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.

The enigma of ammonium mineral speciation in the solar system has no proven solution due to the lack of data on the real minerals serving as space ammonium carriers. We herein report on the discovery of the first ammonium mineral in meteoritic substance and show its relevance to compositional and spectral characteristics ascribed to hypothetical ammonium phases in cometary and asteroidal bodies. Chemically distant from previously inferred volatile organics or ammoniated phyllosilicates, the mineral is an aqueous metal-ammonium sulfate related to the picromerite group-a family of so-called Tutton's salts. Nickeloan boussingaultite, (NH4)2(Mg,Ni)(SO4)26H2O, was discovered in Orgueil, a primitive carbonaceous chondrite closely related to (162173) Ryugu and (101955) Bennu, the C-type asteroids. The available spectroscopic, chemical, and mineralogical data signify that natural sulfates related to boussingaultite-nickelboussingaultite series perfectly fit into the role of bound ammonia carriers under conditions of cometary nuclei and carbonaceous asteroids. The potential technogenic contamination of astromaterial samples and the difficulties in electron microprobe determination of ammonium are discussed in the context of recently published reports on the discovery of lunar and asteroidal ammonium-containing minerals.

Rubinite (IMA 2016-110) is a recently discovered Ti3+-dominant refractory mineral in the garnet group from the solar nebula. It has the Ia (3) over bard garnet-type structure with a = 12.19(1) angstrom, Z = 8, and an end-member formula of Ca3Ti23+Si3O12. Rubinite was identified as micrometer-sized crystals in five refractory Ca,Al-rich inclusions (CAIs) from the CV3 carbonaceous chondrites Allende, Efremovka, and Vigarano. In the Vigarano CAI V3, it occurs in the central portion of an ultra-refractory fragment with Zr,Y,Sc-oxide, spinel, and davisite-diopside, all enclosed within an amoeboid olivine aggregate. In the Allende Compact Type A (CTA) CAI AE01-01, it occurs with gehlenitic melilite, perovskite, spinel, hibonite, davisite, grossmanite, and diopside. In Efremovka, rubinite occurs within gehlenitic melilite with perovskite, spinel, and grossmanite in three CTA CAIs E101, E105, and 40E-1 (in a compound CAI). Rubinite is present in spinel-poor regions in all four of the Efremovka and Allende CAIs, but it is in contact with spinel in the Vigarano inclusion. The mean chemical composition of type rubinite in Allende is (in wt%) CaO 32.68, Ti2O3 14.79, TiO2 13.06, SiO2 28.37 Al2O3 3.82, Sc2O3 1.80, Na2O 1.01, ZrO2, 0.80, MgO 0.79, V2O3 0.61, FeO 0.53, Y2O3 0.07, Cr2O3 0.05, total 98.38, giving rise to an empirical formula of (Ca2.94Na0.08)(Ti(1.04)(3+)Ti(0.59)(4+)Sc(0.13)Mg(0.10)V(0.04)Fe0.04Zr0.03)(Si2.38Al0.38Ti0.244+)O-12, where Ti3+ and Ti4+ are partitioned based on stoichiometry. Efremovka rubinite has a similar composition with a mean empirical formula of (Ca2.97Na0.06)(Ti1.053+Ti0.664+Mg0.12Sc0.09Zr0.03V0.03Y0.01Fe0.01)(Si2.36Al0.48Ti0.164+)O-12. Vigarano rubinite is much more Y-, Sc-, and Zr-rich, having an empirical formula of (Ca1.89Y0.83Mg0.28)(Ti0.593+Sc0.50Zr0.72Mg0.2V0.02Cr0.01)(Si1.64Al1.18Ti0.074+Fe0.06)O-12. All rubinites are Ti3+-rich, but a significant amount (11-46%) of the Ti is 4+. In the Efremovka CTAs, spinel is O-16-rich (Delta O-17 similar to -24 parts per thousand); rubinite and perovskite show limited ranges of Delta O-17 (from -24 to -16 parts per thousand; most analyses range from -24 to -20 parts per thousand); melilite and grossmanite are the most O-16-depleted minerals (Delta O-17 range from similar to -10 to -4 parts per thousand and from -8 to -5 parts per thousand, respectively). In the Allende CTA AE01-01, spinel and hibonite are O-16-rich (Delta O-17 similar to -24 parts per thousand); melilite, rubinite, and perovskite show large ranges in Delta O-17 (from -23 to -3 parts per thousand, from -21 to -6 parts per thousand, and from -14 to -2 parts per thousand, respectively); grossmanite is uniformly O-16-depleted (Delta O-17 similar to-3 parts per thousand). Rubinite formed under highly reducing conditions in the solar nebula by gas-solid condensation and crystallization from a Ca-, Al-, and Ti-rich melt. Subsequently, most rubinite grains in the Allende CAI and some in the Efremovka CAIs may have experienced O-isotope exchange to various degrees with an O-16-depleted (Delta O-17 similar to -2 parts per thousand) aqueous fluid on the CV chondrite parent asteroid. However, crystallization from a Ca,Al,Ti-rich melt that recorded O-isotope exchange with nebular gas with variable Delta O-17 or post-crystallization O-isotope with such gas cannot be excluded. The mineral name is in honor of Alan E. Rubin (b. 1953), a cosmochemist at the University of California, Los Angeles (UCLA), U.S.A., for his many contributions to research in cosmochemistry and mineralogy of meteorites.

