Volume 110, Issue 12

Ertlite, ideally NaAl 3 Al 6 (Si 4 B 2 O 18 )(BO 3 ) 3 (OH) 3 O, is a new, very B-rich mineral of the tourmaline supergroup. It was found at two localities: the holotype in the Sahatany Valley, central Madagascar, and a cotype specimen from Sakangyi, Mogok Township, Mandalay Region, Myanmar. At both localities, the mineral occurs as a late-stage hydrothermal phase in open pockets within highly fractionated, B-rich granitic pegmatites. The holotype occurs as pink to brownish gray or near colorless euhedral crystals and aggregates, up to 10 mm in diameter, with vitreous luster, conchoidal fracture, and white streak. The mineral is uniaxial (−). Holotype ertlite has a Mohs hardness of ca. 7–8, a calculated density of 3.128 g·cm −3 and an superior compatibility index (1 − K P / K C = 0.018). Cotype ertlite has a Mohs hardness of ca. 7–8, a calculated density of 3.135 g·cm −3 and a superior compatibility index (1 − K P / K C = 0.001). Ertlite has trigonal symmetry, space group R 3 m , with a = 15.6509(8) Å, c = 7.0406(5) Å, V = 1493.55(19) Å 3 (holotype) and a = 15.590(2) Å, c = 7.009(1) Å, V = 1475.3(4)Å 3 (cotype, with the lowest unit-cell volume ever recorded for a natural tourmaline); Z = 3. The crystal structures were refined to R 1 = 2.01% and 3.74%, respectively, using room-temperature data sets collected with Mo K α radiation. Crystal-chemical analysis obtained using electron probe microanalysis, laser ablation inductively coupled plasma mass spectroscopy, Raman spectroscopy, and crystal structure refinement resulted in the following empirical holotype and cotype formulas, respectively: X (Na 0.573 Ca 0.220 □ 0.207 ) Σ1.000 Y (Al 2.760 Li 0.187 Mn 0.051 Ti 0.002 ) Σ3.000 Z (Al6.000) T (Si 4.526 B 1.419 Al 0.055 ) Σ6.000 O 18 B (BO 3 ) 3 V (OH 2.669 O 0.331 ) Σ3.000 W (O 0.786 OH 0.188 F 0.026 ) Σ1.000 (holotype); X (Na 0.743 Ca 0.109 □ 0.146 K 0.002 ) Σ1.000 Y (Al 2.836 Li 0.144 Mn 0.002 Fe 0.010 ) Σ2.992 Z (Al 6.000 ) T (Si 4.053 B 1.955 ) Σ6.008 O 18 B (BO 3 ) 3 V (OH) 3.000 W (O 0.716 OH 0.245 F 0.039 ) Σ1.000 (cotype). Ertlite is an oxy-species that belongs to the sodic group of the tourmaline supergroup. The closest end-member compositions of valid tourmaline species are: olenite by the coupled substitution T Si 4+ + V O 2− → T B 3+ + V OH − accompanied by the disorder exchange V O 2− + W OH − → V OH − + W O 2− , alumino-oxy-rossmanite by the coupled substitution X □+ T Si 4+ + T Al 3+ → X Na + +2( T B 3+ ), and darrellhenryite by the coupled substitution Y Li + +2( T Si 4+ ) → Y Al 3+ +2( T B 3+ ). Ertlite was approved by the IMA-CNMNC (IMA 2023-086); the name honors the tourmaline specialist Andreas Ertl-Winand. Ertlite is closely related to synthetic excess-boron tourmalines. Holotype ertlite formed during a late stage of open pocket crystallization in a highly fractionated granitic pegmatite dike of lithium-cesium-tantalum-enriched type (LCT-type) of likely Pan-African age. Cotype ertlite crystallized in a very similar pegmatite environment.

