Icosahedrite, natural icosahedral Al 63 Cu 24 Fe 13 , was discovered in a meteorite about 15 years ago. We have carried out a high-resolution X-ray diffraction study on a sample of this meteoritic mineral at the ESRF. The diffraction pattern turned out to be identical to an intermediate phase observed in synthetic i -AlCuFe during the transformation from the quasicrystalline state to a periodic rhombohedral phase. This particular natural Al 63 Cu 24 Fe 13 grain is an icosahedral quasicrystal on which a modulation by six cosine waves propagating along the fivefold axes is superimposed, with a wavelength of about 20 nm and a polarization in the phason/perpendicular space. By examining the thermodynamic conditions for producing this modulated icosahedral phase at high pressure in the laboratory, we may gain insights into the formation process of the Khatyrka meteorite.

Oxygen fugacity (fO2) controls the speciation of COH fluids in Earth's mantle; a major question is whether the sublithospheric mantle is metal-saturated, maintaining fO2 near the Iron-Wustite (IW) buffer reaction. If so, then COH fluids from this source will be dominated by CH4 + H2, rather than the more oxidized CO2-H2O fluids commonly considered in petrological studies. A key to this question is found in rare but widespread examples of natural mineral assemblages that require unusually low fO2. We summarize an investigation of super-reduced mineral assemblages in corundum xenocrysts from Late Cretaceous alkali-basalt volcanoes on Mt Carmel, northern Israel and related Plio-Pleistocene alluvial deposits. P-T estimates indicate that the corundum xenocrysts crystallized in the uppermost mantle. The well-documented geological controls on the origin of these deposits, and radiometric dating of the super-reduced phases, ensure the "naturalness" of the controversial assemblages and make these mineral par-ageneses a benchmark for evaluation of related occurrences worldwide.The tuffs contain a "basalt-megacryst" mineral suite (zircon, sapphire, ilmenite, spinel). The megacryst chemistry and the geochronology of the zircons indicate that the megacrysts crystallized from broadly syenitic melts that differentiated at subcrustal levels (P ca 1 GPa) within a thick gabbroic underplate built up from Permian through Pliocene time and perhaps into the Pleistocene. Reaction of mantle-derived CH4-H2 fluids with these syenitic melts led to the separation of immiscible Fe0 and Fe-Ti oxide melts near fO2 = IW. Trace-element distributions suggest the syenitic melts then separated into immiscible Si-Al-Na-K-rich and FeO-rich oxide melts; the latter were enriched in HFSE, REE, P and Zr as in other natural and synthetic examples of melt-melt immiscibility.In a model magma chamber the FeO-rich melts would sink, leaving the Si-Al-Na-K melts in an upper zone, both still fluxed by CH4-H2 fluids. At fO2 of DIW-6 to-7 the removal of immiscible Fe-Ti-Si-C silicide melts from the FeO-rich melt would leave a desilicated Ca-Al-Si oxide melt that crystallized high-Ti corundum hibonite cumulates with inclusions requiring fO2 from DIW + 2 to DIW-9, while the less-reduced conjugate silicate melts in the upper levels crystallized low-Ti corundum. Aggregates of skeletal, strongly Ti-zoned corundum crystals. reflect rapid crystallization from very reduced melt-fluid mixtures, probably in fluid-escape channels. Explosive eruptions sampled individual magma chambers at different depths and with different initial compositions, fluid mixtures and fluid dynamics to produce Mt Carmel's mineralogical diversity.A review of similar occurrences worldwide suggests that the Mt Carmel assemblages reflect a fundamental process - the rise of CH4-H2 fluids into the upper mantle --that accompanies mantle-derived magmatism in many tectonic settings. The interaction of these fluids with lithospheric mantle rocks

Experiments aimed at the synthesis of Cr- and Ti-bearing phlogopite in the silicate-carbonate systems peridotite—K2CO3 + H2O and basalt—K2CO3 + H2O at 7 GPa and 900–1200°С were carried out. It is shown that the crystallization of titanium-bearing phlogopite requires subducted crustal material at mantle depths. However, the mantle peridotite should predominate over basalt for Ti-phlogopite crystallization; otherwise, dioctahedral mica (aluminoceladonite) with (Mg + Fe)/VIAl > 1 is formed via the scheme 2VIAl = VITi4+ + VI(Mg + Fe). The competitive behavior of Ti and Cr upon incorporation into phlogopite is considered. It is shown that the presence of >1.3 wt

Chemical and structural data of two Cu-rich coloradoite crystals from Kalgoorlie, Australia, are reported. Two grains with simple stoichiometries, i.e., Hg1 – xCuxTe with x ~0.30, and ~0.22, were characterized by single-crystal X-ray diffraction and electron-probe microanalysis. In the absence of single-crystal data it might be tempting to hypothesize that the presence of large amounts of other elements can induce some ordering leading to distinct mineral species. However, structural analyses show that all of the phases are cubic and crystallize in the space group $$F\overline 4 3m$$ . On the basis of information gained from the chemical and structural characterization it can be concluded that there is a complete solid solution between coloradoite and a possible, still unknown, Cu-coloradoite in nature.

