Volume 109, Issue 11

Tourmaline is a widespread borosilicate mineral that is well known for its variable chemistry. Although a major amount of octahedral Al in tourmaline is commonplace, the occurrence of significant amounts of tetrahedral Al is relatively rare. This paper focuses on tourmaline from the collection of the A.E. Fersman Mineralogical Museum (Russia) originated from Italy with up to 25% of Si replaced by Al at the tetrahedral site. The tourmaline is characterized by optical and scanning electron microscopy, Raman spectroscopy, infrared spectroscopy, Mössbauer spectroscopy, energy-dispersive and wavelength-dispersive X-ray analysis, laser ablation inductively coupled plasma optical emission spectrometry and single-crystal X-ray diffraction. The studied tourmaline occurs as transparent dark blue crystals (with equant external morphology) up to 3 mm in size and forms veinlets cutting a (Mg,Al)-rich metamorphosed mafic-ultramafic rock (Mg >> Fe) composed of spinel, pargasite, clinochlore, phlogopite, and hydroxylapatite. The studied tourmaline meets the criteria defining magnesio-lucchesiite and can be compositionally formed via Tschermak-like ( [6] Me 2+ + [4] Si 4+ ↔ [6] Al 3+ + [4] Al 3+ , where [6] Me 2+ = Mg,Fe) or plagioclase-like ( [9] Ca 2+ + [4] Al 3+ ↔ [9] Na + + [4] Si 4+ ) substitutions. Zones with a relatively high Si content (Si-rich) have pronounced indications of dissolution, while silicon-depleted zones (Si-poor) overgrow Si-rich zones, eventually creating a visible replacement zone of the crystal. We suggest that Si-poor tourmaline results from the Si-rich tourmaline losing Si during a metasomatic process. The resulting empirical crystal-chemical formula for the Si-poor zone is: X C a 0.95 N a 0.03 ◻ 0.02 Σ 1.00 Y M g 1.08 A l 0.98 F e 0.50 2 + F e 0.43 3 + Σ 3.00 Z A l 5.91 F e 0.09 3 + Σ 6.00 T S i 4.57 A l 1.43 Σ 6.00 O 18 $ { }^{X}\left(\mathrm{Ca}_{0.95} \mathrm{Na}_{0.03} \square_{0.02}\right)_{\Sigma 1.00}{ }^{Y}\left(\mathrm{Mg}_{1.08} \mathrm{Al}_{0.98} \mathrm{Fe}_{0.50}^{2+} \mathrm{Fe}_{0.43}^{3+}\right)_{\Sigma 3.00}{ }^{Z}\left(\mathrm{Al}_{5.91} \mathrm{Fe}_{0.09}^{3+}\right)_{\Sigma 6.00}{ }^{T}\left[\left(\mathrm{Si}_{4.57} \mathrm{Al}_{1.43}\right)_{\Sigma 6.00} \mathrm{O}_{18}\right] $(BO 3 ) 3 V (OH) 3 W [O 0.95 (OH) 0.05 ] Σ1.00 [ a = 15.9811(2), c = 7.12520(10) Å, R 1 = 1.7%] and for the Si-rich zone is: X C a 0.89 N a 0.11 Σ 1.00 Y M g 1.55 A l 0.80 F e 0.34 2 + F e 0.31 3 + Σ 3.00 Z A l 5.51 M g 0.44 F e 0.05 3 + Σ 6.00 T S i 5.35 A l 0.65 Σ 6.00 O 18 ${ }^{X}\left(\mathrm{Ca}_{0.89} \mathrm{Na}_{0.11}\right)_{\Sigma 1.00}{ }^{Y}\left(\mathrm{Mg}_{1.55} \mathrm{Al}_{0.80} \mathrm{Fe}_{0.34}^{2+} \mathrm{Fe}_{0.31}^{3+}\right)_{\Sigma 3.00}{ }^{Z}\left(\mathrm{Al}_{5.51} \mathrm{Mg}_{0.44} \mathrm{Fe}_{0.05}^{3+}\right)_{\Sigma 6.00}{ }^{T}\left[\left(\mathrm{Si}_{5.35} \mathrm{Al}_{0.65}\right)_{\Sigma 6.00} \mathrm{O}_{18}\right]$(BO 3 ) 3 V (OH) 3 W [O 0.93 (OH) 0.07 ] Σ1.00 [ a = 15.9621(3), c = 7.14110(10) Å, R 1 = 1.7%]. According to pressure-temperature ( P-T ) calculations of mineral assemblage stability and comparable data on synthetic [4] Al-rich tourmalines, the studied tourmaline was formed at 600–750 °C and 0.10–0.20 GPa. The formation of tetrahedral Al-rich tourmalines requires several unusual factors: (1) desilication of primary rocks and (2) high temperatures and relatively low pressures.