Secondary ionization mass spectrometry (SIMS) is a powerful tool for precise, correlative actinide decay chain dating, trace element analysis, and stable isotope analysis of accessory minerals, offering unrivaled nanogram-scale sampling. Matrix-matched reference materials are a prerequisite for accurate quantification of isotopic compositions by SIMS. For rock-forming and accessory minerals showing partial or complete solid solution, elaborate correction schemes are required for SIMS isotope analysis. Natural zircon (ZrSiO 4 ), often with a nearly stoichiometric end-member composition, has traditionally required less attention to matrix matching between reference materials and unknowns. However, with increasing analytical precision afforded by multi-collection SIMS instrumentation, it is important to experimentally verify this assumption and define its limitations. Here, we focus on Hf in zircon (Zrn), which is isomorphous with hafnon (Hfn), and the fourth most abundant element in natural zircon. Two end-members in the Zrn-Hfn solid solution and three intermediate compositions were synthesized in a MoO 3 -Li 2 MoO 4 flux. Oxygen isotopic compositions of synthetic Zrn-Hfn crystals were determined at the milligram scale by laser fluorination isotope ratio mass spectrometry, and at lateral and depth resolutions of ∼15 and ∼1 μm, respectively, by SIMS. Despite a detected ∼1–3‰ isotopic heterogeneity in flux-grown Zrn-Hfn, a strong correlation between instrumental mass fractionation and the zirconium number Zr#% (atomic Zr/[Zr+Hf] × 100) was observed (Pearson correlation coefficient r = 0.9958), with ∼8.8‰ variation in δ 18 O across the compositional range. For most natural zircon, including common reference materials, the interpolated matrix effect is smaller than typical analytical uncertainties for individual SIMS spots (∼0.1‰). Only δ 18 O analysis of Hf-rich pegmatite zircon by SIMS requires significant (up to ∼3‰) matrix corrections. In such cases, the matrix effect on instrumental mass fractionation can be linearly interpolated between a common low-Hf zircon reference and the synthetic Hfn end-member to within ∼0.1–0.2‰ uncertainty.

Rocks form in three dimensions through time and studying them provides information from inside dynamic systems we cannot otherwise observe. Yet how we typically access the interior of the rocks themselves to gain that information may limit our understanding and influence how we reconstruct the processes that formed them. Here, we demonstrate combined non-destructive 3D X-ray imaging techniques that produce quantitative densitometric and crystallographic maps of entire individual grains inside a rock. Olivine grains throughout a sample of the carbonaceous chondrite Northwest Africa (NWA) 11346 were each characterized by size, shape, composition, zoning intensity, and crystallographic orientation. The addition of 3D crystallographic mapping to calibrated 3D densitometric analysis — used to calculate chemical composition—demonstrates a fully non-destructive petrographic method and provides unique insight. For instance, in our case, using crystallographic data to delineate individual grains and then measuring the 3D size, shape, and composition of each distinguishes variably reset relict grains from those later crystallized after a melting event. Intersection in a 2D slice could not have led to this interpretation because the integration of three-dimensional size, rounding, composition, location, and crystallographic orientation measured from each grain forms the key patterns. Multimodal laboratory X-ray imaging has strong potential to advance 3D petrography.

World-class Carlin-type Au deposits hosted in sedimentary rock were formed when profuse Eocene silicic magmatism swept across northern Nevada in response to arc migration. Carlin-type Au deposits formed along with porphyry/skarn Cu-Mo-W-Au deposits, epithermal Ag-Au deposits, and distal disseminated Ag-Au deposits. But unlike these other Au-bearing deposits that have clear associations with igneous intrusions, Carlin-type ore deposits appear to have formed distant from concealed plutons, and their origin remains controversial. Despite decades of abundant geophysical, geochronological, and geochemical studies suggesting the involvement of magmas, concrete evidence for magmatic involvement is still lacking. Consequently, the involvement of contemporaneous igneous systems remains inferred based on age, proximity, and variable isotopic, geochemical, and geophysical clues. A recent synthesis of deposit models postulates that Carlin-type Au deposits are intrusion-related, but that the causative magmas reside deeper (∼6–12 km) than in typical porphyry and peripheral systems (∼3–5 km), meaning that Carlin-type deposits are perhaps more distal expressions of igneous intrusions. We investigate a collection of “suspect” magmatic systems over a ∼7 m.y. timespan (∼41–34 Ma) that are contemporaneous with and near known Carlin-type ore deposits. We report results of a multifaceted array of in situ geochemical analyses (FTIR, EMP, SHRIMP-RG, LA-ICP-MS) of quartz-hosted melt inclusions, biotite, and quartz to better characterize the pre-eruptive characteristics of these magmas. We also report results of thermobarometry and thermodynamic phase equilibria modeling to help place constraints on magmatic reservoir depths and processes. Rather than a single “flavor” of silicic magma, we observe a surprisingly broad compositional spectrum of rhyolites, with one end of the spectrum exhibiting more arc-like (I-type) characteristics and the other end displaying more post-subduction, thick-crust extensional (A-type) characteristics. This broad compositional spectrum suggests a more complex picture of silicic crustal magmatism operating over a narrow span of time during slab rollback. Despite this spectrum, magmatic systems in this study are consistently ferroan and generally peraluminous, which we interpret as an expression of the relatively elevated geotherm at the time and incorporation of variable amounts of highly peraluminous metasedimentary crustal components. The silicic magma spectrum encompasses a range of mineralization associations, including subduction-related Cu-Mo-W-Au-Ag and post-subduction, thick-crust extensional rare-metal Mo-Sn-W-F-Be-Ag-Au, consistent with the prolific and diverse array of ore deposits that formed during this time. Carlin-type Au deposition appears to be associated with nearly the entire magmatic spectrum. This apparent indifference to silicic magma “flavor” would seem to imply that if magmas are involved in Carlin-type Au deposit genesis, they perhaps do not need to be compositionally specialized and/or possibly are only relevant as heat sources driving circulation to remobilize and redistribute metals.

