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13 pages, 2266 KiB

Open AccessArticle

Phase Transitions in Natural Vanadinite at High Pressures

by Yingxin Liu, Liyun Dai, Xiaojing Lai, Feng Zhu, Dongzhou Zhang, Yi Hu, Sergey Tkachev and Bin Chen

Minerals 2021, 11(11), 1217; https://doi.org/10.3390/min11111217 - 31 Oct 2021

Viewed by 2074

Abstract

The structural stability of vanadinite, Pb₅[VO₄]₃Cl, is reported by high-pressure experiments using synchrotron radiation X-ray diffraction (XRD) and Raman spectroscopy. XRD experiments were performed up to 44.6 GPa and 700 K using an externally-heated diamond anvil cell [...] Read more.

The structural stability of vanadinite, Pb₅[VO₄]₃Cl, is reported by high-pressure experiments using synchrotron radiation X-ray diffraction (XRD) and Raman spectroscopy. XRD experiments were performed up to 44.6 GPa and 700 K using an externally-heated diamond anvil cell (EHDAC), and Raman spectroscopy measurements were performed up to 26.8 GPa at room temperature. XRD experiments revealed a reversible phase transition of vanadinite at 23 GPa and 600 K, which is accompanied by a discontinuous volume reduction and color change of the mineral from transparent to reddish during compression. The high-pressure Raman spectra of vanadinite show apparent changes between 18.0 and 22.8 GPa and finally become amorphous at 26.8 GPa, suggesting structural transitions of this mineral upon compression. The structural changes can be distinguished by the emergence of a new vibrational mode that can be attributed to the distortion of [VO₄] and the larger distortion of the V–O bonds, respectively. The [VO₄] internal modes in vanadinite give isothermal mode Grüneisen parameters varying from 0.149 to 0.286, yielding an average VO₄ internal mode Grüneisen parameters of 0.202. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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14 pages, 2512 KiB

Open AccessArticle

Vibrational and Thermodynamic Properties of Hydrous Iron-Bearing Lowermost Mantle Minerals

by Jiajun Jiang, Joshua M. R. Muir and Feiwu Zhang

Minerals 2021, 11(8), 885; https://doi.org/10.3390/min11080885 - 16 Aug 2021

Viewed by 2143

Abstract

The vibrational and thermodynamic properties of minerals are key to understanding the phase stability and the thermal structure of the Earth’s mantle. In this study, we modeled hydrous iron-bearing bridgmanite (Brg) and post-perovskite (PPv) with different [Fe³⁺-H] defect configurations using first-principles [...] Read more.

The vibrational and thermodynamic properties of minerals are key to understanding the phase stability and the thermal structure of the Earth’s mantle. In this study, we modeled hydrous iron-bearing bridgmanite (Brg) and post-perovskite (PPv) with different [Fe³⁺-H] defect configurations using first-principles calculations combined with quasi-harmonic approximations (QHA). Fe³⁺-H configurations can be vibrationally stable in Brg and PPv; the site occupancy of this defect will strongly affect its thermodynamic properties and particularly its response to pressure. The presence of Fe³⁺-H introduces distinctive high-frequency vibrations to the crystal. The frequency of these peaks is configuration dependence. Of the two defect configurations, [

{Fe}_{Si}^{'} + {OH}^{\cdot}]

makes large effects on the thermodynamic properties of Brg and PPv, whereas [

V_{Mg}^{″} + {Fe}_{Mg}^{\cdot} + {OH}^{\cdot}

] has negligible effects. With an expected lower mantle water concentrations of <1000 wt. ppm the effect of Fe³⁺-H clusters on properties such as heat capacity and thermal expansion is negligible, but the effect on the Grüneisen parameter γ can be significant (~1.2%). This may imply that even a small amount of water may affect the anharmonicity of Fe³⁺-bearing MgSiO₃ in lower mantle conditions and that when calculating the adiabaticity of the mantle, water concentrations need to be considered. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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14 pages, 1854 KiB

