¹L.J. Riches, ^1,2M.D. Suttle, ¹I.A. Franchi, ¹X. Zhao, ^1,2M.M. Grady
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.12.035]
¹School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom
²Planetary Materials Group, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom
Copyright Elsevier

Analysis of carbonate minerals in ungrouped carbonaceous chondrites offer valuable insights into the geological activity on a diverse range of early-formed, hydrated planetesimals in the outer Solar System. Essebi is a C2-ung chondrite, which originated from a water-rich asteroid with close affinities to the CM chondrites group. We performed a detailed geochemical, petrographic and isotopic study of Essebi. Modal mineralogy demonstrates that Essebi is dominated by a poorly crystalline, fine-grained phyllosilicate matrix (mostly a mix of saponite and serpentine ∼63 vol%) with a modest quantity of anhydrous silicates (20 vol%) and accessory magnetite (7.5 vol%), Fe-sulphides (5.5 vol%) and carbonates (2 vol%). Its bulk O-isotope composition (2.71 ‰ δ17O (± 0.018 1σ), 8.11 ‰ δ18O (± 0.002 1σ) and −1.53 ‰ Δ17O (± 0.017 1σ) and 2.56 ‰ δ17O (± 0.040 1σ), 7.65 ‰ δ18O (± 0.009 1σ) and −1.42 ‰ Δ17O (± 0.039 1σ)) places Essebi as part of the “CM field”, although overlapping with the “CR field”. Petrographic observations reveal multiple generations of carbonate that formed both before and after brecciation, exhibiting distinct characteristics that differ from the carbonates found in established groups (CMs). Essebi’s carbonate generations have distinct morphologies and C- and O- isotope compositions and, based on these data, are interpreted as two main generations and a series of other localised carbonate expressions.
The first generation (GA) carbonates formed prior to phyllosilicate growth, and have inferred maximum formation temperatures of +45 °C. They formed under high water-to-rock (W/R) ratios. The second generation (GB) carbonates show lower W/R ratios and at higher, although unquantified temperatures. They formed near the end of the alteration sequence from a residual fluid containing abundant dissolved cations. In addition to the two main generations, we identified a third population of vein carbonates (GC) that partially infilled fractures generated by brecciation. We also identified dolomite (GD) grains found exclusively within an xenolithic clast. This clast displays a more advanced stage of alteration (C1-ung) and shows evidence of fluid leaching after being embedded, resulting in the formation of a localized ring of calcites, referred to as GE, that remain distinct from all other carbonates in this sample.
Despite textural differences, the isotopic trends observed in these Essebi carbonates closely resemble the sequence described by T1 and T2 calcites in CM chondrites, suggesting that multiple distinct episodes of carbonate precipitation, aqueous alteration along a prograde metasomatic sequence, and isotopic evolution from 16O-poor to 16O-rich trajectories were common across several water-rich planetesimals that formed in the outer Solar System.

¹Neil R. Bennett,¹Jessica D. Verschoor,²Josh Wimpenny,^1,2Corliss K. Sio
American Mineralogist 111, 118-127 Link to Article [https://doi.org/10.2138/am-2025-9765]
¹Department of Earth Science, University of Toronto, Toronto, Ontario M5S 1L1, Canada
²Lawrence Livermore National Laboratory, Livermore, California 94550, U.S.A.
Copyright: The Mineralogical Sociwety of America

Iron meteorites record a range of Fe isotope compositions that hold valuable information regarding the evolution of their parent bodies. Interpreting this isotopic variability, however, requires experimental constraints on the equilibrium isotope fractionation between phases. It is thought that the cores of many iron meteorite parent bodies experienced fractional crystallization, during which crystallization of solid iron-nickel occurs from an increasingly non-metal-rich liquid alloy. Phosphorus is one component of this alloy, and this study provides the first constraints on Fe-isotope fractionation between solid and liquid alloys in the Fe-Ni-P system. Experiments comprising Fe and P show a clear enrichment in the light isotopes of Fe in the liquid phase, which increases with the amount of phosphorus. Nickel-bearing samples are offset from the trend defined by Ni-free experiments, which is accounted for by the change in the solid alloy phase from a body-centered cubic to face-centered cubic structure upon the addition of Ni. The increasing light isotope enrichment of the liquid with increasing P content suggests interstitial solution of P, which is known to lengthen Fe-Fe bonds in Fe-P liquids (Waseda and Shiraishi 1977). Results suggest a negligible effect of P on Fe isotope fractionation during planetesimal core crystallization. Iron isotopes may, however, prove useful for identifying the petrogenesis of schreibersite in pallasites and iron meteorites.

