Subjects -> MINES AND MINING INDUSTRY (Total: 82 journals)
 Showing 1 - 42 of 42 Journals sorted by number of followers Stainless Steel World       (Followers: 18) Journal of Applied Geophysics       (Followers: 16) Journal of Metamorphic Geology       (Followers: 15) International Journal of Hospitality & Tourism Administration       (Followers: 14) European Journal of Mineralogy       (Followers: 12) Journal of Geology and Mining Research       (Followers: 11) Contributions to Mineralogy and Petrology       (Followers: 11) Mineral Processing and Extractive Metallurgy : Transactions of the Institutions of Mining and Metallurgy       (Followers: 11) Transactions of Nonferrous Metals Society of China       (Followers: 10) Journal of Human Resources in Hospitality & Tourism       (Followers: 9) Clay Minerals       (Followers: 9) Minerals Engineering       (Followers: 9) Lithos       (Followers: 9) International Journal of Minerals, Metallurgy, and Materials       (Followers: 9) Natural Resources Research       (Followers: 8) Geotechnical and Geological Engineering       (Followers: 8) Rock Mechanics and Rock Engineering       (Followers: 7) International Journal of Rock Mechanics and Mining Sciences       (Followers: 6) Canadian Mineralogist       (Followers: 6) International Journal of Mining Engineering and Mineral Processing       (Followers: 5) Journal of Quality Assurance in Hospitality & Tourism       (Followers: 5) Mine Water and the Environment       (Followers: 5) International Journal of Mining and Mineral Engineering       (Followers: 5) Journal of the Southern African Institute of Mining and Metallurgy       (Followers: 5) Mining Engineering       (Followers: 5) Resources Policy       (Followers: 4) International Journal of Mining Science and Technology       (Followers: 4) Reviews in Mineralogy and Geochemistry       (Followers: 4) Mineral Processing and Extractive Metallurgy Review       (Followers: 4) Applied Earth Science : Transactions of the Institutions of Mining and Metallurgy       (Followers: 4) International Journal of Mining, Reclamation and Environment       (Followers: 4) International Journal of Coal Geology       (Followers: 4) Physics and Chemistry of Minerals       (Followers: 4) Journal of Convention & Event Tourism       (Followers: 4) Mineralium Deposita       (Followers: 4) Lithology and Mineral Resources       (Followers: 3) Journal of Sustainable Mining       (Followers: 3) International Journal of Coal Science & Technology       (Followers: 3) Mining Journal       (Followers: 3) Ghana Mining Journal       (Followers: 3) Geology of Ore Deposits       (Followers: 3) Rocks & Minerals       (Followers: 3) Environmental Geochemistry and Health       (Followers: 2) Journal of Mining Science       (Followers: 2) Geomaterials       (Followers: 2) Mineralogia       (Followers: 2) BHM Berg- und Hüttenmännische Monatshefte       (Followers: 2) Mining Technology : Transactions of the Institutions of Mining and Metallurgy       (Followers: 2) Extractive Industries and Society       (Followers: 2) International Journal of Coal Preparation and Utilization       (Followers: 2) Mineralogy and Petrology       (Followers: 2) Mining Report       (Followers: 2) Neues Jahrbuch für Mineralogie - Abhandlungen       (Followers: 2) Archives of Mining Sciences       (Followers: 2) Journal of Materials Research and Technology       (Followers: 2) Gems & Gemology       (Followers: 1) Journal of Analytical and Numerical Methods in Mining Engineering       (Followers: 1) Rangeland Journal       (Followers: 1) Revista del Instituto de Investigación de la Facultad de Ingeniería Geológica, Minera, Metalurgica y Geográfica       (Followers: 1) Journal of Central South University       (Followers: 1) Mineralogical Magazine       (Followers: 1) CIM Journal Natural Resources & Engineering Mining, Metallurgy & Exploration Podzemni Radovi Rudarsko-geološko-naftni Zbornik Journal of Mining Institute International Journal of Mining and Geo-Engineering Journal of China Coal Society Réalités industrielles Mineral Economics Minerals Gold Bulletin Minerals & Energy - Raw Materials Report
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 Physics and Chemistry of MineralsJournal Prestige (SJR): 0.702 Citation Impact (citeScore): 2Number of Followers: 4      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1432-2021 - ISSN (Online) 0342-1791 Published by Springer-Verlag  [2469 journals]
• Equations of state of clino- and orthoenstatite and phase relations in the
MgSiO3 system at pressures up to 12 GPa and high temperatures