The electrical resistivity (ρ) and thermal conductivity (κ) of the Earth’s core compositions are essential parameters for constraining the core’s thermal state, the inner core age, and the evolutionary history of the geodynamo. However, controversies persist between experimental and computational results regarding the electronic transport properties (ρ and κ) of the Earth’s core. Iron is the major element in the core, and its transport properties under high-pressure and high-temperature conditions are crucial for understanding the core’s thermal state. We measured the ρ values of solid iron using the four-wire van der Pauw method at 300 K and pressures of 3 to 26 GPa within a multi-anvil press. For comparison, we calculated the ρ and κ values of hexagonal close-packed (hcp) iron at 300–4100 K and 22–136 GPa using the first-principles molecular dynamics (FPMD) method. Our calculations generally align with prior studies, indicating that the electrical resistivity of solid hcp iron at Earth’s core-mantle boundary (CMB) conditions is ~76–83 μΩ∙cm. The resistivity of hcp iron changes slightly as it melts from solid to liquid at pressures from 98 to 134 GPa. The effects of temperature and pressure on the Lorenz numbers of solid hcp iron were investigated according to our calculation results and previous studies. Under the CMB’s pressure conditions, the κ of hcp iron initially decreases with increasing temperature and subsequently increases. The electron-electron scattering plays a dominant role at low temperatures and causes the decrease in κ. At high temperatures, the increase of electronic specific heat significantly increases the Lorentz number and κ. Overall, we estimate the κ of solid hcp iron at the CMB’s condition to be 114 ± 6 W/m/K, slightly lower than the room temperature value of 129 ± 9 W/m/K at the same pressure. Our model shows that a 0–525 km thickness of a thermally stratified layer may exist beneath the Earth’s CMB, depending on the core’s heat flow and thermal conductivity.

Davemaoite (CaSiO 3 perovskite) is considered the third most abundant phase in the pyrolytic lower mantle and the second most abundant phase in the subducted mid-ocean ridge basalt (MORB). During the partial melting of the pyrolytic upper mantle, incompatible titanium (Ti) becomes enriched in the basaltic magma, forming Ti-rich MORB. Davemaoite is considered an important Ti-bearing mineral in subducted slabs by forming a Ca(Si,Ti)O 3 solid solution. However, the crystal structure and compressibility of Ca(Si,Ti)O 3 perovskite solid solution at relevant pressure and temperature conditions had not been systematically investigated. In this study, we investigated the structure and equations of state of Ca(Si 0.83 Ti 0.17 )O 3 and Ca(Si 0.75 Ti 0.25 )O 3 perovskites at room temperature up to 82 and 64 GPa, respectively, by synchrotron X-ray diffraction (XRD). We found that both Ca(Si 0.83 Ti 0.17 )O 3 and Ca(Si 0.75 Ti 0.25 )O 3 perovskites have a tetragonal structure up to the maximum pressures investigated. Based on the observed data and compared to pure CaSiO 3 davemaoite, both Ca(Si 0.83 Ti 0.17 )O 3 and Ca(Si 0.75 Ti 0.25 )O 3 perovskites are expected to be less dense up to the core-mantle boundary (CMB), and specifically ~1–2% less dense than CaSiO 3 davemaoite in the pressure range of the transition zone (15–25 GPa). Our results suggest that the presence of Ti-bearing davemaoite phases may result in a reduction in the average density of the subducting slabs, which in turn promotes their stagnation in the lower mantle. The presence of low-density Ti-bearing davemaoite phases and subduction of MORB in the lower mantle may also explain the seismic heterogeneity in the lower mantle, such as large low shear velocity provinces (LLSVPs).