A review of the data available on the composition and abundance of titanium-bearing phases in the Earth’s mantle is provided in the paper. The main attention is paid to the discussion of natural minerals: the patterns of the mineralogy of mantle titanium-bearing phases (rutile, FeTiO3 ilmenite, garnet, pyroxene, spinel and post-spinel phases, phases with ilmenite- and perovskite-type structures, armalcolite) are given, the likely mechanisms of titanium incorporation into mantle phases, as well as the limiting titanium concentrations in these phases are considered. The new experimental data on the composition and conditions of the formation of titanium-bearing minerals and their phase associations at different mantle depths is generalized: phase relations in Ti-bearing systems (MgO–SiO2–TiO2 ± Al2O3) and the influence of titanium on the parameters of the most important phase transformations under the conditions of the mantle are considered. Agreement of the experimental results with the natural data allows us to clarify the patterns of the interphase titanium partitioning and the minor-element composition of the Earth’s deep geospheres.

The Mars exploration rovers have used various remote-sensing instruments over the last two and a half decades. The Chemistry and Camera tool uses laser-induced breakdown spectroscopy to obtain semi-quantitative elemental abundances. The SuperCam instrument is a response to the requirement for remote mineralogy and is also adapted for Raman spectroscopy studies. Both analyzers contain pulsed laser units with Nd:YAG rods and Pockels cells with crystals of rubidium titanyl phosphate, potassium titanyl phosphate and lithium triborate. The specific features of their structure, chemistry, and crystal growth are discussed.

Coarse-grained xenoliths of hibonite + grossite + Mg-Al-V spinel from Cretaceous pyroclastic rocks on Mt. Carmel, N. Israel, and from Sierra de Comechingones, Argentina, include spherules, rods and dense branching structures of native vanadium and V-Al alloys. Microstructures suggest that vanadium melts became immiscible with the host Ca-Al-Mg-Si-O melt, and nucleated as droplets on the surfaces of the oxide phases, principally hibonite. Many extended outward as rods or branching structures as the host oxide crystal grew. The stability of V-0 implies oxygen fugacities >= 9 log units below the Iron-Wustite buffer, suggesting a hydrogendominated atmosphere. This is supported by wt%-levels of hydrogen in gasses released by crushing, by Raman spectroscopy, and by the presence of VH2 among the vanadium balls. The oxide assemblage formed at 1400-1200 degrees C; the solution of hydrogen in the metal could lower the melting point of vanadium to these temperatures. These assemblages probably resulted from reaction between differentiated mafic melts and mantle-derived CH4 + H-2 fluids near the crust-mantle boundary, and they record the most reducing magmatic conditions yet documented on Earth. (C) 2020 Elsevier B.V. All rights reserved.

Biagioniite, ideally Tl 2 SbS 2 , is a new mineral from the Hemlo gold deposit, Marathon, Ontario, Canada. It occurs as very rare anhedral crystals up to 65 μ m across associated with aurostibite, stibarsen and native gold in a calcite matrix. Biagioniite is opaque with a metallic lustre and shows a black streak. In reflected light biagioniite is moderately bireflectant and not pleochroic. Under crossed polars it is weakly anisotropic with blueish to light-blue rotation tints. Internal reflections are absent. Reflectance percentages for the four standard wavelengths ( R min and R max ) are 35.9 and 37.5 (471.1 nm); 34.7 and 36.2 (548.3 nm); 33.8 and 35.3 (586.6 nm); and 31.5 and 33.7 (652.3 nm), respectively. A mean of four electron microprobe analyses gave: Tl 65.12(31), Ag 3.52(9), Sb 20.22(12), S 10.80(8), total 99.66 wt.%, corresponding, on the basis of a total of 5 atoms, to (Tl 1.87 Ag 0.19 ) Σ 2.06 Sb 0.97 S 1.97 . Biagioniite is monoclinic, space group Pc , with a = 11.0895(9), b = 14.3124(11), c = 7.9352(6) Å, β = 96.230(8)°, V = 1252.02(17) Å 3 and Z = 8. The four strongest powder-diffraction lines [ d in Å ( I/I 0 ) ( hkl )] are: 3.56 (100) (310); 3.37 (75) ( (cid:1) 231); 3.79 (60) (012); 3.03 (60) (032). In the crystal structure [ R 1 = 0.024 for 2655 reflections with I > 2 σ ( I )], thallium adopts various coordinations extending from quasi-linear to quasi-tetrahedral. Antimony forms Sb – Sb pairs, which lead to the formula [Tl +1 ] 4 [Sb 2 ] 4+ [S 2 – ] 4 . Biagioniite is isostructural with dervillite, Ag 2 AsS 2 . The new mineral has been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA2019 – 120) and named for Cristian Biagioni, Associate Professor of Mineralogy at the Department of Earth Sciences of the University of Pisa, Italy.

