¹Chi Ma,²Oliver Tschauner,³John G. Spray,⁴Zhongxu Pan
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70129]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
²Department of Geoscience, University of Nevada, Las Vegas, Nevada, USA
³Planetary and Space Science Centre, University of New Brunswick, Fredericton, New Brunswick, Canada
⁴School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui, China
Published by arrangement with John Wiley & Sons

We report a previously unknown aluminosilicate mineral, (Si0.91□0.09)Σ1.00(Al1.46□0.54)Σ2.00O4 with a vacancy-stabilized spinel-type structure (henceforth “SiAl-spinel”). This novel aluminosilicate occurs with coesite, stishovite, and majoritic garnet in a shock melt vein in metaquartzite from the outer collar of the Vredefort Dome, the eroded central uplift of the Vredefort impact structure of South Africa. Formation conditions for this new high-pressure, high-temperature phase are around 10 GPa and 1400°C, upon release from peak shock conditions. Based on its composition and formation conditions, this new high-pressure, high-temperature phase is predicted to be a common occurrence in terrestrial impactites and in subducted slabs.

^1,2Lidia Pittarello,³Valeria De Santis,³Laura Carone,⁴Giovanni Pratesi,⁵Mauro Gemmi,⁵Paola Parlanti,⁶Andreas Steiger-Thirsfeld,⁷Alessandro Di Michele,³Gabriele Giuli
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70134]
¹Naturhistorisches Museum, Mineralogisch-Petrographische Abteilung, Vienna, Austria
²Department of Lithospheric Research, University of Vienna, Vienna, Austria
³Geology Divison, School of Science and Technology, University of Camerino, Camerino, Italy
⁴Department of Earth Sciences, University of Firenze, Firenze, Italy
⁵Electron Crystallography, Istituto Italiano di Tecnologia, Pontedera, Italy
⁶Technische Universit€at Wien, University Service Center for Transmission Electron Microscopy, Vienna, Austria
⁷Department of Physics and Geology, University of Perugia, Perugia, Italy
Published by arrangement with John Wiley & Sons

The occurrence of ringwoodite in shocked L6 ordinary chondrites has been frequently reported, mostly within shock veins. Only recently, ringwoodite has also been found in a fragment from the Alfianello meteorite, occurring as rim or core of olivine clasts in impact melt pockets, in lamellae crosscutting olivine grains in the host rock, and in fine-grained aggregates in association with wadsleyite. In all cases, ringwoodite shows a higher Fe/Mg ratio than the original olivine, whereas wadsleyite shows a lower Fe/Mg ratio than the original olivine. Detailed TEM studies of the occurrence of both high-pressure polymorphs allow the identification of the most likely formation process, explaining the coexistence of these polymorphs. The lack of any crystallographic relationships but the complementary Fe/Mg ratios supports formation of the assemblage through fractional crystallization from impact melt under high (shock) pressure conditions. However, the other occurrences of ringwoodite reported in the same sample, traditionally interpreted as resulting from solid-state transformation, emphasize the heterogeneity of distribution of shock effects and shock-induced processes recorded in a single meteorite.

^1,2,3M. R. Boyd,^1,2M. J. Genge,⁴A. G. Tomkins
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70123]
¹Department of Earth Science and Engineering, Imperial College London, London, UK
²Natural History Museum, London, UK
³Grantham Institute – Climate Change and the Environment, Imperial College London, London, UK
⁴School of Earth, Atmosphere and Environment, Monash University, Melbourne, Victoria, Australia
Published by arrangement with John Wiley & Sons

Natural microspherules are formed by high-temperature processes and are present throughout the geologic record to the present day. We report the discovery of large numbers of microspherules recovered from a rock pavement in the Pilbara region, Western Australia. Textures range from glassy to coarse-grained, with many particles containing crystallites, vesicles, and relict grains. Compositions are non-chondritic and are either dominated by silicates or Fe-Ti-bearing oxides. Spherule and relict grain compositions show strong affinities to the mineralogy of the underlying rock, a Paleoarchean granite gneiss. Bulk compositions suggest formation by a localized melting process with precursors dominated by individual pre-existing minerals, with minimal mixing. Numerical modeling of the formation of spherules suggests formation by rapid quenching, possibly from melt droplets. Modeled cooling times are consistent with compositions that indicate limited evaporation. The compositions and textures of these spherules are not compatible with either microtektites formed by meteor impact or micrometeorites formed by the atmospheric entry of cosmic dust and are instead interpreted to have formed via lightning strikes. Spherules generated by lightning strikes may be present in the geologic record and thus could be used as a paleoclimate proxy where other signatures, such as main mass fulgurites, have not survived.