Abstract: Abstract The equations of state of MgSiO3-pyroxenes (low-pressure clinoenstatite, orthoenstatite and high-pressure clinoenstatite) are constructed using a thermodynamic model based on the Helmholtz free energy and optimization of known experimental measurements and calculated data for these minerals. The obtained equations of state allow us to calculate a full set of thermodynamic and thermoelastic properties as depending on T–P or T–V parameters. We offer open working MS Excel spreadsheets for calculations, which are a convenient tool for solving various user’s tasks. The phase relations in the MgSiO3 system are calculated based on the estimated Gibbs energy for studied MgSiO3-pyroxenes and clarify other calculated data at pressures up to 12 GPa and temperatures up to 2000 K. The obtained orthoenstatite → high-pressure clinoenstatite phase boundary corresponds to the following equation P(GPa) = 0.0021 × T(K) + 4.2. The triple point of equilibrium is determined at 1100 K and 6.5 GPa. Isotropic compressional (P) and shear (S) wave velocities of orthoenstatite and high-pressure clinoenstatite at different pressures are calculated based on the obtained equations of state. The calculated jumps of P- and S-wave velocities of orthoenstatite → high-pressure clinoenstatite phase transition at a pressure of ~ 9 GPa are 0.7 and 5.1%, respectively. The calculated jump of the density of this phase transition at a pressure of 8 GPa, which corresponds to the depth of ~ 250 km, is 2.9%. These results are used to discuss the location of the seismic X-discontinuity at the depths of 250–340 km, which is associated with phase boundaries in enstatite.
PubDate: 2022-08-15

• Overview of HPCAT and capabilities for studying minerals and various other
materials at high-pressure conditions

Abstract: Abstract High-Pressure Collaborative Access Team (HPCAT) is a synchrotron-based facility located at the Advanced Photon Source (APS). With four online experimental stations and various offline capabilities, HPCAT is focused on providing synchrotron x-ray capabilities for high pressure and temperature research and supporting a broad user community. Overall, the array of online/offline capabilities is described, including some of the recent developments for remote user support and the concomitant impact of the current pandemic. General overview of work done at HPCAT and with a focus on some of the minerals relevant work and supporting capabilities is also discussed. With the impending APS-Upgrade (APS-U), there is a considerable effort within HPCAT to improve and add capabilities. These are summarized briefly for each of the end-stations.
PubDate: 2022-08-15

• Phase transitions and compressibility of alkali-bearing double carbonates
at high pressures: a first-principles calculations study

Abstract: Abstract Here, we investigated high-pressure behaviors of four end-members of K-Na-Ca-Mg alkali-bearing double carbonates (K2Mg(CO3)2, K2Ca(CO3)2, Na2Mg(CO3)2, and Na2Ca(CO3)2) using first-principles calculations up to ~ 25 GPa. For K2Mg, K2Ca, and Na2Mg double carbonates, the transitions from rhombohedral structures (R $$\stackrel{\mathrm{-}}{3}$$ m or R $$\stackrel{\mathrm{-}}{3}$$ ) to monoclinic (C2/m) or triclinic (P $$\stackrel{\mathrm{-}}{1}$$ ) structures are predicted. While for Na2Ca(CO3)2, the P21ca structure remains stable across the calculated pressure range. But the high-pressure behavior of Na2Ca double carbonate has changed over 8 GPa: the b-axis becomes more compressible than a-axis; [CO3] –I groups tilt out of the a-b plane upon compression and reverse the direction of rotation at 8 GPa. The parameters for the equations of state of these minerals and their high-pressure phases were all theoretically determined. The predicted transformation is driven by the differences in the compressibility of structural units. The K+ and Na+ coordination polyhedra are more compressible in the structure, compared with the high axial rigidity of C–O bonds in the [CO3] triangle along the a-b plane. Our results provide projections of the high-pressure behaviors of trigonal double carbonates, in part by helping to clarify the relation among the average metallic ionic radius (Ravg), the bulk modulus (K0), and the transition pressure (PT). The transition pressure (PT) is anticorrelated to the average metallic ionic radius (Ravg), and a larger Ravg results in a lower bulk modulus (K0) for the trigonal double carbonates. Furthermore, alkali-bearing double carbonates found as inclusions in the natural diamond may indicate a hydrous parental medium composition and a deeper genesis mechanism.
PubDate: 2022-08-02