X-ray absorption near-edge structure (XANES) spectroscopy enables in situ direct measurements of microscale Fe 2+ /Fe 3+ ratios in minerals and has greatly contributed to the understanding of the redox states during rock formation. Traditionally, the Fe 2+ /Fe 3+ has been quantified based on 1 s →3 d /4 p pre-edge peak features. However, optically anisotropic minerals show significant differences in the absorption of polarized X-rays when measured in different crystallographic orientations, introducing considerable errors in estimates of Fe 2+ /Fe 3+ . Multivariate analysis (MVA) utilizing entire X-ray absorption fine structure (XAFS) spectral features combined with appropriate training data, preprocessing, and hyperparameter optimization, offers a potential solution to this issue. This study examines the X-ray absorption anisotropy of clinopyroxene for six distinct crystallographic orientations relative to X-ray propagation and polarization directions using 11 natural single crystals with a wide range of Fe 3+ /ΣFe (0–0.88) and compositions (diopside, augite, aegirine). We used the full XAFS spectra of the oriented clinopyroxenes to construct MVA models that can accurately estimate Fe 3+ /ΣFe in unknown orientations. Our measurements reveal that most of the XANES absorption-edge peak features display a clear dependence on the polarization direction of the incident X-ray, suggesting that their absorption anisotropy can mainly be ascribed to dipole-allowed 1 s →4 p transition processes. On the other hand, the pre-edge peaks exhibit a complex absorption anisotropy that depends on both the propagation and polarization directions, suggesting a complicated nature of quadrupole-allowed 1 s →3 d transitions enhanced by dipole transitions to mixed 3 d –4 p orbitals. We found that the conventional pre-edge-based determinations of Fe 3+ /ΣFe involve large uncertainties of ±13.5–15.3%Fe 3+ , mainly due to the substantial X-ray absorption anisotropy. Our optimal MVA model, using the least absolute shrinkage and selection operator (Lasso) and trained with autoscaled XANES spectra of oriented clinopyroxenes, can successfully predict %Fe 3+ in clinopyroxenes from within the test data set without prior knowledge of the orientation, with a root-mean-squared error of ±7.8%Fe 3+ . In addition, our results show a good agreement between weighted energy channels of the MVA models and XANES peak features resolved by the polarization-dependent experiment. The MVA coefficients provided in this study offer an effective method for deriving reliable Fe 3+ /ΣFe from XAFS measurements of clinopyroxene, regardless of orientation. This approach highlights the benefits of using features from the pre-edge, main-edge, and post-edge domains of the spectra to establish the relationships.