¹Neeraj Srivastava et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70121]
PRSS, PSDN, Physical Research Laboratory, Ahmedabad, India
Published by arrangement with John Wiley & Sons

Estimating mineral abundance in meteorites provides crucial information about the early solar system and planetary formation processes. This study presents a new empirical approach for the estimation of modal abundance of olivine (Ol), high-calcium pyroxene (HCP), and low-calcium pyroxene (LCP) using band area ratio (BAR), a spectral parameter derived using reflectance spectroscopy. Using spectral data of 22 mineral mixtures acquired from the RELAB spectral library, the BAR values were initially calculated. These BAR values were then plotted against Ol% and HCP%, and based on the trends observed, a set of equations was formulated to get the initial estimate of mineral abundances. To apply these to actual samples, an error reduction framework has been developed that involves determination of a class-specific correction factor (CF) for H, L, and LL types of ordinary chondrites (OCs) to account for the presence of other minerals, metals, and impurities. The CF is a quantitative adjustment that is subtracted from the initial estimates to align calculations with the actual values. After application of the CF, the 1σ uncertainties associated with the abundance estimates were found to be ±1.85% for Ol, ±0.91% for HCP, and ±1.63% for LCP. The study demonstrates the estimation of the mineral abundances of seven OCs, using spectral analysis conducted at the Planetary Remote Sensing Laboratory (PRSL), Physical Research Laboratory (PRL). The proposed approach is robust even for bulk samples analyzed under different viewing geometries and provides a rapid, nondestructive alternative to traditional techniques for mineral abundance estimation in meteorites, planetary samples, and analogs.

¹Martyna Jakubowska,¹Jolanta Gałązka-Friedman,²Marek Woźniak,³Krzysztof Szopa,⁴Katarzyna Brzózka,⁵Barbora Pospíšilová,⁶Agnieszka Grabias
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70122]
¹Faculty of Physics, Warsaw University of Technology, Warsaw, Poland
²Faculty of Biology, University of Warsaw, Warsaw, Poland
³Faculty of Natural Sciences, University of Silesia, Sosnowiec, Poland
⁴Faculty of Mechanical Engineering, Casimir Pulaski Radom University, Radom, Poland
⁵Faculty of Science, Palack´y University Olomouc, Olomouc, Czech Republic
⁶Łukasiewicz Research Network—Institute of Microelectronics and Photonics, Warsaw, Poland
Published by arrangement with John Wiley & Sons

The paper presents a modified version of the 4M method, which is the latest method of classifying ordinary chondrites, based on their Mössbauer spectra measured at room temperature. The proposed changes, including the introduction of a new criterion for assessing which group (H, L, or LL) the meteorite being tested belong to, are expected to improve the plausibility of classification by the 4M method. The modification makes use of the Bayesian analysis and the maximum a posteriori probability. This modified version of the 4M method was tested by attempting to classify 20 samples of ordinary chondrites: 8 of type H, 7 of type L, and 5 of type LL. The results were compared with those obtained by the classical method of ordinary chondrite classification. The vast majority of classification tests performed using the new version of the 4M method were consistent with the classical method for group assignment, except for one L-type sample that was classified differently. It was also shown that the introduction of a new criterion resulted in a significantly better agreement with the established classification than in the case of the level of similarity criterion used in the previous version of the 4M method.

¹N. Randazzo,¹R. W. Hilts,²R. M. Whittal,²B. Reiz,¹V. Olan-Rubio,¹C. D. K. Herd,³I. H. Krouse
Meteoritics & Planetary Science (in Press) Open Access Link to Article [doi: 10.1111/maps.701271]
¹Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada
²Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
³School of Science and Technology, Georgia Gwinnett College, Lawrenceville, Georgia, USA
Published by arrangement with John Wiley & Sons

Solvent extraction is a cornerstone of meteoritic organic and inorganic chemistry,yet the assumption that common solvents act as chemically inert media is becomingincreasingly untenable. This study reports that low-molecular-weight alcohols, particularlymethanol and ethanol, are “non-innocent” solvents when used to extract soluble sulfurspecies from carbonaceous chondrites. Laboratory extractions of Tagish Lake and Allendesamples demonstrate that these alcohols readily esterify meteoritic sulfate, producing largequantities of methyl and ethyl sulfate artifacts. Using isotopically labeled methanol(CD 3 OH) in 1:1 water mixtures, it is shown that >99% of the methyl sulfate signalpreviously attributed to indigenous methyl sulfate is actually solvent-derived. Correctedabundances fall from hundreds of nmol g1 reported in earlier studies to < 0.2 nmol g1 ,revealing that intrinsic methyl sulfate is only a trace constituent. Control experimentsindicate that esterification requires both acidic conditions and solid meteoritic matrices,implicating Fe-bearing phyllosilicates and oxides as heterogeneous catalysts. Additionalexperiments confirm that sulfate ester formation does not occur in solution-only systems,underscoring the catalytic role of mineral–solvent interfaces. These findings not onlynecessitate a downward revision of reported organosulfur inventories in carbonaceouschondrites but also highlight a broader issue: solvent-driven reactions can significantly alterthe apparent chemical record of extraterrestrial materials. It is recommended thatisotope-labeled solvents and mixed-solvent systems are employed as standard practice infuture extractions, both to minimize artifact generation and to maximize analyte coverageacross polarity ranges. Recognizing and mitigating solvent reactivity is essential for ensuringthat laboratory analyses faithfully represent intrinsic extraterrestrial chemistry rather thanexperimental artifacts.