¹W. M. Lawrence,¹B. L. Ehlmann
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2025JE009377]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
Published by arrangement with John Wiley & Sons

CM (Mighei‐type) carbonaceous chondrites host abundant OH/H2O‐bearing phyllosilicatesformed from water‐rock reactions in primitive planetesimals. Their infrared (IR) spectral features resemblethose of C‐type asteroids, making laboratory analyses of CMs essential for interpreting asteroid observations.However, CM chondrites are often breccias composed of lithologies with variable degrees of aqueousalteration, complicating their interpretation. Here we use in situ analytical techniques to characterize spectral‐compositional relationships for phyllosilicates in 8 CM lithologies across two meteorite samples. Micro‐Fourier Transform Infrared (μ‐FTIR) spectra collected from phyllosilicate‐rich matrix regions show that bandpositions of the 3‐μm feature and Si‐O stretch Reststrahlen band (RB) systematically vary with alteration.Additional data from spatially correlated electron microprobe and μ‐FTIR measurements tie spectral variationsto specific cation substitutions in serpentines: the 3‐μm feature shifts from 2.78 to 2.70 μm with increased Mg/Fe in octahedral sites, and the Si‐O stretch RB shifts from 10.8 to 9.8 μm with increased Si/Fe3+ in tetrahedralsites. Co‐variation of these features across the studied CM lithologies defines two successive alteration stages:(1) the Si‐O stretch RB and 3‐μm feature shift to longer and shorter wavelengths, respectively, as Mg‐ andcronstedtite‐rich phyllosilicates form from incipient chondrule alteration; (2) Si‐O stretch RB shifts to shorterwavelengths as Mg‐serpentines replace cronstedtite and Mg‐rich chondrules. These patterns align with inferredchanges in composition and redox state for altering fluids on the CM parent body. Similar features in thespectra of C‐type asteroids may reveal information about conditions of aqueous alteration and constrain modelsof their evolution.

^1,2C. P. Haupt,³A. N. Stojic,³A. Morlok,³I. Weber,¹S. Klemme,³H. Hiesinger,^1,4C. J. Renggli
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008895]
¹Institut für Mineralogie, Universität Münster, Münster, Germany
²ISTO, UMR 7327, University of Orléans, CNRS, BRGM, OSUC, Orléans, France
³Institut für Planetologie, Universität Münster, Münster, Germany
⁴Max-Planck-Institute for Solar System Research, Göttingen, Germany
Published by arrangement with John Wiley & Sons

Laboratory-based mid-infrared (MIR) spectroscopy of terrestrial and planetary analogue materials, combined with chemical and spectral insights from mission-derived data, provides critical tools for advancing our knowledge of planetary surfaces. The returned lunar samples provide information on the chemical variability of the lunar surface. Lunar basalts are notably enriched in TiO2 when compared to their terrestrial equivalents, and are ideal candidates to study the influence of composition on MIR spectral features. We characterized 25 synthetic lunar glasses with variable TiO2 (0.6–18.7 wt%) and SiO2 (35.6–52.1 wt%) in the thermal infrared range using micro-Fourier Transform Infrared Spectrometry (μ-FTIR). Our data reveal a strong linear relationship between the intensity of a spectral shoulder at 14.25 μm (702 cm−1) and the TiO2 content of the analyzed glasses. We suggest that the relationship in our samples reflects an increased distortion of the silicate network with increasing TiO2 concentrations. We observe that TiO2 acts as a network former in specific concentration intervals, thereby affecting the intensity of the observed spectral features in the MIR. This linear relationship is virtually nonexistent in samples that are developing stages of short-range order in the glasses and those samples that show only moderate to low amounts of TiO2. Comparison with data sets from Earth and Mercury analogue materials confirms that the Christiansen Feature (CF) consistently correlates with the SiO2 content, underscoring its robustness as a proxy for glass polymerization across planetary compositions. Finally, we emphasize that incipient crystal nucleation in glassy surfaces affects spectral features in the MIR range.