Open AccessFeature PaperArticle

Crystal Structure Evolution of CaSiO₃ Polymorphs at Earth’s Mantle Pressures

by Sula Milani, Davide Comboni, Paolo Lotti, Patrizia Fumagalli, Luca Ziberna, Juliette Maurice, Michael Hanfland and Marco Merlini

Minerals 2021, 11(6), 652; https://doi.org/10.3390/min11060652 - 19 Jun 2021

Cited by 12 | Viewed by 4761

Abstract

CaSiO₃ polymorphs are abundant in only unique geological settings on the Earth’s surface and are the major Ca-bearing phases at deep mantle condition. An accurate and comprehensive study of their density and structural evolution with pressure and temperature is still lacking. Therefore, [...] Read more.

CaSiO₃ polymorphs are abundant in only unique geological settings on the Earth’s surface and are the major Ca-bearing phases at deep mantle condition. An accurate and comprehensive study of their density and structural evolution with pressure and temperature is still lacking. Therefore, in this study we report the elastic behavior and structural evolution of wollastonite and CaSiO₃-walstromite with pressure. Both minerals are characterized by first order phase transitions to denser structures. The deformations that lead to these transformations allow a volume increase ofthe bigger polyhedra, which might ease cation substitution in the structural sites of these phases. Furthermore, their geometrical features are clear analogies with those predicted and observed for tetrahedrally-structured ultra-high-pressure carbonates, which are unfortunately unquenchable. Indeed, wollastonite and CaSiO₃-walstromite have a close resemblance to ultra-high-pressure chain- and ring-carbonates. This suggests a rich polymorphism also for tetrahedral carbonates, which might increase the compositional range of these phases, including continuous solid solutions involving cations with different size (Ca vs. Mg in particular) and important minor or trace elements incorporation. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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18 pages, 4133 KiB

Open AccessArticle

Investigation on Atomic Structure and Mechanical Property of Na- and Mg-Montmorillonite under High Pressure by First-Principles Calculations

by Jian Zhao, Yu Cao, Lei Wang, Hai-Jiang Zhang and Man-Chao He

Minerals 2021, 11(6), 613; https://doi.org/10.3390/min11060613 - 08 Jun 2021

Cited by 10 | Viewed by 2061

Abstract

Montmorillonite is an important layered phyllosilicate material with many useful physicochemical and mechanical properties, which is widely used in medicine, environmental protection, construction industry, and other fields. In order to a get better understanding of the behavior of montmorillonite under high pressure, we [...] Read more.

Montmorillonite is an important layered phyllosilicate material with many useful physicochemical and mechanical properties, which is widely used in medicine, environmental protection, construction industry, and other fields. In order to a get better understanding of the behavior of montmorillonite under high pressure, we studied its atomic structure, electronic and mechanical properties using density functional theory (DFT), including dispersion corrections, as function of the interlayer Na and Mg cations. At ideal condition, the calculations of lattice constants, bond length, band structure, and elastic modulus of Na- and Mg-montmorillonite are in good agreement with the experimental values. Under high pressure, the lattice constants and major bond lengths decreased with increasing pressure. The calculated electronic properties and band structure show only a slight change under 20 GPa, indicating that the effect of pressure on the electronic properties of Na- and Mg-montmorillonite is weak. The bulk modulus, shear modulus, Young’s modulus, shear wave velocity and compression wave velocity of Na- and Mg-montmorillonite are positively correlated with the external pressure, and the other mechanical parameters have a little change. The calculated studies will be useful to explore experiments in the future from a purely scientific point of view. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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11 pages, 3862 KiB

Open AccessArticle

High-Pressure Raman Spectroscopy and X-ray Diffraction Study on Scottyite, BaCu₂Si₂O₇

by Pei-Lun Lee, Eugene Huang and Jennifer Kung

Minerals 2021, 11(6), 608; https://doi.org/10.3390/min11060608 - 07 Jun 2021

Cited by 2 | Viewed by 2165

Abstract

In situ high-pressure synchrotron X-ray diffraction and Raman spectroscopic experiments of scottyite, BaCu₂Si₂O₇, were carried out in a diamond anvil cell up to 21 GPa at room temperature. X-ray diffraction patterns reveal four new peaks near 3.5, [...] Read more.