Apatite is a common accessory mineral in metamorphic rocks, yet its behavior during progressive metamorphism involving extensive anatexis remains underexplored. To address this issue, we conducted petrographic and geochemical analyses of apatite in a series of amphibolite-to-granulite-facies metapelites and granitic gneisses from the Cona area, Southern Tibet, in the eastern Himalaya. These analyses were complemented by phase equilibrium modeling to characterize mineral reaction sequences during anatexis across different pressure-temperature conditions. The results indicate that the minor and trace element compositions of apatite can effectively differentiate protolith type, metamorphic grade, and anatectic mechanism. Apatites in the granitic gneisses exhibit higher F, light rare earth elements (LREE), Y, and Th contents, but lower Sr and Eu contents, as well as a lower positive slope between Cl and FeO contents in the covariant diagram, compared to those in the metapelites. These differences are attributed to variations in protolith composition and the associated mineral assemblage. In both the metapelites and granitic gneisses, apatite grain sizes increase with metamorphic grade; geochemically, apatite LREE contents, as well as its relative contributions to whole-rock LREE and middle rare earth element (MREE) contents, increase with metamorphic grade. Notably, apatites in samples subjected to biotite dehydration melting show lower FeO and MnO contents and higher Tb N /Lu N ratios than those in samples subjected to muscovite dehydration melting. This observation is linked to the formation of peritectic garnet during biotite dehydration melting. These variations with metamorphic grade can be ascribed to the dissolution of pre-existing LREE-rich monazite and MREE-rich apatite, coupled with the recrystallization of residual grains or new growth through incongruent melting reactions during progressive anatexis. Our findings suggest that apatite can act as both a reactant and a product during crustal anatexis, and its geochemistry can serve as an indicator of anatectic mechanisms. Several processes that were not considered in the equilibrium thermodynamic modeling, such as incongruent melting involving accessory minerals and recrystallization or Ostwald ripening under suprasolidus conditions, might enable apatite to develop larger grain sizes and capture the geochemical signatures of anatectic reactions.

Organic acids involved in biological weathering exhibit a strong affinity toward aluminum, thereby facilitating mineral decomposition and leading to the preferential loss relative to immobile elements. Consequently, the process impedes the reprecipitation of clay minerals and affects the congruency of mineral weathering and elemental cycling. However, the effects of organic acid-dominated biological weathering on the composition and structure of clay minerals in natural systems, including sediments, sedimentary rocks, and soils, remain unclear. In this study, we focused on a reticulate laterite profile from the middle reach of the Yangtze River in China, which is characterized by distinct redox features. We conducted a detailed investigation into various indicators, including clay mineral content and crystallinity, iron minerals, weathering intensity, weathering congruency, and biotic weathering proxies along the profile. Our findings reveal a gradual decrease in weathering intensity from the bottom to the top of the profile, concomitant with a transition from warm, humid to arid conditions. The clay-mineral characteristics show significant differences between the upper modern soil layer, which is nearly devoid of smectite, and the lower plinthic horizon, which is almost entirely devoid of vermiculite. Enhanced biotic weathering was associated with organic acid-driven congruent weathering, favoring the preservation of illite and inhibiting its transformation into kaolinite. However, in the lower part of the profile, there was no apparent coupling between clay mineral changes and congruent weathering. This observation suggests that different organic acids dominate weathering processes in the upper and lower layers. Moreover, the alkaline environment and frequent wetting and drying cycles in the lower soil layers favored the formation of smectite. Compared with biotic weathering, the transformation of clay minerals showed a closer association with the overall trend in changes in weathering intensity, suggesting that both biotic and abiotic weathering factors influence the genesis and transformation of clay minerals. The influence of biotic weathering on the composition and structure of clay minerals in natural systems could have significant implications for global elemental cycling, warranting further exploration.

The fractionation of lithium (Li) isotopes in saprolites under intense weathering conditions, particularly in relation to precipitation and mineral types, remains a crucial yet complex aspect of geochemical studies. This study reports Li isotope compositions from saprolites and unaltered bedrock within a basalt weathering profile on Hainan Island, China, a region known for its high rainfall and low dust levels. We observe that Li concentrations in weathering products (ranging from 2.36 to 10.65 μg g −1 ) are generally higher than in the unaltered bedrock (6.54 μg g −1 ). Correspondingly, the δ 7 Li values of these products range from −9.3‰ to +7.4‰, typically lower than those of unaltered bedrock (+4.3‰). Our findings suggest that the impact of rainwater Li on saprolite Li isotopes is not a straightforward mixing of rainwater and bedrock, but rather is modulated by adsorption and desorption processes involving secondary minerals. Notably, the δ 7 Li values in saprolites correlate with the proportion of specific secondary minerals; saprolite δ 7 Li values rise with increased kaolin minerals and drop with more Fe and Al oxide/hydroxide minerals. Integrating these results with previous studies on suspended sediment leaching, we propose that the higher dissolved δ 7 Li values in basaltic catchments, compared to granitic ones, are due to a greater abundance of Fe-Al (hydro)oxides in basaltic catchments. This mineralogical control on saprolite Li isotopes also implies a potential explanation for the observed variations in river δ 7 Li values under different precipitation regimes, influenced by diverse secondary minerals in riverine suspended loads.