Solfataric alteration at the South Sulfur Bank of the former Kilauea caldera produced opal, Mg- and Fe-rich smectites, gypsum, and jarosite through silica replacement of pyroclastic Keanakako’i ash and leaching of basaltic lavas. This site on the island of Hawaii serves as an analog for formation of several minerals found in altered deposits on Mars. Two distinct alteration environments were characterized in this study, including a light-toned, high-silica, friable outcrop adjacent to the vents and a bedded outcrop containing alternating orange/tan layers composed of smectite, gypsum, jarosite, hydrated silica, and poorly crystalline ferric oxide phases. This banded unit likely represents the deposition of pyroclastic material with variations in chemistry over time that was subsequently altered via moderate hydrothermal and pedogenic processes and leaching of basaltic caprock to enhance the Si, Al, Mg, Fe, and Ca in the altered layers. In the light-toned, friable materials closest to the vents along the base of the outcrop, glassy fragments were extensively altered to opal-A plus anatase. Lab measurements of samples returned from the field were conducted to replicate recent instruments at Mars and provide further characterization of the samples. These include elemental analyses, sample texture, XRD, SEM, VNIR/mid-IR reflectance spectroscopy, TIR emittance spectroscopy, and Mössbauer spectroscopy. Variations in the chemistry and mineralogy of these samples are consistent with alteration through hydrothermal processes as well as brines that may have formed through rain interacting with sulfuric fumes. Silica is present in all altered samples, and the friable pyroclastic ash material with the strongest alteration contains up to 80 wt% SiO 2 . Sulfate mineralization occurred at the South Sulfur Bank through fumarolic action from vents and likely included solfataric alteration from sulfuric gases and steam, as well as oxidation of sulfides in the basaltic caprock. Gypsum and jarosite are typically present in different layers of the altered wall, likely because they require different cations and pH regimes. The presence of both jarosite and gypsum in some samples implies high-sulfate concentrations and the availability of both Ca 2+ and Fe 3+ cations in a brine percolating through the altered ash. Pedogenic conditions are more consistent with the observed Mg-smectites and gypsum in the tan layers, while jarosite and nontronite likely formed under more acidic conditions in the darker orange layers. Assemblages of smectite, Ca-sulfates, and jarosite similar to the banded orange/tan unit in our study are observed on Mars at Gale crater, Noctis Labyrinthus, and Mawrth Vallis, while high-silica outcrops have been identified in parts of Gusev crater, Gale crater, and Nili Patera on Mars.

Sphalerite (ZnS) is a sulfide found in a large variety of ore deposits and is frequently hosted in metamorphic terranes that have undergone deformation and related recrystallization. However, the deformation mechanisms of sphalerite are still poorly understood because recrystallization evidence is barely visible under an optical microscope and may reflect complex and frequently multistage mechanisms. Furthermore, sphalerite may host up to a few thousands of parts per million of critical metals such as gallium (Ga), germanium (Ge), and indium (In). Metamorphic conditions and dynamic recrystallization may have induced local or total redistribution of these elements. Modern techniques such as electron backscattered diffraction analyses (EBSD) and laser-induced breakdown spectroscopy (LIBS) applied on sphalerite allow for the examination of grain boundaries, crystal-plastic deformation, and internal chemical diffusion, which classically reflect active deformation mechanisms. In this study, a microstructural and in situ chemical comparison between four sphalerite types (types 1, 2, 3, and 4) has been made for the first time. The four sphalerite types present different deformation imprints, although they are hosted in a similar geological setting: the Pyrenean Axial Zone and the Montagne Noire Variscan massifs (France). Based on EBSD and LIBS mapping, we describe two regional sphalerite growth stages composed of dark red crystals with polygonal shape (type 1, Bentaillou-Liat deposit) and light- to dark-brown euhedral crystals (type 3, Saint Salvy deposit). New investigation at microscale on sphalerite grains from the Saint-Salvy deposit shows late Cu-Ge-Ga enrichment not only in specific sector zonings but also along grain boundaries, growing crystal edges, and in low-angle misorientations or twin boundaries. Following a deformation event that probably occurred during the Pyrenean-Alpine orogeny, these two sphalerite mineralizations have both endured plastic deformation in a dislocation creep regime and dynamically recovered by subgrain rotation (SGR) mechanism. Two mechanisms of Cu-Ga-Ge spatial redistribution are observed and are key processes for the crystallization of Cu-Ga-Ge-rich minerals in sphalerite veins. The first mechanism involved the in situ redistribution of Cu-Ga-Ge contents from a pre-existing concentration in the sphalerite lattice (type 3, Arre deposit), creating Ge-sulfides (briartite), probably during Pyrenean-Alpine orogeny. Formation of this type of Ge-mineral may be related to solid-state diffusion processes. The second mechanism is associated with the circulation of a Cu-Ga-Ge-rich fluid in surrounding rocks. In the pre-existing polygonal sphalerite from Late-Variscan veins (type 2, Pale Bidau deposit), millimeter-size bands of small (<50 μm), recrystallized sphalerite grains are locally observed. Those domains contain inclusions of Cu (chalcopyrite) and Ga and Ge minerals (brunogeierite, carboirite). Fluid-induced diffusion in the polygonal sphalerite aggregates may occur with superimposed dynamic recrystallization, such as the Late-Variscan veins (type 2, Pale Bidau-type). During post-Variscan time, this fluid enriched in Cu-Ga-Ge largely circulated in the upper-crust of this Variscan terrane. This study highlights the key importance of coupled textural (EBSD) and in situ chemical analyses (LIBS) of diverse sphalerite types at a regional scale to indirectly unravel the origin of vein mineralization, and their related critical metal distribution.