• High-pressure Cr3+ R-line luminescence of zoisite and kyanite: a probe of
octahedral site distortion

Abstract: Abstract The Cr3+ luminescence spectra of zoisite and kyanite, two geologically important minerals, were studied up to 40 and 20 GPa, respectively, in various pressure media. Cr3+ substitutes into the octahedral aluminum sites in both minerals and the R-line luminescence is a particularly sensitive site-specific probe of the octahedral Al site. Unlike many previous studies where Cr3+ luminescence was utilized, both these minerals have multiple highly distorted octahedral sites resulting in very large splitting of their R-lines, ~ 300 cm−1 in zoisite and ~ 360 cm−1 in kyanite (for reference, ruby is 29 cm−1). For zoisite, the R-line splitting increases as pressure increases and more than triples from its ambient value by 40 GPa, while the R-line splitting in kyanite from the M1 and M2 sites does not change when compressed in a Ne pressure medium up to 20 GPa. We do not observe evidence of any phase transitions in either zoisite or kyanite across the pressure range of these new luminescence measurements. We present some high-pressure luminescence results where kyanite was known to be bridged between the diamond anvils and show how these spectra illustrate the different effect of uniaxial relative to hydrostatic stress on luminescence spectra.
PubDate: 2022-08-02

• Atomic and microstructural origin of banded colours in purple-blue variety
of agate from Yozgat Province, Turkey

Abstract: Abstract Agates from Yozgat province are appreciated on the gem market for their white and purple-blue banded colours. In this study, we present a detailed investigation aimed at the identification of the atomic and structural origin of this peculiar colouration of chalcedony. X-ray diffraction and Raman spectroscopy revealed the presence of fine grains of quartz and moganite with a preferential accumulation of the latter in the blue bands. Near-infrared diffuse absorption spectra show overtones of hydroxyls vibrations at 1425, 1900, and 2250 nm. In the visible, the broad absorption at about 500 nm, as well as its behaviour at low temperatures, is compatible with the optical activity of iron impurities in quartz matrices, such as that observed in amethysts. Peak intensities and shapes are very similar for spectra collected in blue and white bands. Accordingly, trace-element composition from laser ablation inductively coupled mass spectrometry confirmed that the two regions have similar Fe content. The perceived changes in band colours are indeed originated by differences in microstructural arrangement and size of the grains visualised through scanning electron microscopy. White and blue stripes have grains of about 5 µm and 300 nm in size, respectively, resulting in an accentuated scattering component for the white bands. Therefore, the unique purple-blue shades typical of Yozgat agates are a combination of iron-related colour centres and scattering effect.
PubDate: 2022-07-26

• GeoSoilEnviroCARS (Sector 13) at the Advanced Photon Source: a
comprehensive synchrotron radiation facility for Earth science research at
ambient and extreme conditions

Abstract: Abstract GeoSoilEnviroCARS (GSECARS) is a comprehensive analytical laboratory for Earth and environmental science research using X-ray beams from the Advanced Photon Source, Argonne National Laboratory. State-of-the-art instruments are available for (1) high-pressure/high- or low-temperature diffraction, total scattering, and spectroscopy (Brillouin, Raman, and VIS-IR) using the laser heated diamond anvil cell (DAC); (2) high-pressure/high-temperature diffraction, scattering, and imaging as well as acoustic emission (AE) and ultrasonics using the large-volume press (LVP); (3) powder, single crystal, and surface/interface diffraction; (4) X-ray absorption fine structure spectroscopy; (5) X-ray fluorescence microprobe analysis; and (6) microtomography. Experiments are facilitated by senior level staff who collaborate on all aspects of the analytical work including experiment design, sample preparation, data collection, data interpretation, and publication preparation. Both technical and scientific synergies occur as a result of the intimate association of the various techniques and scientists experienced in the applications of synchrotron radiation to Earth, environmental, and planetary science problems. The facility includes state-of-the-art instrumentation designed and built in-house, including custom X-ray optics, online and offline laser-based systems, specialized sample environments and positioning systems, as well as pixel-array and multi-crystal energy dispersive X-ray detectors, which are available to be shared among the experimental stations.
PubDate: 2022-07-26

