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We determined the mineral-melt partition coefficients (Di's) and the compositional and/or temperature dependency between grossite, melilite, hibonite, olivine and Ca-, Al-inclusion (CAI)-type liquids for a number of light (LE), high field strength (HFSE), large ion lithophile (LILE), and rare earth (REE) elements including Li, Be, B, Sr, Zr, Nb, Ba, La, Ce, Eu, Dy, Ho, Yb, Hf, Ta, Th. A series of isothermal crystallization experiments was conducted at 5 kbar pressure and IW+1 in graphite capsules. The starting compositions were selected based on the calculated and experimentally confirmed phase relations during condensation in CI dust-enriched systems (Ebel and Grossman, 2000; Ebel, 2006; Ustunisik et al., 2014). Partition coefficients between melt and gehlenite, hibonite, and grossite show that the trace element budget of igneous CAIs is controlled by these three major Al-bearing phases in addition to pyroxene. In general, LE, LILE, REE, and HFSE partition coefficients (by mass) decrease in the order of Di(Gehlenite-Melt) > Di(Hibonite-Melt) > Di(Grossite-Melt). Results suggest that Di(Gehlenite-Melt) vary by a factor of 2-3 in different melt compositions at the same T (~1500 C). Increased melt Al and Ca, relative to earlier work, increases the compatibility of Di(Gehlenite-Melt), and also the compatibility of Di(Hibonite-Melt), especially for La and Ce. Olivine partitioning experiments confirm that olivine contribution to the trace element budget of CAIs is small due to the low Di(Olivine-Melt) at a range of temperatures while D-Eu, Yb(Olivine-Melt) are sensitive to changes in T and oxygen fugacity. The development of a predictive model for partitioning in CAI-type systems would require more experimental data and the use of analytical instruments capable of obtaining single phase analyses for crystals < 5 micron., 23 pages, 15 figures, 5 tables

High concentrations of vanadium cause very unusual coloration in hibonite (purple) and grossite (light violet) crystals in an exotic mineral assemblage from Sierra de Comechingones (Argentina). In the hibonite (CaAl12O19) structure vanadium ions, in various valence states (divalent, trivalent, and tetravalent), may be distributed over five crystallographic sites with coordinations corresponding to different polyhedra, namely, three unequal octahedra [M1 (D3d), M4 (C3ν), and M5 (Cs)], one M3 tetrahedron (C3ν), and one unusual fivefold-coordinated trigonal bipyramid M2 (D3h). Possible locations of vanadium ions in grossite (CaAl4O7) are limited to two crystallographically distinct sites (T1 and T2, both C1) in tetrahedral coordination.The combination of single-crystal X-ray diffraction and absorption spectroscopy techniques aided by chemical analyses has yielded details on the nature of the vanadium-induced color in both hibonite and grossite crystals. In hibonite, both M4 face-sharing octahedral and M2 trigonal bipyramid sites of the R-block are partially occupied by V3+. Strongly polarized bands recorded at relatively low energies in optical absorption spectra indicate that V2+ is located at the M4 octahedral site of the hibonite R-block. Chemical analyses coupled with an accurate determination of the electron densities at structural sites in hibonite suggest that the vanadium ions occupy about 10 and 5% of the M4 and M2 sites, respectively. For grossite, polarized optical absorption spectra reveal no indications of V2+; all observed absorption bands can be assigned to V3+ in tetrahedral coordination. Although not evident by the observed electron densities at the T sites of grossite (due to the low-V content), longer bond distances, and a higher degree of polyhedral distortion suggest that V3+ is located at the T2 site.

We performed high-precision SIMS (secondary ion mass spectrometry) 26Al-26Mg and oxygen isotope analyses of two unique CAIs, “Mesquite” and “Y24”, found in the CO3.05 chondrites Northwest Africa 7892 and Yamato-81020, respectively. Mesquite is unusually large (∼5 × 3 mm) for a CAI from any CO chondrite and exhibits a layered texture comprising a melilite-rich core surrounded by hibonite- and spinel-rich mantle layers and a semi-continuous spinel-dominated rim. The CAI Y24 stands out because of its distinct mineralogy: grossite, hibonite, and spinel are accompanied by abundant ultra-refractory-element-rich phases such as warkite, kangite, and perovskite. Silicates are absent in Y24. Negatively fractionated δ25Mg values of phases in the core and mantle layers of Mesquite suggest that the inclusion as a whole was never molten and, hence, represents an aggregate of condensates. The relatively large grain sizes of melilite in the core (up to ∼300 µm) most likely are the result of solid-state recrystallization and coarsening of melilite in the course of a heating event occurring in the solar nebula. This heating event, however, did not disturb the Al-Mg systematics of Mesquite. Regardless of their position within Mesquite and the phases analyzed, spots analyzed for Al-Mg plot on a single isochron characterized by an initial 26Al/27Al of (4.95 ± 0.08) × 10–5 and a δ26Mg*0 of –0.14 ± 0.05‰. We suggest that this initial 26Al/27Al ratio corresponds to the formation of Mesquite in the solar nebula that was slightly heterogeneous with respect to Mg isotopes. Spinel in the rim is uniform in Δ17O (∼–25‰); in contrast, hibonite in the core and mantle layers, albeit also 16O-rich, show variable oxygen isotope ratios (Δ17O ∼ –15‰ to –23‰), which would be consistent with hibonite condensation in a gas with quickly-changing oxygen isotope compositions. The 16O-poor composition of melilite (Δ17O ∼ –1‰ to 0‰) in the core could be the result of isotope exchange with an 16O-poor gas, perhaps during the heating event that caused the solid-state recrystallization and coarsening of melilite or the result of oxygen isotope exchange with a fluid on the parent body. Abundant calcite, phyllosilicates, and sodalite are witnesses to late-stage and low-temperature alteration of the Mesquite CAI; calcite and phyllosilicates most likely are of terrestrial origin, but sodalite could have formed in the parent body. Inclusion Y24 is irregularly-shaped, indicating a condensation origin. Completely enclosing other phases, warkite forms the matrix of Y24, which could be the result of simultaneous condensation and growth of warkite, grossite, and hibonite. Possibly, spinel formed by replacing grossite or hibonite or both minerals in a gradually cooling gas before any silicates condensed. SIMS analyses indicate that condensation occurred in an 16O-rich gas when 26Al/27Al was (5.4 ± 1.0) × 10–5. Oxygen isotope exchange with an 16O-poor fluid in the parent body or with an 16O-poor gas in a nebular setting caused the 16O-poor compositions in grossite and kangite.

In this investigation, we studied the reaction-sintering between fluorapatite and alumina using natural phosphate and boehmite. The addition of alumina, resulting from the boehmite transitions, to the fluorapatite (FAp) has been carried out to obtain various composites based on FAp, yeelemite, mayenite, grossite (CA2), hibonite (CA6) and β-TCP. Several samples were prepared by varying the boehmite (AlOOH) amount to obtain six compositions which contain after sintering: 5, 10, 15, 20, 25 and 30 wt% of Al2O3. After ball-milling for 5 h, all compositions were sintered in the air for 2 h at different temperatures ranging from 1000 to 1500 °C. The reactions and phase transformations between fluorapatite and boehmite were studied and characterized by DTA/TG, XRD, FT-IR, apparent density and open porosity measurements, micro-hardness and SEM analysis. The micro-hardness and densification of the sintered body showed a marked improvement by increasing the alumina content and sintering temperature. Especially, sample containing 25% alumina exhibited the highest densification at 1400 °C (2.95 g/cm3) and excellent micro-hardness of about 6.5 ± 0.25 GPa. So the preparation of low cost composites based on fluorapatite, yeelimite and grossite from natural phosphate and alumina are feasible.