Scheelite in the Dongyuan porphyry-type W-Mo deposit, South China, occurs both in porphyritic biotite granite and lamprophyre. Three types of scheelite (Sch A , Sch B , and Sch C ) were identified in the porphyritic biotite granite, whereas two types (Sch a and Sch b ) were recognized in the lamprophyre. The incorporation of rare earth elements (REE) into scheelite occurs mainly via the substitution mechanism represented by 2 [VIII] Ca 2+ = [VIII] REE 3+ + [VIII] Na + , and additionally by 3 [VIII] Ca 2+ = 2 [VIII] REE 3+ +Ca□ (where Ca□ denotes a Ca-site vacancy). The REE patterns of Sch A are similar to those of the porphyritic biotite granite, suggesting that Sch A inherited its REE composition directly from the porphyritic biotite granite. Complex textures in scheelite and the similar geochemical signatures of Sch B1 and Sch B3 imply repeated injections of ore-forming fluids into the porphyritic biotite granite during Sch B formation. The evolution of ore-forming fluids, coupled with the precipitation of apatite and early scheelite (Sch A and Sch B ), led to Sch C with more intense enrichment in middle rare earth elements (MREE). Sch a and Sch B share identical REE patterns, indicating precipitation from the same ore-forming fluids. Prior precipitation of zoisite caused a sharp decline in MREE and heavy rare earth element (HREE) concentrations in Sch B relative to Sch A . The europium anomaly in scheelite reflects an initial rise in oxygen fugacity, followed by a slight decrease from Sch A to Sch B and Sch C . Notably, the most oxidizing conditions are recorded in Sch a from the lamprophyre. A binary plot of V vs. As in scheelite from the porphyritic biotite granite mirrors the oxygen fugacity trends inferred from the europium anomaly, suggesting that the V vs. As relationship may serve as a potential fingerprint for oxygen fugacity in scheelite. The decline in the Y/Ho ratio from early to late scheelite stages likely results from self-precipitation of earlier scheelite, considering that REE-Eu (mol) and Y (mol) are incorporated into scheelite at a 2:1 ratio. Calcium necessary for scheelite formation is sourced from sericitization of calcic plagioclase in the porphyritic biotite granite and biotitization of mafic minerals (e.g., hornblende) in the lamprophyre. This study demonstrates that different host rocks significantly influence the evolutionary pathways and physicochemical properties of ore-forming fluids. Water-rock interactions are crucial at multiple stages of scheelite precipitation in the Dongyuan deposit.

Enhanced reverse weathering is pivotal for sustaining the persistent ice-free climate during the mid-Proterozoic despite low solar irradiance. Silicon-rich seawater is considered the primary factor driving reverse weathering; however, authigenic clay minerals, the major products of reverse weathering, are not consistently more abundant in siliceous rocks, implying the existence of additional controlling factors. Here, we analyzed Mesoproterozoic siliceous rocks from the ∼1.1 Ga Songziyuan Formation of South China, using multiple techniques. The results show that berthierine and stilpnomelane, the dominant authigenic clay minerals, are enriched solely under silica-rich, anoxic, and iron-rich micro-environments. These data support the hypothesis that anoxic, iron-rich conditions may have played a crucial role in promoting reverse weathering, specifically the authigenesis of Fe-bearing clay minerals in silica-rich environments. The predominantly short-term, iron-rich conditions [e.g., Fe(II) > 50 μM] in the mid-Proterozoic silica-rich ocean may have enhanced reverse weathering and thereby facilitated long-term ice-free climate conditions.

