Abstract We report the discovery of the second (Al,Cu)‐alloy–bearing micrometeorite, FB‐A2, recovered from Mount Gariglione (southern Italy), representing the sixth such occurrence worldwide. Although chondritic in nature, FB‐A2 differs markedly from previously described microspherules. It is a scoriaceous micrometeorite dominated by silicates and contains a relict clast composed of Mg‐rich olivine and pyroxene phenocrysts set in a Fe‐rich silicate matrix. The particle rim hosts fine aggregates of phosphates, magnetite, Ni‐bearing magnetite, and sulfides, whereas the interior contains nepheline crystals. A 120 μm (Al,Cu)‐alloy grain occurs at one corner of the particle. The porphyritic texture of the clast indicates a chondrule fragment—the first identified in an (Al,Cu)‐bearing micrometeorite—while polyhedral sub‐grain boundaries and metal–sulfide veins record shock metamorphism. Iron‐rich alteration of relict silicates is consistent with high‐temperature (<560 °C) metasomatism typical of CV3 chondrites and is supported by oxygen isotope compositions close to the Carbonaceous Chondrite Anhydrous Mineral Line. Brecciation of chondrule olivine suggests impact‐induced fluid pressure excursions during early Solar System metasomatism, whereas impact melt enveloping elongate olivines indicates a later impact that introduced the (Al,Cu)‐alloys. Overall, the texture, mineralogy, and isotopic composition of FB‐A2 provide the most detailed constraints yet on the origin of (Al,Cu)‐bearing micrometeorites and confirm a genetic link to the Khatyrka meteorite.

We report high-precision lithium (Li) abundances and isotopic compositions of olivine crystals from type I chondrules in carbonaceous chondrites (Murchison, NWA 852, Renazzo) and type II chondrules in ordinary chondrites (NWA 11752, NWA 12462, NWA 12581, NWA 13501). Olivine crystals in type I chondrules exhibit large Li isotopic fractionations both within and between grains, with delta 7Li values ranging from -46.6%o to + 9.9%o and Li concentrations of 3.8-9.0 ppm. Olivine grains in type II chondrules, including Mg-rich relict cores, show delta 7Li values from -38.0%o to + 8.4%o (Li = 0.6-5.6 ppm), while their Fe-rich overgrowths exhibit lower variability, with delta 7Li values between -30.6%o and + 4.7%o (Li = 0.6-11.9 ppm). Our data indicate that the observed variations are not attributable to low-temperature aqueous alteration or dry thermal metamorphism, fractional crystallisation, or simple degassing of the chondrule melt. Instead, the Li isotopic signatures are best explained by kinetic fractionation during open-system gas-melt exchange with a volatile-rich vapour, enriching the chondrule melts in Li. Such open-system processes produced larger isotopic fractionations than expected during closed-system crystallisation. These findings suggest that some type II chondrules may have originated from type I chondrules through reprocessing in an open-system environment, providing new insights into the complex physicochemical evolution of early solar system solids.

The 26Al-26Mg systematics in calcium-aluminum-rich inclusions (CAIs)-the oldest known Solar System solids-has traditionally been used to provide high-resolution temporal constraints on the early Solar System evolution. More recently, the study of variations in the initial Mg isotope composition has emerged as a means to probe for potential compositional heterogeneity in the nascent solar nebula. Here, we report high-precision magnesium isotope data for a collection of 19 CAIs that captures the diversity of refractory inclusions. The data reveal widespread Mg isotope heterogeneity prior to 26Al decay, covering a large range from -0.285 to +0.088‰. Combined with literature data, the distribution of Mg isotope heterogeneity in CAIs forms a continuum and no longer defines distinct populations. Our findings therefore suggest a continuous CAI formation process that captured a rapid temporal change in the composition of infalling material from the parental molecular cloud of the Solar System.

