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Louisfuchsite (IMA 2022-024), with an end-member formula Ca2(Mg4Ti2)(Al4Si2)O20, is a new refractory mineral identified in a Ca-Al-rich inclusion (CAI) from the NWA 4964 CK3.8 carbonaceous chondrite. Louisfuchsite occurs with spinel, perovskite, grossmanite, plus secondary rutile, titanite, and ilmenite in three regions in the CAI. The mean chemical composition of type louisfuchsite by electron probe microanalysis is (wt%) Al2O325.48, SiO218.40, MgO 17.92, TiO215.36, Ti2O33.13, CaO 14.92, FeO 3.30, V2O30.67, Cr2O30.08, total 99.26, giving rise to an empirical formula of Ca2.00(Mg3.44Ti1.494+Fe0.36Ti0.343+Al0.24V0.073+Ca0.06Cr0.01)Σ6.01(Al3.63Si2.37)Σ6.00O20$\begin{array}{} \displaystyle \mathrm{Ca_{2.00}(Mg_{3.44}Ti_{1.49}^{4+}Fe_{0.36}Ti_{0.34}^{3+}Al_{0.24}V_{0.07}^{3+}Ca_{0.06}Cr_{0.01})_{\Sigma6.01}(Al_{3.63}Si_{2.37})_{\Sigma 6.00}O_{20}} \end{array}$. Louisfuchsite has the P1rhönite structure with a= 10.37(1) Å, b= 10.76(1) Å, c= 8.90(1) Å, α = 106.0(1)°, β = 96.0(1)°, γ = 124.7(1)°, V= 741(2) Å3, and Z = 2, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.44 g/cm3. Louisfuchsite is a new refractory phase from the solar nebula, crystallized from an 16O-rich (Δ17O ~ –24 ± 2‰) refractory melt with the initial 26Al/27Al ratio of (5.09 ± 0.58) × 10–5under reduced conditions. The mineral name is in honor of Louis Fuchs (1915–1991), a mineralogist at Argonne National Laboratory, for his many contributions to mineralogical research on meteorites.

The Hayabusa2 spacecraft explored asteroid Ryugu and brought its surface materials to Earth. Ryugu samples resemble Ivuna-type (CI) chondrites—the most chemically primitive meteorites—and contain secondary phyllosilicates and carbonates, which are indicative of aqueous alteration. Understanding the conditions (such as temperature, redox state and fluid composition) during aqueous alteration is crucial to elucidating how Ryugu evolved to its present state, but little is known about the temporal changes in these conditions. Here we show that calcium carbonate (calcite) grains in Ryugu and Ivuna samples have variable 18O/16O and 13C/12C ratios that are, respectively, 24–46‰ and 65–108‰ greater than terrestrial standard values, whereas those of calcium–magnesium carbonate (dolomite) grains are much more homogeneous, ranging within 31–36‰ for oxygen and 67–75‰ for carbon. We infer that the calcite precipitated first over a wide range of temperatures and oxygen partial pressures, and that the proportion of gaseous CO2/CO/CH4molecules changed temporally. By contrast, the dolomite formed later in a more oxygen-rich and thus CO2-dominated environment when the system was approaching equilibrium. The characteristic isotopic compositions of secondary carbonates in Ryugu and Ivuna are not observed for other hydrous meteorites, suggesting a unique evolutionary pathway for their parent asteroid(s).

Machiite (IMA 2016-067), Al2Ti3O9, is a new mineral that occurs as a single euhedral crystal, 4.4 μm in size, in contact with an euhedral corundum grain, 12 μm in size, in a matrix of the Murchison CM2 carbonaceous chondrite. The mean chemical composition of holotype machiite by electron probe microanalysis is (wt%) TiO259.75, Al2O315.97, Sc2O310.29, ZrO29.18, Y2O32.86, FeO 1.09, CaO 0.44, SiO20.20, MgO 0.10, total 99.87, giving rise to an empirical formula (based on 9 oxygen atoms pfu) of (Al1.17Sc0.56Y0.10Ti0.084+Fe0.06Ca0.03Mg0.01)(Ti2.714+Zr0.28Si0.01)O9.$\left( \text{A}{{\text{l}}_{1.17}}\text{S}{{\text{c}}_{0.56}}{{\text{Y}}_{0.10}}\text{Ti}_{0.08}^{4+}\text{F}{{\text{e}}_{0.06}}\text{C}{{\text{a}}_{0.03}}\text{M}{{\text{g}}_{0.01}} \right)\left( \text{Ti}_{2.71}^{4+}\text{Z}{{\text{r}}_{0.28}}\text{S}{{\text{i}}_{0.01}} \right){{\text{O}}_{9}}.$The general formula is (Al,Sc)2(Ti4+,Zr)3O9. The end-member formula is Al2Ti3O9. Machiite has the C2/cschreyerite-type structure with a= 17.10 Å, b= 5.03 Å, c= 7.06 Å, b = 107°, V= 581 Å3, and Z= 4, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 4.27 g/cm3. The machiite crystal is highly 16O-depleted relative to the coexisting corundum grain (ᐃ17O = –0.2 ± 2.4‰ and –24.1 ± 2.6‰, respectively; where ᐃ17O = δ17O– 0.52 × δ18O). Machiite is a new member of the schreyerite (V2Ti3O9) group and a new Sc,Zr-rich ultrarefractory phase formed in the solar nebula, either by gas-solid condensation or as a result of crystallization from a Ca,Al-rich melt having solar-like oxygen isotopic composition (ᐃ17O ~ –25‰) under high-temperature (~1400–1500 °C) and low-pressure (~10-4–10-5bar) conditions in the CAI-forming region near the protosun. The currently observed disequilibrium oxygen isotopic composition between machiite and corundum may indicate that machiite subsequently experienced oxygen isotopic exchange with a planetary-like 16O-poor gaseous reservoir either in the solar nebula or on the CM chondrite parent body. The name machiite is in honor of Chi Ma, mineralogist at California Institute of Technology, for his contributions to meteorite mineralogy and discovery of many new minerals representing extreme conditions of formation.

We report the first natural occurrence and single-crystal X‑ray diffraction study of the Fe-analog of wadsleyite [a= 5.7485(4), b= 11.5761(9), c= 8.3630(7) Å, V= 556.52(7) Å3; space group Imma], spinelloid-structured Fe2SiO4, a missing phase among the predicted high-pressure polymorphs of ferroan olivine, with the composition(Fe1.102+Mg0.80Cr0.043+Mn0.022+Ca0.02Αl0.02Na0.01)Σ2.01(Si0.97Αl0.03)Σ1.00O4.${{\left( \text{Fe}_{1.10}^{2+}\text{M}{{\text{g}}_{0.80}}\text{Cr}_{0.04}^{3+}\text{Mn}_{0.02}^{2+}\text{C}{{\text{a}}_{\text{0}\text{.02}}}\text{A}{{\text{l}}_{\text{0}\text{.02}}}\text{N}{{\text{a}}_{\text{0}\text{.01}}} \right)}_{\Sigma 2.01}}{{\left( \text{S}{{\text{i}}_{\text{0}\text{.97}}}\text{A}{{\text{l}}_{\text{0}\text{.03}}} \right)}_{\Sigma 1.00}}{{\text{O}}_{\text{4}}}.$The new mineral was approved by the International Mineralogical Association (No. 2018-102) and named asimowite in honor of Paul D. Asimow, the Eleanor and John R. McMillan Professor of Geology and Geochemistry at the California Institute of Technology. It was discovered in rare shock-melted silicate droplets embedded in Fe,Ni-metal in both the Suizhou L6 chondrite and the Quebrada Chimborazo (QC) 001 CB3.0 chondrite. Asimowite is rare, but the shock-melted silicate droplets are very frequent in both meteorites, and most of them contain Fe-rich wadsleyite (Fa30–45). Although the existence of such Fe-rich wadsleyite in shock veins may be due to the kinetic reasons, new theoretical and experimental studies of the stability of (Fe,Mg)2SiO4at high temperature (>1800 K) and pressure are clearly needed. This may also have a significant impact on the temperature and chemical estimates of the mantle’s transition zone in Earth.

Adrianite (IMA 2014-028), Ca12(Al4Mg3Si7)O32Cl6, is a new Cl-rich silicate mineral and the Si,Mg analog of wadalite. It occurs with monticellite, grossular, wadalite, and hutcheonite in altered areas along some veins between primary melilite, spinel, and Ti, Al-diopside in a Type B1 FUN (Fractionation and Unidentified Nuclear effects) Ca-Al-rich inclusion (CAI), Egg-3, from the Allende CV3 carbonaceous chondrite. The mean chemical composition of type adrianite by electron probe microanalysis is (wt%) CaO 41.5, SiO227.5, Al2O312.4, MgO 7.3, Na2O 0.41, Cl 13.0, O=Cl –2.94, total 99.2, giving rise to an empirical formula of (Ca11.69Na0.21)(Al3.85Mg2.88Si7.23)O32Cl5.80. The end-member formula is Ca12(Mg5Si9)O32Cl6. Adrianite has the I43dwadalite structure with a= 11.981 Å, V= 1719.8 Å3, and Z= 2, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.03 g/cm3. Adrianite is a new secondary mineral in Allende, apparently formed by alkali-halogen metasomatic alteration of primary CAI minerals such as melilite, anorthite, perovskite, and Ti, Al-diopside on the CV chondrite parent asteroid. Formation of secondary Cl-rich minerals sodalite, adrianite, and wadalite during metasomatic alteration of the Allende CAIs suggests that the metasomatic fluids had Cl-rich compositions. The mineral name is in honor of Adrian J. Brearley, mineralogist at the University of New Mexico, U.S.A., in recognition of his many contributions to the understanding of secondary mineralization in chondritic meteorites.