^1,2A.P. Singh, ³S.S. Pillai, ¹K.K. Marhas, ⁴K.V.N.G. Vikram, ⁴S. Bhattacharya
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2026.117045]
¹Physical Research Laboratory, Ahmedabad, Gujarat, India
²Department of Earth Science, Gujarat University, Ahmedabad, Gujarat, India
³University of Kerala, Thiruvananthapuram, Kerala, India
⁴Space Applications Centre, Ahmedabad, Gujarat, India
Copyright Elsevier

This study investigates the mid-infrared spectral correlation between four Carbonaceous Vigarano (CV) chondrites (Allende, Grosnaja, Efremovka and Leoville) and ten asteroids of Xk, L, & Ld types (Bus- Binzel taxonomy). It leverages the mid-infrared region of the electromagnetic spectrum, which is characterised by prominent peaks indicative of crystalline bond vibrations of silicates and ionic oxides. A novel statistical methodology, integrating four distinct similarity assessment techniques (normalised local change method, covariance, Euclidean distance, and cosine similarity), was employed to determine the spectral similarity coefficient (Z) between the CV chondrites and the chosen asteroids. The highest similarity is observed between the asteroids of L type, i.e., Cantillo et al. (2023) (Cantillo et al., 2023) Victoria, (1284) Kassandra, and (1702) Latvia and the CV chondrites studied here, followed by the Xk type (114) Kassandra. The Z value between Ld asteroids (234) Barbara, (269) Justitia and CVs exhibit low similarities. This study establishes a framework for the statistical comparison of mid-infrared spectra of meteorites and asteroids by accounting for compositional variability within CV chondrites, thereby providing a basis for more detailed investigations into the parent-body association of these meteorites.

^1,2Mark Nestmeyer, ^1,3Alex J. McCoy-West
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2026.03.022]
¹IsoTropics Geochemistry Laboratory, Earth and Environmental Science, James Cook University, Townsville, QLD 4811, Australia
²CSIRO Mineral Resources, Kensington, WA 6151, Australia
³Economic Geology Research Centre, James Cook University, Townsville, QLD 4811, Australia
Copyright Elsevier

The application of rare Earth element stable isotope compositions has become of increasing interest in geochemistry. Recently, studies have begun exploring variations in the stable 146Nd/144Nd isotope ratio in geological samples, with limited isotope fractionation observed in igneous rocks but significantly larger fractionations seen in low temperature systems. Experimental and theoretical studies on the equilibrium isotope fractionation of Nd are widely missing which can support understanding the fractionation of Nd isotopes among Earth’s major reservoirs. Here, we have modelled the isotope fractionation factors for 15 common rock forming and accessory minerals to help understand equilibrium stable isotope fractionation during medium to high temperature processes.
We estimate that mantle melting will produce minimal isotope fractionation while the residual peridotite ought to retain heavier Nd isotopes which could explain a potentially superchondritic composition of the depleted mantle. This can be predicted because in mantle minerals with Mg sites (e.g. olivine, orthopyroxene) substitution of isotopically heavier Nd is preferred compared to minerals with Ca sites (e.g. clinopyroxene), with the latter being the major contributor to basaltic melts. The Earth’s outer core (i.e. sulfide matte) is a potential host of lighter Nd isotopes which we demonstrate favours sulfides over silicates. However, the low partition coefficients of rare Earth elements into the core leads to a composition of the bulk silicate Earth that is indistinguishable from chondrites. A better understanding of the δ146/144Nd composition of the mantle is warranted to elucidate the isotope fractionation of Nd between Earth’s major geochemical reservoirs.
As Nd condenses from the solar nebular gas into primitive material, the mass-independent nuclear field shift effect dominates equilibrium isotope fractionation and produces significant fractionation in δ146/144Nd even at high temperatures (>1000 °C) with the condensed material enriched in lighter Nd isotopes. However, the isotopic compositions reported for refractory inclusions (–1.86 to 2.20 ‰; Hu et al. (2021)) cannot be solely explained by equilibrium isotope fractionation and other mechanisms are required

