Abstract Shock-melt veins in ordinary chondrites record ultrafast, high-pressure mineral transformation reactions. However, resolving the nano- to microscale mineral assemblages that form and quench during these events remains challenging. Here we demonstrate that near-axis transmission Kikuchi diffraction (NA-TKD), combined with scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), can reliably resolve crystal structures and Fe–Mg zoning in sub-micron, high-pressure olivine phases across 10–15 μm fields of view, providing new insights into shock transformation mechanisms. We apply this approach to shock-melt veins in the Catherwood L6 chondrite, where host olivine along the shock-vein margin transforms into dense, randomly oriented clusters of ringwoodite crystallites. These textures indicate rapid solid-state transformation by homogeneous intracrystalline nucleation and interface-controlled growth under strongly overstepped conditions. Olivine fragments entrained within the melt preserve similar ringwoodite-dominated cores but develop Fe-rich reaction zones and Mg-rich wadsleyite rims at melt-wetted grain boundaries, accompanied by interstitial majoritic garnet. These features record brief melt infiltration, partial dissolution, and melt-assisted recrystallization during shock events. Together, the observed microstructures define a two-stage, but spatially heterogeneous transformation sequence: initial solid-state ringwoodite formation followed by localized melt-mediated overprinting and wadsleyite crystallization. This demonstrates that pressure–temperature conditions vary substantially across a single shock-melt vein, allowing multiple transformation mechanisms to operate sequentially or simultaneously within the same system. By enabling phase discrimination, orientation mapping, and coupled chemical–structural analysis at ∼10–30 nm spatial resolution, NA-TKD combined with EDS provides nanoscale crystallographic mapping within the SEM. This approach allows shock transformation sequences to be reconstructed across micrometer-scale fields of view that are difficult to access using SEM and TEM alone, providing a powerful framework for interpreting high-pressure reaction pathways in planetary materials.

We studied lunar regolith breccia meteorite Northwest Africa (NWA) 13967 to explore its mineral and clast inventory with special focus on the ubiquitous occurrence of tissintite-II, a newly recognized, vacancy-rich high-pressure clinopyroxene with a feldspathic, Fe- and Mg-enriched composition. Lithic clasts in NWA 13967 indicate a provenance in the Feldspathic Highlands Terrane on the Moon. Most abundant are cumulate impact melt clasts ("poikilitic granulitic breccias"), granular impact melt rocks, vitric impact melt clasts including impact spherules, and anorthositic clasts, while basalt clasts are rare. The breccia groundmass is mostly fused to flow-textured, vesicular, crystallized impact melt that includes 1 mu m corundum crystals and up to 5 mu m tissintite-II near the contact with lithic clasts. Rare coesite occurs in moganite clasts entrained in the shock-melted groundmass and rimmed by tissintite-II. Petrographic features of NWA 13967 and its bulk rock chemical composition are most similar to the NWA 8046 clan of lunar meteorites, the largest known lunar meteorite. We discuss mineralogical and petrological characteristics of NWA 13967 to unravel chemical and structural changes of the lunar regolith during shock lithification, which may inform the ongoing exploration of the lunar surface.

In this study, we report the discovery of a novel high-pressure phase within the Suizhou shocked meteorite, shedding light on the extreme conditions encountered during meteorite impacts. Utilizing advanced analytical techniques including electron microprobe and single-crystal X-ray diffraction, we identified a previously unknown crystalline structure formed under high pressures and temperatures. The new mineral, ideally Mg3(Si0.5[]0.5)Si2O8 (the symbol [] stands for structural vacancy), was approved by the International Mineralogical Association (IMA 2024–012) and named ohtaniite in honour of Eiji Ohtani. The phase, a new mineral with the pyroxene chemistry but with wadsleyite structure, was characterized by its distinct crystal lattice and unique physical properties, suggesting a transformation induced by shock compression. This finding expands our understanding of shock-induced mineralogical transformations in extraterrestrial materials and offers insights into the dynamic processes shaping meteorite evolution. Further investigations into these high-pressure phases are crucial for unraveling the geological history of meteorites and their significance in planetary science.

Approximately 200 meteorites come from ~10 impact events on the surface of Mars, yet their pre-ejection locations are largely unknown. Here, we combine the results of diverse sets of observations and modeling to constrain the source craters for several groups of martian meteorites. We compute that ejection-paired groups of meteorites are derived from lava flows within the top 26 m of the surface. We link ejection-paired groups to specific source craters and geologic units, providing context for these important samples, reconciling microscopic observations with remote sensing records, and demonstrating the potential to constrain the ages of their source geologic units. Furthermore, we show that there are craters that may have produced martian meteorites not represented in the world’s meteorite collections that have yet to be discovered.

Solar energetic particle events electrically charge the lunar surface and may produce electric fields sufficient to induce dielectric breakdown in regolith grains. We irradiated series of silicate minerals with electrons to determine their physical and chemical response to deep dielectric charging and subsequent breakdown. Two electrical phenomena, flashovers and subsurface dielectric breakdown, produced damage including erosional and eruptive channels, surface pits, comminuted grains, and melt and vapor deposits. Iron abundances strongly affected the scale of damage and the minimum fluence required to reach dielectric breakdown; higher iron abundances required higher fluences to reach the breakdown threshold and produced more areally dense damage with each event. If dielectric breakdown is a prominent space-weathering process on the Moon, it should contribute to differential weathering signatures across the lunar surface as a function of target composition.

