructure and reduced the structure trivalent iron of GMZ bentonite, leading to a decrease in swelling pressure, with a noticeable cumulative dose effect. Additionally, a negative exponential correlation was observed between the maximum swelling pressure and absorbed dose. The effect of γ irradiation significantly influenced the physical and chemical properties of GMZ bentonite.

In this study, we aimed to evaluate the shock-induced behavior of calcite (CaCO₃), a potential source of CO and/or CO₂. To this end, we experimentally investigated the time evolution of calcite during shock compression and decompression processes at shock pressures up to 234 ± 19 GPa using an ultrafast time-resolved X-ray diffraction (XRD) coupled with a laser-driven shock compression system. The XRD analysis of shocked calcite showed that the amorphization occurred in the shock compression stage at pressures above 86 ± 7 GPa, and that the decomposition reaction, i.e., CaCO₃ = CaO + CO₂, was not observed in the decompression stage within the nanosecond timescale. This observation indicated that in addition to pressure and temperature, the shock duration (reaction time) is also a critical factor affecting shock-induced structural changes, such as amorphization and decomposition. Furthermore, the nanosecond laser shock employed in this study may be applied to enhance understanding regarding the impact phenomena of micrometer to submillimeter sized projectiles. The present results suggest that the shock-induced decomposition of calcite does not occur during micrometeorite impacts.

Calcium perovskite is a major component of deep mantle phase assemblages and has been frequently identified, in retrograde form, as polyphase mineral inclusions within sub-lithospheric diamonds. Here experimental observations of synthetic samples demonstrate various properties of calcium perovskite minerals which have relevance for the interpretation of diamond-hosted inclusions. Ambient pressure diffraction and spectroscopy confirm the linear dependence of crystallographic unit cell volume and Raman peak shifts across the entire CaSiO₃-CaTiO₃ binary join. These systematics will allow verification of perovskite structure and constraint of inclusion composition, without destructive analyses, in future studies. Additionally, high pressure observations confirm that calcium perovskite minerals ≳ 80 mol.% CaSiO₃ undergo spontaneous amorphization during decompression at room temperature, meaning they are unrecoverable. Finally, the presence of water appears to expand the calcium perovskite stability field to lower pressure conditions, implying at least some appreciable water-solubility in these minerals.

The seismic mapping of hydrous materials in the Earth’s deep interior requires experimental constraints on the elastic anisotropy of hydrous minerals and phases. Oxyhydroxides like δ-(Al,Fe)OOH are arguably the main hosts of water in the lower mantle. Therefore, constraints on the single-crystal elastic tensor of δ-(Al,Fe)OOH solid solutions are crucial to quantify the elastic anisotropy of this material, and advance the current understanding of the recycling of water into the lower mantle. Yet, experimental data for intermediate compositions are scarce, limiting the understanding of how Fe incorporation affects the single-crystal elastic properties of δ-AlOOH. In this study, we provide experimental constraints on the single-crystal elasticity of two δ-(Al,Fe)OOH solid solutions, with Fe/(Al + Fe) of 0.06(1) and 0.133(3). Large single-crystal samples of δ-(Al,Fe)OOH were synthetized at high pressures and temperatures using a multi-anvil press, and the full elastic stiffness tensors were determined at ambient conditions by combining X-ray diffraction and Brillouin scattering measurements. We show that replacing Al³⁺ with Fe³⁺ in δ-(Al,Fe)OOH lowers the magnitude of most coefficients of the elastic stiffness tensor (c_ij), which translates into a substantial reduction of aggregate moduli and acoustic wave velocities. We further show that, at ambient conditions, the acoustic anisotropy of δ-(Al,Fe)OOH displays no sensitivity to Fe–Al substitution.

In a previous paper we showed that the multiple Einstein method is suitable to determine consistency of data on thermophysical properties and phase diagrams in the system MgO–FeO–SiO₂ for upper mantle and transition zone conditions in the Earth. Here we extend this work to conditions covering the lower mantle, in the temperature range between 0 and 3000 K and pressure range between 20 and 140 GPa, with the goal to determine which data are consistent with each other. The resulting database is used to study the effect of the spin transition in ferropericlase on thermophysical properties and phase diagrams. Although trade-off is present in the model parameters due to the lack of experimental data, we show that models, reduced in complexity, can be used to study the effect of Fe³⁺ on these properties and phase equilibria. We show that the effect of the miscibility gap in ferropericlase, its spin transition and the valence state of Fe does not have a significant visibility in seismic density and velocities isentropes. We demonstrate that the overall composition derived by Chust et al. (J Geophys Res Solid Earth 122:9881–9920, 2018) is suitable to represent PREM and AK135 seismic data to within experimental uncertainty.

Morphological features and internal structure of a large single crystal of moissanite - natural SiC - from a Manchary kimberlite pipe are characterized in detail using complementary methods including optical, atomic force and electron microscopy, cathodoluminescence, Raman spectroscopy and X-ray topography. The sample combines atomically flat (0001) faces decorated with growth macrosteps and with remarkably complex secondary (e.g., (10–13)) faces. These faces contain outcrops of dislocations, remnants of a crystalline film, features consistent with attachment of 3D growth nuclei and other peculiarities. The specimen mainly consists of 6H polytype with admixture of 4H and 15R polytypes. The overall crystalline quality is high, only few growth-related dislocations are visible in X-ray topographs. Morphological features suggest growth of the SiC crystal on a substrate in relatively stable, but nevertheless gradually changing conditions. These changes are reflected in complex internal zoning. As suggested by the growth features, at the last stages the supersaturation increased considerably, possibly resulting from closure of a growth chamber. The growth features are consistent with moissanite formation from a reduced supercritical fluid at moderate temperatures.