In situ high-pressure synchrotron X-ray diffraction and Raman spectroscopic experiments of scottyite, BaCu₂Si₂O₇, were carried out in a diamond anvil cell up to 21 GPa at room temperature. X-ray diffraction patterns reveal four new peaks near 3.5, 3.1, 2.6 and 2.2 Å above 8 GPa, while some peaks of the original phase disappear above 10 GPa. In the Raman experiment, we observed two discontinuities in dν/dP, the slopes of Raman wavenumber (ν) of some vibration modes versus pressure (P), at approximately 8 and 12 GPa, indicating that the Si-O symmetrical and asymmetrical vibration modes change with pressure. Fitting the compression data to Birch–Murnaghan equation yields a bulk modulus of 102 ± 5 GPa for scottyite, assuming K_o′ is four. Scottyite shows anisotropic compressibility along three crystallographic axes, among which c-axis was the most compressible axis, b-axis was the last and a-axis was similar to the c-axis on the compression. Both X-ray and Raman spectroscopic data provide evidences that scottyite undergoes a reversible phase transformation at 8 GPa. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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13 pages, 3446 KiB

Open AccessFeature PaperArticle

Compressibility and Phase Stability of Iron-Rich Ankerite

by Raquel Chuliá-Jordán, David Santamaria-Perez, Javier Ruiz-Fuertes, Alberto Otero-de-la-Roza and Catalin Popescu

Minerals 2021, 11(6), 607; https://doi.org/10.3390/min11060607 - 06 Jun 2021

Cited by 8 | Viewed by 2119

Abstract

The structure of the naturally occurring, iron-rich mineral Ca_1.08(6)Mg_0.24(2)Fe_0.64(4)Mn_0.04(1)(CO₃)₂ ankerite was studied in a joint experimental and computational study. Synchrotron X-ray powder diffraction measurements up to 20 GPa were complemented by density [...] Read more.

The structure of the naturally occurring, iron-rich mineral Ca_1.08(6)Mg_0.24(2)Fe_0.64(4)Mn_0.04(1)(CO₃)₂ ankerite was studied in a joint experimental and computational study. Synchrotron X-ray powder diffraction measurements up to 20 GPa were complemented by density functional theory calculations. The rhombohedral ankerite structure is stable under compression up to 12 GPa. A third-order Birch–Murnaghan equation of state yields V₀ = 328.2(3) Å³, bulk modulus B₀ = 89(4) GPa, and its first-pressure derivative B’₀ = 5.3(8)—values which are in good agreement with those obtained in our calculations for an ideal CaFe(CO₃)₂ ankerite composition. At 12 GPa, the iron-rich ankerite structure undergoes a reversible phase transition that could be a consequence of increasingly non-hydrostatic conditions above 10 GPa. The high-pressure phase could not be characterized. DFT calculations were used to explore the relative stability of several potential high-pressure phases (dolomite-II-, dolomite-III- and dolomite-V-type structures), and suggest that the dolomite-V phase is the thermodynamically stable phase above 5 GPa. A novel high-pressure polymorph more stable than the dolomite-III-type phase for ideal CaFe(CO₃)₂ ankerite was also proposed. This high-pressure phase consists of Fe and Ca atoms in sevenfold and ninefold coordination, respectively, while carbonate groups remain in a trigonal planar configuration. This phase could be a candidate structure for dense carbonates in other compositional systems. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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8 pages, 2015 KiB

Open AccessFeature PaperArticle

Synthesis and Compressibility of Novel Nickel Carbide at Pressures of Earth’s Outer Core

by Timofey Fedotenko, Saiana Khandarkhaeva, Leonid Dubrovinsky, Konstantin Glazyrin, Pavel Sedmak and Natalia Dubrovinskaia

Minerals 2021, 11(5), 516; https://doi.org/10.3390/min11050516 - 13 May 2021

Cited by 5 | Viewed by 2071

Abstract

We report the high-pressure synthesis and the equation of state (EOS) of a novel nickel carbide (Ni₃C). It was synthesized in a diamond anvil cell at 184(5) GPa through a direct reaction of a nickel powder with carbon from the diamond [...] Read more.