Nitrogen is abundant on Earth's surface, comprising 78 vol% of the atmosphere. However, its relative abundance in the bulk silicate Earth, normalized to carbonaceous chondrites, is depleted by about one order of magnitude compared to other volatile elements. The deep Earth, particularly the lower mantle, where the behavior of nitrogen remains poorly understood, has been considered as a strong candidate for solving the so-called "missing" nitrogen problem. Here, we experimentally investigated the effect of iron content on nitrogen solubility in bridgmanite, which constitutes 75 wt% of the lower mantle. High-pressure experiments were conducted using a multi-anvil apparatus at 28 GPa and 1400-1600 degrees C under redox conditions corresponding to those in the lower mantle. Nitrogen solubility in the Fe-bearing bridgmanite increased from 2.1 f 0.3 ppm to 6.9 f 1.5 ppm with increasing FeO content from 1.9 wt% to 7.7 wt% at 1500 degrees C. Based on the temperature dependence of nitrogen solubility in MgSiO3-bridgmanite, nitrogen solubilities in pyrolitic bridgmanite were estimated to be 9.2 f 1.9 ppm (mu g/g) at 1700 degrees C. The estimated nitrogen storage capacity of pyrolitic bridgmanite along a mantle geotherm is 3.6 f 0.8 ppm in the bulk Earth, equivalent to 5.5 f 1.2 PAN (PAN: mass of present atmospheric nitrogen). These results suggest that bridgmanite alone is insufficient to account for the "missing" nitrogen in the present-day bulk Earth, as its nitrogen storage capacity is lower than required to match chondritic volatile abundances. Instead, bridgmanite may have played a key role in segregating nitrogen into the deep mantle during the solidification of the magma ocean.

MESSENGER observations revealed a primary graphite flotation crust on Mercury, implying substantial carbon retention in its magma ocean rather than sequestration into the core. To investigate the conditions enabling this retention, we conducted high-pressure, high-temperature metal-silicate partitioning experiments over a wide range of oxygen fugacities. Carbon behavior is strongly redox dependent: under relatively oxidizing conditions it is highly siderophile, whereas under the reducing conditions relevant to Mercury it becomes significantly less siderophile, promoting carbon retention in silicate melts and graphite crystallization. Modeling of carbon partitioning between the core, mantle, crust, and atmosphere indicates that oxygen fugacities of IW - 6 to IW - 6.5 best reproduce the graphite crust thickness inferred from MESSENGER data. Under these conditions, Mercury's core remains relatively carbon-poor ( < 5000 μ g/g), implying that its density deficit is primarily controlled by other light elements, most likely silicon and sulfur. These results link Mercury's extreme reduction to both its graphite crust and internal chemical structure.

A total of 1222 Micrometeorites (MMs) from the late Devonian period were extracted from 26 kg of carbonates host rock fragments from the Chanxhe section in Belgium, from the Latest Famennian around 360 Myr, through magnetic separation and optical picking following dissolution with mild HCl, making it one of the largest fossil MMs collection, the largest from the late Devonian. The collection shows a wide diversity of texture, comparable to modern day collection but with different distribution. The majority of the MMs were I-type (90 %), with Gtype particles constituting 6 % and S-type particles at 1 %. Some of the S-types spherules are amongst the first silicate-type spherules, and amongst the most well-preserved in terms of texture and composition, to be described in fossil MMs collections. Additionally, intermediate type G/I representing <1 % of the sample are introduced for future fossil MMs classification. Distinguishing extraterrestrial (ET) MMs from terrestrial spherules is challenging due to weathering effects that modify both texture and composition during long residency time on Earth. The Na2O + K2O versus Fe/Si ratio plot is used for distinguishing ET from terrestrial spherules. Using textural and compositional data in combination creates a reliable ET spherule identification. I-type spherules show significant terrestrial alteration with notable loss of Ni and Cr, also observed in S-type spherules, with their silicate phases recrystallized in palagonite. G-type spherules display a mix of characteristics from I-type and S-type MMs. The study also highlights the presence of smaller spherules (<125 mu m) compared to modern micrometeorites (210-330 mu m), attributed to the predominance of I- and G-type spherules and long-term dissolution effects. Despite some alteration for some spherules, due diagenesis of the sedimentary host rocks, the collection shows extremely well-preserved spherules, with even some oxygen isotopes signature being preserved. Indeed, triple oxygen isotope analysis reveals that 5.8 % of the particles are related to ordinary chondrites (OC) and 33 % to carbonaceous chondrites (CCs), yielding a CC/OC ratio of approximately 5.6, with comparable distribution for all major types. Also, 9 % of I- and G/I-types are OC-related. Most I-type spherules likely originate from CM, CR, or H chondrites, with some possibly from iron meteorites. The findings suggest that the source materials of the ET flux have remained relatively consistent over the past 360 Myr, providing insights into historical Solar System events and Earth's environmental changes and extends the study of ET flux to Earth to CC compared to meteorites. In addition, combined with chemical and isotopic proxies and chrome spinel, the fossil MMs could assess the complete flux of cosmic dust to Earth. Finally, the use of fossil MMs could represent potential proxies for paleo-atmospheric oxygen levels and CO2 contents.