Warkite (IMA 2013-129) is a new Sc-rich ultrarefractory mineral in the rhonite group of the sapphirine supergroup. It has a P 1 ¯ aenigmatite-type structure with a = 10.367 A, b = 10.756 A, c = 8.895 A, α = 106°, β = 96°, γ = 125°, and Z = 2, and general formula of Ca2(Sc,Ti,Al,Mg,Zr)6Al6O20. Warkite occurs as micrometer-sized crystals in eleven ultrarefractory Ca,Al-rich inclusions (UR CAIs) from the CM, CV, CO, and CH chondrites. In the CM, CO, and CV CAIs, warkite in the cores coexists with a Ti-rich oxide, either perovskite or kangite; the cores are generally mantled and rimmed by davisite and/or Sc-diopside. In the CH CAIs and one CO CAI, warkite in the cores coexists with perovskite and grossite; the cores are mantled by grossite ± gehlenite, and rimmed by low-Sc, Al-diopside. Therefore, there are two basic families of warkite-bearing inclusions, those containing Sc-rich clinopyroxene but no grossite and those containing grossite but no Sc-rich clinopyroxene. Scandian clinopyroxene in warkite-bearing CAIs generally formed by the reaction of warkite, which supplied most or all of the Sc, Ti, and Al, and a nebular gas that supplied much of the Ca and O and virtually all of the Mg and Si. The presence of Sc-rich clinopyroxenes may reflect exposure of some warkite-bearing CAIs to a dust-rich environment, which would enhance partial pressures of Si-, Mg-, and Ca-bearing species in the vapor and make it oxidizing relative to a dust-poor gas. Warkite in grossite-bearing inclusions is generally Ti3+-enriched relative to those in davisite-bearing inclusions, consistent with their formation in relatively dust-poor, more-reducing environments. Warkite compositions are sensitive to the presence or absence of spinel, melilite, Sc-rich clinopyroxenes, and grossite. Compositional variations of perovskite and warkite grains indicate a connection but, except for late-stage Fe exchange, they did not equilibrate with each other. The presence of at least two trends in Y-Sc among perovskites without corresponding trends in warkite suggests that at least some perovskite formed separately. Warkite-bearing CAIs from CM2s and CO3.0s are uniformly 16O-rich (Δ17O ∼ −23‰), whereas those from metamorphosed COs and CVs are isotopically heterogeneous: warkite, kangite, perovskite, melilite, and davisite are 16O-depleted to various degrees (Δ17O range from −22 to −2‰) relative to hibonite, spinel, and forsterite, all having 16O-rich compositions (Δ17O ∼ − 25 to −20‰). We infer that warkite-bearing CAIs originated in an 16O-rich nebular gas. Subsequently, CAIs from metamorphosed CVs and COs experienced O-isotope exchange with an 16O-depleted external reservoir, most likely aqueous fluids on the CV and CO chondrite parent asteroids; however, O-isotope exchange in the solar nebula cannot be excluded.

Intergrowth oxides, like Aurivillius, Ruddlesden-Popper phase, comprise functional layers and exhibit interesting physical properties. The hitherto known intergrowth structures mainly were composed of closed-packing of oxygen ions, and it is very challenging to develop new types of intergrowth structures. We proposed the possible match between the tridymite and grossite, both of which are purely tetrahedra-based structures. We synthesized Ca2 PbGa8 O15 ((Ca0.5 Pb0.5 Ga2 O4 )2 (CaGa4 O7 )) and its structure was solved by ab-initio method. Pb2+ is vitally important to stabilize this first example of tetrahedra-based intergrowth oxide. The appropriate size difference between Pb2+ and Ca2+ causes the layered type cationic ordering, and reduced the thermodynamic potential, in addition, the high hybridization between Pb 6s6p and O 2p orbitals further consolidate the covalency of the tetrahedra-base framework.

We have found two refractory inclusions in the CO3.00 carbonaceous chondrite Dominion Range (DOM) 08006 that appear to be primary condensates from the early solar nebula. One, inclusion 56–1, contains the first four phases predicted to form by equilibrium gas-solid condensation: corundum; hibonite; grossite; and perovskite. The other, 31–2, contains nine predicted condensate phases: hibonite; grossite; perovskite; melilite; spinel; FeNi metal; diopside; forsterite; and enstatite. Except for melilite/spinel, the phases occur in the predicted sequence from core to rim of the inclusion, which has an irregular shape inconsistent with a molten stage. This inclusion preserves the most complete record of condensation in the early solar nebula that has yet been found. The physical evidence reported here supports equilibrium condensation calculations that predict the observed sequence as well as the assumptions upon which they are based, such as total pressure (~10(−3) atm), bulk system composition (solar), and C—O—H proportions. All phases in both inclusions and the associated ferromagnesian silicates are 16O-rich, with ∆(17)O between −25 and −20‰, implying that this is the original composition of the vast majority of primary condensates and that (16)O-poor compositions observed in many isotopically heterogeneous inclusions are largely due to subsequent isotopic exchange. While the nebula was well-mixed with respect to oxygen isotopic composition, clearly resolved anomalies in Ca and Ti isotopic compositions indicate that some isotopic heterogeneity existed early and was preserved during condensation. Inclusion 31–2 did not incorporate live (26)Al and has nucleosynthetic anomalies in the heavy Ca and Ti isotopes (i.e., δ(48)Ca = 4.3 ± 1.9‰; δ(50)Ti = 8.8 ± 2.0‰). In contrast, inclusion 56–1 has radiogenic (26)Mg excesses yielding a ((26)Al/(27)Al)(0) ratio of (1.0 ± 0.1) × 10(−5) and negative nucleosynthetic isotopic anomalies in Ca (δ(48)Ca = −10.3 ± 4.2‰) and Ti (δ(50)Ti = −4.3 ± 2.9‰). Thus, it represents a deviation from the mutual exclusivity relationship between (26)Al incorporation and large nucleosynthetic anomalies. The reservoirs in which these inclusions formed had similar O-isotopic and different Al-, Ca– and Ti-isotopic compositions, suggesting that while the CAI-forming region was well-mixed with respect to oxygen isotopic composition, clearly resolved anomalies in Ca and Ti isotopic compositions indicate that some isotopic heterogeneity existed and was preserved during condensation.

International audience; Coarse-grained xenoliths of hibonite + grossite + Mg-Al-V spinel from Cretaceous pyroclastic rocks on Mt. Carmel, N. Israel, and from Sierra de Comechingones, Argentina, include spherules, rods and dense branching structures of native vanadium and VAl alloys. Microstructures suggest that vanadium melts became immiscible with the host Ca-Al-Mg-Si-O melt, and nucleated as droplets on the surfaces of the oxide phases, principally hibonite. Many extended outward as rods or branching structures as the host oxide crystal grew. The stability of V0 implies oxygen fugacities ≥9 log units below the Iron-Wustite buffer, suggesting a hydrogen-dominated atmosphere. This is supported by wt%-levels of hydrogen in gasses released by crushing, by Raman spectroscopy, and by the presence of VH2 among the vanadium balls. The oxide assemblage formed at 1400–1200 °C; the solution of hydrogen in the metal could lower the melting point of vanadium to these temperatures. These assemblages probably resulted from reaction between differentiated mafic melts and mantle-derived CH4 + H2 fluids near the crust-mantle boundary, and they record the most reducing magmatic conditions yet documented on Earth.

