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The stabilities of the minerals that can hold water are important for understanding water behavior in the Earth’s deep interior. Recent experimental studies have shown that the incorporation of aluminum enhances the thermal stabilities of hydrous minerals significantly. In this study, the phase relations of hydrous aluminosilicates in the AlOOH-AlSiO3OH system were investigated at 22 GPa and 1400–2275 K using a multi-anvil apparatus. Based on the X-ray diffraction measurements and composition analysis of the recovered samples, we found that the AlSiO4H phase Egg forms a solid solution with δ-AlOOH above 1500 K. Additionally, at temperatures above 1800 K, two unknown hydrous aluminosilicates with compositions Al2.03Si0.97O6H2.03 and Al2.11Si0.88O6H2.11 appeared, depend ing on the bulk composition of the starting materials. Both phases can host large amounts of water, at least up to 2275 K, exceeding the typical mantle geotherm. The extreme thermal stability of hydrous aluminosilicates suggests that deep-subducted crustal rocks could be a possible reservoir of water in the mantle transition zone and the uppermost lower mantle.

Heavy meteorite impacts on Earth’s surface produce melt and vapor that are quenched rapidly and scattered over wide areas as natural glasses with various shapes and characteristic chemistry, which are known as tektites and impact glasses. Their detailed formation conditions have long been debated using mineralogical and geochemical data and numerical simulations of impact melt formations. These impact processes are also related to the formation and evolution of planets. To unravel the formation conditions of impact-induced glasses, we performed shock recovery experiments on a tektite. Recovered samples were characterized by X-ray diffraction, Raman spectroscopy, and X-ray absorption fine structure spectroscopy on the Ti K-edge. Results indicate that the densification by shock compression is subjected to post-shock annealing that alters the density and silicate-framework structures but that the local structures around octahedrally coordinated Ti ions remain in the quenched glass. The relationship between the average Ti-O distance and Ti K pre-edge centroid energy is found to distinguish the valance state of Ti ions between Ti4+ and Ti3+ in the glass. This relationship is useful in understanding the formation conditions of impact-derived natural glasses. The presence of Ti3+ in tektites constrains the formation conditions at extremely high temperatures or reduced environments. However, impact glasses collected near the impact sites do not display such conditions, but instead relatively mild and oxidizing formation conditions. These different formation conditions are consistent with the previous numerical results on the crater size dependence.

Rh-rich and Ir-poor erlichmanite–laurite OsS2–RuS2 solid solutions have been discovered at placers in Haraigawa, Misato-machi, Kumamoto, Japan. Microprobe analysis was performed to identify solid solutions containing few sub-components other than Rh. Approximately 10 at.% Rh was found to be present in the solid-solution samples. Structural refinement was performed using four natural samples: Os0.32Ru0.61Rh0.07S2, Os0.49Ru0.43Rh0.08S2, Os0.58Ru0.33Rh0.08S2 and Os0.81Ru0.09Rh0.10S2. The unit-cell parameters for the solid solutions containing Rh from Haraigawa varied from 5.61826(6) to 5.63142(8) Å. The (Os, Ru, Rh)–S distances in the Os1–x–yRu x Rh y S2 system were almost constant with a small variation of 0.001 Å. Conversely, the S–S distances varied significantly, with variations approaching 0.1 Å. Rh substitution of Os rather than Ru had a larger impact on the crystal structure. The atomic displacement ellipsoid of both cations and anions was almost spherical, and no elongation along the M–S and S–S bond directions was observed. The bulk Debye temperatures were estimated from the Debye–Waller factor for the sulfide site. The bulk Debye temperatures of pure OsS2 and RuS2 were 688 K and 661 K, respectively, which suggests that the melting point of erlichmanite is higher than that of laurite. The high Debye temperature of OsS2 is inconsistent with the crystallisation of laurite prior to erlichmanite from the primitive magma, which suggests that $f_{\rm S_2}$ , rather than temperature, is the main cause of the known crystallisation order. The presence of several percent Rh has a significant effect on the thermal stability of OsS2 and lowers the melting point of the erlichmanite solid solution compared to that of the laurite solid solution.

Single crystals of Ir2S3 (diiridium trisulfide) and Rh2S3 (dirhodium trisulfide) were grown in evacuated silica-glass tubes using a chemical transport method and their crystal structures were determined by single-crystal X-ray diffraction analysis. These compounds have a unique sesquisulfide structure in which pairs of face-sharing octahedra are linked into a three-dimensional structure by further edge- and vertex-sharing. Ir2S3 and Rh2S3 had similar unit-cell parameters and bond distances. The atomic displacement parameter (MSD: mean-square displacement) of each atom in Ir2S3 was considerably smaller than that in Rh2S3. The Debye temperatures (ΘD) estimated from the observed MSDs for the Ir, S1 and S2 sites in Ir2S3 were 259, 576 and 546 K, respectively, and those for Rh, S1 and S2 in Rh2S3 were 337, 533 and 530 K, respectively. The bulk Debye temperature for Ir2S3 kashinite (576 K) was found to rank among the higher values reported for many known sulfides. The bulk Debye temperature for Rh2S3 bowieite (533 K) was lower than that for Ir2S3 kashinite, which crystallizes in the early sequences of mineral crystallization differentiation from the primitive magma in the Earth's mantle.