We investigated the metal nodules, veins, fine‐grained particles of ordinary chondrites (OC) Ash Creek (L6), Ghubara (L5), NWA 6096 (L6), Tsarev (L5), Kunya‐Urgench (H5), NWA 1588 (H3.8), Tamdakht (H5) and Timochin (H5) using optical microscopy, SEM, and LA‐ICP‐MS to determine trace element distributions and understand the origin of these metal components. The metal nodules have a fractionated siderophile element composition differing from OC metal, indicating the elements were distributed during melting. Most nodules and veins are depleted in Cu and the highly refractory siderophile elements (HRSE) Re, Os, Ir, Ru, Pt, and Rh. Nodules and veins are enriched in W, Mo, Ni, Co, Au, As, and Sb compared to OC metal. Kunya‐Urgench metal shows progressive depletion of refractory siderophile elements, likely due to in situ fractionation of liquid metal injected into the chondrite host. We modeled crystallization of L and H chondrite metal melts, producing results similar to the observed compositions, supporting the hypothesis that the metal components may have originated from unfractionated melted in situ primary metal of chondrites. Variations between modeled and observed W, Fe, and Ga abundances suggest varying redox conditions during melting or metamorphism. Tsarev nodule has a unique HRSE zoning recording its high‐temperature thermal history, with modeled cooling to 1300°C in ~1 year, suggesting crystallization in a thermally insulated environment, possibly under a hot layer of impact ejecta. The low‐temperature thermal histories (660–200°C) of investigated meteorites' metal suggest that shock compression and re‐heating may have resulted in a subsolidus decomposition/recrystallization of the metal.