We carried out a coordinated mineralogical and isotopic study of a Wark-Lovering (WL) rim on a Ca,Al-rich inclusion (CAI) from the reduced CV3 chondrite Vigarano. The outermost edge of the CAI mantle is mineralogically and texturally distinct compared to the underlying mantle that is composed of coarse, zoned melilite (Åk(~10–60)) grains. The mantle edge contains fine-grained gehlenite with hibonite and rare grossite that likely formed by rapid crystallization from a melt enriched in Ca and Al. These gehlenite and hibonite layers are surrounded by successive layers of spinel, zoned melilite (Åk(~0–10)), zoned diopside that grades outwards from Al,Ti-rich to Al,Ti-poor, and forsteritic olivine intergrown with diopside. These layered textures are indicative of sequential condensation of spinel, melilite, diopside, and forsterite onto hibonite. Anorthite occurs as a discontinuous layer that corrodes adjacent melilite and Al-diopside, and appears to have replaced them, probably even later than the forsterite layer formation. Based on these observations, we conclude that the WL rim formation was initiated by flash melting and extensive evaporation of the original inclusion edge, followed by subsequent gas-solid reactions under highly dynamic conditions. All the WL rim minerals are (16)O-rich (Δ(17)O = ~−23‰), indicating their formation in an (16)O-rich nebular reservoir. Our Al-Mg measurements of hibonite, spinel, and diopside from the WL rim, as well as spinel and Al,Ti-diopside in the core, define a single, well-correlated isochron with an inferred initial (26)Al/(27)Al ratio of (4.94 ± 0.12) × 10(−5). This indicates that the WL rim formed shortly after the host CAI. In contrast, the lack of (26)Mg excesses in the WL rim anorthite suggest its later formation or later isotopic disturbance in the solar nebula, after (26)Al had decayed.

Ceramic-metal (CaO·Al2O3–Al and CaO·Al2O3–Ag) compounds were prepared by mechanical milling and consolidated through an in-situ sintering process. The aim of this work is to study the effects of the Al and Ag particles to ceramic-base compound, primarily in the microstructure, and its mechanical and antimicrobial properties. Chemical systems with a 1:1M ratio between CaCO3 and Al2O3 powder were formed, with the addition of 10 wt% Al or 10 wt% Ag, respectively. The compound material that consolidated were microstructurally characterized through X-ray diffraction, scanning electron microscopy, optic microscopy, and X-ray computed tomography. In addition, the hardness, the fracture toughness, the transversal elastic modulus, and the antimicrobial property were evaluated. The results of X-ray diffraction identified the formation of the calcium aluminate phases, such as CaO·6Al2O3 (hibonite:CA6), CaO·2Al2O3 (grossite:CA2), and CaO·Al2O3 (krotite:CA); as well as Al and Ag were identified in its respective system. In addition, the mechanical properties show changes compared to the reference material that was synthesized under the same conditions and, finally, these materials also have an antimicrobial effect, against the Staphylococcus bacterium that is common in the oral cavity, when studied in synthetic saliva., pag. 385-395, Centro de Investigación y Desarrollo en Tecnología de Pinturas

Dellagiustaite, ideally Al2V2+O4, is a new spinel-group mineral from Sierra de Comechingones, San Luis, Argentina, where it is found associated with hibonite (containing tubular inclusions, 5–100 μm, of metallic vanadium), grossite, and two other unknown phases with ideal stoichiometry of Ca2Al3O6F and Ca2Al2SiO7. A very similar rock containing dellagiustaite has been found at Mt Carmel (northern Israel), where super-reduced mineral assemblages have crystallized from high-T melts trapped in corundum aggregates (micro-xenoliths) within picritic-tholeiitic lavas ejected from Cretaceous volcanoes. In the holotype, euhedral grains of dellagiustaite are found as inclusions in grossite. The empirical average chemical formula of dellagiustaite is (Al1.09V2+0.91V3+0.87Mg0.08Ti3+0.04Mn0.01)Σ3O4, but it may show limited replacement of V2+ by Mg and of V3+ by Al. As Al is the dominant trivalent cation, the ideal formula is Al2V2+O4 according to the current IMA rules. Dellagiustaite shows the usual space group of spinel-group minerals (Fd3m, R1 = 1.46%) with a = 8.1950(1) Å. The observed mean bond lengths &lt, T–O&gt, = 1.782(2) Å and &lt, M–O&gt, = 2.0445(9) Å, the observed site scattering (T = 13.3 eps, M = 22.5 eps), and the chemical composition show that dellagiustaite is an inverse spinel: T tetrahedra are occupied by Al3+, whereas M octahedra are occupied by V2+ and V3+, leading to the site assignment as TAlM( V0.912+ V0.883+ Al0.093+ Mg0.08 Ti0.033+Mn0.01)O4.

The interaction of Fe–C–O–Cr alloys varying in chromium (0.924–4.760 wt%) and carbon (0.042–1.378 wt%) content with a ceramic substrate having a high content of Al2O3 was studied by experimental wettability tests up to 1600 °C. The degree of interaction was assessed based on changes in contact angles (wetting angles) between the above systems, and through Energy Dispersive X-Ray (EDX), X-Ray Diffraction (XRD) analyses and Scanning Electron Microscopy (SEM). The increasing trend of wetting angles with increasing content of chromium and carbon was found. The results of the analyzes confirmed the effect of carbon (≥0.1 wt%) contained in the alloys on the structural changes in substrate surface within the area under the alloy. The original corundum phase was replaced by new ones (hibonite, grossite, larnite), of which hibonite was present to the highest degree. Furthermore, in the case of low carbon alloy (0.042 wt% C), hibonite was not detected on the substrate surface contrary to chromium-doped corundum.

Grossite (CaAl4O7) is one of the one of the first minerals predicted to condense from a gas of solar composition, and therefore could have recorded isotopic compositions of reservoirs during the earliest stages of the Solar System evolution. Grossite-bearing Ca,Al-rich inclusions (CAIs) are a relatively rare type of refractory inclusions in most carbonaceous chondrite groups, except CHs, where they are dominant. We report new and summarize the existing data on the mineralogy, petrography, oxygen and aluminum-magnesium isotope systematics of grossite-bearing CAIs from the CR, CH, CB, CM, CO, and CV carbonaceous chondrites. Grossite-bearing CAIs from unmetamorphosed (petrologic type 2―3.0) carbonaceous chondrites preserved evidence for heterogeneous distribution of 26Al in the protoplanetary disk. The inferred initial 26Al/27Al ratio [(26Al/27Al)0] in grossite-bearing CAIs is generally bimodal, ˜0 and ˜5×10−5; the intermediate values are rare. CH and CB chondrites are the only groups where vast majority of grossite-bearing CAIs lacks resolvable excess of radiogenic 26Mg. Grossite-bearing CAIs with approximately the canonical (26Al/27Al)0 of ˜5×10−5 are dominant in other chondrite groups. Most grossite-bearing CAIs in type 2–3.0 carbonaceous chondrites have uniform solar-like O-isotope compositions (Δ17O ˜ ‒24±2‰). Grossite-bearing CAIs surrounded by Wark-Lovering rims in CH chondrites are also isotopically uniform, but show a large range of Δ17O, from ˜ ‒40‰ to ˜ ‒5‰, suggesting an early generation of gaseous reservoirs with different oxygen-isotope compositions in the protoplanetary disk. Igneous grossite-bearing CAIs surrounded by igneous rims of ±melilite, Al-diopside, and Ca-rich forsterite, found only in CB and CH chondrites, have uniform 16O-depleted compositions (Δ17O ˜ ‒14‰ to ‒5‰). These CAIs appear to have experienced complete melting and incomplete O-isotope exchange with a 16O-poor (Δ17O ˜ ‒2‰) gas in the CB impact plume generated about 5 Ma after CV CAIs. Grossite-bearing CAIs in metamorphosed (petrologic type >3.0) CO and CV chondrites have heterogeneous Δ17O resulted from mineralogically-controlled isotope exchange with a 16O-poor (Δ17O ˜ ‒2 to 0‰) aqueous fluid on the CO and CV parent asteroids 3–5 Ma after CV CAIs. This exchange affected grossite, krotite, melilite, and perovskite; corundum, hibonite, spinel, diopside, forsterite, and enstatite preserved their initial O-isotope compositions. The internal 26Al-26Mg isochrons in grossite-bearing CAIs from weakly-metamorphosed CO and CV chondrites were not disturbed during this oxygen-isotope exchange. HCCJr is grateful to Klaus Keil for all his sound profession counsel and collegial friendship over the years. He has always been willing to talk and has the generous nature of listening and sharing his thoughts freely and constructively. Professor Klaus Keil has been a mentor to and played a key role in the careers of three of the authors of this paper (ANK, KN, and GRH). He has also influenced the careers of the other authors and most of the people who have worked on meteorites over the past 50+ years. We therefore dedicate this paper to Professor Keil and present it in this Special Issue of Geochemistry.

