Physics and Chemistry of Minerals最新文献

The Raman spectrum of lawsonite is characterized in situ at high temperatures through its dehydration temperature under vacuum. The structural reorganization associated with dehydration appears to initiate in the Si and Al-dominated layer of the structure, and proceeds between 525–550 and 725 °C. The loss of water from the structure appears complex, with the first structural reorganization associated with dehydration occurring at 550 °C, coexistence of lawsonite and the initial dehydration products up to 700 °C, and rapid disappearance of lawsonite between 675 and 725 °C. The dehydration is likely preceded by increased disorder of the hydroxyls within the structure. Indications of enhanced disorder of hydrogen ions at high temperatures include a dramatic decrease in intensity of an O–H librational vibration, large peak broadening of the principal hydroxyl stretch, and the disappearance of a shoulder on the strongest hydroxyl stretching vibration. The thermal anharmonicity of a range of Raman active modes is determined, and a revision to mode assignments is suggested based on the thermal shifts. Under low pressure conditions and our laboratory timescale, the observed product of lawsonite dehydration is the metastable pseudo-hexagonal polymorph of CaAl₂Si₂O₈, dmisteinbergite. Production of dmisteinbergite through intermediate temperature lawsonite dehydration represents a previously unrecognized pathway for its formation, which previously has been limited to low-temperature hydrothermal environments, pyrometamorphic environments, materials rapidly quenching from melts (including in pseudotachylites), and as a retrograde phase from high grade metamorphic environments. The formation of metastable dmisteinbergite from lawsonite is likely facilitated by a topotactic relation between its layered structure and that of lawsonite.

This study investigated the enrichment factor (EF) and geochemical relationships of rare earth elements (REEs) in different grain size fractions of soils collected from Başören village, Kuluncak district, Malatya province, Türkiye. A total of 22 surface soil samples were collected and separated into five grain size fractions (< 75, 75–150, 150–180, 180–250, and > 250 μm), yielding 110 samples. Concentrations of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, Lu, and Y were determined by ICP-MS. EF values ​​were calculated using Al as the reference element, and Pearson correlation was applied to evaluate the relationships between REEs. Strong positive correlations were observed among most REEs (r = 0.999–1.000, p < 0.01), whereas weaker correlations were shown between Eu and Gd elements and La, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Yb, Lu, and Y elements. Moderately positive relationships were determined between Al and REEs, with coefficients of determination (R²) ranging from approximately 0.33 to 0.54, indicating that REE distributions are primarily controlled by aluminosilicate minerals and fine-grained fractions. EF values ​​varied between sampling areas and grain size fractions. While negligible to moderate enrichment was observed in most samples, significant to very high enrichment was observed in some samples, particularly for Gd, Tb, Dy, Ho, and Yb. Samples T16 and T20 showed the highest enrichment levels, with Gd reaching very high enrichment classes (EF = 20–40). The results show that the spatial distribution and enrichment patterns of rare earth elements are largely influenced by lithogenic sources and grain size-dependent mineralogical characteristics.

The crystal structure, infrared, Raman, excitation- and emission-mode photoluminescence spectra as well as thermal behavior of hydrogen- and REE-bearing natural arctite have been studied. The trigonal unit cell parameters are: a = 7.0773(1), c = 41.2197(6) Å, V = 1788.01(4) ų; sp. gr. R(:stackrel{-}{3})m. The crystal structure was solved and refined to the final R = 2.02% based on 848 I > 3σ(I). Taking into account the IR spectroscopy data, the charge-balanced empirical formula calculated for 6 phosphorus atoms is (Z = 3): (H⁺,H₃O⁺)_0.88(Ca_6.62Na_4.40Ba_1.00Ce_0.07La_0.03)_Σ12.12(PO₄)_5.82(HPO₄)_0.18F_2.85(OH)_0.15. The crystal structure of arctite is characterized by the presence of anion-centered [F₃M₁₂] trimers (M = Na, Ca) composed of face-shared anion-centered FM₆ octahedra. The simultaneous presence of basic (Ca²⁺···OH^–) and acid (HPO₄^2–, H₃O⁺, H⁺) species is a specific feature of the studied H-bearing sample. Similar synthetic materials may be of practical interest as luminophores. Luminescent properties of the studied sample are related to the admixed Ce³⁺ and Sm³⁺ ions.