Sierra Gorda 013 (SG 013) is an unusual CBa‐like chondrite containing two texturally different, isotopically identical lithologies—chondritic (L1) and achondritic (L2), which should have a common origin. The metal globules of the L1 metal preserved the magmatic pattern of the siderophile element distribution that indicates they had a fractionated precursor. In this work, the trace element metal composition of lithology 2 was studied, and the revisited LA‐ICP‐MS data on the L1 metal was presented. Lithologies 1 and 2 have Ni and Co in the range of CB chondrites. The Ni‐Co distribution in L1 and depletion in Cr of both lithologies with a negative Cr‐Ni correlation are similar to that of the magmatic irons. Highly refractory siderophile element (HRSE) (W, Re, Os, Ir, Pt, Ru, Rh, and Mo) compositions of the L1 metal are highly fractionated relative to CI, but the L2 metal has a nearly uniform HRSE distribution similar to the depleted patterns of some HRSE‐poor L1 metal compositions. Metal from both lithologies is depleted in volatile siderophile elements. In the L1 metal globules, the metal composition shows definite linear correlations of the HRSE elements versus Ni similar to those observed in many magmatic iron meteorites, distinct from those of the CH/CBb‐zoned metal. Meanwhile, the L2 metal compositions are systematically plotted as limited clusters in the middle of the L1 trends. Based on a fractional crystallization (FC) model of the CR‐like metal composition, it was shown that the distribution of siderophile elements in the metal globules of L1 can cover the full range of the fractional crystallization products of a metallic (Fe‐Ni‐S) liquid from the core of a differentiated body at S content 13 wt%. In contrast, the metal from L2 corresponds to a more limited range of fractional crystallization products and indicates a mixture of the fractionated metal with the primitive metal from the chondritic colliding body. Our results suggest that during a catastrophic impact event when the metallic core of a differentiated body was disrupted, the L1 lithology was quickly cooled in the impact plume, more reduced than that of CB chondrites and avoided equilibration with plume gas and preserved its fractionated HRSE patterns. The distribution of siderophile volatile elements and Au was likely overprinted by high‐temperature processes of volatilization and recondensation to different degrees in the impact plume under disequilibrium conditions. The L2 metal probably avoided equilibration with the plume gas and was affected by thermal metamorphism up to 900°C in the SG 013 parent body, which possibly resulted in the higher W abundance compared to the L1 metal with a magmatic Ir‐W trend due to the redox reactions with silicates under reducing conditions.

Ultrarefractory Ca,Al‐rich inclusions (UR CAIs) in the Sayh al Uhaymir (SaU) 290 CH3 carbonaceous chondrite consist of ultrarefractory Zr,Sc‐rich minerals (allendeite, kangite, tazheranite, warkite, and Y‐perovskite), grossite, grossmanite, hibonite, melilite, and spinel. Several of them have a core–mantle structure with ultrarefractory minerals concentrated in the core. The unfragmented inclusions are surrounded by layers of spinel, melilite, Sc‐diopside, and diopside (not all layers are present around individual inclusions). The UR CAIs have uniform 16 O‐rich compositions: Most inclusions have Δ 17 O of ~ −23 ± 2‰; a grossite‐rich CAI is slightly 16 O‐depleted (Δ 17 O ~ −17‰). The CAIs are highly enriched in Zr, Hf, Sc, Y, and Ti compared to typical and previously studied UR CAIs from CM2, CO3, and CV3 carbonaceous chondrites. Similar to UR CAIs from other chondrites, the ultrarefractory minerals in SaU 290 CAIs are enriched in heavy rare earth elements (HREEs) relative to more volatile light rare earth elements (LREEs). We conclude that (1) UR CAIs from SaU 290 formed by gas–solid condensation from a gaseous reservoir having variable but mostly solar‐like O‐isotope composition, most likely near the proto‐Sun, and were subsequently transported outward to the accretion region of CH chondrites. (2) The UR oxides and silicates are important carriers of UR REE patterns recorded their possible early fractionation.