¹Daniel R. Dunlap, ¹Julia A. Cartwright, ²Piers Koefoed, ⁴Evgenii Krestianinov, ¹Stephen J. Romaniello, ³Carl Agee, ²Yuri Amelin, ¹Meenakshi Wadhwa
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2026.03.014]
¹Arizona State University, School of Earth and Space Exploration, 781 Terrace Mall, Tempe, AZ 85287, USA
²Australian National University, Research School of Earth Sciences, 142 Mills Rd, Acton ACT 2601, Australia
³University of New Mexico, Institute of Meteoritics, 1 University of New Mexico, MSC03 2050, Albuquerque, NM 871312, USA
⁴Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854 USA
Copyright Elsevier

The chronology of ungrouped achondrites provides key insights into the timeline of igneous activity in the early Solar System. Two ungrouped achondrites – Northwest Africa (NWA) 11119 (andesite-dacite) and NWA 8486 and its pair NWA 7325 (olivine gabbro) – are the focus of this study, where their chronologies are investigated using multiple high-resolution techniques. Here we report the lead-lead (207Pb-206Pb) and manganese-chromium (53Mn-53Cr) systematics of NWA 11119, as well as the 207Pb-206Pb systematics of NWA 8486 alongside aluminum-magnesium (26Al-26Mg) systematics for NWA 7325. The U-corrected 207Pb-206Pb ages of NWA 11119 and the combined ages of NWA 7325/8486 are 4566.4 ± 0.8 Ma and 4563.8 ± 1.9 Ma, respectively. Additionally, we report the 53Mn-53Cr age of NWA 11119 to be 4564.4 ± 2.5 Ma and the 26Al-26Mg age of NWA 7325/8486 to be 4563.1 ± 0.3 Ma.
The formation of NWA 11119 requires partial melting of a (likely chondritic) source reservoir leading to eruption of Si rich, alkali depleted magmas, while NWA 7325/8486 likely formed from a chemically fractionated reservoir with superchondritic Al/Mg. The clear geochemical and isotopic similarities of these achondrites, combined with the chronology reported here, is suggestive of formation of these two ungrouped achondrites on a common parent body which likely formed in the inner Solar System and experienced early differentiation under reducing conditions. If these achondrites did share a parent body, it would suggest that primary asteroids in the early Solar System commonly produced mineralogically and geochemically heterogeneous crusts. While mineralogical and geochemical heterogeneity is known to exist in the (mostly mafic) crust of asteroid Vesta, our findings show that even more significant crustal heterogeneity (representing felsic and mafic compositions) may exist on other asteroids.

¹Bianka Babrián, ²Queenie H.S. Chan, ³Jens Najorka, ¹James Malley, ⁴Lee F. White, ^1,3Martin D. Suttle
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2026.03.020]
¹School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
²Department of Earth Sciences, Royal Holloway, University of London, Egham TW20 0EX, UK
³Planetary Materials Group, Natural History Museum, Cromwell Road, London SW7 5BD, UK
⁴Electron Microscopy Suite, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
Copyright Elsevier

We performed a series of low temperature hydrothermal alteration experiments using the highly primitive CO3.00 chondrite DOM 08006 as the protolith to investigate aqueous alteration conditions on carbonaceous planetesimals. Our experiments employed a range of water-to-rock (W/R) ratios by mass (0.2, 0.4, 1.0) and a heating duration of 100 days at 80°C. We also used a short-duration experiment terminated on day 12 to investigate the earliest stages of aqueous alteration. We used isotopically doped 17O-rich water to track isotopic behaviour during alteration and ascertain the effective molar W/R ratios (i.e., the proportion of reacted water) in the experiments. Bulk O-isotope data suggest that the effective W/R ratio achieved by the experimental samples was capped at ∼0.2 at the end of the experiments. This reflects low alteration extents, which we attribute to low matrix permeability that results from the early and continuous precipitation of Fe-bearing phases, likely dominated by Fe-sulphides, into pore spaces, restricting fluid flow and hindering the progression of alteration at these short timescales. Conversely, early hydrothermal fracturing was observed which may lead to “runaway” alteration at longer timescales. Initial W/R ratio had little effect on the style of alteration, except for allowing Mg-serpentine (chrysotile) to form in addition to Fe-serpentine (cronstedtite) in the high W/R (1.0) experiment. Phyllosilicate production doubled over one order of magnitude longer durations, from 12 to 100 days, at similar effective W/R ratios. One sample (Exp-2) experienced initially oxidising conditions, which led to a marked distinction in alteration style dominated by Fe-oxides and Fe-(oxy)hydroxides. This sample also formed framboidal magnetite, showing that this morphology is possible under oxidising conditions and that the presence of ammonia may not be required, as previously suggested. This work is a strong step forward in experimentally recreating a “generic” hydrated chondrite in the nascent stages of aqueous alteration.