A recently described micrometeorite from the Nubian desert (Sudan) contains an exotic Al-Cu-Fe assemblage closely resembling that observed in the Khatyrka chondrite (Suttle et al., 2019; Science Reports 9:12426). We here extend previous investigations of the geochemical, mineralogical, and petrographic characteristics of the Sudan spherule by measuring oxygen isotope ratios in the silicate components and by nano-scale transmission electron microscopy study of a focused ion beam foil that samples the contact between Al-Cu alloys and silicates. O-isotope work indicates an affinity to either OC or CR chondrites, while ruling out a CO or CM precursor. When combined with petrographic evidence we conclude that a CR chondrite parentage is the most likely origin for this micrometeorite. SEM and TEM studies reveal that the Al-Cu alloys mainly consist of Al metal, stolperite (CuAl), and khatyrkite (CuAl2) together with inclusions in stolperite of a new nanometric, still unknown Al-Cu phase with a likely nominal Cu3Al2 stoichiometry. At the interface between the alloy assemblage and the surrounding silicate, there is a thin layer (200 nm) of almost pure MgAl2O4 spinel along with well-defined and almost perfectly spherical metallic droplets, predominantly iron in composition. The study yields additional evidence that Al-Cu alloys, the likely precursors to quasicrystals in Khatyrka, occur naturally. Moreover, it implies the existence of multiple pathways leading to the association in reduced form of these two elements, one highly lithophile and the other strongly chalcophile.

Most meteoritic calcium-rich, aluminum-rich inclusions formed from a reservoir with 26 Al/ 27 Al ≈ 5 × 10 −5 , but some record lower ( 26 Al / 27 Al ) 0 , demanding they sampled a reservoir without live 26 Al. This has been interpreted as evidence for “late injection” of supernova material into our protoplanetary disk. We instead interpret the heterogeneity as chemical, demonstrating that these inclusions are strongly associated with the refractory phases corundum or hibonite. We name them “low- 26 Al/ 27 Al corundum/hibonite inclusions” (LAACHIs). We present a detailed astrophysical model for LAACHI formation in which they derive their Al from presolar corundum, spinel, or hibonite grains 0.5–2 μ m in size with no live 26 Al; live 26 Al is carried on smaller (<50 nm) presolar chromium spinel grains from recent nearby Wolf–Rayet stars or supernovae. In hot (≈1350–1425 K) regions of the disk, these grains and perovskite grains would be the only survivors. These negatively charged grains would grow to sizes 1–10 3 μ m, even incorporating positively charged perovskite grains, but not the small, negatively charged 26 Al-bearing grains. Chemical and isotopic fractionations due to grain charging was a significant process in hot regions of the disk. Our model explains the sizes, compositions, oxygen isotopic signatures, and the large, correlated 48 Ca and 50 Ti anomalies (if carried by presolar perovskite) of LAACHIs, and especially how they incorporated no 26 Al in a solar nebula with uniform, canonical 26 Al/ 27 Al. A late injection of supernova material is obviated, although formation of the Sun in a high-mass star-forming region is demanded.

Most meteoritic calcium-rich, aluminum-rich inclusions (CAIs) formed from a reservoir with ^26 Al/^27 Al≈ 5 × 10^-5, but some record lower (^26 Al/^27 Al)_0, demanding they sampled a reservoir without live ^26 Al. This has been interpreted as evidence for "late injection" of supernova material into our protoplanetary disk. We instead interpret the heterogeneity as chemical, demonstrating that these inclusions are strongly associated with the refractory phases corundum or hibonite. We name them "Low-^26 Al/^27 Al Corundum/Hibonite Inclusions" (LAACHIs). We present a detailed astrophysical model for LAACHI formation in which they derive their Al from presolar corundum, spinel or hibonite grains 0.5 - 2 μ m in size with no live ^26 Al; live ^26 Al is carried on smaller (<50 nm) presolar chromium spinel grains from recent nearby Wolf-Rayet stars or supernovae. In hot (≈ 1350-1425 K) regions of the disk these grains, and perovskite grains, would be the only survivors. These negatively charged grains would grow to sizes 1 - 10^3 μ m, even incorporating positively charged perovskite grains, but not the small, negatively charged ^26 Al-bearing grains. Chemical and isotopic fractionations due to grain charging was a significant process in hot regions of the disk. Our model explains the sizes, compositions, oxygen isotopic signatures, and the large, correlated ^48 Ca and ^50 Ti anomalies (if carried by presolar perovskite) of LAACHIs, and especially how they incorporated no ^26 Al in a solar nebula with uniform, canonical ^26 Al/^27 Al. A late injection of supernova material is obviated, although formation of the Sun in a high-mass star-forming region is demanded.