The first CY chondrite from the Northwest Africa region was studied (NWA 4757). It is a small (5 g) fine-grained monomict microbreccia consisting of abundant matrix (similar to 95 vol%) and rare pseudomorphic chondrules (up to 200 mu m). The meteorite has main characteristics of CY chondrites. The oxygen isotopic composition of NWA 4757 is O-16-poor (delta O-18 = 23.83, delta O-17 = 12.84, Delta O-17 = 0.45 to delta O-18 = 26.96, delta O-17 = 14.50, Delta O-17 = 0.48 +/- 0.03) which is the heaviest among other CY chondrites. NWA 4757 contains abundant sulfides (similar to 20 vol%) and its bulk chemical composition is enriched in sulfur compared to CM chondrites like most other CY chondrites except for Dhofar 225 and Dhofar 735. NWA 4747 was affected by very intensive aqueous alteration corresponding to petrologic type 1.0 before it was affected by thermal metamorphism. Only a few grains of unaltered olivine (Fa10) survived in NWA 4757. In contrast to other CYs, troilite from NWA 4757 are Mn-rich. The matrix is divided into light and dark types in texture and composition. The light matrix is Ca-rich, and Fe-poor compared to the dark matrix. The dehydrated phyllosilicates had serpentine composition with a low saponite content like CY2s. The presence of high-Ni metal and sulfides, chromite and ilmenite and absence of magnetite indicate that under equilibrium conditions, the redox state of the alteration system in the NWA 4757 parent body did not exceed the fugacity of the iron-wustite buffer. After aqueous alteration NWA 4757 experienced intensive thermal metamorphism resulting in a low H2O (1.9 wt%) compared to usual CI and CM chondrites. The Fourier Transform Infrared (FT-IR) spectroscopy of the matrices of NWA 4757 and Mighei (CM2) showed that the NWA 4757 matrix is dominated by Fe-rich finegrained olivine. According to a classification system for thermally metamorphosed hydrated carbonaceous chondrites based on X-ray Powder Diffraction (XRD) data, NWA 4757 is characterized by heating stage IV (>750 degrees C) like CY2s. Since calcite (and even dolomite) survived metamorphism, it should indicate that the peak temperature was not higher than 800 degrees C. Thus, NWA 4757 is the first CY chondrite of thermal stage IV (CY2) which had properties of extremely altered CM1 chondrite before metamorphism and suggestively should be CY2-m1.

Abstract Rubinite (IMA 2016-110) is a recently discovered Ti3+-dominant refractory mineral in the garnet group from the solar nebula. It has the Ia3d garnet-type structure with a = 12.19(1) Å, and Z = 8, and end-member formula of Ca3Ti3+2Si3O12. Rubinite was identified as micrometer-sized crystals in five refractory Ca,Al-rich inclusions (CAIs) from the CV3 carbonaceous chondrites Allende, Efremovka, and Vigarano. In the Vigarano CAI