Ivanova et al. ( ) proposed that the aluminides we described in the Khatyrka meteorite fragments, both crystal and quasicrystal metal phases, were derived from industrial materials used during placer gold mining and that these had been shredded and blast‐propelled into natural meteoritic material that happened to be at the site. The blast hypothesis was not supported by evidence that metal shrapnel or metal parts from mining operations (or from any other industrial use) occur at the site that are similar in composition to the aluminides that we described in Khatyrka; we doubt such compositions would exist because alloys with the compositions we reported have no known industrial applications. We further show that this hypothesis cannot be reconciled geologically, chemically, or physically with our observations. These observations demonstrate that the fragments central to our study have been embedded below gold‐bearing fluvial gravels in undisturbed sediment for at least ~6670 to 8004 14 C years before mining operations commenced. The case presented here thus specifically rules out the blast hypothesis and also presents a challenge to other anthropogenic explanations. We also address each of Ivanova et al.'s points challenging our conclusion that the silicates attached to the aluminides were CV 3 chondritic minerals.

K 2 Sc[Si 2 O 6 ]F exhibits, at room temperature, a (3 + 2)-dimensional incommensurately modulated structure [ a = 8.9878 (1), c = 8.2694 (2) Å, V = 668.01 (2) Å 3 ; superspace group P 4 2 / mnm (α,α,0)000 s (−α,α,0)0000] with modulation wavevectors q 1 = 0.2982 (4)( a * + b *) and q 2 = 0.2982 (4)(− a * + b *). Its low-temperature behaviour has been studied by single-crystal X-ray diffraction. Down to 45 K, the irrational component α of the modulation wavevectors is quite constant varying from 0.2982 (4) (RT), through 0.2955 (8) (120 K), 0.297 (1) (90 K), 0.298 (1) (75 K), to 0.299 (1) (45 K). At 25 K it approaches the commensurate value of one-third [ i.e. 0.332 (3)]: thus indicating that the incommensurate–commensurate phase transition takes place between 45 K and 25 K. The commensurate lock-in phase of K 2 Sc[Si 2 O 6 ]F has been solved and refined with a 3 × 3 × 1 supercell compared with the tetragonal incommensurately modulated structure stable at room temperature. This corresponds to a 3 × 1 × 3 supercell in the pseudo-orthorhombic monoclinic setting of the low-temperature structure, space group P 2/ m , with lattice parameters a = 26.786 (3), b = 8.245 (2) c = 26.824 (3) Å, β = 90.00 (1)°. The structure is a mixed tetrahedral–octahedral framework composed of chains of [ScO 4 F 2 ] octahedra that are interconnected by [Si 4 O 12 ] rings with K atoms in fourfold to ninefold coordination. Distorted [ScO 4 F 2 ] octahedra are connected to distorted Si tetrahedra to form octagonal arrangements closely resembling those observed in the incommensurate structure of fresnoite- and melilite-type compounds.

The Khatyrka meteorite contains both icosahedral and decagonal quasicrystals. In our previous studies, icosahedral quasicrystals have been synthesized and recovered from shock experiments at the interface between CuAl 5 and stainless steel 304 alloys. In this study, we report a new shock recovery experiment aimed at synthesizing decagonal quasicrystals similar to decagonite, natural Al 71 Ni 24 Fe 5 . Aluminum 2024 and permalloy 80 alloys were stacked together and shocked in a stainless steel 304 recovery chamber. Abundant decagonal quasicrystals of average composition Al 73 Ni 19 Fe 4 Cu 2 Mg 0.6 Mo 0.4 Mn 0.3 with traces of Si and Cr were found along the recovered interface between the Al and permalloy. The experiment also synthesized AlNiFe alloy with the B2 (CsCl-type) structure and the metastable Al 9 Ni 2 phase. We present chemical (scanning electron microscopy and electron microprobe) and structural (electron backscatter diffraction and transmission electron microscopy) characterization of the recovered phases and discuss the implications of this shock synthesis for the stability of quasicrystals during high-pressure shocks and for the interpretation of the phase assemblage found in Khatyrka.