• Fast anisotropic Mg and H diffusion in wet forsterite

Abstract: Abstract Adding hydrogen to forsterite strongly increases the diffusion rate of Mg, but the reason for this is unclear. As Mg diffusion in forsterite can influence its electrical conductivity, understanding this process is important. In this study we use density functional theory to predict the diffusivity of H-bearing Mg vacancies and we find that they are around 1000 times slower than H-free Mg vacancies. H-bearing Mg vacancies are many orders of magnitude more concentrated than H-free Mg vacancies, however, and diffusion is a combination of diffusivity and defect concentration. Overall, the presence of hydrated Mg vacancies is predicted to cause a large (multiple orders of magnitude) increase in both diffusion rate and diffusional anisotropy with a strong preference for diffusion in the [001] direction predicted. In models of experimental data, the effect of water concentration on diffusion is often described by a constant best-fitting exponent. Our results suggest that this exponent will vary between 0.5 and 1.6 across common experimental conditions with pressure decreasing and temperature increasing this exponent. These results suggest that Mg diffusion in forsterite could vary considerably throughout upper mantle conditions in ways that cannot be captured with a simple single-exponent model. Comparisons to measures of hydrogen diffusivity suggest that the diffusion of hydrated Mg vacancies also controls the diffusion of hydrogen in (iron-free) forsterite and that our conclusions above also apply to hydrogen diffusion rates and anisotropy. We also find that cation diffusivity likely cannot explain experimental measurements of the effect of water on electrical conductivity in olivine.
PubDate: 2022-07-25

• Ultimate mechanical properties of enstatite

Abstract: Abstract The ultimate mechanical properties of MgSiO3 orthoenstatite (OEN), as characterized here by the ideal strengths, have been calculated under tensile and shear loadings using first-principles calculations. Both ideal tensile strength (ITS) and shear strength (ISS) are computed by applying homogeneous strain increments along high-symmetry directions ([100], [010], and [001]) and low index shear planes ((100), (010), and (001)) of the orthorhombic lattice. We show that the ultimate mechanical properties of OEN are highly anisotropic during tensile loading, with ITS ranging from 4.5 GPa along [001] to 8.7 GPa along [100], and quite isotropic during the shear loading with ISS ranging from 7.4 to 8.9 GPa. During tensile test along [100] and [001], a modified structure close to OEN has been found. This modified structure is more stable than OEN under stress (or strain). We have characterized its elastic and ultimate properties under tensile loading. With ITS ranging from 7.6 GPa along [010] to 25.6 GPa along [001], this modified structure appears to be very anisotropic with exceptional strength along [001].
PubDate: 2022-07-11

• Application of the double-difference relocation method to acoustic
emission events in high-pressure deformation experiments

Abstract: Abstract A methodology has been developed, detailing the theory and workflow, for applying the double-difference relocation method to acoustic emission (AE) event location in high-pressure/high-temperature deformation experiments in the multi-anvil apparatus. The process is predicated on the fact that events originating from a common source region will traverse similar ray paths from the source to the receiver and display similar waveforms in seismograms. This implies their travel-time difference results only from their spatial offset and any velocity heterogeneity along the ray path is negated. To demonstrate the efficacy of this approach we applied it to a transformational faulting experiment on the isostructural olivine analogue Mg2GeO4 under controlled deformation at 2.5 GPa and 700 °C while simultaneously monitoring stress, strain, and acoustic activity. Waveforms from all 1456 AE events were cross-correlated to measure differential arrival times and construct multiplet groups of similar events. In total, 110 multiplets were identified whose size is dominated by two large groups containing 272 and 202 events. Relocation of these two multiplets using the double-difference method significantly reduces event separation and improves location uncertainty by more than an order of magnitude when compared to absolute location techniques whose uncertainty rivals that of the sample size. In particular, event locations of the two largest multiplets reveal two dense clusters whose spatial geometry closely mirrors that of macroscopic faulting displayed in computerized tomography images of the recovered sample. In this way, we are able to link specific faults with their associated AE events, which would otherwise not be possible using traditional absolute location methods.
PubDate: 2022-07-06