The structure refinement and XANES study of two gold–silver–tellurides [Au1+x Ag x Te2, krennerite (x = 0.11–0.13) and sylvanite (x = 0.29–0.31)] are presented and the structures are compared with the prototype structure of calaverite (x = 0.08–0.10). Whereas the latter is well known for being incommensurately modulated at ambient conditions, neither krennerite nor sylvanite present any modulation. This is attributed to the presence of relatively strong Te—Te bonds (bond distances < 2.9 Å) in the two minerals, which are absent in calaverite (bond distances > 3.2 Å). In both tellurides, trivalent gold occurs in slightly distorted square planar coordination, whereas monovalent gold, partly substituted by monovalent silver, presents a 2+2+2 coordination, corresponding to distorted rhombic bipyramids. The differentiation between bonding and non-bonding contacts is obtained by computation of the Effective Coordination Number (ECoN). The CHARge DIstribution (CHARDI) analysis is satisfactory for both tellurides but suggests that the Te—Te bond in the [Te3]2− anion is not entirely homopolar. Both tellurides can therefore be described as Madelung-type compounds, despite the presence of Te–Te in both structures.

High-temperature X-ray diffraction (XRD) experiments up to T = 2710 °C have been performed on ZrSiO4 and ZrO2 powders, using the container-less levitation technique. A two-dimensional imaging plate (IP) detector was used for short-time observation. The diffraction data in a wide area was projected in one dimension. The unit cell parameters, thermal expansions, and c/a ratios for ZrSiO4 (space group I41/amd and Z = 4), tetragonal ZrO2 (space group P42/nmc and Z = 2) and cubic ZrO2 (space group F m 3 ‾ m $Fm3‾{}m$ and Z = 4) were measured to understand the high-temperature behaviors. The transition temperature between tetragonal and cubic ZrO2 was specified to be between 2430 and 2540 °C. The pre-transitional behavior was observed around 2200 °C. As no clear change in unit cell volume is evident, the phase boundary between the tetragonal and the cubic phase has been shown to be a positive slope. The ZrO2 and ZrO2–SiO2 phase diagrams are proposed based on the chemical composition and the crystal structure.

Single crystals of Ni3Se2 (trinickel diselenide) and NiSe (nickel selenide) with stoichiometric chemical compositions were grown in evacuated silica-glass tubes. The chemical compositions of the single crystals of Ni3Se2 and NiSe were determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS). The crystal structures of Ni3Se2 [rhombohedral, space group R32, a = 6.02813 (13), c = 7.24883 (16) Å, Z = 3] and NiSe [hexagonal, space group P63/mmc, a = 3.66147 (10), c = 5.35766 (16) Å, Z = 2] were analyzed by single-crystal X-ray diffraction and refined to yield R values of 0.020 and 0.018 for 117 and 85 unique reflections, respectively, with F o > 4σ(F o). R32 is a Sohncke type of space group where enantiomeric structures can exist; the single-domain structure obtained by the refinement was confirmed to be correct by a Flack parameter of −0.05 (2). The existence of Ni—Ni bonds was confirmed in both compounds, in addition to the Ni—Se bonds. The value of the atomic displacement parameter (mean-square displacement) of each atom in NiSe was larger than that in Ni3Se2. The larger amplitude of the atoms in NiSe corresponds to longer Ni—Se and Ni—Ni bond lengths in NiSe than in Ni3Se2. The Debye temperatures, θD, estimated from observed mean-square displacements for Ni and Se in Ni3Se2, were 322 and 298 K, respectively, while those for Ni and Se in NiSe were 246 and 241 K, respectively. The existence of large cavities in the structure and the weak bonding force are likely responsible for the brittle and soft nature of the NiSe crystal.