During the world's first nuclear explosion, in 1945, glassy melts called "trinitites", mostly derived from the sands at the surface of the test site, formed and were deposited at or near the hypocenter. The processes of formation of this fallout remain unclear. Here, we show how the oxygen and silicon isotopic compositions of three trinitites allow to refine their formation scenario. The three samples are typical of trinitites, being composed of various crystalline phases and of glassy phases divided into three chemical groups (CaMgFe, alkali, silica) that are mixed in various proportions in the three samples. The three samples show a large range of oxygen and silicon isotopic variations (-10.9 f 0.6 G delta 30Si G 4.2 f 0.6 %o, and 2.3 f 0.4 G delta 18O G 24.2 f 0.5 %o). At variance with the Hiroshima fallout deposits, no oxygen mass-independent isotopic fractionation was found in the three trinitites. The chemical and isotopic compositions of the chemical groups reveal that they result from different processes: the silica phases are molten fragments of the site material, while the CaMgFe and alkali phases are produced by the mixing of condensates and molten site material. Models show that the observed silicon isotopic variations resulted from Rayleigh distillation during condensation of the gaseous species injected into the cloud, while the variability in composition of the site materials also played an important role for controlling the oxygen isotopic compositions. From these observations, a general scenario, beginning with the vaporization of the site surface, producing a depression, is proposed. The vaporized material condensed and grew by agglomeration with other condensates and liquid materials. These agglomerates rained on the surface and quenched, forming the trinitites. This scenario is different from the formation of the Hiroshima glasses but shows some similarities to tektite formation.

Ordinary, enstatite, and Rumuruti type have the lowest abundance of refractory inclusions amongst chondritic meteorites. Calcium-aluminum-rich inclusions (CAIs) within these are hallmarked by a relatively small average diameter of similar to 45 mu m (size range 4-382 mu m). One CAI, one amoeboid olivine aggregate (AOA), one spinel-bearing chondrule, and two aluminum-rich chondrules from Semarkona (LL3.00) along with one CAI each from Allan Hills (ALHA) 81251 (LL3.2) and Chainpur (LL3.4) were identified following an extensive search. These objects were studied for their petrography, mineral chemistry, relative (Al-26) chronology, and three oxygen isotopic compositions. The initial Al-26/Al-27 ratio of (4.96 +/- 0.14) x 10(-5) (2 sigma) in a type A CAI in Chainpur, the largest size (1500 x 1200 mu m) found so far in the noncarbonaceous (ordinary) chondrites, forming in an O-16-rich early solar system reservoir (Delta O-17 = -24 parts per thousand) is consistent with previous studies. The Chainpur CAI 1 has a Wark-Lovering rim, the first reported case within the noncarbonaceous chondrites. The hibonite-pyroxene spherule in ALHA81251 (CAI 1) is the first reported caseof a hibonite-pyroxene spherule in the ordinary chondrites of these rare objects (similar to 12 known so far) within meteorites. The hibonite-pyroxene spherule in ALHA81251 has a low abundance of Al-26/Al-27 ratio of (1.2 +/- 0.6) x 10(-5) with Delta O-17 of similar to -14.5 parts per thousand +/- 2.0 parts per thousand. An olivine-phyric Al-rich chondrule in Semarkona (Ch 54) formed at similar to 0.9 Ma with Delta O-17 of similar to 0 parts per thousand, while Semarkona (Ch 44) formed in a relatively O-16-rich reservoir with Delta O-17 of similar to -2.0 parts per thousand. The spinel-bearing chondrule in Semarkona (Ch 205) shows no resolved excess in Delta Mg-26 and has a planetary-like oxygen isotopic composition. Oxygen isotope composition and Al-26-Mg-26 relative chronology of these objects confirm their origin and evolutionunder cosmochemical conditions similar to their "typical" carbonaceous kindred and extend the knowledge of the cosmochemical environment in the early solar system.