We report the high-pressure synthesis and the equation of state (EOS) of a novel nickel carbide (Ni₃C). It was synthesized in a diamond anvil cell at 184(5) GPa through a direct reaction of a nickel powder with carbon from the diamond anvils upon heating at 3500 (200) K. Ni₃C has the cementite-type structure (Pnma space group, a = 4.519(2) Å, b = 5.801(2) Å, c = 4.009(3) Å), which was solved and refined based on in-situ synchrotron single-crystal X-ray diffraction. The pressure-volume data of Ni₃C was obtained on decompression at room temperature and fitted to the 3rd order Burch-Murnaghan equation of state with the following parameters: V₀ = 147.7(8) Å³, K₀ = 157(10) GPa, and K₀′ = 7.8(6). Our results contribute to the understanding of the phase composition and properties of Earth’s outer core. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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20 pages, 3269 KiB

Open AccessArticle

Composition and Pressure Effects on Partitioning of Ferrous Iron in Iron-Rich Lower Mantle Heterogeneities

by Susannah M. Dorfman, Farhang Nabiei, Charles-Edouard Boukaré, Vitali B. Prakapenka, Marco Cantoni, James Badro and Philippe Gillet

Minerals 2021, 11(5), 512; https://doi.org/10.3390/min11050512 - 12 May 2021

Cited by 3 | Viewed by 3082

Abstract

Both seismic observations of dense low shear velocity regions and models of magma ocean crystallization and mantle dynamics support enrichment of iron in Earth’s lowermost mantle. Physical properties of iron-rich lower mantle heterogeneities in the modern Earth depend on distribution of iron between [...] Read more.

Both seismic observations of dense low shear velocity regions and models of magma ocean crystallization and mantle dynamics support enrichment of iron in Earth’s lowermost mantle. Physical properties of iron-rich lower mantle heterogeneities in the modern Earth depend on distribution of iron between coexisting lower mantle phases (Mg,Fe)O magnesiowüstite, (Mg,Fe)SiO₃ bridgmanite, and (Mg,Fe)SiO₃ post-perovskite. The partitioning of iron between these phases was investigated in synthetic ferrous-iron-rich olivine compositions (Mg_0.55Fe_0.45)₂SiO₄ and (Mg_0.28Fe_0.72)₂SiO₄ at lower mantle conditions ranging from 33–128 GPa and 1900–3000 K in the laser-heated diamond anvil cell. The resulting phase assemblages were characterized by a combination of in situ X-ray diffraction and ex situ transmission electron microscopy. The exchange coefficient between bridgmanite and magnesiowüstite decreases with pressure and bulk Fe# and increases with temperature. Thermodynamic modeling determines that incorporation and partitioning of iron in bridgmanite are explained well by excess volume associated with Mg-Fe exchange. Partitioning results are used to model compositions and densities of mantle phase assemblages as a function of pressure, FeO-content and SiO₂-content. Unlike average mantle compositions, iron-rich compositions in the mantle exhibit negative dependence of density on SiO₂-content at all mantle depths, an important finding for interpretation of deep lower mantle structures. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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12 pages, 1401 KiB

Open AccessArticle

Ni Doping: A Viable Route to Make Body-Centered-Cubic Fe Stable at Earth’s Inner Core

by Swastika Chatterjee, Sujoy Ghosh and Tanusri Saha-Dasgupta

Minerals 2021, 11(3), 258; https://doi.org/10.3390/min11030258 - 02 Mar 2021

Cited by 7 | Viewed by 2917

Abstract

With the goal of answering the highly debated question of whether the presence of Ni at the Earth’s inner core can make body-centered cubic (bcc) Fe stable, we performed a computational study based on first-principles calculations on bcc, hexagonal closed packed (hcp), and [...] Read more.