Addibischoffite (IMA 2015-006), Ca2Al6Al6O20, is a new calcium aluminate mineral that occurs with hibonite, perovskite, kushiroite, Ti-kushiroite, spinel, melilite, anorthite, and FeNi-metal in the core of a Ca-Al-rich inclusion (CAI) in the Acfer 214 CH3carbonaceous chondrite. The mean chemical composition of type addibischoffite measured by electron probe microanalysis is (wt%)Al2O344.63, CaO 15.36, SiO214.62, V2O310.64, MgO 9.13,Ti2O34.70, FeO 0.46 total 99.55, giving rise to an empirical formula of (Ca2.00)(Al2.55Mg1.73V1.083+Ti0.503+Ca0.09Fe0.052+)∑6.01(Al4.14Si1.86)O20.$\rm(Ca_{2.00}){(Al_{2.55}Mg_{1.73}V_{1.08}^{3+}Ti^{3+}_{0.50}Ca_{0.09}Fe^{2+}_{0.05})_{\sum6.01}(Al_{4.14}Si_{1.86})O_{20}}.$ The general formula is Ca2(Al,Mg,V,Ti)6(Al,Si)6O20. The end-member formula is Ca2Al6Al6O20. Addibischoffite has the P1aenigmatite structure with a=10.367 Å, b =10.756 Å, c= 8.895 Å, α =106.0°, β = 96.0°, γ =124.7°, V= 739.7 Å3, and Z = 2, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.41 g/cm3. Addibischoffite is a new member of the warkite (Ca2Sc6Al6O20) group and a new refractory phase formed in the solar nebula, most likely as a result of crystallization from an 16O-rich Ca, Al-rich melt under high-temperature (~1575 °C) and low-pressure (~10−4to 10−5bar) conditions in the CAI-forming region near the protosun, providing a new puzzle piece toward understanding the details of nebular processes. The name is in honor of Addi Bischoff, cosmochemist at University of Münster, Germany, for his many contributions to research on mineralogy of carbonaceous chondrites, including CAIs in CH chondrites.

Hutcheonite (IMA 2013-029), Ca3Ti2(SiAl2)O12, is a new garnet mineral that occurs with monticellite, grossular, and wadalite in secondary alteration areas along some cracks between primary melilite, spinel, and Ti,Al-diopside in a Type B1 Fractionation and Unidentified Nuclear effects (FUN) Ca-Alrich inclusion (CAI) Egg-3 from the Allende CV (Vigarano type) carbonaceous chondrite. The mean chemical composition of type hutcheonite by electron probe microanalysis is (wt%) CaO 34.6, TiO225.3, SiO220.9, Al2O315.7, MgO 2.1, FeO 0.7, V2O30.5, total 99.8, giving rise to an empirical formula of Ca2.99(Ti4+1.53Mg0.25Al0.17Fe2+0.05V3+0.03)(Si1.68Al1.32)O12. The end-member formula is Ca3Ti2(SiAl2)O12. Hutcheonite has the Ia3̄d garnet structure with a = 11.843 Å, V = 1661.06 Å3, and Z = 8, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.86 g/cm3. Hutcheonite is a new secondary phase in Allende, apparently formed by iron-alkali-halogen metasomatic alteration of the primary CAI phases like melilite, perovskite, and Ti,Al-diopside on the CV chondrite parent asteroid. Formation of the secondary Ti-rich minerals like hutcheonite during the metasomatic alteration of the Allende CAIs suggests some mobility of Ti during the alteration. The mineral name is in honor of Ian D. Hutcheon, a cosmochemist at Lawrence Livermore National Laboratory, California, U.S.A.

Dmisteinbergite, CaAl2Si2O8with P63/mcm structure, was identified in a rounded coarse-grained igneous Type B2 Ca-,Al-rich inclusion (CAI) STP-1 from the Allende CV3 carbonaceous chondrite. STP-1 belongs to a very rare type of refractory inclusions, Fractionation and Unknown Nuclear effects (FUN) CAIs, which experienced melt evaporation and crystallization at low total gas pressure (P < 10-6 bar) in a high-temperature (>1200 °C) region, possibly near the proto-Sun and were subsequently radially transported away from region, possibly by a disk wind. The Allende dmisteinbergite occurs as irregular single crystals (100-600 mm in size) in contact with gehlenitic melilite and Al,Ti-diopside, poikilitically enclosing euhedral spinel, and rare anorthite. It is colorless and transparent. The mean chemical composition, determined by electron microprobe analysis, is (wt%) SiO242.6, Al2O336.9, CaO 20.2, MgO 0.05, sum 99.75, giving rise to an empirical formula of Ca1.01Al1.96Si2.02O8. Its electron backscatter diffraction patterns are a good match to that of synthetic CaAl2Si2O8with the P63/mcm structure and the unit cell a = 5.10 Å, c = 14.72 Å, and Z = 2. Dmisteinbergite could have crystallized from a silicate melt at high temperature (~1200-1400 °C) via rapid cooling. Dmisteinbergite in Allende, the first find in a meteorite, is a new member of refractory silicates, among the first solid materials formed in the solar nebula

Preliminary analysis of the oxygen isotopic composition of the solar wind recorded by the Genesis spacecraft suggests that the Sun is 16O-rich compared to most chondrules, fine-grained chondrite matrices, and bulk compositions of chondrites, achondrites, and terrestrial planets (D17O = -26.5%0 +- 5.6%0 and -33%0 +- 8%0 (2s) versus D17O [?] +-5%0). The inferred 16O-rich composition of the Sun is similar or slightly lighter than the 16O-rich compositions of amoeboid olivine aggregates and typical calcium-aluminum-rich inclusions (CAIs) from primitive (unmetamorphosed) chondrites (D17O = -24%0 +- 2%0), which are believed to have condensed from and been melted in a gas of approximately solar composition (dust/gas ratio [?] 0.01 by weight) within the first 0.1 Myr of the solar system formation. Based on solar system abundances, 26% of the solar system oxygen must be initially contained in dust and 74% in gas. Because solar oxygen is dominated by the gas component, these observations suggest that oxygen isotopic composition of the solar nebula gas was initially 16O-rich. Due to significant thermal processing of the protosolar molecular cloud silicate dust (primordial dust) in the solar nebula and its possible isotope exchange with the isotopically evolved solar nebula gas, the mean oxygen isotopic composition of the primordial dust is not known. In CO self-shielding models, it is assumed that primordial dust and solar nebula gas had initially identical, 16O-rich compositions, similar to that of the Sun (D17O [?] -25%0 or -35%0), and solids subsequently evolved toward the terrestrial value (D17O = 0). However, there is no clear evidence that the oxygen isotopic compositions of the solar system solids evolved in the direction of increasing D17O with time and no 16O-rich primordial dust have yet been discovered. Here we argue that the assumption of the CO self-shielding models that primordial dust and solar nebula gas had initially identical 16O-rich compositions is incorrect. We show that igneous CAIs with highly fractionated oxygen isotopic compositions, fractionation and unidentified nuclear effects (FUN), and fractionation (F) CAIs, have D17O ranging from -0.5%0 to -24.8%0. Within an individual FUN or F CAI, oxygen isotopic compositions of spinel, forsterite, and pyroxene define a mass-dependent fractionation trend with a constant D17O value. The degree of mass-dependent fractionation of these minerals correlates with the sequence of their crystallization from the host CAI melt. These observations and evaporation experiments on CAI-like melts indicate that FUN and F CAIs formed by melting of solid precursors with diverse D17O values in vacuum (total pressure < 10-6 atm). We interpret the observed range of D17O values among FUN and F CAIs as the result of varying degrees of equilibration between 16O-poor dust and 16O-rich nebular gas and suggest the former is characteristic of the primordial dust. The distinctly different oxygen isotopic compositions of the primordial solar nebula dust and gas could have resulted from Galactic chemical evolution or from pollution of the protosolar molecular cloud by a massive star (>50) ejecta. The 16O-depleted compositions of chondrules, fine-grained matrices, chondrites, and achondrites compared to the Sun's value reflect their formation in the protoplanetary disk regions with enhanced dust/gas ratio (up to 105x solar).

