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<jats:title>Abstract</jats:title> <jats:p>The Chemical Vapor Transport (CVT) Reaction is an important and efficient method of synthesizing pyrite crystals. CVT-grown pyrites have been comprehensively investigated for physical properties and elemental chemical compositions. However, the isotopic compositions have not been investigated. In this study, four series of pyrite crystals (PY3, PY4, PY5, and PY6) were synthesized using the CVT method, with PY5 undoped and the others doped with nickel. The synthesized crystals were characterized qualitatively with confocal laser Raman microspectroscopy and quantitatively by EMPA, LA-ICP-MS, SIMS, and IRMS. The synthetic products are irregular polycrystalline aggregates or cubic and octahedral monocrystals, with characteristic Raman bands at ~344 cm–1, ~380 cm–1/377 cm–1, ~427 cm–1/430 cm–1, and S/Fe weight and atomic ratios of 1.15–1.17 and 2.01–2.04, respectively, indicative of pyrite. The pyrites contain traces of inevitable impurities such as Si and Br. The nickel contents of Ni-doped pyrites are heterogeneous, 39–27 300 ppm for PY3, 24–21 700 ppm for PY4, and 57–2610 ppm for PY6. By comparison, the δ34S values obtained by SIMS are relatively homogeneous (PY3 = 17.3 ± 0.9‰, PY4 = 17.7 ± 0.8‰, PY5 = 17.9 ± 0.8‰, PY6 = 17.7 ± 0.6‰, ±2SD), and are consistent with IRMS δ34S values (17.8 ± 0.2‰ for PY3, 18.3 ± 0.9‰ for PY4, 18.2 ± 0.3‰ for PY5, 18.1 ± 0.1‰ for PY6, ±2SD). The homogeneity of 34S/32S suggests that CVT has the potential to synthesize reference materials for the determination of sulfur isotopic composition of pyrite using in situ techniques. Additionally, we also investigated the matrix effects of nickel in pyrite on the measurement of 34S/32S by SIMS, and a preliminary equation of Δ34S (‰) = –0.59 × Ni (wt%)0.27 (R2 = 0.3), where Δ34S is the discrepancy between in situ and bulk δ34S values, was derived for calibration.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Bridgmanite, the most abundant mineral in the lower mantle, can play an essential role in deep-Earth hydrogen storage and circulation processes. To better evaluate the hydrogen storage capacity and its substitution mechanism in bridgmanite occurring in nature, we have synthesized high-quality single-crystal bridgmanite with a composition of (Mg0.88Fe0.052+Fe0.053+Al0.03)(Si0.88Al0.11H0.01)O3 at nearly water-saturated environments relevant to topmost lower mantle pressure and temperature conditions. The crystallographic site position of hydrogen in the synthetic (Fe,Al)-bearing bridgmanite is evaluated by a time-of-flight single-crystal neutron diffraction scheme, together with supporting evidence from polarized infrared spectroscopy. Analysis of the results shows that the primary hydrogen site has an OH bond direction nearly parallel to the crystallographic b axis of the orthorhombic bridgmanite lattice, where hydrogen is located along the line between two oxygen anions to form a straight geometry of covalent and hydrogen bonds. Our modeled results show that hydrogen is incorporated into the crystal structure via coupled substitution of Al3+ and H+ simultaneously exchanging for Si4+, which does not require any cation vacancy. The concentration of hydrogen evaluated by secondary-ion mass spectrometry and neutron diffraction is ~0.1 wt% H2O and consistent with each other, showing that neutron diffraction can be an alternative quantitative means for the characterization of trace amounts of hydrogen and its site occupancy in nominally anhydrous minerals.