Near-liquidus crystallization experiments were performed on a high-Mg andesite from the Izu-Bonin-Mariana forearc to study the effect of H 2 O on the orthopyroxene crystallization temperature. Experiments were conducted at 200 and 500 MPa in an internally heated pressure vessel at temperatures ranging from 1260 to 1075 °C. Orthopyroxene was the liquidus phase at both investigated pressures. H 2 O contents in quenched glasses were quantified via Raman spectroscopy. The liquidus depression for orthopyroxene at 200 MPa can be described by the following equation: ΔTdry liq =26.02(±1.84)⋅CH2O0.933(±0.050), ${\it \Delta} T^{\text {dry liq }}=26.02( \pm 1.84) \cdot C_{\mathrm{H}_2 \mathrm{O}}^{0.933( \pm 0.050)},$where Δ T dry liq is the difference between the anhydrous liquidus temperature (in °C) and the liquidus at a specific melt water concentration CH2O $C_{\mathrm{H}_2 \mathrm{O}}$(in wt%). The liquidus depression curve at 500 MPa can be described by a linear equation: ΔTdry liq =25.72(±0.20)⋅CH2O. ${\it \Delta} T^{\text {dry liq }}=25.72( \pm 0.20) \cdot C_{\mathrm{H}_2 \mathrm{O}} .$The experimental data set demonstrates that the orthopyroxene liquidus depression shows no significant pressure dependence with respect to absolute melt H 2 O concentrations. Thermodynamic and petrological models predict a more pronounced nonlinear behavior and generally overestimate the role of H 2 O on orthopyroxene liquidus depression at H 2 O contents below 5 wt% while partly underestimating it at higher H 2 O contents. Comparing our data set with experimental results taken from literature obtained for a high-Mg basaltic andesite and different boninites confirms the validity of our orthopyroxene liquidus parameterization for a wider range of melt compositions. A comparison with previous experimental data obtained for olivine and plagioclase shows that the effect of H 2 O on the depression of the liquidus temperature of orthopyroxene is slightly lower than for olivine while the plagioclase liquidus temperature is depressed more significantly in the presence of H 2 O. Our experimental data can be used for predicting liquidus temperatures for hydrous melts in which orthopyroxene appears as the liquidus phase. Moreover, the empirical parameterization can be incorporated in petrological models to improve modeling of crystallization paths of hydrous magmas.

Bradleyite, a sodium phosphate-magnesium carbonate, Na 3 Mg(PO 4 )(CO 3 ), occurs in sedimentary salt rocks and in igneous, carbonatitic, and kimberlitic rocks. In this paper, we present the characteristics of a bradleyite sample found in a new geological environment as an inclusion in a diamond from the Córigo Sorriso placer deposit in Mato Grosso State, Brazil, where other unusual mineral inclusions in diamond were earlier identified. Bradleyite is part of a polymineral inclusion, comprising a porous aggregate of grains <150 nm in size, hosted within a dolomite crystal. The studied bradleyite is characterized by the highest MgO+FeO concentrations and the lowest Na content among bradleyites from other localities. It demonstrates significant variability in composition, particularly Na (28.75–37.84 mass % Na 2 O). Nitrogen was also detected by EDS analysis. We report for the first time the ab initio crystal structure of natural bradleyite. It has monoclinic symmetry, with cell parameters a = 8.684 Å, b = 6.804 Å, c = 5.074 Å, and β = 90.34°. The structure was solved ab initio and refined using dynamical scattering theory in space group P 2 1 / m , confirming the model obtained from powder XRD analysis of synthetic analogs. The final structure model converged to a formula Na 3 (Mg 0.86 Fe 0.14 )(PO 4 )(CO 3 ), Z = 2. Bradleyite is a polygenetic mineral. In continental salt deposits, it forms under atmospheric pressure during sedimentation. In deep-formed igneous rocks, such as kimberlites and carbonatites, bradleyite occurs as a product of late-stage crystallization of carbonatitic melt and as a primary-crystallized phase in deep-seated minerals, such as olivine, ilmenite, chrome spinel, and magnetite. Our findings demonstrate its stability in diamond and diamond-forming environments and that it may be considered a product of crystallization from a primary melt inclusion.

