Physics and Chemistry of Minerals最新文献

In this work, we measured heat capacity and enthalpy of formation of synthetic mimetite phases with composition Pb₅(AsO₄)₃Cl_0.8(CO₃)_0.1 Pb₅(AsO₄)₃F, Pb₅(AsO₄)₃Br_0.8(CO₃)_0.1, Pb₅(AsO₄)₃OH_0.86(CO₃)_0.07, and Pb₅(AsO₄)₃I_0.45OH_0.35(CO₃)_0.1. Heat capacity has been measured using relaxation calorimetry and differential scanning calorimetry in the temperature range of 2.1–300 K and 280–770 K, respectively. The standard third-law entropy of phases in question, derived from the low-temperature heat capacity measurements, is S°_298.15K = 638.9 ± 4.5, 627.8 ± 4.4, 639.7 ± 4.5, 630.5 ± 4.5 and 637.7 ± 4.5 J mol⁻¹ K⁻¹, respectively. The measured enthalpies of formation derived from acid solution calorimetry are − 3068.7 ± 9.4, − 3001.4 ± 3.5, − 2963.4 ± 9.2, − 2919.1 ± 9.1, and − 2936.3 ± 8.7 kJ mol⁻¹, respectively. Some of the thermodynamic values deviate from previously determined data, most likely because of carbonate substitution in our samples.

We investigate the influence of short-range Mg–Fe cation ordering on the elastic and vibrational properties of olivine (Fe_xxMg_1-x)₂SiO₄ (0 < x < 1) and ferropericlase (Fe_xxMg_1-x)O (0 < x < 1) solid solutions using atomistic simulations based on empirical force fields. Supercells representing distinct local distributions of Mg and Fe cations around equiatomic composition (Fe:Mg 50:50, x 0.5) were generated and structurally relaxed. Short range order states include cation clustering, random cation ordering and preferred heteroatom paring. In both solid solution series, bulk physical properties, such as elastic moduli and seismic velocities, are primarily controlled by overall composition rather than the specific local cation arrangement. However, vibrational properties such as heat capacity and the phonon dispersion curves reveal a stronger sensitivity to short-range order. This sensitivity is enhanced in structurally simpler ferropericlase, while the increased structural complexity of olivine suppresses these differences.      

Two samples of natural gem-quality diaspore (“zultanite”) from Turkey and, for comparison, one sample of high-chromium diaspore from Saranovskoye chromite deposit in northern Urals, were studied by optical absorption spectroscopy. In the polarized spectra of “zultanites” there are two broad bands of Cr³⁺, caused by electronic spin-allowed transitions ⁴A_2g → ⁴T_2g and ⁴A_2g → ⁴T_1g, split by a low-symmetry crystal field of Cr³⁺ in the distorted octahedral structural position of Al³⁺. The spectral positions of the bands, especially of the former one, are close to that in Cr³⁺-bearing chrysoberyl (alexandrite), that causes a weak alexandrite-effect in “zultanites”. A few much weaker bands may be assigned to the spin-forbidden electronic transitions of Fe³⁺, also substituting Al³⁺ ions in the octahedral positions of the diaspore structure. The origin of a series of relatively narrow absorption bands in near UV-range, appearing on the background of a strong high-energy absorption edge, is not quite clear. A strong pleochroic absorption edge in the IR range is undoubtedly caused by O–H vibrations of hydroxyl groups in the structure of diaspore (α-AlOOH).

This study re-evaluates the selected area electron diffraction (SAED) patterns and electron energy-loss spectrum (EELS) presented by Shumilova et al. (https://doi.org/10.1134/S1028334X11110201), who have reported that they have found natural hexagonal 2H diamond in samples from the Kumdykol (Kumdy-Kol) diamond deposit. A thorough re-evaluation of the original SAED data indicates that a diffraction pattern previously attributed to monocrystalline 2H diamond is, with a very high degree of certainty, not the claimed phase, since it exhibits a much stronger resemblance with the calculated pattern of a high-pressure phase of 2H graphite, and even more with the pattern of a cubic, high-pressure form of silicon carbide. Due to the absence of EDX data, the question regarding the precise composition of this crystalline species could not be conclusively resolved. Furthermore, a second SAED pattern, previously interpreted as a 3C–2H diamond intergrowth, was found compatible with a topotactic 2H graphite–3C mineral association, known as ‘diaphite’, or with sp³-bonded polytypes (3C–2nH, n = 2, 4). A carbon core-loss EEL spectrum, which was used in Shumilova et al. (Dokl Earth Sci 441:1552–1554, 2011) to confirm the presence of 2H diamond, was found to match with that of the 3C diamond structure. While these results do not rule out the natural occurrence of 2H diamonds in general, the re-assessment of the in Shumilova et al. (Dokl Earth Sci 441:1552–1554, 2011) published SAED and EELS data provides no concrete evidence for the presence of monocrystalline 2H diamond in the earlier examined specimens from the Kumdykol site. A correction of the in Shumilova et al. (Dokl Earth Sci 441:1552–1554, 2011) made claims is therefore of significance, to avoid further bias in the ongoing discussion on the nature of the mineral lonsdaleite.

