Physics and Chemistry of Minerals最新文献

We have conducted electrical conductivity measurements of FeCO₃ siderite under high pressure up to 63 GPa in order to understand the nature and effect of iron spin transition and its influence on the geophysical properties of siderite, which is an end-member of major carbonate minerals. The results from Raman and Mössbauer spectroscopic measurements show that the high- to low-spin transition of iron occurs at around 50 GPa in agreement with previous studies. A sharp decrease of the electrical conductivity was also observed at around 50 GP, which is associated with the spin transition in iron. Although the stability of FeCO₃ siderite may be limited under high-temperature conditions along with the mantle geotherm, solid solutions in the MgCO₃-FeCO₃ system, Mg_1-xFe_xCO₃, could be stable up to the pressure-temperature condition of the lowermost mantle. The pressure-temperature range of the spin transition in Mg_1-xFe_xCO₃ is narrower than those of the major lower mantle minerals, ferropericlase and bridgmanite, and thus the drop of the electrical conductivity induced by the spin transition could be clearer under lower mantle conditions. Therefore, the existence of Mg_1-xFe_xCO₃ may affect the observed heterogeneity of electrical conductivity in the mid-lower mantle.

In the present review work, it is proposed to carry out a bibliographic analysis about the thermal behaviour of the dolomitic mineral. The state of the art of dolomite currently indicates a growing use as a refractory material due to the cheaper alternative it represents compared to other materials such as magnesium oxide. The importance of dolomite apart from its application in the steel industry lies in the fact that it has expanded to other industrial fields such as the production of catalysts, catalyst supports, and industrial effluent purification materials. In these and other applications, understanding the thermal behaviour of the material is necessary to evaluate the feasibility of application. In this review, the different experimental proposals developed over time in terms of thermal behaviour are studied, emphasizing the reaction mechanisms that have been proposed in different investigations.

The thermal expansion coefficient of talc has been measured using a high-temperature thermal optical expansion apparatus over a temperature range of 296 to 1473 K. The results show a gradual increase in the thermal expansion coefficient between 296 and 1086 K, and a rapid and substantial increase between 1086 and 1316 K, but exhibit a decline trend between 1316 and 1473 K. At lower temperatures, changes in crystal structure are the primary mechanism governing thermal expansion; at higher temperatures, the dehydration phase transition and the resulting formation of cracks are the primary contributors to thermal expansion. The volume of talc exhibits a linear increase with temperature, described by the equation:(V/{V}_{0}=1+2.153 left( pm 0.011right)times {10}^{-5} left(T-296right)). At high temperatures (573–1073 K), by fitting the expansion data to the Grüneisen thermal equation of state, bulk modulus K_0​ = 47.3 ± 0.9 GPa, pressure derivative ({K}_{0}^{{prime }}left(Tright)) = 6.2 ± 0.4, cell volume V₀​ = 904.5 ± 0.6 ų, and Debye temperature θ = 829.3 ± 0.6 K were obtained at 0 K. The presence of talc reduces the density of subduction zones, facilitating the exhumation of oceanic eclogites.

Phase transformations of the charoite mineral induced by thermal treatment at high temperatures were studied by simultaneous monitoring of the thermogravimetry, differential scanning calorimetry, and mass spectrometry curves up to its melting temperature range (~ 1300 °C). The chemical composition and phase state of the initial and melted samples were characterized using electron-probe micro-analysis, X-ray photoemission spectroscopy, X-ray powder diffraction, and Raman spectroscopy. It was demonstrated that continuous heating (10 °C/min) up to ~ 500 °C resulting in a mass loss of ~ 5 wt. % was due to crystallization water release and dehydroxylation, while oxygen release and carbonate inclusion decomposition were observed at a higher temperature. The endothermic peak with a heat effect of 82 J/g observed at 970 ÷ 1050 °C was attributed to the charoite-to-wollastonite transition detected by real-time X-ray powder diffraction in this temperature range. Above 1100 °C, another extended endothermic effect was fixed, which was presumably due to the formation of pseudowollastonite and pre-melting processes. The melting of the charoite sample using the floating zone technique resulted in its transformation to pseudowollastonite and caused a significant color change from lilac to rose pink.