Oxygen is one of the major rock-forming elements in the solar system and the third most abundant element of the Sun. Oxygen isotopic composition of the Sun, however, is not known due to a poor resolution of astronomical spectroscopic measurements. Several D17O values have been proposed for the composition of the Sun based on (1) the oxygen isotopic measurements of the solar wind implanted into metallic particles in lunar soil (< -20%0 by Hashizume & Chaussidon and [?] +26%0 by Ireland et al.), (2) the solar wind returned by the Genesis spacecraft (-27%0 +- 6%0 by McKeegan et al.), and (3) the mineralogically pristine calcium-aluminum-rich inclusions (CAIs) (-23.3%0 +- 1.9%0 by Makide et al. and -35%0 by Gounelle et al.). CAIs are the oldest solar system solids, and are believed to have formed by evaporation, condensation, and melting processes in hot nebular region(s) when the Sun was infalling (Class 0) or evolved (Class 1) protostar. Corundum (Al2O3) is thermodynamically the first condensate from a cooling gas of solar composition. Corundum-bearing CAIs, however, are exceptionally rare, suggesting either continuous reaction of the corundum condensates with a cooling nebular gas and their replacement by hibonite (CaAl12O19) or their destruction by melting together with less refractory condensates during formation of igneous CAIs. In contrast to the corundum-bearing CAIs, isolated micrometer-sized corundum grains are common in the acid-resistant residues from unmetamorphosed chondrites. These grains could have avoided multistage reprocessing during CAI formation and, therefore, can potentially provide constraints on the initial oxygen isotopic composition of the solar nebula, and, hence, of the Sun. Here we report oxygen isotopic compositions of [?]60 micrometer-sized corundum grains in the acid-resistant residues from unequilibrated ordinary chondrites (Semarkona (LL3.0), Bishunpur (LL3.1), Roosevelt County 075 (H3.2)) and unmetamorphosed carbonaceous chondrites (Orgueil (CI1), Murray (CM2), and Alan Hills A77307 (CO3.0)) measured with a Cameca ims-1280 ion microprobe. All corundum grains, except two, are 16O-rich (D17O = -22.7%0 +- 8.5%0, 2s), and compositionally similar to the mineralogically pristine CAIs from the CR carbonaceous chondrites (-23.3%0 +- 1.9%0, 2s), and solar wind returned by the Genesis spacecraft (-27%0 +- 6%0, 2s). One corundum grain is highly 17O-enriched (d17O [?] +60%0, d18O [?] -40%0) and is probably of the presolar origin; the origin of another 17O-rich grain (d17O [?] -15%0, d18O [?] -35%0) is unclear. We conclude that the 16O-rich corundum grains in the acid-resistant residues from unequilibrated ordinary and unmetamorphosed carbonaceous chondrites recorded initial oxygen isotopic composition of the solar nebula, and, hence, of the Sun. Our inferred oxygen isotopic composition of the Sun is inconsistent with the more extreme 16O-rich value (D17O [?] -35%0) proposed by Gounelle et al. on the basis of two extremely 16O-rich CAIs from the CH/CB-like chondrite Isheyevo and with the 16O-poor value observed as a component of the solar wind implanted into the metallic particles in lunar soil (Ireland et al.).

In agreement with previous work, we show that the presence of the short-lived radionuclide (SLR) 26Al in the early solar system was unlikely (less than 2% a priori probability) to be the result of direct introduction of supernova (SN) ejecta into the gaseous disk during the Class II stage of protosolar evolution. We also show that Bondi-Hoyle accretion of any contaminated residual gas from the Sun's natal star cluster contributed negligible 26Al to the primordial solar system. Our calculations are consistent with the absence of the oxygen isotopic signature expected with any late introduction of SN ejecta into the protoplanetary disk. Instead, the presence of 26Al in the oldest solar system solids (calcium-aluminum-rich inclusions (CAIs)) and its apparent uniform distribution with the inferred canonical 26Al/27Al ratio of (4.5-5) x 10-5 support the inheritance of 26Al from the Sun's parent giant molecular cloud. We propose that this radionuclide originated in a prior generation of massive stars that formed in the same molecular cloud and contaminated that cloud by Wolf-Rayet winds. We calculated the Galactic distribution of 26Al/27Al ratios that arise from such contamination using the established embedded cluster mass and stellar initial mass functions, published nucleosynthetic yields from the winds of massive stars, and by assuming rapid and uniform mixing into the cloud. Although our model predicts that the majority of stellar systems contain no 26Al from massive stars, and that the a priori probability that the 26Al/27Al ratio will reach or exceed the canonical solar system value is only [?]6%, the maximum in the distribution of nonzero values is close to the canonical 26Al/27Al ratio. We find that the Sun most likely formed 4-5 million years (Myr) after the massive stars that were the source of 26Al. Furthermore, our model can explain the initial solar system abundance of a second, co-occurring SLR, 41Ca, if [?]5 x 105 yr elapsed between ejection of the radionuclides and the formation of CAIs. The presence of a third radionuclide, 60Fe, can be quantitatively explained if (1) the Sun formed immediately after the first SNe from the earlier generation of stars; (2) only 5% of SN ejecta was incorporated into the molecular cloud, or (3) the radionuclide originated in an even earlier generation of stars whose contributions to other radionuclides with a shorter half-life had completely decayed.

Abstract—–The CH/CB‐like chondrite Isheyevo consists of metal‐rich (70–90 vol% Fe,Ni‐metal) and metal‐poor (7–20 vol% Fe,Ni‐metal) lithologies which differ in size and relative abundance of Fe,Ni‐metal and chondrules, as well as proportions of porphyritic versus non‐porphyritic chondrules. Here, we describe the mineralogy and petrography of Ca,Al‐rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs) in these lithologies. Based on mineralogy, refractory inclusions can be divided into hibonite‐rich (39%), grossite‐rich (16%), melilite‐rich (19%), spinel‐rich (14%), pyroxene‐anorthite‐rich (8%), fine‐grained spinel‐rich CAIs (1%), and AOAs (4%). There are no systematic differences in the inclusion types or their relative abundances between the lithologies. About 55% of the Isheyevo CAIs are very refractory (hibonite‐rich and grossite‐rich) objects, 20–240 μm in size, which appear to have crystallized from rapidly cooling melts. These inclusions are texturally and mineralogically similar to the majority of CAIs in CH and CB chondrites. They are distinctly different from CAIs in other carbonaceous chondrite groups dominated by the spinel‐pyroxene ± melilite CAIs and AOAs. The remaining 45% of inclusions are less refractory objects (melilite‐, spinel‐ and pyroxene‐rich CAIs and AOAs), 40–300 μm in size, which are texturally and mineralogically similar to those in other chondrite groups. Both types of CAIs are found as relict objects inside porphyritic chondrules indicating recycling during chondrule formation.

Abstract—Isheyevo is a metal‐rich carbonaceous chondrite that contains several lithologies with different abundances of Fe,Ni metal (7–90 vol%). The metal‐rich lithologies with 50–60 vol% of Fe,Ni metal are dominant. The metal‐rich and metal‐poor lithologies are most similar to the CBband CH carbonaceous chondrites, respectively, providing a potential link between these chondrite groups. All lithologies experienced shock metamorphism of shock stage S4. All consist of similar components—Fe,Ni metal, chondrules, refractory inclusions (Ca, Al‐rich inclusions [CAIs] and amoeboid olivine aggregates [AOAs]), and heavily hydrated lithic clasts—but show differences in their modal abundances, chondrule sizes, and proportions of porphyritic versus non‐porphyritic chondrules. Bulk chemical and oxygen isotopic compositions are in the range of CH and CB chondrites. Bulk nitrogen isotopic composition is highly enriched in 15N (δ15N = 1122‰). The magnetic fraction is very similar to the bulk sample in terms of both nitrogen release pattern and isotopic profile; the non‐magnetic fraction contains significantly less heavy N. Carbon released at high temperatures shows a relatively heavy isotope signature. Similarly to CBbchondrites, ∼20% of Fe,Ni‐metal grains in Isheyevo are chemically zoned. Similarly to CH chondrites, some metal grains are Ni‐rich (>20 wt% Ni). In contrast to CBband CH chondrites, most metal grains are thermally decomposed into Ni‐rich and Ni‐poor phases. Similar to CH chondrites, chondrules have porphyritic and non‐porphyritic textures and ferromagnesian (type I and II), silica‐rich, and aluminum‐rich bulk compositions. Some of the layered ferromagnesian chondrules are surrounded by ferrous olivine or phyllosilicate rims. Phyllosilicates in chondrule rims are compositionally distinct from those in the hydrated lithic clasts. Similarly to CH chondrites, CAIs are dominated by the hibonite‐, grossite‐, and melilite‐rich types; AOAs are very rare. We infer that Isheyevo is a complex mixture of materials formed by different processes and under different physico‐chemical conditions. Chondrules and refractory inclusions of two populations, metal grains, and heavily hydrated clasts accreted together into the Isheyevo parent asteroid in a region of the protoplanetary disk depleted in fine‐grained dust. Such a scenario is consistent with the presence of solar wind—implanted noble gases in Isheyevo and with its comparatively old K‐Ar age. We cannot exclude that the K‐Ar system was affected by a later collisional event. The cosmic‐ray exposure (CRE) age of Isheyevo determined by cosmogenic 38Ar is ∼34 Ma, similar to that of the Bencubbin (CBa) meteorite.

Ca,Al-rich inclusions (CAIs) are believed to have formed by evaporation, condensation, and melting of the pre-existing solids during the earliest stages of the solar system evolution. Most CAIs in unmetamorphosed chondrites contain detectable excesses of 26Mg(26Mg*), a decay product of the short-lived radionuclide 26Al ( T1/2 [?] 730,000 yr), that correspond to an initial 26Al/27Al ratio of ~ (4-7) x 10[?]5. It is suggested that 26Al was injected into the protosolar molecular cloud or protoplanetary disk by a nearby core-collapse supernova (SN Type II) and uniformly distributed in the solar system; CAI formation started shortly after injection of 26Al and lasted less than 20,000 yr . Here we show that CAIs from the metal-rich carbonaceous chondrites Acfer 214 (CH) and Isheyevo (CH/CB-like) have a bimodal distribution of 26Mg*. Most CAIs composed of grossite (CaAl4O7), hibonite (CaAl12O19), Al-rich pyroxene, perovskite (CaTiO3), and gehlenitic melilite (Ca2Al2SiO7-Ca2MgSi2O7) show either unresolvable or small 26Mg* corresponding to an initial 26Al/27Al ratio of ~ 4 x 10[?]7. Some of the grossite-rich CAIs and the less refractory inclusions composed of melilite, spinel (MgAl2O4), Al,Ti-pyroxene, and anorthite (CaAl2Si2O8) have large 26Mg* corresponding to the initial 26Al/27Al ratio of ~ 5 x 10[?]5. The 26Al-poor and 26Al-rich CAIs are characterized by 16O-rich (D 17O < [?] 20%0) compositions typical of CAIs. We suggest that the 26Al-poor and 26Al-rich CAIs represent samples of at least two generations of CAIs formed before and after injection of 26Al into the solar system, respectively. Model yields of 16O,17O, and 18O for SN wind prior to explosion, during explosion, and in total, combined with the observations that both 26Al-poor and 26Al-rich CAIs plot on a three-isotope oxygen diagram (d17O vs. d18O) along a single line with a slope of ~1 are consistent with injection of 26Al with the SN wind into the protosolar molecular cloud rather with the SN explosion into the disk.