Hydropyrochlore, ideally (H 2 O,□) 2 Nb 2 (O,OH) 6 (H 2 O), is a cubic mineral (space group Fd 3 m , a = 10.56–10.59 Å, Z = 8) belonging to the pyrochlore supergroup (general formula: A 2– m B 2 X 6– w Y 1– n ). The K-rich variety of this species is unique to the Lueshe syenitic-carbonatitic deposit (D.R. Congo), where it occurs as the alteration product of primary (Ca,Na) 2 Nb 2 O 6 F pyrochlores. The structure of this mineral is made of a B 2 X 6 (B = Nb, Ti; X = O, OH) framework that generates tunnels along the [110] direction, where the interstitial sites are partially occupied by water molecules and minor amounts of different cations. These features form the basis for the ion-exchange properties of hydropyrochlore, making it a promising candidate as a mineral sink for heavy metals (e.g., Tl + ) dispersed in aqueous matrices, with interesting environmental implications. Tl + incorporation was induced through imbibition experiments in a diluted Clerici solution using single crystals of hydropyrochlore from Lueshe (D.R. Congo); the modifications induced by Tl + incorporation were then evaluated using single-crystal X-ray diffraction (SCXRD), electron microprobe analyses (EMPA), and Fourier transform infrared (FTIR) spectroscopy. After Tl + imbibition, a dramatic increase of the A-site electron density (n.e – from ~4 to ~60) confirms the entry of a substantial amount of Tl + at this site (up to about 70%), leading to a lengthening of the A-X distances and the consequent expansion of the unit cell. A decrease of the site scattering at the Y′ site (from ~9 to ~4 e – ) also occurs, suggesting a loss of aqueous species. Although the predominance of neutral H 2 O molecules at the interstitial sites of hydropyrochlore from Lueshe is widely accepted by the mineralogical community, our crystal-chemical and FTIR data provide evidence that the dominant species might be the hydronium ion, with significant implications on the nomenclature of the pyrochlore supergroup. Understanding the crystallographic aspects of hydropyrochlore as a potential waste form for monovalent thallium immobilization not only addresses a pressing environmental concern but also contributes to the broader field of waste management.

Amphibole and pyroxenes are the main reservoirs of rare earth elements (REEs) in the lithospheric mantle that has been affected by hydrous metasomatism. In this study, we developed semi-empirical models for REE partitioning between orthopyroxene and amphibole and between clinopyroxene and amphibole. These models were formulated on the basis of parameterized lattice strain models of mineral-melt REE partitioning for orthopyroxene, clinopyroxene, and amphibole, and they were calibrated using major element and REE data of amphibole and pyroxenes in natural mantle samples from intraplate settings. The mineral-melt REE partitioning models suggest that amphibole is not in equilibrium with coexisting pyroxenes in the mantle samples and that the amphibole crystallized at a lower temperature than that of the pyroxenes. We estimated the apparent amphibole crystallization temperature using major element compositions of the amphibole and established temperature- and composition-dependent models that can be used to predict apparent pyroxene-amphibole REE partition coefficients for amphibole-bearing peridotite and pyroxenite from intraplate lithospheric mantle. Apparent pyroxene-amphibole REE partition coefficients predicted by the models can be used to infer REE contents of amphibole from REE contents of coexisting pyroxenes. This is especially useful when the grain size of amphibole is too small for trace element analysis.