The Antarctic carbonaceous chondrites DOM 08004 and DOM 08006 have been paired and classified as CO3.0s. There is some uncertainty as to whether they should be paired and whether they are best classified as CO chondrites, but they provide an opportunity for the study of refractory inclusions that have not been modified by parent body processes. In this work, refractory inclusions in thin sections of DOM 08004 and 08006 are studied and compared with inclusions in ALHA77307 (CO3.0) and Acfer 094 (C3.0, ungrouped). Results show that the DOM samples have refractory inclusion populations that are similar to each other but not typical of CO3 chondrites; main differences are that the DOM samples are slightly richer in inclusions in general and, more specifically, in the proportions of grossite-bearing inclusions. In DOM 08004 and DOM 08006, 12.4% and 6.6%, respectively, of the inclusions are grossite-bearing. This is higher than the proportion found in Acfer 094 (5.2%), whereas none were found in ALHA77307. Like those in Acfer 094, DOM inclusions are small (mostly

For the first time, data are presented from a detailed investigation of all components of the NWA 470 CH-type carbonaceous chondrite. The meteorite’s major characteristics are a high metal content with a solar Co/Ni ratio, a majority of chemically-zoned metal grains, cryptocrystalline chondrules, grossite- and hibonite-bearing refractory inclusions, the presence of SiO2 objects and the lack of a fine-grained matrix. The bulk chemical and isotope composition of oxygen in the meteorite is typical for CH chondrites. However, among all CH chondrites, NWA 470 is the most enriched in iron. Notable among the chondrite’s components are refractory inclusions and chondrules of several different generations, which may have formed under either canonical nebular or dust-rich conditions. In general, the origin of refractory inclusions, SiO2 objects and zoned metal can be explained through fractional condensation with partial isolation of the condensates. Dark inclusions were probably included in the material of CH chondrites from a different parent body, similar in composition to CM chondrites. After mixing of these multiple types of material during accretion, the components of NWA 470 were not further affected by aqueous alteration or thermal metamorphic processes, and the components’ primary characteristics have been preserved.

Detailed structural and spectroscopic characterisations have been carried out on the inclusions and the surface oxides present on edge-burst hot-rolled steel coils. Surface scales were characterised through X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. Evidence of different types of regular and non-stoichiometric Fe-oxides was found on the cracked surface of the steel wire. Along with the surface scales inclusions with calcium aluminate and spinel was characterized using Raman spectroscopy. The usefulness of Raman spectroscopy has been explored in detail for the characterisation of these inclusions; especially when XRD information ceases to be a limiting tool. The samples collected from the clogged nozzle area were found to be of grossite (CaO·2Al 2 O 3 ) phase and this was also observed in the inclusions in the finished coils. It was found that this particular calcium aluminate phase has a detrimental effect on casting and final finished steel products.

Condensation models describe the equilibrium distribution of elements between coexisting mineral solid solutions, silicate liquid, and vapor in a closed chemical system, vapor phase always present, using equations of state of the phases involved at a fixed total P (< 1 bar) and temperature T. The VAPORS code uses a CaO-MgO-Al$_2$O$_3$-SiO$_2$ liquid model at T above the stability field of olivine and the MELTS algorithm at lower T. Quenched high-T crystal + liquid assemblages are preserved in meteorites as Type B Ca-, Al-rich inclusions (CAIs) and olivine-rich ferromagnesian chondrules. Experimental tests of compositional regions may clarify the nature of the phases present, the phase boundaries, and the partition of trace elements among these phases. Twenty-three Pt-loop equilibrium experiments in seven phase fields on twelve bulk compositions at specific T and dust enrichment factors tested the predicted stability fields of forsteritic olivine (Mg$_2$SiO$_4$), enstatite (MgSiO$_3$), Cr-bearing spinel (MgAl$_2$O$_4$), perovskite (CaTiO$_3$), melilite (Ca$_2$Al$_2$SiO$_7$ - Ca$_2$Mg$_2$Si$_2$O$_7$) and/or grossite (CaAl4O7) crystallizing from liquid. Experimental results for forsterite, enstatite, and grossite are in very good agreement with predictions, both in chemistry and phase abundances. On the other hand, the stability of spinel with olivine, and stability of perovskite and gehlenite are quite different from predictions. Perovskite is absent in all experiments. Even at low oxygen fugacity (IW-3.4), the most TiO$_2$-rich experiments do not crystallize Al-, Ti-bearing calcic pyroxene. The stability of spinel and olivine together is limited to a smaller phase field than is predicted. The melilite stability field is much larger than predicted, indicating a deficiency of current liquid or melilite activity models. In that respect, these experiments contribute to improving the data for calibrating thermodynamic models including MELTS., 17 pages, 5 figures, 5 tables

SEM/EDX analysis has been applied in order to assess the mineralogical transformations occurring during high temperature treatment of several different anthracites. At 1000 °C (carbonization) loss of CO2 from carbonates, S from sulfides and OH and/or H2O from clays occurs, transforming these minerals to other inorganic phases such as lime, pyrrhotite, and (Na, Mg) K-aluminosilicates, among others. Heat treatment of the carbonized samples up to 1500, 2000, and 2500 °C resulted in: i) a decrease in oxygenated mineralogical phases, which are transformed to higher temperature silicates (grossite, anorthite, kushiroite, etc.); ii) carbide formation (SiC, TiC or Al4C3) by carbothermal reactions; iii) formation of alloys, especially a Pb–Sn alloy; and iv) formation of iron silicides (Fe2Si), iron phosphides (Fe3P), and nitrides (TiN and AlN). The new mineral phases are closely related to the mineral matter in the raw anthracite samples. Thus, samples richer in Ca–Mg phases (carbonates and phosphates) produced minerals such as monticellite, pyrope, gehlenite, grossite and kushiroite; samples richer in Al-bearing phases (boehmite and diaspore) gave rise to phases such as mullite, corundum and spinel; and Si–Al bearing phases (clay minerals) were associated with the formation of minerals such as panunzite, plagioclase and cristobalite. At the highest temperature of the process the majority of the elements vaporized, and Ti seems to be the only element in the original mineral matter that withstands treatment to 2500 °C.