Abstract—We report in situ magnesium isotope measurements of 7 porphyritic magnesium‐rich (type I) chondrules, 1 aluminum‐rich chondrule, and 16 refractory inclusions (14 Ca‐Al‐rich inclusions [CAIs] and 2 amoeboid olivine aggregates [AOAs]) from the ungrouped carbonaceous chondrite Acfer 094 using a Cameca IMS 6f ion microprobe. Both AOAs and 9 CAIs show radiogenic 26Mg excesses corresponding to initial 26Al/27Al ratios between ∼5 × 10−5∼7 × 10−5suggesting that formation of the Acfer 094 CAIs may have lasted for ∼300,000 years. Four CAIs show no evidence for radiogenic 26Mg; three of these inclusions (a corundum‐rich, a grossite‐rich, and a pyroxene‐hibonite spherule CAI) are very refractory objects and show deficits in 26Mg, suggesting that they probably never contained 26Al. The fourth object without evidence for radiogenic 26Mg is an anorthite‐rich, igneous (type C) CAI that could have experienced late‐stage melting that reset its Al‐Mg systematics. Significant excesses in 26Mg were observed in two chondrules. The inferred 26Al/27Al ratios in these two chondrules are (10.3 ± 7.4) × 10−6(6.0 ± 3.8) × 10−6(errors are 2σ), suggesting formation 1.6+1.2‐0.6and 2.2+0.4‐0.3Myr after CAIs with the canonical 26Al/27Al ratio of 5 × 10−5. These age differences are consistent with the inferred age differences between CAIs and chondrules in primitive ordinary (LL3.0–LL3.1) and carbonaceous (CO3.0) chondrites.

Abstract—We describe the mineralogy, petrology, oxygen, and magnesium isotope compositions of three coarse‐grained, igneous, anorthite‐rich (type C) Ca‐Al‐rich inclusions (CAIs) (ABC, TS26, and 93) that are associated with ferromagnesian chondrule‐like silicate materials from the CV carbonaceous chondrite Allende. The CAIs consist of lath‐shaped anorthite (An99), Cr‐bearing Al‐Ti‐diopside (Al and Ti contents are highly variable), spinel, and highly åkermanitic and Na‐rich melilite (Åk63–74, 0.4–0.6 wt% Na2O). TS26 and 93 lack Wark‐Lovering rim layers; ABC is a CAI fragment missing the outermost part. The peripheral portions of TS26 and ABC are enriched in SiO2and depleted in TiO2and Al2O3compared to their cores and contain relict ferromagnesian chondrule fragments composed of forsteritic olivine (Fa6–8) and low‐Ca pyroxene/pigeonite (Fs1Wo1–9). The relict grains are corroded by Al‐Ti‐diopside of the host CAIs and surrounded by haloes of augite (Fs0.5Wo30–42). The outer portion of CAI 93 enriched in spinel is overgrown by coarse‐grained pigeonite (Fs0.5–2Wo5–17), augite (Fs0.5Wo38–42), and anorthitic plagioclase (An84). Relict olivine and low‐Ca pyroxene/pigeonite in ABC and TS26, and the pigeonite‐augite rim around 93 are 16O‐poor (Δ17O ∼ −1‰ to −8‰). Spinel and Al‐Ti‐diopside in cores of CAIs ABC, TS26, and 93 are 16O‐enriched (Δ17O down to −20‰), whereas Al‐Ti‐diopside in the outer zones, as well as melilite and anorthite, are 16O‐depleted to various degrees (Δ17O = −11‰ to 2‰). In contrast to typical Allende CAIs that have the canonical initial 26Al/27Al ratio of ∼5 × 10−5ABC, 93, and TS26 are 26Al‐poor with (26Al/27Al)0ratios of (4.7 ± 1.4) × 10−6(1.5 ± 1.8) × 10−6<1.2 × 10−6respectively. We conclude that ABC, TS26, and 93 experienced remelting with addition of ferromagnesian chondrule silicates and incomplete oxygen isotopic exchange in an 16O‐poor gaseous reservoir, probably in the chondrule‐forming region. This melting episode could have reset the 26Al‐26Mg systematics of the host CAIs, suggesting it occurred ∼2 Myr after formation of most CAIs. These observations and the common presence of relict CAIs inside chondrules suggest that CAIs predated formation of chondrules.

Relict Ca-Al-rich inclusions (CAIs) in chondrules crystallized before their host chondrules and were subsequently partly melted together with chondrule precursors during chondrule formation. Like most CAIs, relict CAIs are 16O enriched (D17O < -20%0) compared to their host chondrules (D17O > -9%0). Hibonite in a relict CAI from the ungrouped carbonaceous chondrite Adelaide has a large excess of radiogenic 26Mg (26Mg*) from the decay of 26Al, corresponding to an initial 26Al/27Al ratio [(26Al/27Al)I] of (3.7 +- 0.5) x 10-5; in contrast, melilite in this CAI and plagioclase in the host chondrule show no evidence for 26Mg* [(26Al/27Al)I of <5 x 10-6]. Grossite in a relict CAI from the CH carbonaceous chondrite PAT 91546 has little 26Mg*, corresponding to a (26Al/27Al)I of (1.7 +- 1.3) x 10-6. Three other relict CAIs and their host chondrules from the ungrouped carbonaceous chondrite Acfer 094, CH chondrite Acfer 182, and H3.4 ordinary chondrite Sharps do not have detectable 26Mg* [(26Al/27Al)I < 1 x 10-5, <(4-6) x 10-6, and <1.3 x 10-5, respectively]. Isotopic data combined with mineralogical observations suggest that relict CAIs formed in an 16O-rich gaseous reservoir before their host chondrules, which originated in an 16O-poor gas. The Adelaide CAI was incorporated into its host chondrule after 26Al had mostly decayed, at least 2 Myr after the CAI formed, and this event reset 26Al-26Mg systematics.

Abstract—The Tagish Lake carbonaceous chondrite consists of heavily aqueously altered chondrules, CAIs, and larger mineral fragments in a fine‐grained, phyllosilicate‐dominated matrix. The vast majority of the coarse‐grained components in this meteorite are surrounded by continuous, 1.5 to >200 μm wide, fine‐grained, accretionary rims, which are well known from meteorites belonging to petrological types 2 and 3 and whose origin and modification is still a matter of debate. Texturally, the fine‐grained rims in Tagish Lake are very similar throughout the entire meteorite and independent of the nature of the enclosed object. They typically display sharp boundaries to the core object and more gradational contacts to the meteorite matrix. Compared to the matrix, the rims are much more finegrained and characterized by a significantly lower porosity. The rims consist of an unequilibrated assemblage of phyllosilicates, Fe,Ni sulfides, magnetites, low‐Ca pyroxenes, and forsteritic olivines, and are, except for a much lower abundance of carbonates, very similar to the Tagish Lake matrix. Electron microprobe and synchrotron X‐ray microprobe analyses show that matrix and rims are also very similar in composition and that the rims differ significantly from matrix and bulk meteorite only by being depleted in Ca. X‐ray elemental mapping and mineralogical observations indicate that Ca was lost during aqueous alteration from the enclosed objects and preferentially crystallized as carbonates in the porous matrix. The analyses also show that Ca is strongly fractionated from Al in the rims, whereas there is no fractionation of the Ti/Al‐ratios. Our data suggest that the fine‐grained rims in Tagish Lake initially formed by accretion in the solar nebula and were subsequently modified by in situ alteration on the parent body. This pervasive alteration removed any potential evidence for pre‐accretionary alteration but did not change the overall texture of the Tagish Lake meteorite.

Abstract—We have studied the CB carbonaceous chondrites Queen Alexandra Range (QUE) 94411, Hammadah al Hamra (HH) 237, and Bencubbin with an emphasis on the petrographical and mineralogical effects of the shock processing that these meteorite assemblages have undergone. Iron‐nickel metal and chondrule silicates are the main components in these meteorites. These high‐temperature components are held together by shock melts consisting of droplets of dendritically intergrown Fe,Ni‐metal/sulfide embedded in silicate glass, which is substantially more FeO‐rich (30–40 wt%) than the chondrule silicates (FeO <5 wt%). Fine‐grained matrix material, which is a major component in most other chondrite classes, is extremely scarce in QUE 94411 and HH 237, and has not been observed in Bencubbin. This material occurs as rare, hydrated matrix lumps with major and minor element abundances roughly similar to the ferrous silicate shock melts (and CI). We infer that hydrated, fine‐grained material, compositionally similar to these matrix lumps, was originally present between the Fe,Ni‐metal grains and chondrules, but was preferentially shock melted. Other shock‐related features in QUE 94411, HH 237, and Bencubbin include an alignment and occasionally strong plastic deformation of metal and chondrule fragments.