Hydrogen may be recycled into the Earth’s lower mantle by subduction and stabilized in solid solutions between phase H (MgSiO 4 H 2 ), δ-AlOOH, ε-FeOOH, and SiO 2 post-stishovite. In high-pressure oxyhydroxide phases, hydrogen is incorporated following the typical (OHO) sequence, adopting the asymmetric configuration O-H⋯O that evolves into a symmetric disordered state upon compression. Moreover, these iron-bearing aluminum oxyhydroxides [δ-(Al,Fe)OOH] present a structural phase transition from P 2 1 nm to Pnnm as pressure increases. Here, the single-crystal elasticity of the P 2 1 nm phase of δ-(Al 0.97 Fe 0.03 )OOH has been experimentally determined across the P 2 1 nm → Pnnm transition up to 7.94(2) GPa by simultaneous single-crystal X-ray diffraction (XRD) and Brillouin scattering at high pressures. The transition appears to be continuous, and it can be described with a second-, fourth-, and sixth-order terms Landau potential. Our results reveal an enhanced unit-cell volume compressibility, which is linked to an increase of the b - and a -axes linear compressibility in the P 2 1 nm phase of δ-(Al 0.97 Fe 0.03 )OOH prior to the transition. In addition, we observed the presence of elastic softening in the P 2 1 nm phase that mostly impacts the elastic stiffness coefficients c 12 , c 22 , and c 23 . The observed elastic anomalies cause a significant change in the pressure dependence of the adiabatic bulk modulus ( K S ). These results provide a better understanding of the relation between elasticity, P 2 1 nm → Pnnm structural phase transition, and hydrogen dynamics in δ-(Al 0.97 Fe 0.03 )OOH, which may be applied to other O-H⋯O-bettring phases.

Highly evolved granites can be important hosts of rare earth element (REE) resources, and more importantly, they commonly serve as the protolith for regolith-hosted REE deposits to form during weathering. Highly evolved granites in the Zudong pluton, South China, are extremely rich in the heavy (H)REE (up to 8000 ppm total HREE), and display significant REE fractionation. Moreover, the HREE enrichment is positively correlated with the degree of REE fractionation, indicating a unique process in preferentially enriching the HREE during the evolution of the granites. Multiple stages of hydrothermal re-mobilization of the REE can account for the HREE mineralization, and these are recorded in the texture and composition of the zircon. In these processes, fluctuations in the F activity of the fluid caused alternating dissolution-reprecipitation and continuous growth of the zircon. REE were repeatedly mobilized and enriched in the fluid to precipitate the major HREE mineral synchysite-(Y), and partially incorporated into the growth zone of zircon, while other elements were largely lost to the fluid during the extensive dissolution of the rock-forming minerals. LREE were also likely substantially mobilized in the late hydrothermal stage and lost through complexation with Cl, causing the significant LREE depletion and, thus REE fractionation. This process continuously enriched host granites in the HREE to a potentially economic grade, making them favorable protoliths for subsequent supergene regolith-hosted HREE deposits.

Tin mineralization of significant economic importance occurs across the continental portion of the Cameroon Line (CL). Tin deposits therein occur as both primary and secondary (residual and alluvial) ore. Though the temporal and, by inference, the genetic link between Sn mineralization and the host granite had long been modeled and widely accepted worldwide, in the CL, however, the age of the granite hosting cassiterite is poorly constrained, preventing a robust assessment of the temporal and genetic relationship between the Sn mineralization and its host rock. Here, we present in-situ zircon and cassiterite laser ablation inductively coupled mass spectrometry (LA-ICP-MS) U-Pb data in order not only to constrain the age of the granitic rock hosting the primary Sn ore but also to bracket the time frame of Sn mineralization, with respect to the magmatic-hydrothermal evolution of the parental magma of the host granite. Zircon from two greisen-altered, cassiterite-bearing granite samples yield overlapping and concordant ages of 64.21 ± 0.59 Ma and 65.46 ± 0.95 Ma, respectively, which are also overlapping with regional granite magmatism in the CL (ca. 65–30 Ma). On the other hand, cassiterite, which is spatially associated with the Paleocene zircon, yields Lower Eocene ages of 54.99 ± 0.35 Ma and 56.08 ± 0.46 Ma. The ca. 10 Myr time gap between zircon and cassiterite suggests that the granite is a passive host not genetically related to the Sn mineralization, which may be linked to a younger, concealed intrusion of ca. 55 Ma. This finding contrasts with the most widely accepted petrogenetic model of tin granite, according to which Sn mineralization and the host granite are cogenetic.