V3, it occurs in the central portion of an ultrarefractory fragment with Zr,Y,Sc-oxide, spinel and davisite-diopside, all enclosed within an amoeboid olivine aggregate. In the Allende Compact Type A (CTA) CAI AE01-01, it occurs with gehlenitic melilite, perovskite, spinel, hibonite, davisite, grossmanite, and diopside. In Efremovka, rubinite occurs within gehlenitic melilite with perovskite, spinel, and grossmanite in three CTA CAIs E101, E105, and 40E-1 (in a compound CAI). Rubinite is present in spinel-poor regions in all four of the Efremovka and Allende CAIs but it is in contact with spinel in the Vigarano inclusion. The mean chemical composition of type rubinite in Allende is (in wt%) CaO 32.68, Ti2O3 14.79, TiO2 13.06, SiO2 28.37 Al2O3 3.82, Sc2O3 1.80, Na2O 1.01, ZrO2, 0.80, MgO 0.79, V2O3 0.61, FeO 0.53, Y2O3 0.07, Cr2O3 0.05, total 98.38, giving rise to an empirical formula of (Ca2.94Na0.08)(Ti3+1.04Ti4+0.59Sc0.13Mg0.10V0.04Fe0.04Zr0.03)(Si2.38Al0.38Ti4+0.24)O12, where Ti3+ and Ti4+ are partitioned based on stoichiometry. Efremovka rubinite has a similar composition with a mean empirical formula of (Ca2.97Na0.06)(Ti3+1.05Ti4+0.66Mg0.12Sc0.09Zr0.03V0.03Y0.01Fe0.01)(Si2.36Al0.48Ti4+0.16)O12. Vigarano rubinite is much more Y-, Sc-, and Zr-rich, having an empirical formula of (Ca1.89Y0.83Mg0.28)(Ti3+0.59Sc0.50Zr0.72Mg0.2V0.02Cr0.01)(Si1.64Al1.18Ti4+0.07Fe0.06)O12. All rubinites are Ti3+-rich but a significant amount (11–46%) of the Ti is 4+. In the Efremovka CTAs, spinel is 16O-rich (Δ17O ~ –24‰); rubinite and perovskite show limited ranges of Δ17O (from –24 to –16‰; most analyses range from –24 to –20‰); melilite and grossmanite are the most 16O-depleted minerals (Δ17O range from ~ –10 to –4‰ and from –8 to –5‰, respectively). In the Allende CTA AE01-01, spinel and hibonite are 16O-rich (Δ17O ~ –24‰); melilite, rubinite and perovskite show large ranges in Δ17O (from –23 to –3‰, from –21 to –6‰, and from –14 to – 2‰, respectively); grossmanite is uniformly 16O-depleted (Δ17O ~ –3‰). Rubinite formed under highly reducing conditions in the solar nebula by gas-solid condensation and by crystallization from a Ca, Al, and Ti-rich melt. Subsequently, most rubinite grains in the Allende CAI and some in the Efremovka CAIs may have experienced O-isotope exchange to a various degree with an 16O-depleted (Δ17O ~ – 2‰) aqueous fluid on the CV chondrite parent asteroid. However, crystallization from a Ca,Al,Ti-rich melt that recorded O-isotope exchange: with nebular gas with variable Δ17O or post-crystallization O-isotope with such gas cannot be excluded. The mineral name is in honor of Alan E. Rubin (b. 1953), a cosmochemist at University of California, Los Angeles (UCLA), USA, for his many contributions to research in cosmochemistry and mineralogy of meteorites.