Abstract—Oxygen isotopes have been measured by ion microprobe in individual minerals (spinel, Al‐Ti‐diopside, melilite, and anorthite) within four relatively unaltered, fine‐grained, spinel‐rich Ca‐Al‐rich inclusions (CAIs) from the reduced CV chondrite Efremovka. Spinel is uniformly 16O‐rich (Δ17O ≤ −20‰) in all four CAIs; Al‐Ti‐diopside is similarly 16O‐rich in all but one CAI, where it has smaller 16O excesses (‐15‰ ≤ Δ17O ≤ −10‰). Anorthite and melilite vary widely in composition from 16O‐rich to 16O‐poor (‐22‰ ≤ Δ17O ≤ −5‰). Two of the CAIs are known to have group II volatility‐fractionated rare‐earth‐element patterns, which is typical of this variety of CAI and which suggests formation by condensation. The association of such trace element patterns with 16O‐enrichment in these CAIs suggests that they formed by gas‐solid condensation from an 16O‐rich gas. They subsequently experienced thermal processing in an 16O‐poor reservoir, resulting in partial oxygen isotope exchange. Within each inclusion, oxygen isotope variations from mineral to mineral are consistent with solid‐state oxygen self‐diffusion at the grain‐to‐grain scale, but such a model is not consistent with isotopic variations at a larger scale in two of the CAIs. The spatial association of 16O depletions with both elevated Fe contents in spinel and the presence of nepheline suggests that late‐stage iron‐alkali metasomatism played some role in modifying the isotopic patterns in some CAIs. One of the CAIs is a compound object consisting of a coarse‐grained, melilite‐rich (type A) lithology joined to a fine‐grained, spinel‐rich one. Melilite and anorthite in the fine‐grained portion are mainly 16O‐rich, whereas melilite in the type A portion ranges from 16O‐rich to 16O‐poor, suggesting that oxygen isotope exchange predated the joining together of the two parts and that both 16O‐rich and 16O‐poor gaseous reservoirs existed simultaneously in the early solar nebula.

The most abundant matrix minerals in chondritic meteorites--hydrated phyllosilicates and ferrous olivine crystals--formed predominantly in asteroids during fluid-assisted metamorphism. We infer that they formed from minerals present in three less altered carbonaceous chondrites that have silicate matrices composed largely of micrometer- and nanometer-sized grains of crystalline forsterite Mg2SiO4 and enstatite MgSiO3 and amorphous, ferromagnesian silicate. Compositional and structural features of enstatite and forsterite suggest that they formed as condensates that cooled below 1300 K at ~1000 K hr-1. Most amorphous silicates are likely to be solar nebula condensates also, as matrix, which is approximately solar in composition, is unlikely to be a mixture of genetically unrelated materials with different compositions. Since chondrules cooled at 10-1000 K hr-1 and matrix and chondrules are chemically complementary, most matrix silicates probably formed close to chondrules in transient heating events. Shock heating is favored, as nebular shocks capable of melting millimeter-sized aggregates vaporize dust. The crystalline and amorphous silicates in the primitive chondrite matrices share many characteristic features with silicates in chondritic interplanetary dust particles, suggesting that most of the crystalline silicates and possibly some amorphous silicates in the interplanetary dust particles are also nebular condensates. Except for small amounts of refractory oxides from the innermost region where refractory inclusions formed and presolar dust, most of the crystalline silicate dust that accreted into chondritic asteroids and long-period comets appears to have formed from shock heating at ~2-10 AU. Forsterite crystals around young stars may have a similar origin.

Changes in the chemical and isotopic composition of the solar nebula with time are reflected in the properties of different constituents that are preserved in chondritic meteorites. CR-group carbonaceous chondrites are among the most primitive of all chondrite types and must have preserved solar nebula records largely unchanged. We have analyzed the oxygen and magnesium isotopes in a range of the CR constituents of different formation temperatures and ages, including refractory inclusions and chondrules of various types. The results provide new constraints on the time variation of the oxygen isotopic composition of the inner (<5 AU) solar nebula--the region where refractory inclusions and chondrules most likely formed. A chronology based on the decay of short-lived 26Al (t1/2 ~ 0.73 Myr) indicates that the inner solar nebula gas was 16O-rich when refractory inclusions formed, but less than 0.8 Myr later, gas in the inner solar nebula became 16O-poor, and this state persisted at least until CR chondrules formed ~1-2 Myr later. We suggest that the inner solar nebula became 16O-poor because meter-sized icy bodies, which were enriched in 17O and 18O as a result of isotopic self-shielding during the ultraviolet photodissociation of CO in the protosolar molecular cloud or protoplanetary disk, agglomerated outside the snow line, drifted rapidly toward the Sun, and evaporated at the snow line. This led to significant enrichment in 16O-depleted water, which then spread through the inner solar system. Astronomical studies of the spatial and temporal variations of water abundance in protoplanetary disks may clarify these processes.

Abstract—The outer portions of many type I chondrules (Fa and Fs <5 mol%) in CR chondrites (except Renazzo and Al Rais) consist of silica‐rich igneous rims (SIRs). The host chondrules are often layered and have a porphyritic core surrounded by a coarse‐grained igneous rim rich in low‐Ca pyroxene. The SIRs are sulfide‐free and consist of igneously‐zoned low‐Ca and high‐Ca pyroxenes, glassy mesostasis, Fe, Ni‐metal nodules, and a nearly pure SiO2phase. The high‐Ca pyroxenes in these rims are enriched in Cr (up to 3.5 wt% Cr2O3) and Mn (up to 4.4 wt% MnO) and depleted in Al and Ti relative to those in the host chondrules, and contain detectable Na (up to 0.2 wt% Na2O). Mesostases show systematic compositional variations: Si, Na, K, and Mn contents increase, whereas Ca, Mg, Al, and Cr contents decrease from chondrule core, through pyroxene‐rich igneous rim (PIR), and to SIR; FeO content remains nearly constant. Glass melt inclusions in olivine phenocrysts in the chondrule cores have high Ca and Al, and low Si, with Na, K, and Mn contents that are below electron microprobe detection limits. Fe, Ni‐metal grains in SIRs are depleted in Ni and Co relative to those in the host chondrules. The presence of sulfide‐free, SIRs around sulfide‐free type I chondrules in CR chondrites may indicate that these chondrules formed at high (>800 K) ambient nebular temperatures and escaped remelting at lower ambient temperatures. We suggest that these rims formed either by gas‐solid condensation of silica‐normative materials onto chondrule surfaces and subsequent incomplete melting, or by direct SiO(gas)condensation into chondrule melts. In either case, the condensation occurred from a fractionated, nebular gas enriched in Si, Na, K, Mn, and Cr relative to Mg. The fractionation of these lithophile elements could be due to isolation (in the chondrules) of the higher temperature condensates from reaction with the nebular gas or to evaporation‐recondensation of these elements during chondrule formation. These mechanisms and the observed increase in pyroxene/olivine ratio toward the peripheries of most type I chondrules in CR, CV, and ordinary chondrites may explain the origin of olivine‐rich and pyroxene‐rich chondrules in general.

Abstract—Fine‐grained, spinel‐rich inclusions in the reduced CV chondrites Efremovka and Leoville consist of spinel, melilite, anorthite, Al‐diopside, and minor hibonite and perovskite; forsterite is very rare. Several CAIs are surrounded by forsterite‐rich accretionary rims. In contrast to heavily altered fine‐grained CAIs in the oxidized CV chondrite Allende, those in the reduced CVs experienced very little alteration (secondary nepheline and sodalite are rare). The Efremovka and Leoville fine‐grained CAIs are 16O‐enriched and, like their Allende counterparts, generally have volatility fractionated group II rare earth element patterns. Three out of 13 fine‐grained CAIs we studied are structurally uniform and consist of small concentrically zoned nodules having spinel ± hibonite ± perovskite cores surrounded by layers of melilite and Al‐diopside. Other fine‐grained CAIs show an overall structural zonation defined by modal mineralogy differences between the inclusion cores and mantles. The cores are melilite‐free and consist of tiny spinel ± hibonite ± perovskite grains surrounded by layers of anorthite and Al‐diopside. The mantles are calcium‐enriched, magnesium‐depleted and coarsergrained relative to the cores; they generally contain abundant melilite but have less spinel and anorthite than the cores. The bulk compositions of fine‐grained CAIs generally show significant fractionation of Al from Ca and Ti, with Ca and Ti being depleted relative to Al; they are similar to those of coarsegrained, type C igneous CAIs, and thus are reasonable candidate precursors for the latter. The finegrained CAIs originally formed as aggregates of spinel‐perovskite‐melilite ± hibonite gas‐solid condensates from a reservoir that was 16O‐enriched but depleted in the most refractory REEs. These aggregates later experienced low‐temperature gas‐solid nebular reactions with gaseous SiO and Mg to form Al‐diopside and ±anorthite. The zoned structures of many of the fine‐grained inclusions may be the result of subsequent reheating that resulted in the evaporative loss of SiO and Mg and the formation of melilite. The inferred multi‐stage formation history of fine‐grained inclusions in Efremovka and Leoville is consistent with a complex formation history of coarse‐grained CAIs in CV chondrites.