This study investigated the interfacial reaction kinetics and related phenomena between CaO-SiO2-MgO-Al2O3 flux and Fe-xMn-yAl (x = 10 and 20 mass pct, y = 1, 3, and 6 mass pct) steel, which simulates transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) steels at 1873 K (1600 °C). It also examines the effect of changes in the composition of the steel and slag phases on the interfacial reaction rate and the reaction mechanisms. The content of Al and Si in the 1 mass pct Al-containing steel was found to change rapidly within the first 15 minutes of the reaction, but then it remained relatively constant. The content of Al and Si in the 3 to 6 mass pct Al-containing steels, in contrast, changed continuously throughout the entire reaction time. In addition, the content of Mn in the 1 mass pct Al-containing steels initially decreased with increasing time, but the content did not change in the 3 to 6 mass pct Al-containing steels. Furthermore, the mass transfer coefficient of Al, kAl, in the 1 mass pct Al-containing systems was significantly higher than that in other systems; i.e., the kAl can be arranged such that 1 mass pct Al systems >> 3 mass pct Al systems ≥ 6 mass pct Al systems. The compositions of the final slags were close to the saturation lines of the [Mg,Mn]Al2O4 and MgAl2O4 spinels when the slags reacted with 1 mass pct Al and 3 to 6 mass pct Al-containing steels, respectively. These results, which show the effect of Al content on the reaction phenomena, can be explained by the significant increase in the apparent viscosity of the slags that reacted with the 3 to 6 mass pct Al-containing steels. This reaction was likely caused by the precipitation of solid compounds such as MgAl2O4 spinel and CaAl4O7 grossite at locally alumina-enriched areas in the slag phase. This analysis is in good accordance with the combination of Higbie’s surface renewal model and the Eyring equation.

In situ oxygen-isotope measurements of calcium–aluminum-rich inclusions (CAIs) from the metal-rich carbonaceous chondrites Isheyevo (CH/CB-like), Acfer 214 paired with Acfer 182 (CH), QUE 94411 paired with QUE 94627 (CBb), and Hammadah al Hamra 237 (CBb) revealed the presence of a common population of igneous, isotopically uniform, 16O-depleted inclusions: Δ17O (average ± 2 standard deviations) = −7 ± 4‰, −6 ± 5‰, and −8 ± 3‰, respectively. All CAIs from CBs and a significant fraction of those from CHs and Isheyevo are 16O-depleted. Most of the 16O-depleted CAIs consist of Ti-poor Al-diopside, spinel, melilite, and forsterite and surrounded by a single- and double-layered rim of forsterite ± diopside. The 16O-depleted CAIs composed of hibonite, grossite, melilite, and spinel, and surrounded by the multilayered melilite + diopside ± forsterite rims are less common. Some of the 16O-depleted refractory igneous inclusions composed of Al-diopside, forsterite, and ±spinel have chondrule-like textures (skeletal or barred). They are mineralogically most similar to Al-diopside-rich chondrules found in metal-rich carbonaceous chondrites and composed of Al-diopside, forsterite, Al-rich low-Ca pyroxene, ±glassy mesostasis, and ±spinel, suggesting there is a continuum between these objects. We suggest that (i) most of the isotopically uniform and 16O-depleted CAIs resulted from remelting of pre-existing, possibly 16O-rich refractory inclusions. The remelting may have occurred during formation of the magnesian, non-porphyritic (cryptocrystalline and skeletal) chondrules in CHs, CBs, and Isheyevo either by an unspecified, late, single-stage, highly-energetic event or in an impact-generated plume previously hypothesized for their origin; both mechanisms probably occurred in the solar nebula (i.e., in the presence of the nebula gas). The forsterite ± pyroxene rims around 16O-depleted CAIs may have resulted from evaporation–recondensation of silicon and magnesium during this event. Some of the Al-diopside-rich CAIs may have formed by evaporation of the Al-rich chondrule melts. (ii) In addition to these components, the CHs and Isheyevo contain a high abundance of chondrules and refractory inclusions formed by the commonly inferred nebular processes – evaporation, condensation, and incomplete melting of dust aggregates during multiple transient heating events. These include 16O-rich CAIs, amoeboid olivine aggregates, and ferromagnesian and aluminum-rich chondrules with porphyritic textures. Such components are also present in CB chondrites, but they are exceptionally rare. These observations indicate that there are multiple generations of CAIs in metal-rich carbonaceous chondrites. (iii) Because the isotopically uniform, 16O-depleted, igneous CAIs and the magnesian cryptocrystalline and skeletal olivine–pyroxene chondrules are found almost exclusively in metal-rich carbonaceous chondrites, the hypothesized impact-plume mechanism of chondrule formation and recycling of CAIs are not common processes.

Agglomeratic olivine objects (AO objects) and possibly related chondrules in three ordinary chondrites (NWA 4910 [LL3.1], NWA 3127 [LL3.1], Sahara 98175 [LL3.5]) were studied using petrographic and microanalytical techniques to evaluate the origins of these materials. AO objects are mixtures of fine-grained (⩽5–10 μm-diameter) ferroan (Fa 12–35 ) olivine, troilite that is often concentrated towards the periphery of objects, pyroxene, feldspathic material, relict magnesian olivine and pyroxene grains, and relict chondrules. One micro-CAI with a grossite core was also found. AO objects commonly rim chondrules. AO objects show transitional variations in texture and chemistry with Type II chondrules, ranging from AO objects that are finer grained and show no evidence of melting (AO-U objects), to weakly melted and more melted AO objects (AO-WM and AO-M objects, respectively), to fine-grained Type II chondrules (olivine grain size ∼5–60 μm), to coarse-grained Type II chondrules (olivine grain size ∼10–250 μm across); S contents and Na/Al values are typically higher in AO objects than in Type II chondrules. The properties of AO objects and Type II chondrules are interpreted to reflect progressive heating of dust of quasi-chondritic composition, accompanied by grain coarsening during melting, partial loss of the most volatile elements (chiefly S, also Na) during evaporative melting, and back-reaction with gas, to form troilite-rimmed AO objects. Data-model comparisons suggest that progressive heating of chondritic dust to form AO objects and Type II chondrules could have occurred in a dusty environment to yield a transient, oxidizing gas of high pressure (∼10 −3 bar), with gas derived from vaporized dust being much (>500–1000× or even up to 10 4 –10 5 ×) more abundant than ambient solar composition gas. AO objects are protochondrules, but are themselves composed of chondrule debris of different types, suggesting that they represent one step of a chondrule recycling process that also included chondrule disaggregation and additional chemical processing. Our data appear to be compatible with the nebular shock wave model for chondrule formation.