The lack of benchmark data on the real minerals, native ammonium carriers in Solar System gives rise to controversial opinions on extraterrestrial ammonium reservoirs. We herein report on discovery of the first mineral carrier of meteoritic ammonium and show its relevance to the compositional and spectral characteristics of cometary and asteroidal bodies. Chemically distant from previously inferred volatile organics or ammoniated phyllosilicates, it is an aqueous metal-ammonium sulfate related to a family of so-called Tutton salts. Nickeloan boussingaultite, (NH4)2(Mg,Ni)(SO4)2 6H2O, occurs in Orgueil, a primitive carbonaceous chondrite closely related to (162173) Ryugu and (101955) Bennu, the C-type asteroids. The available spectroscopic, chemical and mineralogical data signify that natural Tutton salts perfectly fit into the role of ammonium reservoir under conditions of cometary nuclei and carbonaceous asteroids.

Isolated corundum grains and corundum +/- Mg-deltalumite [(Al,Mg)(Al, square)(2)O-4] +/- hibonite assemblages were investigated in the CH3.0 metal-rich carbonaceous chondrite Sayh al Uhaymir (SaU) 290. Although very refractory inclusions containing abundant Zr- and Sc-rich oxides and silicates, hibonite, grossite, or perovskite have been previously described in CH chondrites, this is the first discovery of corundum and Mg-deltalumite in CHs and the first discovery of Mg-deltalumite in nature. Magnesium-deltalumite can be indexed by the Fd3m spinel-type structure and gives a perfect fit to the synthetic Al-rich spinel cells. Corundum-Mg-deltalumite grains, 5-20 mu m in size, are occasionally rimmed by a thin layer of hibonite replacing corundum. Some corundum grains contain tiny inclusions of ultrarefractory Zr,Sc-rich minerals and platinum-group element (PGE) nuggets. All corundum, hibonite, and Mg-deltalumite grains studied have O-16-rich compositions (average Delta O-17 +/- 2SD = -22 +/- 3 parts per thousand). Two corundum grains show evidence for significant mass-dependent fractionation of oxygen isotopes: Delta O-18 similar to +34 parts per thousand and similar to +19 parts per thousand. We suggest that the SaU 290 corundum-rich objects were formed by evaporation and/or condensation in a hot nebular region close to the proto-sun where the ambient temperature was close to the condensation temperature of corundum. A corundum grain with tiny inclusions of Zr- and Sc-rich phases and PGE metal nuggets recorded formation temperatures higher than the condensation temperature of corundum. Two corundum-rich objects with highly fractionated oxygen isotopes must have crystallized from a melt that experienced evaporation. Corundum grains corroded by hibonite recorded gas-solid interaction in this region during its cooling. The Mg-deltalumite +/- corundum +/- hibonite objects were formed by rapid crystallization of high-temperature (>2000 degrees C) refractory melts. The lack of minerals with condensation temperatures below those of corundum and hibonite in the SaU 290 corundum-rich objects suggests that after formation, these objects were rapidly removed from the hot nebular region by disk wind and/or by turbulent diffusion and disk spreading.

The CB (Bencubbin-like) metal-rich carbonaceous chondrites are subdivided into the CBa and CBb subgroups. The CBa chondrites are composed predominantly of similar to cm-sized skeletal olivine chondrules and unzoned Fe,Ni-metal +/- troilite nodules. The CBb chondrites are finer grained than the CB(a)s and consist of chemically zoned and unzoned Fe,Ni-metal grains, Fe,Ni-metal +/- troilite nodules, cryptocrystalline and skeletal olivine chondrules, and rare refractory inclusions. Both subgroups contain exceptionally rare porphyritic chondrules and no interchondrule fine-grained matrix, and are interpreted as the products of a gas-melt impact plume formed by a high-velocity collision between differentiated planetesimals about 4562 Ma. The anomalous metal-rich carbonaceous chondrites, Fountain Hills and Sierra Gorda 013 (SG 013), have bulk oxygen isotopic compositions similar to those of other CBs but contain coarse-grained igneous clasts/porphyritic chondrule-like objects composed of olivine, low-Ca-pyroxene, and minor plagioclase and high-Ca pyroxene as well as barred olivine and skeletal olivine chondrules. Cryptocrystalline chondrules, zoned Fe,Ni-metal grains, and interchondrule fine-grained matrix are absent. In SG 013, Fe,Ni-metal (similar to 80 vol%) occurs as several mm-sized nodules; magnesiochromite (Mg-chromite) is accessory; daubreelite and schreibersite are minor; troilite is absent. In Fountain Hills, Fe,Ni-metal (similar to 25 vol%) is dispersed between chondrules and silicate clasts; chromite and sulfides are absent. In addition to a dominant chondritic lithology, SG 013 contains a chondrule-free lithology composed of Fe,Ni-metal nodules (similar to 25 vol%), coarse-grained olivine and low-Ca pyroxene, interstitial high-Ca pyroxene and anorthitic plagioclase, and Mg-chromite. Here, we report on oxygen isotopic compositions of olivine, low-Ca pyroxene, and +/- Mg-chromite in Fountain Hills and both lithologies of SG 013 measured in situ using an ion microprobe. Oxygen isotope compositions of olivine, low-Ca pyroxene, and Mg-chromite in these meteorites are similar to those of magnesian non-porphyritic chondrules in CBa and CBb chondrites: on a three-isotope oxygen diagram (delta O-17 vs. delta O-18), they plot close to a slope-1 (primitive chondrule mineral) line and have a very narrow range of Delta O-17 (=delta(17)O0.52 x delta O-18) values, similar to 2.5 +/- 0.9& (avr +/- 2SD). No isotopically distinct relict grains have been identified in porphyritic chondrule-like objects. We suggest that magnesian nonporphyritic (barred olivine, skeletal olivine, cryptocrystalline) chondrules in the CBas, CBbs, and porphyritic chondrule-like objects in SG 013 and Fountain Hills formed in different zones of the CB impact plume characterized by variable pressure, temperature, cooling rates, and redox conditions. The achondritic lithology in SG 013 represents fragments of one of the colliding bodies and therefore one of the CB chondrule precursors. Fountain Hills was subsequently modified by impact melting; Fe,Ni-metal and sulfides were partially lost during this process.