• Grain growth inhibited during grain size-sensitive creep in
polycrystalline ice: an energy dissipation-rate perspective

Abstract: Abstract Experiments in which two identical polycrystalline ice Ih specimens are simultaneously subjected to the same time–temperature history while one of the specimens is actively deformed via grain size-sensitive (GSS) creep demonstrate distinctly different microstructural evolution: for particular ranges of starting grain size and differential stress, grains do not grow in the deforming specimen. Ice Ih specimens having initial, uniform grain sizes in the range d = 6–63 μm were tested in pairs that were subjected to identical time–temperature conditions (durations t = 4–12 days; T = 240 K) but of which only one was subjected to differential stress (σ1 = 0.25–1.85 MPa; σ3 = 0). Comparing specimens within a pair, for those with coarser initial grain size, the deformed specimens exhibit suppressed or no grain growth. Our results are interpreted from the perspective of nonequilibrium thermodynamics, specifically comparing the energy dissipation rates associated with both grain growth and plastic flow: if the rate of energy dissipation associated with flow exceeds that of grain growth, the grains will not grow. An examination of the limited database on GSS flow and grain growth in silicates conforms to our analysis. The results are applied to the question of the mechanical evolution of terrestrial glaciers and to the ice-rich shells of the outer satellites.
PubDate: 2022-07-02

• Equation of state of elbaite at high pressure up to 21.1 GPa and room
temperature

Abstract: Abstract The equation of the state of a natural elbaite sample has been investigated at room temperature and up to 21.1 GPa for the first time using in situ synchrotron X-ray diffraction in this study. No phase transition is observed on elbaite over the experimental pressure range. The pressure–volume data were fitted by the third-order Birch-Murnaghan equation of state (EoS) with the zero-pressure unit-cell volume V0 = 1540.7 (6) Å3, the zero-pressure bulk modulus KT0 = 114.7 (7) GPa, and its pressure derivative K'T0 = 4.2 (1), while obtained V0 = 1540.1 (4) Å3 and KT0 = 116.4 (4) GPa when fixed K'T0 = 4. Furthermore, the axial compressional behavior of elbaite was also fitted with a linearized third-order Birch-Murnaghan EoS, the obtained axial moduli for a-axis and c-axis are Ka0 = 201 (4) GPa and Kc0 = 60 (1) GPa, respectively. The axial compressibilities of a-axis and c-axis are βa = 1.66 × 10–3 GPa−1 and βc = 5.56 × 10–3 GPa−1 with an anisotropic ratio of βa: βc = 0.30: 1.00, which shows an intense axial compression anisotropy. The potential influencing factors on the bulk moduli and the anisotropic linear compressibilities of tourmalines were further discussed.
PubDate: 2022-07-02

• Thermal annealing of fission and ion tracks in epidote

Abstract: Abstract Fission tracks are used for geologic age-dating and for the reconstruction of thermal histories of Earth’s upper crust. However, there remains a gap in the understanding between the atomic-scale annealing mechanism of latent (unetched) fission tracks and the observations of etched tracks at the micrometer scale. This is because the structure of latent fission tracks is lost during the leaching process. We have conducted the first comparison of the thermal-annealing behavior of latent and etched tracks in epidote, using transmission electron microscopy (TEM) and optical microscopy, respectively. For high-resolution TEM observations, we used ion tracks instead of fission tracks to control the density of tracks, and we demonstrated that latent ion tracks are amorphous in epidote. The reduction in diameters of latent tracks is insignificant after thermal annealing at 800 °C for 24 h, indicating that the track diameter does not appear to change substantially until the final stage of annealing. The optical observations show that the parallel etched ion-induced tracks have a lower track density reduction rate at or below 500 °C and an accelerated reduction rate above 500 °C as compared with randomly oriented fission tracks. However, the two types of tracks display a comparable thermal-annealing behavior as evidenced by the fit of the two curves for the normalized density of ion and fission tracks as a function of temperature with the same equation but with different fitting parameters. Thus, ion-induced tracks can be used to simulate fission tracks in epidote and provide a basis for understanding the annealing of latent and etched tracks.
PubDate: 2022-06-29