Iron oxide nanoparticles (IO-NPs) featuring synergistic hematite (α-Fe₂O₃) and goethite (α-FeO(OH)) phases were successfully synthesized via an eco-friendly green method using Pelargonium graveolens leaf extract as a natural reducing and stabilizing agent, with ferric chloride hexahydrate as the precursor. By systematically varying precursor concentration (25–200 mM) and applying controlled thermal annealing, we precisely tuned the phase composition: higher precursor concentrations favored goethite formation, while lower precursor concentration and elevated annealing temperatures promoted hematite crystallization. This dual-phase system facilitates enhanced electron transfer and reactive oxygen species (ROS) generation through Fe²⁺/Fe³⁺ redox cycling, underpinning the nanoparticles improved antibacterial efficacy. Comprehensive characterization was performed using field emission scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRPD), Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, and optical band gap analysis. Crystallite sizes and lattice strains were estimated via multiple models, including Scherrer, Monshi–Scherrer, Williamson–Hall, and size–strain plot methods, elucidating relationships between phase composition and structural attributes. Morphological studies revealed elongated hematite and needle-like goethite structures, with phase-dependent vibrational features confirmed by spectroscopic analyses. Antibacterial activities were assessed against Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) strains using well diffusion assays. Goethite-rich IO-NPs exhibited notable inhibition zones, achieving 25 ± 2 mm against S. aureus, attributed to enhanced ROS-mediated bacterial inactivation. Commercial gentamicin served as a positive control, contextualizing the clinical relevance of the green-synthesized IO-NPs. This work demonstrates that green synthesis-driven phase control enhances antibacterial performance via synergistic iron oxide phases and redox mechanisms, highlighting the potential of eco-friendly IO-NPs for sustainable biomedical and environmental applications.

Graphical Abstract

To date, studies on water distribution in opals (SiO₂.nH₂O, amorphous and porous) have considered opal exclusively in terms of silica structures (nanograins and aggregates such as spheres) without considering the, yet intrinsic, silica gel component. Consequently, its role in controlling both the water content and the distribution of water species (H₂O, SiOH) is still unresolved. In this study, Raman spectroscopy was applied to four calibrated synthetic opals representing varying ratios of silica structure and silica gel. The aim is to assess the nature of water in opal, especially regarding its bi-component nature. Our results show that an increase in the silica gel content in synthetic opals affects the content, type and proportion of water species by: (1) increasing the contribution of the bonded molecular water preferentially located in the porosity (H₂O type B) and the silanol groups present in the total amorphous structure (SiOH type A); (2) decreasing of the contribution of free molecular water (H₂O type A) and silanols groups adsorbed at the silica structure surface (SiOH type B). Moreover, the synthetic sample composed exclusively of silica structures (Op 1:0), which represent the theoretical model use to date, shows a systematic different behaviour to the other sample containing silica gel. All this exhibit that the silica gel phase plays an important role in the repartition of water in natural opals.

We report the dependence of the optical band gap on the crystallite size of SnO₂, co-occurring with impurities of Al, Cl, Ca, Fe, Mg, Na, and Si. SnO₂ nanoparticles with rod-like and polyhedral nanostructures were produced by precipitation methods using SnCl₄ as a precursor. The SnCl₄ precursor was synthesized through the chlorination of a pyrometallurgical product derived from tin ingots. The as-synthesized SnO₂ were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), transmission electron microscopy with energy-dispersive spectroscopy (TEM-EDS), X-ray photoelectron spectroscopy (XPS), and UV–Vis’s spectroscopy. The rod-like and polyhedral SnO₂ particles exhibited a tetragonal crystal structure (space group P4₂/mnm). The band gap estimated from the UV–Vis spectra ranged from 3.58 to 3.70 eV. Quantum confinement effects were observed in the increase of the optical band gap as the crystallite size of SnO₂ decreased. A blue shift in the optical absorption was observed in SnO₂ nanoparticles with elevated chloride concentration.

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.