Ab initio calculations were performed to estimate the energy preference of Ca²⁺ substitution by La³⁺ with compensating incorporation of an additional F⁻ ion at the (111) twin boundary of fluorite (CaF₂). Model structures of polytypes and polysomes, which are periodic stacking faults within the cubic fluorite matrix, were constructed and optimized using density functional theory (DFT). Our results indicate that the twin boundary has a strong tendency to trap lanthanum cations. These findings suggest that the twin boundaries in CaF₂ may act as active sites for the accumulation of rare-earth elements, providing potential routes for modifying the functional properties of the materials. Conversely, addition of lanthanoids may promote growth twinning of fluorite.

The high-temperature volumetric and axial thermal expansion behaviors of ilmenite (FeTiO₃) and geikielite (MgTiO₃) were examined up to 773 K using in situ synchrotron X-ray diffraction. No phase transitions were observed within the experimental temperature range. The temperature–volume data were fitted using the Berman (1988)’s equation, yielding V₀ = 316.50(3) ų and α_V0 = 3.73(4) × 10^–5 K⁻¹ for FeTiO₃, and V₀ = 308.20(1) ų and α_V0 = 2.95(9) × 10^–5 K⁻¹ for MgTiO₃. In addition, axial thermal expansion analysis showed that FeTiO₃ has a₀ = 5.0865(1) Å, α_a0 = 1.41(1) × 10^–5 K⁻¹, c₀ = 14.0858(4) Å, and α_c0 = 0.92(2) × 10^–5 K⁻¹, while MgTiO₃ has a₀ = 5.0585(1) Å, α_a0 = 0.85(3) × 10^–5 K⁻¹, c₀ = 13.9084(4) Å, and α_c0 = 1.23(3) × 10^–5 K⁻¹. The results demonstrate that FeTiO₃ exhibits more stable volumetric expansion with increasing temperature than MgTiO_3. However, FeTiO₃ and MgTiO₃ display opposite trends in axial expansion: the a-axis expands more than the c-axis in FeTiO₃ (α_a0/α_c0 = 1.53), whereas in MgTiO₃, the c-axis expands more (α_a0/α_c0 = 0.69). These differences mainly reflect the distinct nature of the A-site cations: the 3d electrons of Fe²⁺ affect the rigidity and thermal response of Fe–O and Ti–O bonds, while Fe-related magnetic exchange interactions and associated magnetoelastic coupling may further constrain Fe–O bond expansion and reduce the thermal expansion of FeTiO₃.

Strontium hexaferrite (SrM) powders were prepared by solid-state reaction using celestite and magnetite/hematite. Energy dispersive X-ray fluorescence spectrometry, X-ray diffractometry (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry were used for analyses. The precursor ores were purified by hand-sorting and magnetic separation. Magnetic separation yielded 75% magnetite and 25% hematite in iron ore. Strontium reached a single phase of (rm SrSO_4) via hand-sorting. XRD confirmed single-phase (rm SrFe_{12}O_{19}) sample with hexagonal symmetry (space group (rm P6_{3}/mmc)). EDS analyse confirmed that the percentage of elements is in agreement with the expected stoichiometry for the hexaferrite phase. Initial SrM sample exhibited magnetization at maximum field of (rm 56~emu/g) and coercive field of (rm 632~Oe). Although remanence and coercivity were lower than expected for the initial SrM sample, due to wide particle size distribution observed in SEM images, by optimizing synthesis parameters, particularly annealing at (950^circ )C, the coercivity increased by nearly eightfold, reaching 4.96 kOe. The sample annealed at 950 (^circ )C also exhibited a maximum energy product of (rm (BH)_{max}approx 3.20~MGOe) and an estimated magnetocrystalline anisotropy constant of (rm K_1sim 3.6times 10^6~erg/cm^3). Microstructural evidence confirmed the predominance of particles in the monodomain regime, which justifies the increase in the coercive field. The results demonstrate that microstructural control is decisive for tuning the magnetic response of SrM, enabling the large-scale viability of this synthesis route for the production of high-coercivity hexaferrites, using a direct mixture of minerals instead of conventional industrial reagents.