• High-pressure behaviour of stellerite: single-crystal X-ray diffraction
study

Abstract: Abstract The high-pressure (HP) behavior of natural stellerite Ca4.00Na0.16 (H2O)32  [Al8.16Si27.84O72] has been studied by single-crystal X-ray diffraction using a diamond-anvil cell under pressures up to 4.5 GPa, with a 4:1 ethanol:water mixture and paraffin as pressure-transmitting media. The changes in the structure of stellerite at high pressures, especially the STI framework deformation, are similar to those in Na-rich stilbite Ca4.00Na1.47 (H2O)30  [Al9.47Si26.53O72]. Both stilbite and stellerite udergo pressure-induced hydration, in which H2O molecules first occupy partly vacant sites and then the initially vacant positions. Some difference in the behavior of the two minerals is due to the presence of Na+ cations in stilbite. Sodium occupies positions in the 10-membered ring and prevents H2O molecules from penetrating near the ring center. Meanwhile, both stellerite and stilbite can fill the initially vacant sites in the 8-membered ring at high pressures. The pressure-induced changes, including the reduction of H2O sites in the cation coordination and a total number of H2O molecules, are less significant in Na-bearing stilbite than in stellerite.
PubDate: 2022-06-29

• In-situ high-pressure and high-temperature spectroscopic studies of
phengite in ultrahigh-pressure eclogite: implications for water transport
during ultra-deep continental subduction

Abstract: Abstract Pressure and temperature responses of natural phengite [K0.93Na0.03(Al1.46Mg0.45Fe0.09)(Si3.59Al0.39Ti0.02)O10(OH1.94F0.06)] in ultrahigh-pressure eclogite from the main hole of the China Continental Scientific Drilling Project (CCSD), the Dabie-Sulu orogenic belt have been studied using in-situ high-pressure mid-infrared and high-temperature Raman spectroscopic measurements up to ~ 20 GPa and 800 °C, respectively. Linear positive pressure dependences were observed for the infrared absorption bands associated with the aluminosilicate vibrations up to ~ 19 GPa, indicating the steady compression of the structure framework. The frequencies of the O–H stretching doublet bands, initially at 3601 and 3626 cm−1, displayed linear downshifts up to 16.6 GPa at − 2.02 and − 2.72 cm−1/GPa, respectively, implying high stability of the hydroxyl groups under compression. In the high-temperature Raman spectra, the bands initially centered at 265, 420, 703 cm−1, and the O–H stretching modes at 3620 cm−1 exhibited modest linear negative shifts with increasing temperature up to 800 °C. Comparisons between experimental results of the present study and those of the previous studies make it plausible that phengite with a higher Si content, i.e., a higher tetrahedral Si/Al ratio, would have higher stabilities under both high pressure and high temperature, and is likely to transport water to greater depths during subduction processes.
PubDate: 2022-06-23

• Crystal structure and investigation of Bi2TeO6·nH2O (0 ≤ n ≤
$${\raise0.5ex\hbox{\scriptstyle 2} \kern-0.1em/\kern-0.15em \lower0.25ex\hbox{\scriptstyle 3}}$$ 2 / 3 ): natural and synthetic
montanite