A chromium-bearing wadsleyite (Cr-Wad) was synthesized in the model system Mg2SiO4–MgCr2O4 at 14 GPa and 1600 °C and studied from the chemical and structural point of views. Microprobe data gave the formula Mg1.930Cr0.120Si0.945O4, on the basis of 4 oxygen atoms. The crystal structure has been studied by single-crystal X-ray diffraction. The orthorhombic unit-cell parameters are: a = 5.6909(5) Å, b = 11.4640(10) Å, c = 8.2406(9) Å, V = 537.62(9) Å3, Z = 8. The structure, space group Imma, was refined to R 1 = 5.99% in anisotropic approximation using 1135 reflections with F o > 4σ(F o) and 43 parameters. Chromium was found to substitute for both Mg at the octahedral sites and Si at the tetrahedral site, according to the reaction VIMg2+ + IVSi4+ = VICr3+ + IVCr3+. On the whole, the structural topology is nearly identical to that of pure wadsleyite. The successful synthesis of Cr-Wad may be important for the thermobarometry of mantle phase associations.

AbstractThe crystal structure and the chemical composition of uklonskovite from the holotype material was reinvestigated to shed light on its correct chemical formula. On the basis of information gained from this characterization, we revised the formula from NaMg(SO4)OH·2H2O to NaMg(SO4)F·2H2O (F instead of OH). A careful analysis of the structural details together with a critical review of all the chemical data listed in the scientific literature for uklonskovite support our redefinition. We also present Raman data for the mineral for the first time. Our proposal was approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (voting proposal 16-J).

In the manganesiferous ores associated with the metacherts of the ophiolitic sequences at the Cerchiara mine, Eastern Liguria (Italy), a new Mn-bearing mineral belonging to the mica group has been recently found and characterized. High resolution transmission electron microscopy and electron diffraction tomography studies confirm that the mineral belongs to the mica group. Unit-cell parameters from the powder diffraction pattern are: a = 5.149(1), b = 8.915(1), c = 10.304(1) angstrom,beta = 102.03(1)degrees, space group C2 or C2/m. On the basis of the electron paramagnetic resonance spectroscopic results, the Mn4+ content represents a very subordinate fraction of the total Mn, the remaining occurring as Mn3+. The Raman spectrum clearly indicates the presence of OH groups in the structure. Laser-ablation inductively-coupled-plasma mass-spectrometry measurements assess the presence of considerable amounts of Li.Assuming all Mn as Mn3+ and 22 negative charges, the empirical formula can be expressed as: (K-0.83 square (0.17))(Mn1.143+Mg0.80Li0.20Fe0:023+)(Si3.89Al0.10)O-10[(OH)(1.92)F-0.08] with the sum of the octahedral cations indicating a 'transitional' character between a di- and a tri-octahedral structure. This formula corresponds ideally to the Mn3+ analogue of celadonite, thus expanding the range of solid solution in the celadonite family. The ideal end-member formula KMn3+MgSi4O10(OH)(2) can be easily related to celadonite by the homovalent substitution Mn-VI(3+)-> Fe-VI(3+). The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association, (IMA 2015-052).

The high-pressure silicate K1.5Mg2Si2O7H0.5, synthesized and characterized by Welch et al. [(2012), Am. Mineral. 97, 1849-1857], has been re-examined with the aim of determining the nature of the superstructure noted in their study. The composition corresponds to a 1:1 combination of KMg2Si2O7H and K2Mg2Si2O7 end-members, but it is not a solid solution. Single-crystal X-ray diffraction data for one of the original K1.5Mg2Si2O7H0.5 crystals synthesized at 16 GPa/1573 K, has been collected using a much longer exposure time in order to improve the intensity statistics of weak superlattice reflections identified by Welch et al. (2012). The superstructure has been determined using a superspace approach as having the superspace group Cmcm(0,β,0)00s and t0 = 1/16 with refined parameters a = 8.7623 (10), b = 5.0703 (7), c = 13.2505 (11) Å, V = 588.69 (12) Å3. This structure corresponds to one with the conventional space group Pbnm and unit-cell parameters a = 8.7623 (10), b = 20.281 (3), c = 13.2505 (11) Å, V = 2354.7 (5) Å3 and is based upon a super-sheet motif in which ordering involves rows of pairs of vacant interlayer K sites. This is the third topologically distinct structure type for the KMg2Si2O7H-K2Mg2Si2O7 join and suggests that there is very limited solid solution, and so it can be expected that each of the three structures (P63cm, P\bar 3 1m and Pbnm) has its own stability field, rather than being part of a continuous compositional series based upon a single structure type. As such, K1.5Mg2Si2O7H0.5 should be considered as a potentially significant host of K in the Earth's mantle.