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The phase relations of Al-bearing magnetite were investigated between 6–22 GPa and 1000–1550 °C using a multi-anvil apparatus. This study demonstrates that the spinel-structured phase persists up to ~9–10 GPa at 1100–1400 °C irrespective of the amount of hercynite (FeAl2O4) component present (20, 40, or 60 mol%). At ~10 GPa, the assemblage Fe2(Al,Fe)2O5 + (Al,Fe)2O3 forms and remains stable up to 16–20 GPa and 1200–1550 °C. Fe2(Al,Fe)2O5 adopts the CaFe3O5-type structure with the Cmcm space group. At 18–22 GPa and T &amp;gt;1300 °C the assemblage Fe3(Fe,Al)4O9 + (Al,Fe)2O3 becomes stable. Fe3(Fe,Al)4O9 is isostructural with Fe7O9, having the monoclinic structure of the C2/m space group. At T &amp;lt;1300 °C, Fe3(Fe,Al)4O9 + (Al,Fe)2O3 gives way to the assemblage of a hp-Fe(Fe,Al)2O4 + (Al,Fe)2O3. This hp-Fe(Fe,Al)2O4 phase is unquenchable; a defect-bearing spinel-structured phase was recovered instead, and it contained numerous lamellae parallel to {100} or {113} planes and notably less Al than the initial starting composition. While low-pressure spinel can have a complete solid solution between Fe3+-Al, the post-spinel phases have only very limited Al solubility, with a maximum of ~0.1 cpfu Al in hp-Fe(Fe,Al)2O4, ~0.3 cpfu in Fe2(Fe,Al)2O5, and ~0.4 cpfu in Fe3(Fe,Al)4O9, respectively. As a result, the phase relations of Fe(Fe0.8Al0.2)2O4 can also be applied to bulk compositions richer in Al with the only difference being that larger amounts of an (Al,Fe)2O3 phase are present.</jats:p> <jats:p>Coexisting rhombohedral-structured phases demonstrate that the binary miscibility gap established at low pressure between hematite and corundum is still valid up to 20 GPa. Since iron oxides (e.g., magnetite) with variable Al contents are found in extraterrestrial rocks or as inclusions in diamond, constraints on their high-P-T-fO2 stability might help unravel their formation conditions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The geographic provenance of minerals provides key insights into a range of geologic problems, including the source of gem materials. The tourmaline supergroup is unparalleled in its ability to record and preserve extensive chemical signatures of its formational environment. To evaluate the likelihood that tourmalines of similar compositions from separate geographic localities could be differentiated, a multivariate statistical approach has been utilized on two complementary data sets. These chemical analytical data sets of copper-bearing “Paraíba” tourmaline include data sets acquired with Laser Induced Breakdown Spectroscopy (LIBS) and electron microprobe analysis (EMPA).</jats:p> <jats:p>Fifty-four samples of copper-bearing tourmalines from known source locations from Brazil (São José de Batalha of Paraíba state and the neighboring Rio Grande do Norte state), Mozambique, and Nigeria, were analyzed using LIBS with a subset of these samples analyzed by EMP. Data sets obtained by each method were evaluated with multivariate statistics (PCA, PLSR). Although the sample set is limited, sequential PLSR modeling of the spectra clearly distinguished the four localities with high success: &amp;gt;95% for LIBS and &amp;gt;87% for EMP. The statistical analyses of the two techniques, LIBS and EMP, suggest that each technique emphasizes different elements for discrimination when considered in the context of the available data. The elements Cu, Mn, Fe, Mg, Ti, Zn, K, H, Co, and V were significant in LIBS chemometric models. Statistically significant elements in EMP models were Mn, Cu, Al, Ca, K, and F. Each technique results in a robust determination for geographic provenance of tourmalines with comparable compositions. The significant distinguishing chemical elements reflect geochemical distinctions in each host environment that are imparted on the tourmaline. Multivariate statistics applied to LIBS and EMP data provide an effective tool for provenance discrimination of Paraíba tourmalines, distinguishing Brazilian-sourced samples from African-sourced materials. These data provide new methods for separating the geographic origin of minerals with very similar composition such as demonstrated here for copper-bearing tourmalines.