– Acfer 094 is an unshocked, nearly unaltered carbonaceous chondrite with an unusual suite of refractory inclusions. The refractory inclusions in a newly prepared thin section and a small aliquot of disaggregated material were studied to compare the population with previous work, and to report new or unusual inclusion types. A total of 289 Ca-, Al-rich inclusions in the thin section and 67 among the disaggregated material, having a total of 31 different mineral assemblages, were found. Inclusions are largely free of secondary alteration products, and are typically ≤200 μm across. The most common are gehlenitic melilite+spinel±perovskite, spinel+perovskite, and spinel with a thin, silicate rim, typically melilite±diopside. Such rims and (thicker) mantles are very common among Acfer 094 inclusions, and they exhibit a variety of zoning patterns with respect to akermanite and FeO contents. In the thin section, about 13% of the inclusions contain hibonite and approximately 5% are grossite-bearing; in the disaggregated material, the percentages are 14 and 9, respectively, comparable to previous work. Among the unusual inclusions are a fine-grained, porous, Ti-rich hibonite+spinel+perovskite+melilite inclusion with a compact, coarse, Ti-poor hibonite+spinel+melilite clast; two inclusions in which hibonite has reacted to form grossite; two inclusions with FeO-rich spinel; and a small object consisting of fassaite enclosing euhedral spinel, the first fragment of a Type B inclusion reported from Acfer 094. Inclusions similar to those found in CM or CV chondrites are rare; Acfer 094 contains a distinctive population of inclusions. The population, dominated by small, melilite-bearing inclusions, is most similar to that of CO chondrites. A distinguishing feature is that in Acfer 094, almost every phase in almost every refractory inclusion contains 0.5–1.5 wt% FeO. A lack of diffusion gradients and the pristinity of the matrix imply that the inclusions experienced prolonged exposure to FeO-bearing fluid prior to accretion into the Acfer 094 parent body. There are no known nebular conditions under which the refractory phases found in the present samples could acquire FeO enrichments to the observed levels. The most likely setting is therefore in an earlier, FeO-rich parent body. The inclusions were ejected from this parent body, mixed with typical CAIs, chondrules, amoeboid olivine aggregates, and amorphous material, and incorporated into the Acfer 094 parent body.

Krotite, CaAl_2O_4, occurs as the dominant phase in an unusual Ca-,Al-rich refractory inclusion from the NWA 1934 CV3 carbonaceous chondrite. Krotite occupies the central and mantle portions of the inclusion along with minor perovskite, gehlenite, hercynite, and Cl-bearing mayenite, and trace hexamolybdenum. A layered rim surrounds the krotite-bearing regions, consisting from inside to outside of grossite, mixed hibonite, and spinel, then gehlenite with an outermost layer composed of Al-rich diopside. Krotite was identified by XRD, SEM-EBSD, micro-Raman, and electron microprobe. The mean chemical composition determined by electron microprobe analysis of krotite is (wt%) Al_2O_3 63.50, CaO 35.73, sum 99.23, with an empirical formula calculated on the basis of 4 O atoms of Ca_(1.02)Al_(1.99)O_4. Single-crystal XRD reveals that krotite is monoclinic, P2_1/n; a = 8.6996(3), b = 8.0994(3), c = 15.217(1) A, β = 90.188(6), and Z = 12. It has a stuffed tridymite structure, which was refined from single-crystal data to R_1 = 0.0161 for 1014 F_o > 4σF reflections. Krotite is colorless and transparent with a vitreous luster and white streak. Mohs hardness is ~6½. The mineral is brittle, with a conchoidal fracture. The calculated density is 2.94 g/cm3. Krotite is biaxial (–), α = 1.608(2), β = 1.629(2), γ = 1.635(2) (white light), 2V_(meas) = 54.4(5)°, and 2V_(calc) = 55.6°. No dispersion was observed. The optical orientation is X = b; Y ≈ a; Z ≈ c. Pleochroism is colorless to very pale gray, X > Y = Z. Krotite is a low-pressure CaAl_2O_4 mineral, likely formed by condensation or crystallization from a melt in the solar nebula. This is the first reported occurrence of krotite in nature and it is one of the earliest minerals formed in the solar system.

– An anomalous Ca-Al-Fe-rich spherical inclusion (CAFI) was found in the Vigarano CV3 chondrite. The CAFI has an igneous texture and contains large amounts of almost pure and coarse-grained hercynite grains (approximately 56 vol%) as well as refractory phases such as grossite and perovskite. However, melilite and Mg-spinel, which are common in ordinary Ca-Al-rich inclusions, are very rare (

Indirect nuclear spin-spin (J) couplings between (31)P, (27)Al, and (17)O are computed for Cl(3)POAlCl(3), Ph(3)PO, Ph(3)PAlCl(3), Al(H(2)O)(6)(3+), an aluminophosphate model system, and grossite model systems, using the B3LYP hybrid functional and the pcJ-n and aug-pcJ-n basis sets. The results provide computational corroboration of the existence of J coupling constants between (31)P, (17)O, and (27)Al of suitable magnitude for INEPT-style experiments in which connectivity is established as a result of magnetization transfer using these couplings. Potentially useful correlations between structure (bond lengths, angles, dihedrals) and the coupling constants (1)J((27)Al, (17)O), (1)J((31)P, (17)O), and (2)J((31)P, (27)Al) are presented. Calculated values of near zero for both (1)J((27)Al, (17)O) and (2)J((31)P, (27)Al), depending on the molecule and the geometry, suggest that some structurally important correlations could be absent in NMR spectra which rely on magnetization transfers solely based on these isotropic coupling constants.

We have detected 138 presolar silicate, 20 presolar oxide and three presolar complex grains within the carbonaceous chondrite Acfer 094 by NanoSIMS oxygen isotope mapping. These grains were further investigated by scanning electron microscopy (SEM) and Auger electron spectroscopy for morphological and chemical details and their distribution within the meteorite matrix. The three complex grains consist of Al-rich oxides (grossite and hibonite) attached to non-stoichiometric Si-rich silicates. Refractory Al-rich oxides therefore serve as seed nuclei for silicates to condense onto, which is proposed by condensation theory and astronomical observations. However, in the majority of presolar silicates we did not find any indications for large subgrains. Most of the grains (80%) belong to O isotope Group I ( 17 O-enriched) and come from 1 to 2.5 M� asymptotic giant branch (AGB) stars of close-to-solar or slightly lower-than-solar metallicity. About 60% of these grains are irregular in shape; � 40% display elliptical morphologies together with smooth, platy surfaces. Three grains with large 17 O enrichments ( 17 O/ 16 O>3 � 10 � 3 ) have highly irregular shapes and are very small ( 0.5) more likely exhibit elliptical, smooth surfaces (14 out of 18 grains), which is an indication that these grains have not been strongly altered since their circumstellar condensation. We identified only one grain similar to the “glass with embedded metal and sulfides” (GEMS) with a statistically significant sulfur content (>2–3 at.%). It remains unclear why the typical high-sulfur GEMS grains are only found in interplanetary dust particles, but have not yet been unequivocally identified in primitive meteorites.

We report both oxygen- and magnesium-isotope compositions measured in situ using a Cameca ims-1280 ion microprobe in 20 of 166 CAIs identified in 47 polished sections of 15 CR2 (Renazzo-type) carbonaceous chondrites. Two additional CAIs were measured for oxygen isotopes only. Most CR2 CAIs are mineralogically pristine; only few contain secondary phyllosilicates, sodalite, and carbonates – most likely products of aqueous alteration on the CR2 chondrite parent asteroid. Spinel, hibonite, grossite, anorthite, and melilite in 18 CAIs have 16O-rich (Δ17O = −23.3 ± 1.9‰, 2σ error) compositions and show no evidence for postcrystallization isotopic exchange commonly observed in CAIs from metamorphosed CV carbonaceous chondrites. The inferred initial 26Al/27Al ratios, (26Al/27Al)0, in 15 of 16 16O-rich CAIs measured are consistent with the canonical value of (4.5–5) × 10−5 and a short duration ( 0.9 + 2.2 - 0.7 My. Eight of the 166 CR2 CAIs identified are associated with chondrule materials, indicating that they experienced late-stage, incomplete melting during chondrule formation. Three of these CAIs show large variations in oxygen-isotope compositions (Δ17O ranges from −23.5‰ to −1.7‰), suggesting dilution by 16O-depleted chondrule material and possibly exchange with an 16O-poor (Δ17O > −5‰) nebular gas. The low inferred (26Al/27Al)0 ratios of these CAIs ( 2 My after crystallization of CAIs with the canonical (26Al/27Al)0 and suggest evolution of the oxygen-isotope composition of the inner solar nebula on a similar or a shorter timescale. Because CAIs in CR2 and CV chondrites appear to have originated in a similarly 16O-rich reservoir and only a small number of CR2 and CV CAIs were affected by chondrule melting events in an 16O-poor gaseous reservoir, the commonly observed oxygen-isotope heterogeneity in CAIs from metamorphosed CV chondrites is most likely due to fluid–solid isotope exchange on the CV asteroidal body rather than gas–melt exchange. This conclusion does not preclude that some CV CAIs experienced oxygen-isotope exchange during remelting, instead it implies that such remelting is unlikely to be the dominant process responsible for oxygen-isotope heterogeneity in CV CAIs. The mineralogy, oxygen and magnesium-isotope compositions of CAIs in CR2 chondrites are different from those in the metal-rich, CH and CB carbonaceous chondrites, providing no justification for grouping CR, CH and CB chondrites into the CR clan.