Synthetic Sc-bearing clinozoisite on the Ca₂Al₃Si₃O₁₂(OH)-Ca₂Al₂Sc³⁺Si₃O₁₂(OH) join was studied by single-crystal X-ray diffraction to understand better the distribution of Sc³⁺ among the octahedral sites, M1-M3, and its effect on the structure of epidote-group minerals. Oxide starting materials of Ca₂Al₂(Al_1-p)Sc_pSi₃O_12.5 composition with p = 0.5 and 1.0 were employed, and clinozoisite was successfully synthesized at P_H2O = 1.2–1.5 GPa and T = 700–800 °C. The Sc content in clinozoisite varies and attains 0.61 atoms per formula unit (apfu) from p = 1.0 starting material. Two Sc-bearing clinozoisite crystals from the product of p = 0.5 starting material (Run 20) were used for X-ray crystal structural analysis. The unit-cell parameters are a = 8.8815(4), b = 5.6095(2), c = 10.1466(5) Å, β = 115.318(6)º, and V = 457.0(1) ų for 20B, and a = 8.885(1), b = 5.6119(4), c = 10.153(1) Å, β = 115.27(2)º, and V = 457.9(4) ų for 20D. The resulting Sc³⁺ occupancies among the octahedral sites are ^M1Al_1.0^M2Al_1.0^M3(Al_0.684(7)Sc³⁺_0.316) for the former and ^M1Al_1.0^M2Al_1.0^M3(Al_0.629(6)Sc³⁺_0.371) for the latter, i.e., Sc³⁺ exclusively occupies M3. The mean ionic distance of < M3–O > increases with increasing Sc content at M3, but it tends to be slightly shorter than the expected value using the regression line based on the structural data of synthetic Ca₂(Al, Me³⁺)₃Si₃O₁₂(OH) clinozoisite. It is due to the reduced distortion of M3O₆ octahedra caused by the short M3–O1 and M3–O8 distances. Although the angular variance ends up at a similar value to the Al-Fe³⁺ epidote, the variation of ∠Oi–M3-Oi angles is different. The Sc-bearing clinozoisite has greater ∠O1–M3–O1’, but smaller ∠O2–M3–O2’ and ∠O2–M3–O4 relative to Al-Fe³⁺ series ones. Due to different local chemical surroundings, multiple peaks are present in the OH stretching region of Raman spectra. Three OH-stretching peaks, centered at 3342, 3382, and 3468 cm⁻¹ are assigned to the local configuration O10–H···O4–(^M1Al^M1Al^M3Sc³⁺) and O10–H···O4–(^M1Al^M1Al^M3Al), and O10–H···O2, respectively.

To support the role of proximal and remote sensing in geological rare earth element (REE) resource exploration, we studied the reflectance spectroscopy of synthetic single- and mixed-REE phosphate phases. Synthesis yielded monazite for the elements La to Gd, and xenotime for Dy to Lu and Y. Visible-to-shortwave infrared (350–2500 nm) reflectance spectra of synthetic single-REE monazites and xenotimes can be used to identify the ions responsible for the absorption features in natural monazites and xenotimes. Nd³⁺, Pr³⁺ and Sm³⁺ produce the main absorption features in monazites. In natural xenotime, Dy³⁺, Er³⁺, Ho³⁺ and Tb³⁺ ions cause the prevalent absorptions. The majority of the REE-related absorption features are due to photons exciting electrons within the 4f subshell of the trivalent lanthanide ions to elevated energy levels resulting from spin-orbit coupling. There are small (< 20 nm) shifts in the wavelengths of these absorptions depending on the nature of the ligands. The energy levels are further split by crystal field effects, manifested in the reflectance spectra as closely spaced (∼ 5–20 nm) multiplets within the larger absorption features. Superimposed on the electronic absorptions are vibrational absorptions in the H₂O molecule or within [OH]⁻, [CO₃]²⁻ and [PO₄]³⁻ functional groups, but so far only the carbonate-related spectral features seem usable as a diagnostic tool in REE-bearing minerals. Altogether, our study creates a strengthened knowledge base for detection of REE using reflectance spectroscopy and provides a starting point for the identification of REE and their host minerals in mineral resources by means of hyperspectral methods.