During the last days of this year, Cosmochemistry Papers will be on Christmas break. Normal service will commence on January, 5th, 2024 .

Merry Christmas & Happy New Year to everyone!

¹Abdelmadjid Seddiki, ²Bertrand Moine, ³Jérôme Bascou, ¹Ratiba Kared, ³Jean Yves Cottin, ⁴Marguerite Godard, ⁵François Faure, ⁶Richard C. Greenwood, ¹Ian A. Franchi
Chemie der Erde (Geochemistry) (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2025.126363]
¹Laboratoire Géoressources, Environnement et Risques Naturels (GEOREN), Université d’Oran2, BP: 1510, Oran, 31000, Algeria
²Laboratoire Magmas et Volcans, F-63000, CNRS, IRD, OPGC, Université Clermont Auvergne, Clermont-Ferrand, France
³Université Jean Monnet, CNRS, LGL-TPE, UMR5276, F-42023, Saint-Etienne, France
⁴Géosciences Montpellier, Université Montpellier II, Place Eugène Bataillon, 34095, Montpellier, cedex5, France
⁵CRPG, Université Henri Poincaré de Nancy, 15, rue Notre-Dame des Pauvres, B.P. 20, 54501, Vandoeuvre-lès-Nancy, France
⁶Planetary and Space Sciences Research Institute, Open University, Milton Keynes, MK7 6AA, UK
Copyright Elsvier

Northwest Africa (NWA) 4269 is an anomalous monomict eucrite that is characterized by a very high content of metallic iron (~ 3 %). It shows various textures (relict magmatic sub-ophitic, granulitic areas as coarse and fine-grained). NWA 4269 also shows petrographic evidence of secondary sub-solidus reheating events. Pyroxenes have homogeneous compositions and are iron-rich. NWA 4269 is metamorphosed type 5. It has a normal HED oxygen isotope composition. The chemical composition of NWA 4269 has characteristics similar to that of Nuevo-Laredo trend eucrites. Metal is extremely abundant in the fine-grained areas (~ 10 %). Metal also has a very low Ni content (Ni < 0.1 %) that excludes a direct origin from a chondrite-like impactor. Origin of the pure-Fe groundmass metal remains enigmatic. The high metal content in NWA 4269 can be interpreted as having formed via the reduction of FeO and probably also by desulfidation of pre-existing troilite. Iron metal could have formed by deposition from a Fe-rich fluid that, probably after an event that triggered sudden reduction. NWA 4269 has normal HED oxygen isotope compositions and interpreted as belonging to the 4-Vesta asteroid.

¹I. Weber, ¹M.P. Reitze, ¹T. Heyer, ¹A. Morlok, ¹T. Grund, ¹H. Hiesinger
Advances in Space Sciences (in Press) Open Access Link to Article [https://doi.org/10.1016/j.asr.2025.12.048]
¹Universität Münster, Institut für Planetologie, Wilhelm-Klemm-Str. 10, 48149 Münster

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Roberto Conconi,¹Hugues Leroux,²Maya Marinova,¹Sylvain Laforet,¹Damien Jacob,³Léna Jossé,³Alice Aléon-Toppani,³Zélia Dionnet,³Rosario Brunetto,¹Corentin Le Guillou
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70083]
¹Universite de Lille, CNRS, INRAE, Centrale Lille, UMR 8207-UMET-Unit et Materiaux et Transformations, Villeneuve d’Ascq,France
²Universite de Lille, CNRS, INRAE, Centrale Lille, Universit´e Artois, FR 2638-IMEC-Institut Michel-Eugene Chevreul,Villeneuve d’Ascq, France
³Universite Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, Orsay, France
Published by arrangement with John Wiley & Sons