With the goal of answering the highly debated question of whether the presence of Ni at the Earth’s inner core can make body-centered cubic (bcc) Fe stable, we performed a computational study based on first-principles calculations on bcc, hexagonal closed packed (hcp), and face-centered cubic (fcc) structures of the Fe_1−xNi_x alloys (x = 0, 0.0312, 0.042, 0.0625, 0.084, 0.125, 0.14, 0.175) at 200–364 GPa and investigated their relative stability. Our thorough study reveals that the stability of Ni-doped bcc Fe is crucially dependent on the nature of the distribution of Ni in the Fe matrix. We confirm this observation by considering several possible configurations for a given concentration of Ni doping. Our theoretical evidence suggests that Ni-doped bcc Fe could be a stable phase at the Earth’s inner core condition as compared to its hcp and fcc counterparts. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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12 pages, 1854 KiB

Open AccessArticle

Structure Analysis of Natural Wangdaodeite—LiNbO₃-Type FeTiO₃

by Oliver Tschauner, Chi Ma, Matthew G. Newville and Antonio Lanzirotti

Minerals 2020, 10(12), 1072; https://doi.org/10.3390/min10121072 - 30 Nov 2020

Cited by 3 | Viewed by 2726

Abstract

This paper reports the first structure refinement of natural wangdaodeite, LiNbO₃-type FeTiO₃ from the Ries impact structure. Wangdaodeite occurs together with recrystallized ilmenite clasts in shock melt veins which have experienced peak shock pressures of between 17 and 22 GPa. [...] Read more.

This paper reports the first structure refinement of natural wangdaodeite, LiNbO₃-type FeTiO₃ from the Ries impact structure. Wangdaodeite occurs together with recrystallized ilmenite clasts in shock melt veins which have experienced peak shock pressures of between 17 and 22 GPa. Comparison of natural and synthetic wangdaodeite points toward a correlation between the distortion of ferrate- and titanate-polyhedra and the c/a ratio of the unit cell. The Raman spectrum of wangdaodeite is calculated based on the refined structure. Comparison to the reported spectrum of the type-material shows that the Raman peak at 738–740 cm⁻¹ is indicative for this phase, whereas other features in type-wangdaodeite are tentatively assigned to disordered ilmenite. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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10 pages, 2736 KiB

Open AccessFeature PaperArticle

Structural Study of δ-AlOOH Up to 29 GPa

by Dariia Simonova, Elena Bykova, Maxim Bykov, Takaaki Kawazoe, Arkadiy Simonov, Natalia Dubrovinskaia and Leonid Dubrovinsky

Minerals 2020, 10(12), 1055; https://doi.org/10.3390/min10121055 - 26 Nov 2020

Cited by 9 | Viewed by 2509

Abstract

A structure and equation of the state of δ-AlOOH has been studied at room temperature, up to 29.35 GPa, by means of single crystal X-ray diffraction in a diamond anvil cell using synchrotron radiation. Above ~10 GPa, we observed a phase transition with [...] Read more.