Abstract: Abstract The crystal structure of montanite has been determined using single-crystal X-ray diffraction on a synthetic sample, supported by powder X-ray diffraction (PXRD), electron microprobe analysis (EPMA) and thermogravimetric analyses (TGA). Montanite was first described in 1868 as Bi2TeO6·nH2O (n = 1 or 2). The determination of the crystal structure of synthetic montanite (refined composition Bi2TeO6·0.22H2O) has led to the reassignment of the formula to Bi2TeO6·nH2O where 0 ≤ n ≤  $${\raise0.5ex\hbox{\(\scriptstyle 2$$} \kern-0.1em/\kern-0.15em \lower0.25ex\hbox{$$\scriptstyle 3$$}}\) rather than the commonly reported Bi2TeO6·2H2O. This change has been accepted by the IMA–CNMNC, Proposal 22-A. The PXRD pattern simulated from the crystal structure of synthetic montanite is a satisfactory match for PXRD scans collected on both historical and recent natural samples, showing their equivalence. Two specimens attributed to the original discoverer of montanite (Frederick A. Genth) from the cotype localities (Highland Mining District, Montana and David Beck’s mine, North Carolina, USA) have been designated as neotypes. Montanite crystallises in space group P $$\overline{6 }$$ , with the unit-cell parameters a = 9.1195(14) Å, c = 5.5694(8) Å, V = 401.13(14) Å3, and three formula units in the unit cell. The crystal structure of montanite is formed from a framework of BiOn and TeO6 polyhedra. Half of the Bi3+ and all of the Te6+ cations are coordinated by six oxygen atoms in trigonal-prismatic arrangements (the first example of this configuration reported for Te6+), while the remaining Bi3+ cations are coordinated by seven O sites. The H2O groups in montanite are structurally incorporated into the network of cavities formed by the three-dimensional framework, with other cavity space occupied by the stereoactive 6s2 lone pair of Bi3+ cations. While evidence for a supercell was observed in synthetic montanite, the subcell refinement of montanite adequately indexes all reflections in the PXRD patterns observed in all natural montanite samples analysed in this study, verifying the identity of montanite as a mineral.
PubDate: 2022-06-09
DOI: 10.1007/s00269-022-01198-2

• On the crystal-chemistry of meyerhofferite, CaB3O3(OH)5·H2O

Abstract: Abstract The crystal structure and crystal chemistry of meyerhofferite, ideally CaB3O3(OH)5·H2O, was investigated by a multi-methodological approach based on titrimetric determination of boron, gravimetric determination of calcium, determination of fluorine by ion selective electrode, determination of water content by heating, other minor elements by inductively coupled plasma atomic emission spectroscopy, along with single-crystal synchrotron X-ray and neutron diffraction. The concentration of more than 50 chemical elements was measured. The combination of these techniques proves that the composition of meyerhofferite approaches the ideal one (i.e., (Ca1.012Mg0.003) (B2.984Si0.001)O3(OH)5·1.018H2O), with only a modest fraction of Mg (with MgO ≈ 0.03 wt%) replacing Ca, and with Si the only potential substituent of tetrahedral B (with SiO2 ≈ 0.02 wt%). The content of REE and other minor elements is, overall, not significant, including that of fluorine as a potential OH− substituent (i.e., < 0.01 wt%). These findings have some relevant geochemical and technical implications, here discussed. The X-ray and neutron structure model obtained in this study prove that the building units of the structure of meyerhofferite consist of: two BO2(OH)2 tetrahedra and one BO2(OH) triangle, linked by corner-sharing to form [B3O3(OH)5]2− rings, and distorted Ca-polyhedra (with CN = 8, CaO3(OH)4(OH2)), linked by edge-sharing to form infinite chains along [001]. The B3O3(OH)5 rings are connected to the Ca-polyhedra chains by corner- and edge-sharing, on two sides of the chains. These heteropolyhedral chains, made by Ca-polyhedra and B3O3(OH)5 rings, are mutually connected through hydrogen bonding only, giving rise to the tri-dimensional edifice of meyerhofferite. The neutron structure refinement showed no evidence of static or dynamic disorder pertaining to the H sites; their libration regime was found to be significantly anisotropic. At least seven of the nine oxygen sites of the structure are involved in H-bonding, as donors or as acceptors. The role played by the H-bonding scheme on the physical properties of meyerhofferite is discussed.
PubDate: 2022-06-09
DOI: 10.1007/s00269-022-01199-1

• Thermodynamic properties of geikielite (MgTiO3) and ilmenite (FeTiO3)
derived from vibrational methods combined with Raman and infrared
spectroscopic data