Sulfur is a minor element in magmas but one of the major volatile elements released in volcanic systems, from the magma to the fluid phase upon ascent. Not only are sulfur gasses potentially toxic for humans and plants, they are also involved in causing drastic climate changes after major volcanic eruptions. Therefore, studies are carried out by the geoscience community to assess the magmatic sulfur flux by looking at the sulfur content and isotopes in erupted products, with the ultimate aim of improving understanding of the sulfur cycle in subduction zones. Kyushu Island in Japan hosts 25 volcanoes, among which 11 are active and represent a natural hazard for the local population. It is perhaps the most suitable site for the study of the sulfur cycle for its availability of recent volcanic deposits and its many highly monitored volcanoes. We investigated sulfur and sulfur isotope compositions of the magma source of Kyushu Island arc using olivine-hosted melt inclusions in mafic tephras and lavas, from eight volcanoes (nine Holocene samples) going from Northern Kyushu with Oninomi, Yufu, Kuju, and Aso, to Southern Kyushu volcanoes such as Kirishima-Ohachidake, Kirishima-Shinmoedake, Sumiyoshi-ike, and Kaimondake, and one back arc volcano, Fukue-Onidake. We measured major, trace and volatile elements and S isotopes (δ34S) in melt inclusions. Magma composition recorded in the inclusions ranges from basalt to andesite (SiO2 ranging from 40.3 to 60.7 wt%). For each edifice, we identified the least degassed and least differentiated compositions based on volatile and trace element systematics and selected the melt inclusions closest to their primitive melts. Comparing these primitive magmas, Sr/Y underlines a compositional dichotomy between volcanoes from northern (Sr/Y > 20) and southern Kyushu (Sr/Y

Lead telluride is a well-established material for direct conversion of heat into electricity. However, the aspects of the heat transport phenomena for PbTe-alloys remain not fully understood. Here, for the first time, origins of the phonon scattering in Pb1−xSnxTe compounds were studied through changes in the effective anharmonic pair potential obtained from X-ray Absorption Fine Structure (XAFS) spectroscopy. Results indicate that the interatomic pair potential of Pb–Te and Sn–Te bonds changes with the level of substitution x and that the anharmonicity of bonds in the solid solution is increased leading to the lower values of the lattice thermal conductivity. Furthermore, due to the existence of a soft TO mode in Pb1−xSnxTe, the Gruneisen parameter γE determined using XAFS much more precisely corresponds with the changes of lattice thermal conductivity κlat compared to γS obtained from the speed of sound measurements. This study explains the observed drastic reduction in κL in Pb1−xSnxTe solid solution (2.3 W m−1 K−1 for PbTe vs. 1.0 W m−1 K−1 for Pb0.75Sn0.25Te), due to changes in the interatomic pair potential of Pb–Te and Sn–Te and provides guidelines into its effective modification related to thermal transport in alloys based on PbTe. The estimated range of low thermal conductivity for the PbTe–SnTe solid solutions (

The structure refinement and XANES study of two gold-silver-tellurides [Au

Single crystals of synthetic reidite and natural radiation-damaged zircon from Okueyama, Japan were investigated using X-ray diffraction. The pressure-induced zircon–reidite transition is described by the twisting and translations of SiO4 tetrahedra with disappearance of the SiO4–ZrO8 shared edges. The lattice of radiation-damaged zircons expands mainly from α-decays of radioactive elements such as U and Th. Although old radiation-damaged zircons show anomolous lattice distortion, young radiation-damaged zircons do not show such distortions. These distortions are caused by thermal recovery that suppresses the Si4+–Zr4+ repulsion between the SiO4 tetrahedron and ZrO8 dodecahedron. These changes in structure can be understood by considering the cation–cation repulsion between the SiO4–ZrO8 shared edges.

The stability of hauerite (MnS2) as compared to that of pyrite (FeS2) can be explained by the long Mn–S distance and departure from the typical pyrite-type structures. The structural differences of MnX2 compounds (X=S, Se, and Te) are the result of spin configurations that are different than those of other MX2 compounds; however, the arrangement of d-electrons and the size of the ions in MnX2 compounds do not clearly explain why Mn2+ in MnX2 does not exist as a low spin state. To investigate the structural differences of MnX2 compounds, we synthesized single-crystal MnTe2 and MnSe2 and performed single-crsytal X-ray diffraction experiments. The single-crystal X-ray diffraction experiments were conducted on MnTe2 [a=6.9513(1) Å, u-parameter=0.38554(2), space group Pa3̅, Z=4], MnSe2 [a=6.4275(2) Å, u-parameter=0.39358(2)], MnS2 [hauerite; a=6.1013(1) Å, u-parameter=0.40105(4), obtained from Osorezan, Aomori, Japan], and FeS2 [pyrite; a=5.4190(1) Å, u-parameter 0.38484(5), obtained from Kawarakoba, Nagasaki, Japan]. The X-ray intensity datasets of these compounds do not show any evidence of symmetry reduction. In MnS2, the S–S distance is 2.0915(8) Å, which is significantly shorter than that of FeS2 (2.1618(9) Å), and the mean square displacement of S (U 11=0.00915(9) Å2) is smaller than that of Mn (U 11=0.01137(9) Å2). The thermal vibration characteristics of MnX2 compounds are significantly different than those of FeS2. Based on structural refinement data, we discuss the low spin state of MnX2 compounds and the structural stability of pyrite-type structures.