Secondary Ca,Fe-rich minerals (CFM; diopside-hedenbergite, andradite, wollastonite, kirschteinite) are widespread in the Allende carbonaceous chondrite. About 90 vol% of the total CaO content of the Allende matrix is concentrated in CFM. The conditions and environment (solar nebular or asteroidal) of this alteration are still matters of controversial scientific discussion. Here we present evidence for late-stage, high-temperature processes recorded in Ca,Fe-rich rims around Allende dark inclusions 3529 and IV-1 studied using scanning (SEM) and transmission electron microscopy (TEM), and electron probe microanalysis. The rims show a multilayered structure, with the outermost layer intergrown with the matrix olivines and chondrule fragments of the Allende host, indicative of in situ formation. The central portion of the rim around IV-1 contains several wollastonite polytypes (a polysynthetically twinned polytype of pseudowollastonite, wollastonite-2M, and wollastonite-1T) and an intergrowth of hedenbergite-PM (primitive monoclinic) and augite-hedenbergitess. These findings require temperatures above 1000 °C and fast cooling rates after formation of the central part of the rim. The close occurrences of three different polymorphs of wollastonite suggest that this process was highly localized and may have resulted from shock metamorphism.

Secondary Ca,Fe-rich minerals (CFM; diopside-hedenbergite, andradite, wollastonite, kirschteinite) are widespread in the Allende carbonaceous chondrite. About 90 vol% of the total CaO content of the Allende matrix is concentrated in CFM. The conditions and environment (solar nebular or asteroidal) of this alteration are still matters of controversial scientific discussion. Here we present evidence for late-stage, high-temperature processes recorded in Ca,Fe-rich rims around Allende dark inclusions 3529 and IV-1 studied using scanning (SEM) and transmission electron microscopy (TEM), and electron probe microanalysis. The rims show a multilayered structure, with the outermost layer intergrown with the matrix olivines and chondrule fragments of the Allende host, indicative of in situ formation. The central portion of the rim around IV-1 contains several wollastonite polytypes (a polysynthetically twinned polytype of pseudowollastonite, wollastonite-2M, and wollastonite-1T) and an intergrowth of hedenbergite-PM (primitive monoclinic) and augite-hedenbergitess. These findings require temperatures above 1000 °C and fast cooling rates after formation of the central part of the rim. The close occurrences of three different polymorphs of wollastonite suggest that this process was highly localized and may have resulted from shock metamorphism.

Abstract—Calcium‐aluminum‐rich refractory inclusions (CAIs) in CR chondrites are rare (<1 vol%), fairly small (<500 μm) and irregularly‐shaped, and most of them are fragmented. Based on the mineralogy and petrography, they can be divided into grossite ± hibonite‐rich, melilite‐rich, and pyroxene‐anorthite‐rich CAIs. Other types of refractory objects include fine‐grained spinel‐melilite‐pyroxene aggregates and amoeboid olivine aggregates (AOAs). Some of the pyroxene‐anorthite‐rich CAIs have igneous textures, and most melilite‐rich CAIs share similarities to both the fluffy and compact type A CAIs found in CV chondrites. One major difference between these CAIs and those in CV, CM, and CO chondrites is that secondary mineral phases are rare.

Abstract—In this paper, we review the mineralogy and chemistry of calcium‐aluminum‐rich inclusions (CAIs), chondrules, FeNi‐metal, and fine‐grained materials of the CR chondrite clan, including CR, CH, and the metal‐rich CB chondrites Queen Alexandra Range 94411, Hammadah al Hamra 237, Bencubbin, Gujba, and Weatherford. The members of the CR chondrite clan are among the most pristine early solar system materials, which largely escaped thermal processing in an asteroidal setting (Bencubbin, Weatherford, and Gujba may be exceptions) and provide important constraints on the solar nebula models. These constraints include (1) multiplicity of CAI formation; (2) formation of CAIs and chondrules in spatially separated nebular regions; (3) formation of CAIs in gaseous reservoir(s) having 16O‐rich isotopic compositions; chondrules appear to have formed in the presence of 16O‐poor nebular gas; (4) isolation of CAIs and chondrules from nebular gas at various ambient temperatures; (5) heterogeneous distribution of 26Al in the solar nebula; and (6) absence of matrix material in the regions of CAI and chondrule formation.

Abstract—Fine‐grained, heavily‐hydrated lithic clasts in the metal‐rich (CB) chondrites Queen Alexandra Range (QUE) 94411 and Hammadah al Hamra 237 and CH chondrites, such as Patuxent Range (PAT) 91546 and Allan Hills (ALH) 85085, are mineralogically similar suggesting genetic relationship between these meteorites. These clasts contain no anhydrous silicates and consist of framboidal and platelet magnetite, prismatic sulfides (pentlandite and pyrrhotite), and Fe‐Mn‐Mg‐bearing Ca‐carbonates set in a phyllosilicate‐rich matrix. Two types of phyllosilicates were identified: serpentine, with basal spacing of ˜0.73 nm, and saponite, with basal spacings of about 1.1–1.2 nm. Chondrules and FeNi‐metal grains in CB and CH chondrites are believed to have formed at high temperature (>1300 K) by condensation in a solar nebula region that experienced complete vaporization. The absence of aqueous alteration of chondrules and metal grains in CB and CH chondrites indicates that the clasts experienced hydration in an asteroidal setting prior to incorporation into the CH and CB parent bodies. The hydrated clasts were either incorporated during regolith gardening or accreted together with chondrules and FeNi‐metal grains after these high‐temperature components had been transported from their hot formation region to a much colder region of the solar nebula.

Abstract—Plagioclase‐rich chondrules (PRCs) in the reduced CV chondrites Efremovka, Leoville, Vigarano and Grosvenor Mountains (GRO) 94329 consist of magnesian low‐Ca pyroxene, Al‐Ti‐Cr‐rich pigeonite and augite, forsterite, anorthitic plagioclase, FeNi‐metal‐sulfide nodules, and crystalline mesostasis composed of silica, anorthitic plagioclase and Al‐Ti‐Cr‐rich augite. The silica grains in the mesostases of the CV PRCs are typically replaced by hedenbergitic pyroxenes, whereas anorthitic plagioclase is replaced by feldspathoids (nepheline and minor sodalite). Some of the PRCs contain regions that are texturally and mineralogically similar to type I chondrules and consist of forsterite, low‐Ca pyroxene and abundant FeNi‐metal nodules. Several PRCs are surrounded by igneous rims or form independent compound objects. Twelve PRCs contain relic calcium‐aluminum‐rich inclusions (CAIs) composed of anorthite, spinel, high‐Ca pyroxene, ± forsterite, and ± Al‐rich low‐Ca pyroxene. Anorthite of these CAIs is generally more heavily replaced by feldspathoids than anorthitic plagioclase of the host chondrules. This suggests that either the alteration predated formation of the PRCs or that anorthite of the relic CAIs was more susceptible to the alteration than anorthitic plagioclase of the host chondrules. These observations and the presence of igneous rims around PRCs and independent compound PRCs suggest that the CV PRCs may have had a complex, multistage formation history compared to a more simple formation history of the CR PRCs.

Abstract—Anorthite‐rich chondrules in CR and CH carbonaceous chondrites consist of magnesian low‐Ca pyroxene and forsterite phenocrysts, FeNi‐metal nodules, interstitial anorthite, Al‐Ti‐Cr‐rich low‐Ca and high‐Ca pyroxenes, and crystalline mesostasis composed of silica, anorthite and high‐Ca pyroxene. Three anorthite‐rich chondrules contain relic calcium‐aluminum‐rich inclusions (CAIs) composed of anorthite, spinel, ±Al‐diopside, and ± forsterite. A few chondrules contain regions which are texturally and mineralogically similar to magnesian (type I) chondrules and consist of forsterite, low‐Ca pyroxene and abundant FeNi‐metal nodules. Anorthite‐rich chondrules in CR and CH chondrites are mineralogically similar to those in CV and CO carbonaceous chondrites, but contain no secondary nepheline, sodalite or ferrosilite. Relatively high abundances of moderately‐volatile elements such as Cr, Mn and Si in the anorthite‐rich chondrules suggest that these chondrules could not have been produced by volatilization of the ferromagnesian chondrule precursors or by melting of the refractory materials only. We infer instead that anorthite‐rich chondrules in carbonaceous chondrites formed by melting of the reduced chondrule precursors (olivine, pyroxenes, FeNi‐metal) mixed with the refractory materials, including relic CAIs, composed of anorthite, spinel, high‐Ca pyroxene and forsterite. The observed mineralogical and textural similarities of the anorthite‐rich chondrules in several carbonaceous chondrite groups (CV, CO, CH, CR) may indicate that these chondrules formed in the region(s) intermediate between the regions where CAIs and ferromagnesian chondrules originated. This may explain the relative enrichment of anorthite‐rich chondrules in 16O compared to typical ferromagnesian chondrules (Russell et al., 2000).