A structure and equation of the state of δ-AlOOH has been studied at room temperature, up to 29.35 GPa, by means of single crystal X-ray diffraction in a diamond anvil cell using synchrotron radiation. Above ~10 GPa, we observed a phase transition with symmetry changes from

P 2_{1} n m

to

P n n m

. Pressure-volume data were fitted with the second order Birch-Murnaghan equation of state and showed that, at the phase transition, the bulk modulus (K₀) of the calculated wrt 0 pressure increases from 142(5) to 216(5) GPa. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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7 pages, 1287 KiB

Open AccessArticle

Structure and Stability of Iron Fluoride at High Pressure–Temperature and Implication for a New Reservoir of Fluorine in the Deep Earth

by Yanhao Lin, Qingyang Hu, Li Zhu and Yue Meng

Minerals 2020, 10(9), 783; https://doi.org/10.3390/min10090783 - 05 Sep 2020

Cited by 7 | Viewed by 3114

Abstract

Fluorine (F) is the most abundant halogen in the bulk silicate Earth. F plays an important role in geochemical and biological systems, but its abundance and distribution in the terrestrial mantle are still unclear. Recent studies suggested that F reservoirs in the deep [...] Read more.

Fluorine (F) is the most abundant halogen in the bulk silicate Earth. F plays an important role in geochemical and biological systems, but its abundance and distribution in the terrestrial mantle are still unclear. Recent studies suggested that F reservoirs in the deep mantle are potentially hosted in terrestrial oxide minerals, especially in aluminous bridgmanite. However, the knowledge about the formation and stability field of fluoride in the Earth’s interior is rare. In this study, we combine in situ laser-heated diamond anvil cell, synchrotron X-ray diffraction, and first-principles structure search to show that a new tetragonal structure of FeF₃ is stable at pressures of 78–130 GPa and temperatures up to ~1900 K. Simulation predicted the tetragonal phase takes a much denser structure due to the rotation of FeF₆ octahedral units. The equations of states of tetragonal FeF₃ are determined by experiment and verified by simulation. Our results indicate that FeF₃ can be a potential key phase for storing F in the Earth’s lower mantle and may explain some mantle-derived magma with high F concentration. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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20 pages, 4477 KiB

Open AccessArticle

Topaz, a Potential Volatile-Carrier in Cold Subduction Zone: Constraint from Synchrotron X-ray Diffraction and Raman Spectroscopy at High Temperature and High Pressure

by Shijie Huang, Jingui Xu, Chunfa Chen, Bo Li, Zhilin Ye, Wei Chen, Yunqian Kuang, Dawei Fan, Wenge Zhou and Maining Ma

Minerals 2020, 10(9), 780; https://doi.org/10.3390/min10090780 - 03 Sep 2020

Cited by 6 | Viewed by 3496

Abstract

The equation of state and stability of topaz at high-pressure/high-temperature conditions have been investigated by in situ synchrotron X-ray diffraction (XRD) and Raman spectroscopy in this study. No phase transition occurs on topaz over the experimental pressure–temperature (P-T [...] Read more.

The equation of state and stability of topaz at high-pressure/high-temperature conditions have been investigated by in situ synchrotron X-ray diffraction (XRD) and Raman spectroscopy in this study. No phase transition occurs on topaz over the experimental pressure–temperature (P-T) 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 = 343.86 (9) Å³, the zero-pressure bulk modulus K₀ = 172 (3) GPa, and its pressure derivative K’₀ = 1.3 (4), while the obtained K₀ = 155 (2) GPa when fixed K’₀ = 4. In the pressure range of 0–24.4 GPa, the vibration modes of in-plane bending OH-groups for topaz show non-linear changes with the increase in pressure, while the other vibration modes show linear changes. Moreover, the temperature–volume data were fitted by Fei’s thermal equation with the thermal expansion coefficient α₃₀₀ = 1.9 (1) × 10⁻⁵ K⁻¹ at 300 K. Finally, the P-T stability of topaz was studied by a synchrotron-based single-crystal XRD at simultaneously high P-T conditions up to ~10.9 GPa and 700 K, which shows that topaz may maintain a metastable state at depths above 370 km in the upper mantle along the coldest subducting slab geotherm. Thus, topaz may be a potential volatile-carrier in the cold subduction zone. It can carry hydrogen and fluorine elements into the deep upper mantle and further affect the geochemical behavior of the upper mantle. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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12 pages, 2607 KiB

Open AccessArticle

First-Principles Study of the Elastic Properties of Nickel Sulfide Minerals under High Pressure

by Qiuyuan Zhang, Ye Tian, Shanqi Liu, Peipei Yang and Yongbing Li

Minerals 2020, 10(9), 737; https://doi.org/10.3390/min10090737 - 21 Aug 2020

Cited by 5 | Viewed by 2571

Abstract

Nickel sulfide minerals, an important type of metal sulfides, are the major component of mantle sulfides. They are also one of the important windows for mantle partial melting, mantle metasomatism, and mantle fluid mineralization. The elasticity plays an important role in understanding the [...] Read more.