We report the discovery of a (Al,Cu)-bearing micrometeorite recovered at the top of Mt. Gariglione (Italy). The micrometeorite exhibits a highly vesicular scoriaceous structure characterized by broadly chondritic silicate-dominated composition (S-type) with relict phenocrystals of forsteritic olivine dispersed in a Ca-rich silicate glass with pyroxene composition, droplets of FeNi metal, oxides and sporadic Ni-rich sulphides embedded in a magnetite rim. The oxygen 3-isotope analyses give values close to the slope similar to 1 CCAM. A reduced assemblage of (Al,Cu)-alloys partially fills the open voids of the micrometeorite and shows variable compositions: from almost pure Cu up to Al-dominated phases with a predominance of khatyrkite, stolperite and unnamed Cu3Al2. Locally, small grains (about 1-2 mu m in size) embedded in stolperite show a Fe-Si enrichment and are characterized by a long-range ordering resembling a quasicrystalline structure. This finding represents a unique natural quasicrystal approximant with composition Al52Cu31Fe10Si7.

Contrary to all terrestrial rocks, planets and meteorites exhibit oxygen isotope variations decorrelated with the mass difference of their atomic nuclei. It has been proposed that, in the protosolar nebula (PSN), these variations could result from mass independent isotopic fractionation (MIF) either during specific chemical reactions similar to those responsible for the formation of ozone in the Earth's atmosphere or during ultraviolet (UV)-photolysis of carbon monoxide (CO) gas in the PSN. However, these potential chemical MIF reactions (Chem-MIFs) are not identified in conditions close to the PSN, and there is no experimental demonstration that large MIF signature can be transferred to solids forming in the PSN. Here, we show that MIFs, up to 60‰ depletion in 16O, are produced by high-temperature reactions in a plasma during the condensation of carbonaceous solids from a gas containing two of the most abundant PSN molecular species (H2O and CH4). This effect is attributed to the formation in the plasma of the activated complex H2O2* followed by its stabilization by reactions with CHx• radicals. Although it is premature to assert that this reaction represents the main process resulting in MIF of oxygen isotopes in the solar system, our result demonstrates the potential importance of a Chem-MIF effect in a PSN where plasma zones develop.

High-precision Ni isotope analyses of the differentiated andesitic meteorite Erg Chech 002 (EC 002), the oldest known crustal fragment of a planetesimal, show that short-lived 60 Fe was present in the early solar system with an initial 60 Fe/ 56 Fe ratio of (7.71 ± 0.47) × 10 −9 , which is five times more precise than previous estimates and is proposed to be the reference value for further studies. Using this ratio, the Ni isotopic composition of EC 002 implies that metal segregation in the source of the EC 002 parental melts took place 0.82 − 0.60 + 0.61 million years (Myr) after solar system formation, and similar very early metal-silicate differentiation ages are obtained for 4-Vesta ( 0.95 − 0.76 + 0.95 Myr) and the angrite parent body ( 2.27 − 1.29 + 1.98 Myr). Such an early age dictates a specific accretion and differentiation history for the EC 002 parent body, with metal segregation occurring at relatively low temperatures (1000° to 1200°C), followed by a high-temperature silicate melting event.