In situ X-ray diffraction and Raman spectroscopy of a synthetic whitlockite, Ca 9 Mg(PO 3 OH) (PO 4 ) 6 , have been conducted at high pressures or high temperatures. The results show that whitlockite is stable up to ~15 GPa at ambient temperature and undergoes a thermally induced dehydrogenation to merrillite above 973 K at ambient pressure. The obtained pressure-volume data were fitted using a third-order Birch-Murnaghan equation of state, yielding an isothermal bulk modulus of K 0 = 79(4) GPa with a pressure derivative of K0′ $\begin{array}{} \displaystyle K_0' \end{array}$ = 4.3(6). When K0′ $\begin{array}{} \displaystyle K_0' \end{array}$ was fixed at 4, the refined isothermal bulk modulus was 81(1) GPa. The volumetric thermal expansion coefficient (α V ) is 4.05(8) × 10 −5 K −1 , and the axial thermal expansion coefficients (α a and α c ) are 1.07(5) × 10 −5 K −1 and 1.91(6) × 10 −5 K −1 . Both compressibility and thermal expansion show an axial anisotropy. The effects of pressure and temperature on the Raman spectra of whitlockite have been quantitatively analyzed. The isothermal and isobaric mode Grüneisen parameters and the intrinsic anharmonic mode parameters of whitlockite were derived. Some amounts of OH − -bearing whitlockite may be preserved in meteorites if whitlockite undergoes a low-temperature process.

Investigating mineral/melt Sn partitioning at high temperatures and pressures is a difficult task because Sn is a redox-sensitive multivalent element and easily alloys with noble metal sample capsules. To obtain accurate Sn partition coefficients between titanite, ilmenite, and granitic melts, we developed single capsule Pt or Au and double capsule Pt 95 Rh 5 (or Au)-Re designs to avoid significant Sn loss at a controlled oxygen fugacity ( f O 2 ). With these new capsule designs, we performed piston-cylinder experiments of Sn partitioning between titanite, ilmenite, and granitic melts. The experimental P - T - f O 2 conditions were 0.5–1.0 GPa, 850–1000 °C, and ~QFM+8 to ~QFM-4 (quartz-fayalite-magnetite, QFM, buffer), with f O 2 controlled by the solid buffers of Ru-RuO 2 , Re-ReO 2 , Co-CoO, graphite, and Fe-FeO. The obtained mineral/melt Sn partition coefficients ( DSnmin/melt $\begin{array}{} \displaystyle D_{\mathrm{Sn}}^{\mathrm{min} / \mathrm{melt}} \end{array}$) are 0.48–184.75 for titanite and 0.03–69.45 for ilmenite at the experimental conditions. The DSnmin/melt $\begin{array}{} \displaystyle D_{\mathrm{Sn}}^{\mathrm{min} / \mathrm{melt}} \end{array}$ values are largely dependent on f O 2 , although the effects of temperature and melt composition are also observed. DSnTtn/melt $\begin{array}{} \displaystyle D_{\mathrm{Sn}}^{\mathrm{Ttn} / \mathrm{melt}} \end{array}$ strongly decreases with decreasing f O 2 , from ~46–185 at the most oxidizing conditions (Ru-RuO 2 buffer), to ~2–16 at moderately oxidizing to moderately reducing conditions (Re-ReO 2 to Co-CoO and graphite buffers), to < 1 at the most reducing conditions (Fe-FeO buffer). DSnIlm/melt $\begin{array}{} \displaystyle D_{\mathrm{Sn}}^{\mathrm{Ilm} / \mathrm{melt}} \end{array}$ exhibits a variation trend similar to DSnTtn/melt $\begin{array}{} \displaystyle D_{\mathrm{Sn}}^{\mathrm{Ttn} / \mathrm{melt}} \end{array}$ but is always lower than DSnTtn/melt $\begin{array}{} \displaystyle D_{\mathrm{Sn}}^{\mathrm{Ttn} / \mathrm{melt}} \end{array}$ at a given f O 2 . These DSnmin/melt $\begin{array}{} \displaystyle D_{\mathrm{Sn}}^{\mathrm{min} / \mathrm{melt}} \end{array}$ values can be applied to quantitatively assess the mineralization potential of granitic magmas. Using DSnTtn/melt $\begin{array}{} \displaystyle D_{\mathrm{Sn}}^{\mathrm{Ttn} / \mathrm{melt}} \end{array}$, we estimate that Sn contents are ~150–400 ppm in the pre-mineralization magmas of the tin-mineralized Qitianling plutons (South China).