A natural iron-bearing oxysulfide, named cafeosite after its chemical composition, is a unique example of a mineral that simultaneously contains iron in three oxidation states: Fe3+, Fe2+, and intermediate between Fe2+ and Fe-0 involved in metallic-type FeFe bonding. Cafeosite was discovered in metamorphosed carbonaceous chondrite Dhofar 225, which is classified as CM-anomalous but likely related to the CY (Yamato-type) group. The mineral occurs as tiny anhedral grains that coalesce into irregular aggregates up to 20 mu m, commonly encrusted by micrometer-thick troilite or pyrrhotite rims. The grains are randomly disseminated within a chondrite matrix composed of thermally altered phyllosilicates. Associated accessory minerals are troilite, pyrrhotite, Fe-rich, Al-bearing olivine, unknown Al-bearing Fe sulfide, Al-rich chromite, kamacite, awaruite, pentlandite, escolaite, and perovskite. In reflected light, cafeosite is gray, with no internal reflections. Anisotropy is moderate, bireflectance in gray hues. Infrared microspectroscopy did not reveal any bands attributable to (OH)(-), H2O or CO32- vibrations. Owing to the small grain size, the crystal structure of the mineral has been studied using synthetic analog, which was found to be isostructural with natural cafeosite based on electron backscatter diffraction (EBSD) data. Cafeosite is orthorhombic, space group Cmce (#64), a 17.4856(9), b 11.1516 (5), c 11.1543(5) angstrom, V 2175.0(2) angstrom(3), Z = 8, D-x = 4.11 g cm(-3). The crystal structure has been solved and refined to R-1 = 0.039 for 1105 unique reflections. Chemical composition of both natural and synthetic cafeosite corresponds to the formula Ca4Fe32+Fe23+(square Fe-1-x(x))O6S4 where (square Fe-1-x(x)) denotes structural vacancy partially occupied by semimetallic-type Fe (x = 0.2-0.3). The ideal endmember formula of the mineral is Ca4Fe32+Fe23+square O6S4. Cafeosite was likely formed from previously altered precursor material of Dhofar 225, which, like common CM chondrites, consisted of phyllosilicates, Ca-bearing carbonates, tochilinite-like sulfides-hydroxides and pyrrhotite. During thermal metamorphism at temperatures between 750 and 900 degrees C, sulfides-hydroxides were partly sintered with calcined carbonates and iron oxides, resulting in cafeosite formation. Due to varying and redox-dependent contents of Fe3+ and Fe2+, as well as the presence of metallic-type Fe in the structure, cafeosite could be regarded as a single-phase redox indicator alternative to the known triple-phase buffers, for example, iron-magnetite-pyrrhotite (IM-Po), iron-wustite-pyrrhotite (IW-Po) and magnetite-wustite-pyrrhotite (MW-Po) systems. Discovery of cafeosite provides insight into a previously obscured aspect of CY-chondrite formation: the redox conditions of thermal metamorphism on carbonaceous asteroids.