Samples returned from asteroid Ryugu by the Hayabusa2 mission are dominated by fine-grained matrix material made of phyllosilicates and nanosulfides. Here, we report the mineralogical, textural, and chemical characteristics of nanosulfide-rich regions identified in Ryugu particles. High-resolution scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy reveal nanoscale heterogeneities in sulfide composition and morphology, indicating formation under variable conditions. Nanosulfide-rich regions are dominated by the presence of mackinawite (FeS) and pyrrhotite (Fe1-xS), in different proportions. Mackinawite, identified for the first time in Ryugu, occurs as well-crystallized lamellar crystals with some areas containing greigite (Fe3S4) and others showing signs of oxidation. In contrast, pyrrhotite appears either as euhedral nanocrystals or as structurally complex grains composed of stacked platy segments, which are characterized by numerous defects, including inclusions and planar defects. The distribution and associations of these phases are consistent with low-temperature aqueous alteration under alkaline and reducing conditions, likely occurring in Ryugu’s parent body. The presence of mackinawite implies complex thermodynamic and kinetic constraints and suggests the presence of localized fluids in which Fe concentrations exceeded those of S by an order of magnitude.

^1,2Walter Alvarez
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70084]
¹Department of Earth and Planetary Science, University of California, Berkeley, California, USA
²Osservatorio Geologico di Coldigioco, Apiro, Italy
Published by arrangement with John Wiley & Sons

Astronomy and geology: the first deals with myriad, enormous, unreachable objects seen at great distances and at very low resolution; the other investigates one tiny (by comparison) object, Earth, at close range, from planetary scale down to almost atomic resolution in the laboratory. Planetary Science, studying solar system objects, to some extent bridges the gap between astronomy and geology. Astronomers mostly look up; geologists mostly look down. This paper lists cases where studies in one of those fields have contributed to understanding in the other. The central focus is on investigations of the Cretaceous and Paleogene pelagic Scaglia limestone in the Italian Apennine Mountains where geologic studies bear on five classes of solar system objects. The classes are separated by three orders of magnitude in size: the Moon-forming impactor, bolides that form craters on Earth, meteorites, meteor-forming grains, and extraterrestrial dust. The paper closes by calling attention to LIGO, the Laser Interferometer Gravitational-Wave Observatory, in which astronomical discoveries made by looking down have yielded a geological discovery done by looking up. LIGO has detected distant collisions involving black holes and neutron stars by measuring infinitesimal distortions of the Earth, which in turn have shown that at least some of Earth’s supply of heavy elements has been created by collisions of pairs of neutron stars—a major contribution to geochemistry and cosmochemistry.

¹N. Zimmermann,¹M. Safari,¹H. Nekvasil
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [ https://doi.org/10.1029/2024JE008906]
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008906]
¹Department of Geosciences, Stony Brook University, Stony Brook, NY, USA
Published by arrangement with John Wiley & Sons

Martian magmas compositionally resemble those from terrestrial continental hotspot magmatic suites, characterized by low OH and high Cl and S contents. The magmatic gases exsolved from such magmas transport a variety of metal complexes and, upon cooling, precipitate vapor-deposits into vugs and fractures within rocks and on the surfaces of pyroclastics, which are then added to surface fines. Experiments investigated trace element behavior during magmatic degassing as a potential signature of this magmatic process. Low-pressure experimental degassing of P-rich basaltic magma containing Cl, Br, S, minor OH, and trace elements (Sr, Ge, Ga, Zn, Pb, Rb, Cs, Se, Cu, La, and Lu) demonstrated that the gas-transported trace metals become incorporated into vapor-deposited Cs-Pb-Zn-Rb-bearing halides, Ge-Ga-bearing iron oxides, Zn-Se-Cu-bearing sulfides, alkali and iron sulfates, Ge-bearing silicates, rare earth phosphates, and elemental metals. Low-OH and high-Cl magmatic systems produce a variety of halides but inhibit Fe-oxide formation. S-rich systems produce vapor-deposited Na-, K-, and Fe-sulfates, Zn-Cu-Se bearing sulfides, and iron oxides. These results provide a signature for determining the possibility of a significant role for magmatic gas in producing secondary minerals and volatile trace element enrichment in the Gusev plains, Columbia Hills, Jezero crater, and Gale crater. A hallmark of vapor-deposited phases is the presence of local heterogeneities in “alteration” phases and in trace element signatures due to the superposition of high and low temperature phases.