Extraterrestrial dust exhibits a wide range of textural, chemical and oxygen isotopic compositions due to the heterogeneity of their precursors and modification during atmospheric entry. Experimental heating provides an opportunity to investigate the relationship between thermal processing and micrometeorite composition for a known precursor material. We conducted experiments to simulate the atmospheric entry of micrometeorites (MMs) using controlled, short-duration (10-50 s) flash heating (400-1600 degrees C) of CI chondrite chips (<1500 lm) in atmospheric air (1 bar, 21% O2) combined with microanalysis (textures, chemical and isotopic compositions) of the experimental products. The heated chips closely resemble natural samples, with materials similar to unmelted MMs, partially melted (scoriaceous) MMs and fully melted cosmic spherules produced. We reproduced several key features such as dehydration cracks, magnetite rims, volatile gas release, vesicle formation and coalescence, melting and quench cooling. Our parameter space allows for discriminating peak temperature and heating duration effects. Peak temperature is the first-order control on MM mineralogy, while heating duration controls vesicle coalescence and homogenization. When compared against previous heating experiments, our data demonstrates that CI chondrite dust is more thermally resistant, relative to CM chondrite dust, by approximately +200 degrees C. The 207 measurement of O-isotopes allows, for the first time, petrographic effects (such as volatile degassing and melting) to be correlated against bulk O-isotope evolution. Our results demonstrate findings applicable to CI chondrites and potentially to all fine-grained hydrated carbonaceous chondrite dust grains: (1) O-isotope variations arising during sub-solidus heating are dominated by the release of water from phyllosilicates, forcing the residual MM composition towards its anhydrous precursor composition. (2) Oxygen isotope compositions undergo the most significant changes at supra-solidus temperatures. As previously demonstrated and now empirically confirmed, most of these changes are driven by a mass-dependent fractionation effect caused by evaporation, which shifts residual rock compositions toward heavier values. Mixing with atmospheric air alters compositions toward the terrestrial fractionation line. Notably, these two processes do not begin simultaneously. Our data indicate that at 1200 degrees C, isotopic evolution is dominated by evaporative mass loss. However, at higher temperatures (1400-1600 degrees C), both pronounced evaporation and mixing with atmospheric oxygen become active, resulting in a more complex isotopic signature. (3) The total change in D17O during heating up to 1600 degrees C is < 3 parts per thousand and in most scenarios < 2 parts per thousand. (c) 2025 China University of Geosciences (Beijing) and Peking University. Published by Elsevier B.V. on behalf of China University of Geosciences (Beijing). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Secondary ion mass spectrometry (SIMS) is often used to determine the sulfur contents and isotope ratios of metallic alloys in meteorites or high‐pressure experimental samples. However, SIMS analyses involve calibration and the determination of instrumental mass fractionation in reference materials with a matrix composition similar to that of the unknown samples. To provide metallic reference materials adapted to S measurements via SIMS, we synthesised a series of twenty‐eight alloys comprising four FeNi(±Si) compositions (Fe95Ni5, Fe90Ni10, Fe80Ni20, and Fe80Ni15Si5) with S contents varying from 100 μg g−1 to 4 g/100g using the “melt spinning” method, which guarantees that the metal alloys are rapidly quenched at ~ 106 K s−1. Sulfur contents were determined at the Service d'Analyse des Roches et Minéraux at the CRPG and absolute δ34S values were determined by multi‐collector ICP‐MS (MC‐ICP‐MS, ThermoScientific Neptune) and isotope ratio mass spectrometry (Thermoscientific Delta V). A δ34S value of 16.01 ± 0.31‰ was consistently obtained using the MC‐ICP‐MS, which was indistinguishable of the δ34S value of the FeS starting material (15.95 ± 0.08‰). It suggests that S did not undergo isotopic fractionation during the melting process. Of fifteen samples containing ≤ 5000 μg g−1 S, SIMS measurements with 15‐μm‐diameter spots were repeatable to within 10% relative (1 standard deviation, 1s) for S contents and 2‰ for δ34S values. However, samples containing > 5000 μg g−1 S showed FeNi–FeS immiscibility, leading to minor dispersion of the S mass fractions and δ34S values. No matrix effect was observed for Fe‐Ni, Si, or S contents in terms of the calibration curves and instrumental mass fractionation. We ultimately recommend eight samples as reliable reference materials for S isotopic measurements by SIMS, which we can share worldwide with other laboratories.