Kumdykolite is a polymorph of albite that has been predominantly identified within crystallized melt inclusions in high-temperature metamorphic rocks. This study reports a new occurrence of kumdykolite that formed during internal mineral carbonation within amphibole-hosted fluid inclusions in post-collisional hornblendite from the Dabie orogen, central China. Amphibole in the hornblendite trapped CO 2 -rich fluid inclusions at the magmatic stage, and mineral carbonation, referring to the reaction of mineral rich in divalent cations and CO 2 into carbonate, occurred in situ within the fluid inclusions due to the interaction between trapped CO 2 -rich fluids and host amphibole during cooling of the hornblendite. Kumdykolite was produced along with calcite, dolomite, chlorite, talc, a SiO 2 phase (quartz or cristobalite), a TiO 2 phase (rutile or anatase), and mica during internal mineral carbonation within the fluid inclusions. It is estimated that kumdykolite in the fluid inclusions crystallized under near-surface conditions, which are significantly different from the conditions of crystallization proposed in previous studies. It is further inferred that kumdykolite may crystallize metastably across the stability field of albite, and the presence of kumdykolite is not indicative of extreme thermobaric and fluid-absent conditions.

Louisfuchsite (IMA 2022-024), with an end-member formula Ca 2 (Mg 4 Ti 2 )(Al 4 Si 2 )O 20 , is a new refractory mineral identified in a Ca-Al-rich inclusion (CAI) from the NWA 4964 CK3.8 carbonaceous chondrite. Louisfuchsite occurs with spinel, perovskite, grossmanite, plus secondary rutile, titanite, and ilmenite in three regions in the CAI. The mean chemical composition of type louisfuchsite by electron probe microanalysis is (wt%) Al 2 O 3 25.48, SiO 2 18.40, MgO 17.92, TiO 2 15.36, Ti 2 O 3 3.13, CaO 14.92, FeO 3.30, V 2 O 3 0.67, Cr 2 O 3 0.08, total 99.26, giving rise to an empirical formula of Ca2.00(Mg3.44Ti1.494+Fe0.36Ti0.343+Al0.24V0.073+Ca0.06Cr0.01)Σ 6.01(Al3.63Si2.37)Σ 6.00O20 $\begin{array}{} \displaystyle \mathrm{Ca_{2.00}(Mg_{3.44}Ti_{1.49}^{4+}Fe_{0.36}Ti_{0.34}^{3+}Al_{0.24}V_{0.07}^{3+}Ca_{0.06}Cr_{0.01})_{\Sigma6.01}(Al_{3.63}Si_{2.37})_{\Sigma 6.00}O_{20}} \end{array}$. Louisfuchsite has the P 1 rhönite structure with a = 10.37(1) Å, b = 10.76(1) Å, c = 8.90(1) Å, α = 106.0(1)°, β = 96.0(1)°, γ = 124.7(1)°, V = 741(2) Å 3 , and Z = 2, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.44 g/cm 3 . Louisfuchsite is a new refractory phase from the solar nebula, crystallized from an 16 O-rich (Δ 17 O ~ –24 ± 2‰) refractory melt with the initial 26 Al/ 27 Al ratio of (5.09 ± 0.58) × 10 –5 under reduced conditions. The mineral name is in honor of Louis Fuchs (1915–1991), a mineralogist at Argonne National Laboratory, for his many contributions to mineralogical research on meteorites.