Significance: The origin of diamonds in ureilites is still a debated issue among the scientific community, with significant implications for the sizes of early Solar System bodies. We investigated three diamond-bearing ureilites by a multimethodological approach using scanning electron microscopy, micro X-ray diffraction, transmission electron microscopy, and micro-Raman spectroscopy, with the aim of determining the origin of the diamonds. Our results show that formation of both microdiamonds and nanodiamonds in ureilites can be explained by impact shock events on a small planetesimal and does not require long growth times at high static pressures within a Mercury- or Mars-sized body.

Meteoritical Bulletin 110 contains the 2802 meteorites approved by the Nomenclature Committee of the Meteoritical Society in 2021. It includes 10 falls (Arpu Kuilpu, Djadjarm, Glendale, Kindberg, Madura Cave, Motopi Pan, Orconuma, Punggur, Tihigrin, Winchcombe), with 2014 ordinary chondrites (including 1 ungrouped ordinary chondrite), 220 carbonaceous chondrites (including 11 ungrouped), 212 HED achondrites, 69 lunar meteorites, 62 ureilites, 43 iron meteorites, 35 Martian meteorites, 31 Rumuruti chondrites, 27 primitive achondrites, 24 mesosiderites, 19 relict meteorites (all iron meteorites), 15 pallasites, 13 enstatite chondrites, 11 ungrouped achondrites, 7 enstatite achondrites. Of the meteorites classified in 2021, 1270 are from Antarctica, 1049 from Africa, 329 from South America, 123 from Asia, 20 from North America, 6 from Europe, 3 from Oceania, and 2 from unknown locations.

Miller Range (MIL) 090340 and MIL 090206 are olivine‐rich achondrites originally classified as ureilites. We investigate their petrography, mineral compositions, olivine Cr valences, equilibration temperatures, and (for MIL 090340) oxygen isotope compositions, and compare them with ureilites and other olivine‐rich achondrites. We conclude that they are brachinite‐like achondrites that provide new insights into the petrogenesis of brachinite clan meteorites. MIL 090340,6 has a granoblastic texture and consists of ~97 modal % by area olivine (Fo = molar Mg/[Mg+Fe] = 71.3 ± 0.6). It also contains minor to trace augite, chromite, chlorapatite, orthopyroxene, metal, troilite, and terrestrial Fe‐oxides. Approximately 80% by area of MIL 090206,5 has a granoblastic texture of olivine (Fo 72.3 ± 0.1) plus minor augite and chromite, similar to MIL 090340 but also containing minor plagioclase. The rest of the section consists of a single crystal of orthopyroxene (~11 × 3 mm), poikilitically enclosing rounded grains of olivine (Fo = 76.1 ± 0.6), augite, chromite, metal, and sulfide. Equilibration temperatures for MIL 090340 and MIL 090206, calculated from olivine‐spinel, olivine‐augite, and two‐pyroxene thermometry range from ~800 to 930 °C. In both samples, symplectic intergrowths of Ca‐poor orthopyroxene + opaque phases (Fe‐oxides, sulfide, metal) occur as rims on and veins/patches within olivine. Before terrestrial weathering, the opaques were probably mostly sulfide, with minor metal. All petrologic properties of MIL 090340 and MIL 090206 are consistent with those of brachinite clan meteorites, and largely distinct from those of ureilites. Oxygen isotope compositions of olivine in MIL 090340 (δ¹⁸O = 5.08 ± 0.30‰, δ¹⁷O = 2.44 ± 0.21‰, and Δ¹⁷O = −0.20 ± 0.12‰) are also within the range of brachinite clan meteorites, and well distinguished from ureilites. Olivine Cr valences in MIL 090340 and the granoblastic area of MIL 090206 are 2.57 ± 0.06 and 2.59 ± 0.07, respectively, similar to those of three brachinites also analyzed here (Brachina, Hughes 026, Nova 003). They are higher than those of olivine in ureilites, even those containing chromite. The valence systematics of MIL 090340, MIL 090206, and the three analyzed brachinites (lower Fo = more oxidized Cr) are consistent with previous evidence that brachinite‐like parent bodies were inherently more oxidized than the ureilite parent body. The symplectic orthopyroxene + sulfide/metal assemblages in MIL 090340, MIL 090206, and many brachinite clan meteorites have superficial similarities to characteristic “reduction rims” in ureilites. However, they differ significantly in detail. They likely formed by reaction of olivine with S‐rich fluids, with only minor reduction. MIL 090340 and the granoblastic area of MIL 090206 are similar in modal mineralogy and texture to most brachinites, but have higher Fo values typical of brachinite‐like achondrites. The poikilitic pyroxene area of MIL 090206 is more typical of brachinite‐like achondrites. The majority of their properties suggest that MIL 090340 and MIL 090206 are residues of low‐degree partial melting. The poikilitic area of MIL 090206 could be a result of limited melt migration, with trapping and recrystallization of a small volume of melt in the residual matrix. These two samples are so similar in mineral compositions, Cr valence, and cosmic ray exposure ages that they could be derived from the same lithologic unit on a common parent body.