Abstract: Abstract We present a model for the lattice vibrational density of states of MgTiO3 (geikielite) and FeTiO3 (ilmenite) that predicts thermodynamic properties, in agreement with observational data. The model is based on Kieffer’s method combined with spectroscopic data. For both substances experimental data sets are influenced by non-stoichiometry. For geikielite that affects the volume, whereas for ilmenite volume and bulk modulus are affected. We show that Kieffer’s method enables predicting bulk moduli in pressure–temperature space. We demonstrate that intrinsic anharmonicity or electronic effects significantly affect the heat capacity of ilmenite, whereas that is not the case for geikielite. We use Kieffer’s method to derive multiple-Einstein models, from which we demonstrate that thermodynamic properties are insignificantly influenced by dispersion in Grüneisen, mode-q and anharmonicity parameters for both substances. We show that our results enable predicting thermodynamic properties and shear modulus of the solid solution formed from geikielite and ilmenite. Geikielite and ilmenite are added to our thermodynamic database for the system MgO–SiO2–FeO, to enable modeling phase stability and physical properties of titanium-rich reservoirs in the Earth’s Moon.
PubDate: 2022-06-09
DOI: 10.1007/s00269-022-01195-5

• Picosecond acoustics: a new way to access elastic properties of materials
at pressure and temperature conditions of planetary interiors

Abstract: Abstract Picosecond acoustics is an optical pump-probe technique allowing to access thermoelastic properties and sound velocities of a large variety of materials under extreme conditions. Coupled with diamond anvil cells and laser heating, picosecond acoustics measurements offer the possibility to probe materials over a pressure and temperature range directly pertinent for the deep planetary interiors. In this paper we highlight the capabilities and versatility of this technique by presenting some recent applications on materials of geophysical interest. All the independent components of the elastic tensor of MgO are simultaneously determined by measurements on a single crystal at ambient conditions. Compressional sound velocity is measured at high pressure on an iron-carbon alloy and on polycrystalline argon. First laser heating test measurements performed on molybdenum at high pressure are also presented. These examples demonstrate that picosecond acoustics is a valuable alternative to already existing techniques for determining the physical properties of samples under extreme pressure and temperature conditions.
PubDate: 2022-06-01
DOI: 10.1007/s00269-022-01194-6

• Recent developments on high-pressure single-crystal X-ray diffraction at
the Partnership for eXtreme Xtallography (PX2) program

Abstract: Abstract Single-crystal X-ray diffraction is an established method to constrain the structure and chemistry of crystalline minerals under high-pressure conditions. Partnership for eXtreme Xtallography (PX2) is a high-pressure crystallographic research program dedicated to diamond anvil cell research. Located at the experimental station 13-BM-C of the Advanced Photon Source, PX2 provides 10 µm-level focused X-rays at a fixed energy of 28.6 keV, a 6-circle heavy duty diffractometer and a state-of-the-art Pilatus3 1 M photon-counting detector, optimized for a variety of advanced crystallography experiments. A suite of auxiliary equipment including a compact multipurpose optical table and remote membrane-based pressure control has been installed to facilitate the experiments. Resistive and laser heating capabilities have been commissioned to provide high-temperature sample environments for the study of the planetary interior. In this manuscript we present a few examples to demonstrate the experimental capabilities at PX2.
PubDate: 2022-05-22
DOI: 10.1007/s00269-022-01197-3

• Chemical analysis of trace elements at the nanoscale in samples recovered
from laser-heated diamond anvil cell experiments

Abstract: Abstract High pressure and high temperature experiments performed with laser-heated diamond anvil cells (LH-DAC) are being extensively used in geosciences to study matter at conditions prevailing in planetary interiors. Due to the size of the apparatus itself, the samples that are produced are extremely small, on the order of few tens of micrometers. There are several ways to analyze the samples and extract physical, chemical or structural information, using either in situ or ex situ methods. In this paper, we compare two nanoprobe techniques, namely nano-XRF and NanoSIMS, that can be used to analyze recovered samples synthetized in a LH-DAC. With these techniques, it is possible to extract the spatial distribution of chemical elements in the samples. We show the results for several standards and discuss the importance of proper calibration for the acquisition of quantifiable results. We used these two nanoprobe techniques to retrieve elemental ratios of dilute species (few tens of ppm) in quenched experimental molten samples relevant for the formation of the iron-rich core of the Earth. We finally discuss the applications of such probes to constrain the partitioning of trace elements between metal and silicate phases, with a focus on moderately siderophile elements, tungsten and molybdenum.
PubDate: 2022-05-20
DOI: 10.1007/s00269-022-01193-7

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