We detected additional CAI-like material in STARDUST mission samples of comet 81P/Wild 2. Two highly refractory cometary dust fragments were identified in the impact track 110 [C2012, 0, 110, 0, 0] by applying high resolution synchrotron induced confocal and conventional XRF analysis (HR SR-XRF). The use of a polycapillary lens in front of the detector for confocal spectroscopy dramatically improves the fidelity of particle measurements by removing contribution from the surrounding aerogel. The high spatial resolution (300 × 300 nm2; 300 × 1000 nm2) obtained allowed the detailed non-destructive in situ (trapped in aerogel) study of impacted grains at the sub-μm level. For the two largest particles of the track, the terminal particle and a second particle along the impact track, Ca concentration is up to 30 times higher than CI and Ti is enriched by a factor of 2 compared to CI. High resolution (HR) SR-XRF mapping also reveals that the highest concentrations of Ca, Ti, Fe (and Ni) measured within each grain belongs to different areas of the respective maps which indicate that the particles are composed of several chemically diverse mineral phases. This is in agreement with the finding of a complex phase assemblage of highly refractory minerals in the first ever detected Stardust mission CAI grain “Inti” of Track 25. Principle component analysis (PCA) is a powerful tool for extracting the dominant mineral components and was applied to the two grains indicating that regions in the terminal particle and the second particle are consistent with anorthite or grossite and gehlenite, monticellite or Dmitryivanovite (CaAl2O4), respectively. Our new findings demonstrate that the HR SR-XRF with confocal geometry and PCA analysis is capable of identifying CAI-like fragments without the need to extract particles from the aerogel matrix which is a time-consuming, complex and destructive process. Furthermore, the detection of new CAI-like fragments in the coma dust of comet 81P/Wild 2 strengthens the observation that strong mixing effects and, therefore, mass transport before or during comet formation must have occurred at least up to the region where Kuiper Belt comets formed (∼30 AU).

Calcium-aluminum-rich inclusions (CAIs) from the metal-rich (CH/CB-like) carbonaceous chondrite Isheyevo are mineralogically pristine and show no evidence for postcrystallization alteration. Many of them are composed of very refractory minerals, such as hibonite (CaAl12O19), grossite (CaAl4O7), aluminum-rich pyroxene, and perovskite (CaTiO3). Twenty-eight out of 35 studied CAIs from Isheyevo have oxygen isotopic compositions similar to those of CAIs from the CM and CR carbonaceous chondrites (?17O ~ ?20?). Five igneous CAIs are 16O-depleted to a level observed in Isheyevo chondrules (?17O ?10?), suggesting remelting and isotope exchange in an 16O-poor gaseous reservoir. Two CAIs, WA9 and B1, show the highest enrichment in 16O (?17O ~ ?68?, ?18O ~ ?66?, ?17O ~ ?34?) ever observed among refractory inclusions. In the context of the self-shielding model for the evolution of oxygen isotopes in the solar accretion disk, these CAIs may have recorded the initial oxygen isotopic composition of the solar system, and hence of the Sun.

Dmitryivanovite (CaAl 2 O 4 ) is a newly described, calcium aluminum oxide from the Northwest Africa 470 (NWA470) CH3 chondrite (Ivanova et al. 2002). NWA470 contains abundant small Ca,Al-rich inclusions (CAIs), and dmitryivanovite, whose composition is close to stoichiometric CaAl 2 O 4 [Ca 1.000 (Al 1.993 Si 0.003 Ti 0.002 ) 1.998 O 4 ], was found in one of these CAIs. It occurs as ~10 μm subhedral grains intergrown with grossite (CaAl 4 O 7 ), perovskite, and melilite. Electron backscatter diffraction (EBSD) analysis revealed that dmitryivanovite is a high-pressure polymorph of CaAl 2 O 4 ( a = 7.95, b = 8.62, c = 10.25 A, β = 93.1°, space group P 2 1 / c , and Z = 12). Dmitryivanovite is the third phase to be described from nature in the binary system of CaO–Al 2 O 3 , the other two being hibonite (CaAl 12 O 19 ) and grossite (CaAl 4 O 7 )—all are found in CAIs. The presence of CaAl 2 O 4 in NWA470 suggests a local elevated dust/gas ratio in the solar nebula. The phase diagram of CaAl 2 O 4 shows that ~2 GPa is required to stabilize the high-pressure CaAl 2 O 4 polymorph at 1327 °C, above which CaAl 2 O 4 condenses from the solar nebula. Because it is unlikely that the solar nebula ever had such a high total gas pressure, it appears more probable that condensation of the low-pressure polymorph occurred in the solar nebula with an enhanced dust-to-gas ratio and that subsequently the high-pressure polymorph was produced by shock metamorphism, most likely after the CaAl 2 O 4 -bearing CAI was incorporated into the NWA470 parent asteroid.

Rumuruti chondrites (R chondrites) constitute a well-characterized chondrite group different from carbonaceous, ordinary, and enstatite chondrites. Many of these meteorites are breccias containing primitive type 3 fragments as well as fragments of higher petrologic type. Ca,Al-rich inclusions (CAIs) occur within all lithologies. Here, we present the results of our search for and analysis of Al-rich objects in Rumuruti chondrites. We studied 20 R chondrites and found 126 Ca,Al-rich objects (101 CAIs, 19 Al-rich chondrules, and 6 spinel-rich fragments). Based on mineralogical characterization and analysis by SEM and electron microprobe, the inclusions can be grouped into six different types: (1) simple concentric spinel-rich inclusions (42), (2) fassaite-rich spherules, (3) complex spinel-rich CAIs (53), (4) complex diopside-rich inclusions, (5) Al-rich chondrules, and (6) Al-rich (spinel-rich) fragments. The simple concentric and complex spinel-rich CAIs have abundant spinel and, based on the presence or absence of different major phases (fassaite, hibonite, Na,Al-(Cl)-rich alteration products), can be subdivided into several subgroups. Although there are some similarities between CAIs from R chondrites and inclusions from other chondrite groups with respect to their mineral assemblages, abundance, and size, the overall assemblage of CAIs is distinct to the R-chondrite group. Some Ca,Al-rich inclusions appear to be primitive (e.g., low FeO-contents in spinel, low abundances of Na,Al-(Cl)-rich alteration products; abundant perovskite), whereas others were highly altered by nebular and/or parent body processes (e.g., high concentrations of FeO and ZnO in spinel, ilmenite instead of perovskite, abundant Na,Al- (Cl)-rich alteration products). There is complete absence of grossite and melilite, which are common in CAIs from most other groups. CAIs from equilibrated R-chondrite lithologies have abundant secondary Ab-rich plagioclase (oligoclase) and differ from those in unequilibrated type 3 lithologies which have nepheline and sodalite instead.