Abstract—Primary minerals in calcium‐aluminum‐rich inclusions (CAIs), Al‐rich and ferromagnesian chondrules in each chondrite group have δ18O values that typically range from −50 to +5%0. Neglecting effects due to minor mass fractionations, the oxygen isotopic data for each chondrite group and for micrometeorites define lines on the three‐isotope plot with slopes of 1.01 ± 0.06 and intercepts of −2 ± 1. This suggests that the same kind of nebular process produced the 16O variations among chondrules and CAIs in all groups. Chemical and isotopic properties of some CAIs and chondrules strongly suggest that they formed from solar nebula condensates. This is incompatible with the existing two‐component model for oxygen isotopes in which chondrules and CAIs were derived from heated and melted 16O‐rich presolar dust that exchanged oxygen with 16O‐poor nebular gas. Some FUN CAIs (inclusions with isotope anomalies due to fractionation and unknown nuclear effects) have chemical and isotopic compositions indicating they are evaporative residues of presolar material, which is incompatible with 16O fractionation during mass‐independent gas phase reactions in the solar nebula. There is only one plausible reason why solar nebula condensates and evaporative residues of presolar materials are both enriched in 16O. Condensation must have occurred in a nebular region where the oxygen was largely derived from evaporated 16O‐rich dust. A simple model suggests that dust was enriched (or gas was depleted) relative to cosmic proportions by factors of ∼10 to >50 prior to condensation for most CAIs and factors of 1–5 for chondrule precursor material. We infer that dust‐gas fractionation prior to evaporation and condensation was more important in establishing the oxygen isotopic composition of CAIs and chondrules than any subsequent exchange with nebular gases. Dust‐gas fractionation may have occurred near the inner edge of the disk where nebular gases accreted into the protosun and Shu and colleagues suggest that CAIs formed.

Abstract—The metal‐rich chondrites Hammadah al Hamra (HH) 237 and Queen Alexandra Range (QUE) 94411, paired with QUE 94627, contain relatively rare (<1 vol%) calcium‐aluminum‐rich inclusions (CAIs) and Al‐diopside‐rich chondrules. Forty CAIs and CAI fragments and seven Al‐diopside‐rich chondrules were identified in HH 237 and QUE 94411/94627. The CAIs, ∼50–400 μm in apparent diameter, include (a) 22 (56%) pyroxene‐spinel ± melilite (+forsterite rim), (b) 11 (28%) forsterite‐bearing, pyroxene‐spinel ± melilite ± anorthite (+forsterite rim) (c) 2 (5%) grossite‐rich (+spinel‐melilite‐pyroxene rim), (d) 2 (5%) hibonite‐melilite (+spinel‐pyroxene ± forsterite rim), (e) 1 (2%) hibonite‐bearing, spinel‐perovskite (+melilite‐pyroxene rim), (f) 1 (2%) spinel‐melilite‐pyroxene‐anorthite, and (g) 1 (2%) amoeboid olivine aggregate. Each type of CAI is known to exist in other chondrite groups, but the high abundance of pyroxene‐spinel ± melilite CAIs with igneous textures and surrounded by a forsterite rim are unique features of HH 237 and QUE 94411/94627. Additionally, oxygen isotopes consistently show relatively heavy compositions with Δ17O ranging from −6%0 to −10%0 (1σ = 1.3%0) for all analyzed CAI minerals (grossite, hibonite, melilite, pyroxene, spinel). This suggests that the CAIs formed in a reservoir isotopically distinct from the reservoir(s) where “normal”, 16O‐rich (Δ17O < −20%0) CAIs in most other chondritic meteorites formed.

Abstract—It was suggested that multilayered accretionary rims composed of ferrous olivine, andradite, wollastonite, salite‐hedenbergitic pyroxenes, nepheline, and Ni‐rich sulfides around Allende calcium‐aluminum‐rich inclusions (CAIs) are aggregates of gas‐solid condensates which reflect significant fluctuations in physico‐chemical conditions in the slowly cooling solar nebula and grain/gas separation processes. In order to test this model, we studied the mineralogy of accretionary rims around one type A CAI (E104) and one type B CAI (E48) from the reduced CV3 chondrite Efremovka, which is less altered than Allende. In contrast to the Allende accretionary rims, those in Efremovka consist of coarse‐grained (20–40 μm), anhedral forsterite (Fa1–8), Fe, Ni‐metal nodules, amoeboid olivine aggregates (AOAs) and fine‐grained CAIs composed of Al‐diopside, anorthite, and spinel, ± forsterite. Although the fine‐grained CAIs, AOAs and host CAIs are virtually unaltered, a hibonite‐spinel‐perovskite CAI in the E48 accretionary rim experienced extensive alteration, which resulted in the formation of Fe‐rich, Zn‐bearing spinel, and a Ca, Al, Si‐hydrous mineral. Forsterites in the accretionary rims typically show an aggregational nature and consist of small olivine grains with numerous pores and tiny inclusions of Al‐rich minerals. No evidence for the replacement of forsterite by enstatite was found; no chondrule fragments were identified in the accretionary rims.

Abstract—Amoeboid olivine aggregates (AOAs) from the reduced CV chondrites Efremovka, Leoville and Vigarano are irregularly‐shaped objects, up to 5 mm in size, composed of forsteritic olivine (Fa<10) and a refractory, Ca, Al‐rich component. The AOAs are depleted in moderately volatile elements (Mn, Cr, Na, K), Fe, Ni‐metal and sulfides and contain no low‐Ca pyroxene. The refractory component consists of fine‐grained calcium‐aluminum‐rich inclusions (CAIs) composed of Al‐diopside, anorthite (An100), and magnesium‐rich spinel (∼1 wt% FeO) or fine‐grained intergrowths of these minerals; secondary nepheline and sodalite are very minor. This indicates that AOAs from the reduced CV chondrites are more pristine than those from the oxidized CV chondrites Allende and Mokoia. Although AOAs from the reduced CV chondrites show evidence for high‐temperature nebular annealing (e.g., forsterite grain boundaries form 120° triple junctions) and possibly a minor degree of melting of Al‐diopside‐anorthite materials, none of the AOAs studied appear to have experienced extensive (>50%) melting. We infer that AOAs are aggregates of high‐temperature nebular condensates, which formed in CAI‐forming regions, and that they were absent from chondrule‐forming regions at the time of chondrule formation. The absence of low‐Ca pyroxene and depletion in moderately volatile elements (Mn, Cr, Na, K) suggest that AOAs were either removed from CAI‐forming regions prior to condensation of these elements and low‐Ca pyroxene or gas‐solid condensation of low‐Ca‐pyroxene was kinetically inhibited.

Abstract—In situion microprobe analyses of spinel in refractory calcium‐aluminium‐rich inclusions (CAIs) from type 3 EH chondrites yield 16O‐rich compositions (δ 18O and δ 17O about‐40‰). Spinel and feldspar in a CAI from an EL3 chondrite have significantly heavier isotopic compositions (δ 18O and δ 17O about −5‰). A regression through the data results in a line with slope 1.0 on a three‐isotope plot, similar to isotopic results from unaltered minerals in CAIs from carbonaceous chondrites. The existence of CAIs with 16O‐rich and 16O‐poor compositions in carbonaceous as well as enstatite chondrites indicates that CAIs formed in at least two temporally or spatially distinct oxygen reservoirs. General similarities in oxygen isotopic compositions of CAIs from enstatite, carbonaceous, and ordinary chondrites indicate a common nebular mechanism or locale for the production of most CAIs.

Abstract—Thermodynamic analysis of the compositional profiles across large chemically‐zoned Fe, Ni metal grains in the Bencubbin‐like chondrite Queen Alexandra Range (QUE) 94411 suggests that these grains formed by non‐equilibrium gas‐solid condensation under variable oxidizing conditions, isolation degree, and Cr depletion factors. The oxidizing conditions must have resulted from the complete vaporization of nebular regions with enhanced dust/gas ratios (∼ 10–40 × solar). Because the origin of each of the metal grains studied requires different condensation parameters (dust/gas ratio, isolation degree, and Cr depletion factor), a high degree of heterogeneity in the formation region of the Bencubbin‐like chondrite metal is required. To preserve compositional zoning of the metal grains and prevent their melting and sulfidization, the grains must have been removed from the hot condensation region into cold regions where the accretion of the Bencubbin‐like asteroidal body took place.

Abstract—The carbonaceous chondrite MacAlpine Hills (MAC) 88107 has bulk composition and mineralogy that are intermediate between those of CO and CM chondrites. This meteorite experienced minor alteration and a low degree of thermal metamorphism (petrologic type 3.1) and escaped post‐accretional brecciation. The alteration resulted in the formation of fayalite (Fa90–100). Al‐free hedenbergite (∼Fs50Wo50), phyllosilicates (saponite‐serpentine intergrowths), magnetite, and Ni‐bearing sulfides (pyrrhotite and pentlandite). Fayalite and hedenbergite typically occur as veins, which start at the opaque nodules in the chondrule peripheries, crosscut fine‐grained rims and either terminate at the boundaries with the neighboring fine‐grained rims or continue as layers between these rims. These observations suggest that fayalite and hedenbergite crystallized after accretion and compaction of the fine‐grained rims. Fayalite also overgrows isolated forsteritic (Fa1–5) and fayalitic (Fa20–40) olivine grains without any evidence for Fe‐Mg interdiffusion; it also replaces massive magnetite‐sulfide grains. The initial 53Mn/55Mn ratio of (1.58 ± 0.26) × 10−6in the MAC 88107 fayalite corresponds to an age difference between the formation of fayalite and refractory inclusions in Allende of either ∼9 or 18 Ma, depending upon the value of the solar system initial abundance of 53Mn used in age calculations.