Access to synchrotron X-ray facilities has become an important aspect for many disciplines in experimental Earth science. This is especially important for studies that rely on probing samples in situ under natural conditions different from the ones found at the surface of the Earth. The non-ambient condition Earth science program at the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, offers a variety of tools utilizing the infra-red and hard X-ray spectrum that allow Earth scientists to probe Earth and environmental materials at variable conditions of pressure, stress, temperature, atmospheric composition, and humidity. These facilities are important tools for the user community in that they offer not only considerable capacity (non-ambient condition diffraction) but also complementary (IR spectroscopy, microtomography), and in some cases unique (Laue microdiffraction) instruments. The availability of the ALS’ in situ probes to the Earth science community grows especially critical during the ongoing dark time of the Advanced Photon Source in Chicago, which massively reduces available in situ synchrotron user time in North America.

Nefedovite, Na₅Ca₄(PO₄)₄F, has been investigated by in situ high-temperature powder (30–690 °C) and single crystal (27–827 °C) X-ray diffraction and Raman spectroscopy. Nefedovite is tetragonal, space group I-4, a = 11.6560(2), c = 5.4062(2) Å, V = 734.50(2) ų (R₁ = 0.0149). Nefedovite is a 1D antiperovskite, since its crystal structure contains chains of corner-sharing anion-centered [FCa₄Na₂]⁹⁺ octahedra. The chains are parallel to the c direction. Nefedovite is stable up to 727 °C and undergoes a displacive phase transition in the temperature range 277–327 °C. With increasing temperature, the PO₄ tetrahedra in the crystal structure of nefedovite gradually rotate around the imaginary fourfold inversion axes aligning the O2^…O3 edge parallel to [110], which ultimately leads to the appearance of the mirror plane perpendicular to the c direction and the change of space group from I-4 (82) to I4/m (87). The crystal structure of nefedovite expands strongly anisotropically with the direction of the maximum thermal expansion oriented perpendicular to the chains of anion-centered octahedra. The information-based structural complexity analysis demonstrates that both low- and high-temperature modifications of nefedovite are structurally simple with the I_G,total value less than 100 bits per unit cell. The structural complexity decreases along the phase transition, which is typical for displacive phase transitions.

Aside from its economic value, davidite and its synthetic analogs may have potential applications in materials science. The unique properties of the crichtonite group minerals, including davidite-(La), make them attractive candidates for high-level waste (HLW) immobilization. We studied the thermal evolution of the metamict davidite-(La) from the Radium Hill, Australia. The investigation of the temperature-induced crystallization process was conducted, and the thermal expansion coefficients (TEC) for the recrystallized davidite (RD) were determined for the first time. Our results demonstrate that RD has relatively low TEC indicating its thermophysical stability. The following TECs of davidite- (La) for the temperature range 25–1200 °C were obtained: (overline{mathrm{alpha }}) _a = (overline{mathrm{alpha }}) _b = 9.96 (3) × 10^–6 ºC⁻¹; (overline{mathrm{alpha }}) _c = 10.79 (4) × 10^–6 ºC⁻¹. The character of the thermal expansion is in agreement with the structure characterized by layers stacked along the c axis. The volume TEC α_V = 24.81 (47)—36.80 (48) × 10^–6 ºC⁻¹. Davidite-(La) exhibits an almost isotropic thermal expansion and shows one of the most superior thermal performances in comparison to the other mineral-like phases utilized for the immobilization of HLW.

Iron hydroxide FeO₂H_x (x ≤ 1) and ferrous iron chloride FeCl₂ can adopt the HP-PdF₂-type (space group: (P{a_{overline 3 }}), Z = 4) structure in the lowermost mantle, potentially contributing to the geochemical cycles of hydrogen and chlorine within Earth’s deep interior, respectively. Here we investigate the high-pressure behavior of HP-PdF₂-type FeCl₂ by X-ray diffraction (XRD) and Raman measurements in laser-heated diamond anvil cells. Our results show that HP-PdF₂-type FeCl₂ can be formed at 60‒67 GPa and 1650‒1850 K. Upon cold decompression, the diffraction peaks at pressures above 10 GPa can be indexed to the HP-PdF₂-type structure. Intriguingly, the calculated cell volumes reveal a remarkable decrease of ΔV / V = ∼ 14% between 36 and 40 GPa, which is possibly caused by a pressure-induced spin transition of Fe²⁺ (HS: high-spin → LS: low-spin). We also observe distinct changes in Raman spectra at 33‒35 GPa, practically coinciding with the onset pressures of isostructural phase transition in XRD results. Our observations combined with previous studies conducted at megabar pressures suggest that HP-PdF₂-type FeCl₂, with a wide pressure stability range, if present in subducting slabs, could facilitate the transport of chlorine from the middle lower mantle to the outer core.