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) × 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 × 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 × 10−5. The 26Al-poor and 26Al-rich CAIs are characterized by 16O-rich (Δ -->17O < − 20‰) 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 (δ17O vs. δ18O) 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.

A new combustion synthesis process for production of TiAl from TiO2, Al, Ca and KClO4 has been developed. In a closed reaction vessel, this process gets started at about 505°C with the reaction between Ca and KClO4 yielding CaO and KCl. Subsequent two-stage reaction between TiO2 and Al leads to formation of titanium aluminides and α-Al2O3. Then the reaction between α-Al2O3 and CaO results in formation of CaAl4O7 (grossite). The overall reaction scheme can be represented as 6TiO2 + 22Al + 4KClO4 + 4Ca = 6TiAl + 4CaAl4O7 + 4KCl. The temperature reached in the process (1950°C) is high enough for the melting of TiAl and CaAl4O7 and evaporation of KCl.

The 17 O NMR spectra of glasses quenched from melts at high pressure are often difficult to interpret due to overlapping peaks and lack of crystalline model compounds. High-pressure aluminosilicate glasses often contain significant amounts of [5] Al and [6] Al, thus these high-pressure glasses must contain oxygen bonded to high-coordinated aluminum. The 17 O NMR parameters for the minerals jadeite, pyrope, grossular, and mullite are presented to assist interpretation of glass spectra and to help test quantum chemical calculations. The 17 O NMR parameters for jadeite and grossular support previous peak assignments of oxygen bonded to Si and high-coordinated Al in high-pressure glasses as well as quantum chemical calculations. The oxygen tricluster in mullite is very similar to the previously observed tricluster in grossite (CaAl 4 O 7 ) and suspected triclusters in glasses. We also present 27 Al NMR spectra for pyrope, grossular, and mullite.

Hot-pressed alumina samples, with 5 wt.% additions of CaO:SiO2 possessing molar ratios ranging between 1:5 and 10:1 were studied by electron microscopy. Marked differences in microstructure (e.g. grain size, secondary crystalline phases and grain boundary film thickness) were observed, which depended on the composition of sintering additives. The compositions of glassy phases in triple pockets and in grain boundaries varied markedly depending on sintering additives, but also within individual specimens. High residual compressive stresses were measured in alumina grains of samples which contained low thermal expansion crystalline phases such as anorthite and grossite, while gehlenite-containing samples were correspondingly less stressed.

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 (Δ17O -9‰). 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) × 10-5; in contrast, melilite in this CAI and plagioclase in the host chondrule show no evidence for 26Mg* [(26Al/27Al)I of

The aluminum-rich (>10 wt% Al2O3) objects in the CH carbonaceous chondrite North West Africa (NWA) 739 include Ca,Al-rich inclusions (CAIs), Al-rich chondrules, and isolated mineral grains (spinel, plagioclase, glass). Based on the major mineralogy, 54 refractory inclusions found in about 1 cm2 polished section of NWA 739 can be divided into hibonite-rich (16%), grossite-rich (26%), melilite-rich (28%), spinel-pyroxene-rich (16%) CAIs, and amoeboid olivine aggregates, (AOA's, 17%). Most CAIs are rounded, 25–185 μm (average=70 μm) in apparent diameter, contain abundant, tiny perovskite grains, and typically surrounded by a single- or double-layered rim composed of melilite and/or Al-diopside; occasionally, layers of spinel+hibonite and forsterite are observed. The AOAs are irregularly shaped, 100–250 μm (average=175 μm) in size, and consist of forsterite, Fe,Ni-metal, and CAIs composed of Al-diopside, anorthite, and minor spinel. One AOA contains compact, rounded melilite-spinel-perovskite CAIs and low-Ca pyroxene replacing forsterite. The Al-rich (>10 wt% bulk Al2O3) chondrules are divided into Al-diopside-rich and plagioclase-rich. The Al-diopside-rich chondrules, 50–310 μm (average=165 μm) in apparent diameter, consist of Al-diopside, skeletal forsterite, spinel, ±Al-rich low-Ca pyroxene, and ±mesostasis. The plagioclase-rich chondrules, 120–455 μm (average=285 μm) in apparent diameter, are composed of low-Ca and high-Ca pyroxenes, forsterite, anorthitic plagioclase, Fe,Ni-metal nodules, and mesostasis. The isolated spinel occurs as coarse, 50–125 μm in size, subhedral grains, which are probably the fragments of Al-diopside chondrules. The isolated plagioclase grains are too coarse (60–120 μm) to have been produced by disintegration of chondrules or CAIs; they range in composition from nearly pure anorthite to nearly pure albite; their origin is unclear. The Al-rich objects show no evidence for Fe-alkali metasomatic or aqueous alteration; the only exception is an Al-rich chondrule fragment with anorthite replaced by nepheline. They are texturally and mineralogically similar to those in other CH chondrites studied (Acfer 182, ALH85085, PAT91467, NWA 770), but are distinct from the Al-rich objects in other chondrite groups (CM, CO, CR, CV). The CH CAIs are dominated by very refractory minerals, such as hibonite, grossite, perovskite and gehlenitic melilite, and appear to have experienced very low degrees of high-temperature alteration reactions. These include replacement of grossite by melilite, of melilite by anorthite, diopside, and spinel, and of forsterite by low-Ca pyroxene. Only a few CAIs show evidence for melting and multilayered Wark-Lovering rims. These observations may suggest that CH CAIs experienced rather simple formation history and escaped extensive recycling. In order to preserve the high-temperature mineral assemblages, they must have been efficiently isolated from the hot nebular region, like some chondrules and the zoned Fe,Ni-metal grains in CH chondrites.

The phenomenon of crystallization was implemented in the synthetic V-bearing steelwork slag based on the composition of factory slag from the Masteel Co., and the possibility of undercooling as a technique to precipitate V-concentration phase was demonstrated. The effect of 20 wt% Al2O3 additive introduced into the slag on intensifing the precipitation was also investigated. X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX) were used to investigate the slag after heat treatment. It is demonstrated that gehlenite and grossite are the major crystalline phases. Whitlockite with a high content of V2O5 (called V-concentration phase hereafter) nucleates homogenously and hetergenously and grows with decreasing undercooling. At 1548 K, the crystals of V-concentration phase grow up as the duration of time, with a medium grain size of 25 μm at 300 min holding time.

Heat capacity (CV) and entropy (S) as a function of temperature were calculated for phases in the CaO-Al2O3 system from vibrational spectra using a quasi-harmonic model. Calculated values of CV at 298 K for the calcium aluminates may have uncertainties as small as ±1%, based on comparison with published calorimetric data for CaO, Al2O3, and CaAl2O4. For hibonite (CaAl12O19), we predict CP as 519.3 J/mol-K and S as 391.7 J/mol-K, at 298 K. For grossite (CaAl4O7), calculated values of CP as 195.9 J/mol-K and of S as 172.0 J/mol-K are slightly smaller than the available calorimetric data at 298 K, consistent with calorimetric data having been obtained from samples containing ∼10 wt% hibonite impurities. Thermal conductivity at 298 K (k0) is predicted from peak widths of the vibrational modes using the damped harmonic oscillator model of a phonon gas. Calculations of k0 for CaO and Al2O3 differ from the measurements by 17% and 5%, respectively. The discrepancy for lime is larger due to uncertainties in its peak widths. This comparison suggests that our results for the calcium aluminates should be more accurate than conventional measurements of k0 which are commonly uncertain by ∼25%.