— This publication reviews principal recent studies of the earliest solid material in the Solar System: refractory objects, which include Ca,Al inclusions (CAIs), some chondrules, and amoeboid olivine aggregates (AOAs), with more attention paid to Ca,Al inclusions. We do not consider the ices because they do not belong to stony material, and do not consider the presolar grains that were already present in the Solar System when it was formed and were preserved in the primitive chondrites material. The review consists of an introduction, several chapters, a conclusion, a list of references, and a list of special abbreviations. Additional material is published in the Supplementary. The reference list presents the results of previous studies conducted over the past 50 years and highlights the new challenges facing researchers in the study of CAIs, then describes the most modern methods of study and approaches, the results on the chronology of the processes of the early Solar System, morphology, mineralogy, and petrography of new, little-studied representatives of CAIs from various types of chondrite material (CV3 and CH–CB), isotopic and geochemical characteristics of these objects, including REE distribution in ultrarefractory CAIs. One chapter is devoted to the search for genetic relationships between the types of CAIs and the study of the main processes that formed CAIs; this chapter also reviews results of theoretical modeling and experimental studies of the evaporation process. The conclusion summarizes principal conclusions drawn from the data and summarizes the principal results of the long-term study of refractory objects in chondrites.

The paper investigates the effect of ultrasonic impact treatment on the structure and microhardness of constructional steel 10G2FBYu (GOST). Ultrasonic impact treatment of these steel was carried out an air temperature of -30 °C.

Metal‐rich carbonaceous CB chondrites are generally assumed to be materials accreted from the gas–dust plume formed in catastrophic collisions of planetesimals, at least one of which was differentiated into a metal core and silicate shell. Micron‐sized inclusions of siliceous alkali‐rich glasses associated with sulfides were found in the metal globules of the Sierra Gorda 013 (SG 013), a CBa‐like chondrite. These inclusions are unusual carriers of volatile alkalis which are commonly depleted in CB chondrites. The inclusions are presented by two types: (1) Al‐bearing Nb‐poor glass associated with daubréelite and (2) Nb‐bearing Ca,Al,Mg‐poor glass associated with an unknown Na‐bearing Cr‐sulfide. The glass compositions do not correspond to equilibrium condensation, evaporation, or melting. The Nb‐bearing glass has a superchondritic Nb/Ta ratio (31) most likely indicating the fractionation of Nb and Ta in the high‐temperature gas–dust impact plume due to condensation from vapor or evaporation of precursor Nb‐rich particles. The glasses are interpreted as reaction products between refractory plume condensate particles (or possibly planetary or chondritic solids) with relatively low‐temperature K‐Na‐Si‐rich gas in oxidized conditions, possibly in a common plume vapor reservoir. Compositional differences indicate that the glasses and sulfides originated from several different sources under different fO 2 , fS 2 , and T conditions and were likely combined together and transported to the metal globule formation region by material flows in the heterogeneous impact plume. The glass–sulfide particles were enclosed in the globules aggregated from smaller solid or molten metal grains. The metal globules were further melted during transport to the high‐temperature plume region or by plume shockwave heating. Thus, the composition of the glasses, the host metal, and the main mass of SG 013 shows dynamic heterogeneity of physical conditions and impact plume composition after a large‐scale planetesimal collision.

We conducted a first investigation of the Rb-Sr and Sm-Nd isotopic systems of chondrules from rare metal-rich chondrites: the G chondrite Sierra Gorda 009 (SG 009) and the CBa-like chondrite Sierra Gorda 013 (SG 013). Isotopic data were obtained by isotopic dilution methods using multi-collector TIMS spectrometer. Chondrules from both meteorites have low and variable Rb/Sr and Sm/Nd ratios relative to CI. The isotopic data do not produce obvious isochrons due to the heterogeneity of isotopic composition of the chondrule precursors and disturbance of the Rb-Sr and Sm-Nd isotopic systems in chondrules of both meteorites due to inheritance of isotopic heterogeneity in the colliding bodies (chondritic and differentiated) in high-temperature impact plume processes. Shock events and metamorphism after accretion of the SG 013 parent bodies did not result in homogenization of strontium and neodymium isotopes. In general, our data indicate that the Rb-Sr and Sm-Nd isotopic systems probably are not reliable enough to use them for dating of chondrules from the unique chondrites such as SG 009 and SG 013.