Abstract—We report in situmeasurements of O‐isotopic compositions of magnetite and primary and secondary olivine in the highly unequilibrated oxidized CV chondrites Kaba and Mokoia. In both meteorites, the magnetite and the secondary olivine (fayalite, Fa90–100) have O‐isotopic compositions near the terrestrial fractionation (TF) line; the mean Δ17O (= δ17O‐0.52 × δ18O) value is about −1%‰. In contrast, the compositions of nearby primary (chondrule), low‐FeO olivines (Fa1–2) are well below the TF line; Δ17O values range from −3 to −9%‰. Krot et al.(1998) summarized evidence indicating that the secondary phases in these chondrites formed by aqueous alteration in an asteroidal setting. The compositions of magnetite and fayalite in Kaba and Mokoia imply that the O‐isotopic composition of the oxidant was near or somewhat above the TF line. In Mokoia the fayalite and magnetite differ in δ18O by ∼20%‰, whereas these same materials in Kaba have virtually identical compositions. The difference between Mokoia magnetite and fayalite may indicate formation in isotopic equilibrium in a water‐rich environment at low temperatures, ∼300 K. In contrast, the similar compositions of these phases in Kaba may indicate formation of the fayalite by replacement of preexisting magnetite in dry environment, with the O coming entirely from the precursor magnetite and silica. The Δ17O of the oxidant incorporated into the CV parent body (as phyllosilicates or H2O) appears to have been much (7–8%‰) lower than that in that incorporated into the LL parent body (Choi et al, 1998), which suggests that the O‐isotopic composition of the nebular gas was spatially or temporally variable.

Abstract—Like calcium‐aluminum‐rich inclusions (CAIs) from carbonaceous and ordinary chondrites, enstatite chondrite CAIs are composed of refractory minerals such as spinel, perovskite, Al, Ti‐diopside, melilite, hibonite, and anorthitic plagioclase, which may be partially to completely surrounded by halos of Na‐(±Cl)‐rich minerals. Porous, aggregate, and compact textures of the refractory cores in enstatite chondrite CAIs and rare Wark—Lovering rims are also similar to CAIs from other chondrite groups. However, the small size (<100μm), low abundance (<1% by mode in thin section), occurrence of only spinel or hibonite‐rich types, and presence of primary Ti‐(±V)‐oxides, and secondary geikelite and Ti, Fe‐sulfides distinguish the assemblage of enstatite chondrite CAIs from other groups.

Abstract—The CV (Vigarano‐type) chondrites are a petrologically diverse group of meteorites that are divided into the reduced and the Bali‐like and Allende‐like oxidized subgroups largely based on secondary mineralogy (Weisberg et al., 1997; Krot et al., 1998b). Some chondrules and calcium‐aluminum‐rich inclusions (CAIs) in the reduced CV chondrite Vigarano show alteration features similar to those in Allende: metal is oxidized to magnetite; low‐Ca pyroxene, forsterite, and magnetite are rimmed and veined by ferrous olivine (Fs40–50); and plagioclase mesostases and melilite are replaced by nepheline and sodalite (Sylvester et al., 1993; Kimura and Ikeda, 1996, 1997, 1998).

Previous studies of ordinary chondrites (OC) reported isolated microchondrules within the fine-grained or clastic matrix of many type-3 samples; larger sets of microchondrules have also been found as rare clasts in type-3 OC. We report here another major setting for microchondrules; large numbers (n ≥ 100) of microchondrules (≤40 μm in apparent diameter) occur together with irregularly shaped fragments in fine-grained rims around four low-FeO porphyritic olivine chondrules and one barred olivine chondrule. These chondrules are from LL3.1 Bishunpur, L3.4 EET90161, L3.4 EET90261, LL3.4 Piancaldoli, and LL3.0 Semarkona. The two kinds of microchondrules observed are (1) numerous low-FeO radial and cryptocrystalline microchondrules consisting of low-Ca pyroxene and (2) relatively rare high-FeO olivine microchondrules. Both types of microchondrules are embedded in high-FeO fine-grained matrix materials; they are typically accompanied by irregularly shaped pyroxene fragments that form a continuum in composition and shape with the low-FeO microchondrules. The pyroxene-rich surfaces of the host chondrules project into the surrounding rims as peninsulas with rounded embayments, consistent with remelting; although on average less ferroan, the peninsulas overlap the fragments and low-FeO microchondrules in composition and appear to have been the main source of these objects.

Abstract—The oxidized CV3 chondrites can be divided into two major subgroups or lithologies, Bali‐like (CV3oxB) and Allende‐like (CV3oxA), in which chondrules, calcium‐aluminum‐rich inclusions (CAIs) and matrices show characteristic alteration features (Weisberg et al, 1997; Krot et al, 1997d; Kimura and Ikeda, 1997). The CV3oxBlithology is present in Bali, Kaba, parts of the Mokoia breccia and, possibly, in Grosnaja and Allan Hills (ALH) 85006. It is characterized by the presence of the secondary low‐Ca phyllosilicates (saponite and sodium phlogopite), magnetite, Ni‐rich sulfides, fayalite (Fa>90), Ca‐Fe‐rich pyroxenes (Fs10–50Wo45–50) and andradite. Phyllosilicates replace primary Ca‐rich minerals in chondrules and CAIs, which suggests mobilization of Ca during aqueous alteration. Magnetite nodules are replaced to various degrees by fayalite, Ca‐Fe‐rich pyroxenes and minor andradite. Fayalite veins crosscut fine‐grained rims around chondrules and extend into the matrix. Thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures (<300 °C) in the presence of aqueous solutions. Oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large Δ18Ofayalite‐magnetitefractionation (∼20%). We infer that phyllosilicates, magnetite, fayalite, Ca‐Fe‐rich pyroxenes and andradite formed at relatively low temperatures (<300 °C) by fluid‐rock interaction in an asteroidal environment.

Abstract—We have studied an Allende dark inclusion by optical microscopy, scanning electron microscopy, electron microprobe analysis and transmission electron microscopy. The inclusion consists of chondrules, isolated olivines and matrix, which, as in the Allende host, is mainly composed of 5–20 μm long lath‐shaped fayalitic grains with a narrow compositional range (Fa42 ± 2) and nepheline. Olivine phenocrysts in chondrules and isolated olivine grains show various degrees of replacement by 5–10 μm wide fayalitic rims (Fa39 ± 2) and 100–1000 μm wide translucent zones, which consist of 5–20 μm long lath‐shaped fayalitic grains (Fa41 ± 1) intergrown with nepheline. These fayalitic olivines, like those in the matrix of the dark inclusion, contain 10–20 nm sized inclusions of chromite, hercynite, and Fe‐Ni sulfides. The fayalitic rims around remnant olivines are texturally and compositionally identical to those in Allende host, suggesting that they have similar origins. Chondrules are surrounded by opaque rims consisting of tiny lath‐shaped fayalitic olivines (<1–3 μm long) intergrown with nepheline. As in the Allende host, fayalitic olivine veins may crosscut altered chondrules, fine‐grained chondrule rims and extend into the matrix, indicating that alteration occurred after accretion.

Abstract—We have characterized Ca‐Fe‐rich silicates (salite‐hedenbergite pyroxenes (Fs10–50Wo45–50), andradite (Ca3Fe2Si3O12), kirschsteinite (CaFeSiO4), and wollastonite (Ca3Si3O9)) in the type I chondrules and matrices in the Bali‐like and Allende‐like oxidized CV3 chondrites and Allende dark inclusions. In type I chondrules in the Bali‐like CV3 chondrites, metal is oxidized to magnetite; magnetite‐sulfide nodules are replaced by Ca‐Fe‐rich pyroxenes with minor andradite and pure fayalite. We infer that Ca‐Fe‐rich pyroxenes, andradite, fayalite, magnetite, and phyllosilicates (which occur in mesostases) formed at relatively low temperatures (<300 °C) in the presence of aqueous solutions. Thermodynamic analysis of phase relations in the Si‐Fe‐Ca‐O‐H system and large O isotopic fractionation of the coexisting magnetite and fayalite (∼20%) (Krot et al., 1998) are consistent with this interpretation.

Abstract—Carbonates in Martian meteorite Allan Hills 84001 occur as grains on pyroxene grain boundaries, in crushed zones, and as disks, veins, and irregularly shaped grains in healed pyroxene fractures. Some carbonate disks have tapered Mg‐rich edges and are accompanied by smaller, thinner and relatively homogeneous, magnesite microdisks. Except for the microdisks, all types of carbonate grains show the same unique chemical zoning pattern on MgCO3‐FeCO3‐CaCO3plots. This chemical characteristic and the close spatial association of diverse carbonate types show that all carbonates formed by a similar process. The heterogeneous distribution of carbonates in fractures, tapered shapes of some disks, and the localized occurrence of Mg‐rich microdisks appear to be incompatible with growth from an externally derived CO2‐rich fluid that changed in composition over time. These features suggest instead that the fractures were closed as carbonates grew from an internally derived fluid and that the microdisks formed from a residual Mg‐rich fluid that was squeezed along fractures.

Abundant carbide-magnetite assemblages occur in matrix, chondrules, and chondrule rims in several H3, L3, and LL3 chondrites. Carbides, cohenite ((Fe,Ni)3C), and haxonite ((Fe,Ni)23C6) show compositional variations between different meteorites and appreciable ranges within meteorites. Carbides in H chondrites have lower Co contents (0–0.6 wt%) than those in L and LL chondrites (0.3–1.2 wt%). Metal associated with carbides and magnetite consists of high-Ni (50–70 wt%) taenite and, in L and LL chondrites, Co-rich (up to 35 wt%) kamacite; minor element contents of troilite and magnetite are very low. Textural observations indicate that carbide-magnetite assemblages formed by replacement of metal-sulfide nodules. The high Co contents of residual kamacite in association with carbides indicates that Co is not incorporated into carbides (i.e., Fe/Co is much higher in the carbides than in kamacite). Because Ni in carbides and magnetite is low, the Ni contents of residual taenite tend to be high. Ni-rich sulfides were found only in LL3 chondrites, possibly indicating their more extensive oxidation and/or aqueous alteration.