The goal of classifying shock metamorphic features in meteorites is to estimate the corresponding shock pressure conditions. However, the temperature variability of shock metamorphism is equally important and can result in a diverse and heterogeneous set of shock features in samples with a common overall shock pressure. In particular, high-pressure (HP) minerals, which were previously used as a solid indicator of high shock pressure in meteorites, require complex pressure–temperature–time ( P–T–t ) histories to form and survive. First, parts of the sample must be heated to melting temperatures, at high pressure, to enable rapid formation of HP minerals before pressure release. Second, the HP minerals must be rapidly cooled to below a critical temperature, before the pressure returns to ambient conditions, to avoid retrograde transformation to their low-pressure polymorphs. These two constraints require the sample to contain large temperature heterogeneities, e.g. melt veins in a cooler groundmass, during shock. In this study, we calculated shock temperatures and possible P–T paths of chondritic and differentiated mafic–ultramafic rocks for various shock pressures. These P–T conditions and paths, combined with observations from shocked meteorites, are used to constrain shock conditions and P–T – t histories of HP-mineral bearing samples. The need for rapid thermal quench of HP phases requires a relatively low bulk-shock temperature and therefore moderate shock pressures below ~ 30 GPa, which matches the stabilities of these HP minerals. The low-temperature moderate-pressure host rock generally shows moderate shock-deformation features consistent with S4 and, less commonly, S5 shock stages. Shock pressures in excess of 50 GPa in meteorites result in melt breccias with high overall post-shock temperatures that anneal out HP-mineral signatures. The presence of ringwoodite, which is commonly considered an indicator of the S6 shock stage, is inconsistent with pressures in excess of 30 GPa and does not represent shock conditions different from S4 shock conditions. Indeed, ringwoodite and coexisting HP minerals should be considered as robust evidence for moderate shock pressures (S4) rather than extreme shock (S6) near whole-rock melting.

Coesite embedded in silica glass in suevite from the Xiuyan crater has been studied by scanning and transmission electron microscopy to better understand the mechanisms at formation of coesite. Coesite grains in this study mainly occur as vein‐like aggregates (10–40 μm in width) and irregular aggregates (IAs; <40 μm in size). Both aggregate types are composed of subhedral to anhedral coesite crystals with random orientations. Most of the crystals are 100–1000 nm in size, and some display twinning. The shape, twinning, and random orientation of coesite crystals suggest rapid crystallization in amorphous silica that became supercooled. The center of vein‐like aggregates crystallized from localized silica melt within diaplectic silica glass, whereas the rim of vein‐like aggregates and IAs crystallized from diaplectic silica glass. The size and amount of coesite crystals in the vein‐like aggregate vary greatly from the rim to the center of such veins. Microstructures suggest that the crystals nucleated heterogeneously at the outer rim of the vein and nucleated homogeneously within the vein. IAs do not show any changes in size and amount of coesite crystals from the rim to core of such aggregates. Coesite crystals in IAs primarily nucleate heterogeneously in diaplectic silica glass. It can be concluded that vein‐like coesite aggregates are mainly formed by crystallization from silica melt, and irregular coesite aggregates should be formed by solid‐state transformation of diaplectic silica glass.

NIQUE TO STUDY SHOCK MELT VEINS IN ORDINARY CHONDRITES. J. Moreau1, A. Jõeleht1, J. Plado1, S. Hietala1,2, T. Sharp3, A. N. Stojic4, S. Schwinger5, J. Aruväli1, T. Thomberg61, L. Hecht7, C. Hamann7. 1Department of Geology, University of Tartu, Estonia (juulia.moreau@ ut .ee), 2Geological Survey of Finland, 3School Of Earth and Space Exploration, Arizona State University, USA, 4Institut für Planetologie, Universität Münster, Germany, 5German Aerospace Center (DLR), Berlin, Germany, 6Institute of Chemistry, University of Tartu, Estonia, 7Museum für Naturkunde, Berlin, Germany.

Bridgmanite, MgSiO3 with perovskite structure, is considered the most abundant mineral on Earth. On the lower mantle, it contains Fe and Al that strongly influence its behavior. Experimentalists have debated whether iron may exist in a mixed valence state, coexistence of Fe2+ and Fe3+ in bridgmanite, through charge disproportionation. Here, we report the discovery of Fe-rich aluminous bridgmanite coexisting with metallic iron in a shock vein of the Suizhou meteorite. This is the first direct evidence in nature of the Fe disproportionation reaction, which so far has only been observed in some high-pressure experiments. Furthermore, our discovery supports the idea that the disproportionation reaction would have played a key role in redox processes and the evolution of Earth.

LABORATORY-IRRADIATED NORTHWEST AFRICA 12008. M. L. Shusterman1, T. G. Sharp1, M. S. Robinson1, Z. Rahman2, L. P. Keller2, C. A. Dukes3, C. Bu3 and M. A. Roldan4, 1School of Earth and Space Exploration, Arizona State University (E-mail: Morgan.Shusterman@asu.edu). 2ARES, XI3, NASA/JSC. 3Laboratory for Astrophysics and Surface Physics, University of Virginia, 4Eyring Materials Center, Arizona State University.