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Natural and anthropogenic chelating ligands play important roles in promoting mineral dissolution during water-rock interactions. To address the remaining issue of how chelating ligands participate in the dissolution of minerals, this study investigated the dissolution characteristics of seven types of silicate minerals in the presence of a chelating ligand, N,N-bis(carboxymethyl)-L-glutamic acid (GLDA), which is a glutamic acid derivative, through batch dissolution experiments. The results showed that the dissolution of all types of silicate minerals, i.e., olivine (nesosilicate), epidote (sorosilicate), tourmaline (cyclosilicate), enstatite (single-chain inosilicate), hornblende (double-chain inosilicate), biotite (phyllosilicate), and anorthite (tectosilicate), can be enhanced by up to two orders of magnitude at both pH 4 and 8. The chelating ligand particularly facilitated the dissolution of minerals with a higher Al content, such as tourmaline and anorthite. Furthermore, the presence of chelating ligands enhanced the leaching of not only metals but also Si from minerals, resulting in a more congruent characteristic of mineral dissolution. A possible mechanism is that the chelating ligand adsorbs onto the negatively charged the mineral surface, which attracts more H+ and polarizes Si-O and Mg-O bonds, thereby dissolving the minerals at a faster rate. These results have significant implications for understanding the dissolution of minerals in nature and for the application of chelating agents in geological and materials engineering.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The conditions of pyrite (Py) stability inform the extent of S mobility during prograde metamorphism, the formation of orogenic Au deposits, and the S cycle in subduction zones. The variables that affect Py stability and chalcophile element mobility are investigated in the Pacific Rim Terrane of Vancouver Island, Canada, where sulfide-bearing carbonaceous sediments have been metamorphosed from 230 to 600 °C and 4 kbar by mid-ocean ridge subduction in a hot fore arc setting during the Eocene. The petrographic evidence in the rocks shows Py can coexist with pyrrhotite (Po) over a wide temperature window to &amp;gt;550 °C as preserved in porphyroblasts of andalusite, staurolite, and garnet. Conversely, equilibrium phase diagrams constructed for the rock compositions conflict with observations and suggest the breakdown of primary Py occurs over a narrow temperature range below 400 °C. The phase diagrams are consistent with the coexistence of Py and Po up to lower amphibolite facies only if S locally comprises a much greater proportion involved in a reaction than that of the overall bulk-rock composition used in the calculations. While the chemistry of the bulk rocks and Po included in porphyroblasts show mobilization of H2O and S with increasing metamorphic grade of the forearc, this process appears unrelated to the distribution of chalcophile elements or Au deposits found in the Pacific Rim Terrane.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>There is an extensive range of carbon substances with poorly ordered structures that are not well understood. Yet they are important indicators of conditions of related geological processes. The carbon minerals include nanocrystalline graphite, natural analogs of glass-like carbon (GLC)—shungite and impact ultrahigh-pressure GLC, recently discovered ultranocrystalline diamond, as well as natural carbon nanocomposites of diamond, lonsdaleite, and graphite. Studying these natural carbon substances using a standard Raman approach with excitation by visible radiation may lead to a significant distortion of the understanding of their phase states. This paper presents in detail for the first time the spectral features of natural, poorly ordered, and multiphase sp2-sp3 carbon composites by multi-wave Raman spectroscopy using laser excitations from visible to ultraviolet light applied to natural low-ordered carbon substances—nanocrystalline graphite and shungite, nanocrystalline and ultranocrystalline diamond, and multiphase carbon aggregates. The carbon state resolution advantages of ultraviolet Raman spectroscopy for phase analysis of nanostructured and poorly ordered polycomponent carbon substances containing sp2- and sp3-carbons are presented. Raman spectroscopy with ultraviolet excitation can also be applied in the analysis of industrial carbon materials, such as glassy carbon and functional carbon nanocomposites, including ultranocrystalline diamond, lonsdaleite, and amorphous sp3-carbon components.</jats:p>