Grain boundaries are an important part of many polycrystalline mineral aggregates, possessing unique geometries and chemistries but they are often poorly understood due to the many complexities of studying such large geometrically diverse regions. In this work we shall examine the surfaces of the mineral forsterite in order to understand their controlling behaviour and mechanisms. We shall use a combination of density functional theory and both machine learning and classically trained forcefields. We find that for purposes of partitioning and surface energies most grain boundaries are similar to their constituent planar surfaces. Our main finding is that the relative energies of forsterite surfaces are highly sensitive to T and P and that their planar distributions are not static in real environments. Increasing T at low P can lead to growth of (010) surfaces while increasing T and P together can lead to the growth of (111) surfaces. In mantle conditions we predict a strong favourability of (111) surfaces that increases with depth but with large, sometimes non-monotonic shifts in the favourability of other surfaces. We also demonstrate that changing the surface distribution can lead to changes in crystal properties. The high temperature stabilisation of (010) is driven by a novel collective motion of Mg atoms along [100] channels which will also lead to a large, non-linear, anisotropic increase in grain boundary diffusion as (010) surfaces grow with temperature. We show that partitioning of water to forsterite surfaces is highly surface specific and driven by local chemistry enabling the possibility of hidden reservoirs in the Earth produced by changing surface plane distributions.

In-situ manufacturing and resource utilization on the lunar surface present a core challenge for establishing a sustainable lunar base, where the self-sufficiency of metal materials is particularly critical. Therefore, this study presented a novel method for extracting metallic iron from Fe₃O₄ via laser vacuum (1.0 × 10^− 3 Pa) high-temperature (1930 K to 2360 K) decomposition, which could serve as a reference for in-situ metal extraction on the Moon. First, the feasibility of this approach was verified through thermodynamic calculations. Subsequently, the effects of laser power and irradiation time on the vacuum smelting process of Fe₃O₄ were systematically investigated. The results indicated that the content of metallic iron in the product reached its maximum value (31.71%) at a laser power of 800 W and an irradiation time of 4 min. Furthermore, the distribution, morphology, and particle size of metallic iron in the product were investigated by scanning electron microscopy and X-ray computed tomography. The metallic iron was primarily enriched in the lower region of the product, presenting as aggregates of irregular fine particles. The particle size distribution was predominantly in the range of 10 to 100 μm (98%), with minor amounts in the 100 to 200 μm (1%) and 200 to 500 μm (1%) ranges.

Optical absorption spectroscopic investigation of a zircon from Afghanistan, unique in both size and color, show evidence that it represents a new type of purple color in this mineral. By microprobe and laser ablation-inductively coupled plasm (LA-ICP-MS) mass spectrometry analyses, the material is nearly pure ZrSiO₄. The contents of Nb, P, F, Na and Mn are under the detection limits in all point analyses. The mean values of K, Ca, Ti, Sm, Gd, Pb and Ho contents are below 0.001 apfu. The dark-purple, nearly black color of the zircon is thermally unstable. At annealing from 400 to 900 °C it gradually vanishes due to decrease of intensities of the high-energy absorption edge, the broad absorption bands with maxima at ~ 17,970 and 23,900 cm^− 1 (E⊥c) and ~ 18,620, 23,680 and 26,240 cm^− 1 (E||c). Intensities of the weak narrow lines of absorption, which are very likely caused by electronic spin-forbidden ff-transitions of uranium and REE ions, remain unchanged. The origin of the zircon is unclear. By ²⁰⁶Pb/²³⁸U radiometric age ~ 1909 million years, it is Proterozoic.

Cryptomelane (K-OMS-2) (K(Mn⁴⁺, Mn²⁺)₈O₁₆) is a manganese-oxide mineral that is abundant in soils and rock coatings globally and is gaining importance in materials science and industrial mineralogy. The crystal structure is composed of 2 × 2 octahedra that creates a tunnel space for K⁺. Low-weight percent (wt%) europium (Eu)-doped, high-wt% Eu-doped, low-wt% cerium (Ce)-doped, and high-wt% Ce-doped cryptomelane were synthesized for dynamic shock compression experiments using laser-driven flyer plates. Powder X-ray diffraction (XRD), high resolution inductively coupled plasma mass spectroscopy (HR-ICP-MS), transmission electron microscopy (TEM), and Raman spectroscopy (RS) were utilized to characterize the materials pre-shock. TEM and RS analysis of post-shocked material found that high-wt% Eu- and high-wt% Ce-cryptomelane were the most resistant to shock, showing the least amount of peak changes in RS and few amorphous regions in TEM. RS and TEM indicate disorder and defects are present in both high-wt% versions, such as changes in Mn–O bond length, wavy lattice fringes, and amorphous regions near the crystal surface. This study concludes that doped cryptomelane is more resistant to shock compression than unmodified cryptomelane. This study supports the previously proposed thixotropic rebound model as the proposed mechanism for cryptomelane’s shock resistance. During the shock wave, the nanoporosity of the material allows for the material to compress as the shock wave passes through the crystals before relaxing into a similar position as the original state. The addition of higher bond strength metals appears to enhance this overall effect. The results provide context for new material applications and future molecular dynamic modeling.