Nickel sulfide minerals, an important type of metal sulfides, are the major component of mantle sulfides. They are also one of the important windows for mantle partial melting, mantle metasomatism, and mantle fluid mineralization. The elasticity plays an important role in understanding the deformation and elastic wave propagation of minerals, and it is the key parameter for interpreting seismic wave velocity in terms of the composition of the Earth’s interior. Based on first-principles methods, the crystal structure, equation of state, elastic constants, elastic modulus, mechanical stability, elastic anisotropy, and elastic wave velocity of millerite (NiS), heazlewoodite (Ni₃S₂), and polydymite (Ni₃S₄) under high pressure are investigated. Our calculated results show that the crystal structures of these Ni sulfides are well predicted. These Ni sulfides are mechanically stable under the high pressure of the upper mantle. The elastic constants show different changing trends with increasing pressure. The bulk modulus of these Ni sulfides increases linearly with pressure, whereas shear modulus is less sensitive to pressure. The universal elastic anisotropic index A^U also shows different changing trends with pressure. Furthermore, the elastic wave velocities of Ni sulfides are much lower than those of olivine and enstatite. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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16 pages, 3851 KiB

Open AccessArticle

The Effect of Pulsed Laser Heating on the Stability of Ferropericlase at High Pressures

by Georgios Aprilis, Anna Pakhomova, Stella Chariton, Saiana Khandarkhaeva, Caterina Melai, Elena Bykova, Maxim Bykov, Timofey Fedotenko, Egor Koemets, Catherine McCammon, Aleksandr I. Chumakov, Michael Hanfland, Natalia Dubrovinskaia and Leonid Dubrovinsky

Minerals 2020, 10(6), 542; https://doi.org/10.3390/min10060542 - 16 Jun 2020

Cited by 2 | Viewed by 2225

Abstract

It is widely accepted that the lower mantle consists of mainly three major minerals—ferropericlase, bridgmanite and calcium silicate perovskite. Ferropericlase ((Mg,Fe)O) is the second most abundant of the three, comprising approximately 16–20 wt% of the lower mantle. The stability of ferropericlase at conditions [...] Read more.

It is widely accepted that the lower mantle consists of mainly three major minerals—ferropericlase, bridgmanite and calcium silicate perovskite. Ferropericlase ((Mg,Fe)O) is the second most abundant of the three, comprising approximately 16–20 wt% of the lower mantle. The stability of ferropericlase at conditions of the lowermost mantle has been highly investigated, with controversial results. Amongst other reasons, the experimental conditions during laser heating (such as duration and achieved temperature) have been suggested as a possible explanation for the discrepancy. In this study, we investigate the effect of pulsed laser heating on the stability of ferropericlase, with a geochemically relevant composition of Mg_0.76Fe_0.24O (Fp24) at pressure conditions corresponding to the upper part of the lower mantle and at a wide temperature range. We report on the decomposition of Fp24 with the formation of a high-pressure (Mg,Fe)₃O₄ phase with CaTi₂O₄-type structure, as well as the dissociation of Fp24 into Fe-rich and Mg-rich phases induced by pulsed laser heating. Our results provide further arguments that the chemical composition of the lower mantle is more complex than initially thought, and that the compositional inhomogeneity is not only a characteristic of the lowermost part, but includes depths as shallow as below the transition zone. Full article

(This article belongs to the Special Issue Minerals under Extreme Conditions)

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