The ionic radii of rare earth elements (REE: Sc, Y, and the lanthanides) are key to interpreting partitioning behavior between minerals and melts for use as petrogenetic tracers and thermometry. Of REE, Y commonly has the highest concentration and serves as a reference against which other REE concentrations or partition coefficients can be compared. Here, we show that published experimental data on mineral-melt partitioning of REE imply the ionic radius of Y 3+ is smaller than commonly assumed by 0.001 Å for sixfold coordination to 0.005 Å for eightfold and ninefold coordination. This difference reconciles the partitioning behavior of Y 3+ with that of other REE and improves reference states for interpreting trace element systematics in rocks. Thermobarometry can be highly sensitive to assumed ionic radii, and downward correction of the Y 3+ ionic radius improves some REE-based temperatures by hundreds of degrees. Future studies that employ the most common tabulations of ionic radii of the REE (Shannon 1976) should use an ionic radius of Y 3+ of 0.899, 1.014, and 1.070 Å for six-, eight-, and ninefold coordination, respectively; alternatively, the ionic radius of Y can be scaled to that of Ho 3+ × 0.9984. More generally, trace element partitioning data, coupled with theoretical models, provide an exact method for refining effective relative ionic radii in minerals where direct structural determinations are not possible.

The underestimated rhenium (Re) concentration of continental crust is crucial for resolving the “missing Re puzzle” in the silicate Earth. Previous studies attributed the unknown Re reservoir in the continental crust to sulfide cumulates in the lower crust. However, the impact of aqueous fluids on Re abundance in the continental crust has been largely overlooked due to a lack of partition coefficients between fluids and silicate melts DRefluid / melt . $\left(D_{\mathrm{Re}}^{\text {fluid } / \text { melt }}\right) .$To address this gap, we conducted partitioning experiments at 0.5 GPa and 850 °C under oxidized conditions (∼hematite-magnetite buffer) to determine the DRefluid / melt . $D_{\operatorname{Re}}^{\text {fluid } / \text { melt }} .$Our goal was to investigate how fluid exsolution influences Re distribution in the crust. Our experiments revealed that the D values ranged from 4 to 108 for Re. Interestingly, these D values were not related to the concentration of F−,Cl−,and CO32−, $\mathrm{F}^{-}, \mathrm{Cl}^{-}, \text {and } \mathrm{CO}_3^{2-},$ but increased as the H 2 O fugacity in aqueous fluids increased. Numerical modeling suggests that magmatic fluids can extract a significant fraction of Re (∼80%) during arc-magma differentiation, leading to Re depletion in the upper continental crust. Therefore, we believe that aqueous fluids play a dominant role in depleting Re content in the continental crust, whereas sulfide accumulation plays a very limited role.

Tourmaline is the most abundant natural borosilicate, an important indicator of its host rock chemistry and formation conditions, as well as a valuable material for various industrial applications. In this work, V-rich tourmaline crystals were grown ( T = 650 °C, P = 100 MPa) for the first time in two systems: (V1) V 2 O 3 –Al 2 O 3 –SiO 2 –B 2 O 3 –H 2 O and (V2) Na 2 O–MgO–V 2 O 3 –Al 2 O 3 –SiO 2 –B 2 O 3 –H 2 O. Newly formed overgrowth layers of tourmaline on an elbaite seed are dark green, up to 0.7 mm in thickness, and contain up to ∼12 wt% V 2 O 3 [∼1.6 atoms per formula unit (apfu)] and ∼41 wt% V 2 O 3 (∼6 apfu) for the system V1 and V2, respectively. Synthetic tourmalines V1 [ a = 7.0988(1), b = 9.4274(2), c = 9.4279(2) Å, α = 113.920(2)°, β = 104.551(2)°, γ = 104.515(2)°] and V2 [ a = 7.3390(1), b = 9.6075(2), c = 9.6077(2) Å, α = 113.742(2)°, β = 104.721(2)°, γ = 104.786(2)°] are triclinic ( P 1) due to cation ordering and could be considered as dimorphs of the V-dominant analog of alumino-oxy-rossmanite (V1) and oxy-vanadium-dravite (V2). Formation of V-rich tourmalines does not require high temperatures or pressures and is constrained by the simultaneous abundance of boron and vanadium in the mineral-forming medium. The stability of the crystal structure of V-rich tourmaline is increased by the incorporation of Mg cations, thereby reducing the disproportion of the octahedra in V,Al-rich species.