¹A.Skulteti,^2,3A.Kereszturi,⁴ M.Szabo,⁵Zs Kereszty,⁶F.Cipriani
Planetary and Space Sciences (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.104855]
¹Research Centre for Astronomy and Earth Sciences, Geographical Institute, Hungary
²Research Centre for Astronomy and Earth Sciences, Konkoly Thege Miklos Astronomical Institute, Hungary
³European Astrobiology Institute, UK
⁴Research Centre for Astronomy and Earth Sciences, Institute for Geological and Geochemical Research, Hungary
⁵International Meteorite Collectors Association, Hungary
⁶European Space Agency, ESTEC/TEC-EPS, Keplerlaan 1, 2200AG, Noordwijk, the Netherlands

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Alexander N. Krot,¹Kazuhide Nagashima,²George R. Rossman
American Mineralogist 105, 239–243 Link to Article [https://doi.org/10.2138/am-2020-7185]
¹Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96822, U.S.A.
Division of Geological and Planetary Sciences, California Institute of
²Technology, Pasadena, California 91125, U.S.A.
Copyright: The Mineralogical Society of America

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%) TiO₂ 59.75, Al₂O₃ 15.97, Sc₂O₃ 10.29, ZrO₂ 9.18, Y₂O₃ 2.86, FeO 1.09, CaO 0.44, SiO₂ 0.20, MgO 0.10, total 99.87, giving rise to an empirical formula (based on 9 oxygen atoms pfu) of (Al_1.17Sc_0.56Y_0.10Ti4+0.08Ti0.084+Fe_0.06Ca_0.03Mg_0.01)(⁠Ti4+2.71Ti2.714+Zr_0.28Si_0.01)O₉. The general formula is (Al,Sc)₂(Ti⁴⁺,Zr)₃O₉. The end-member formula is Al₂Ti₃O₉. Machiite has the C2/c schreyerite-type structure with a = 17.10 Å, b = 5.03 Å, c = 7.06 Å, β = 107°, V = 581 ų, 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 (Δ¹⁷O = –0.2 ± 2.4‰ and –24.1 ± 2.6‰, respectively; where Δ¹⁷O = 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 (Δ¹⁷O~ –25‰) under high-temperature (~1400–1500 °C) and low-pressure (~10^-4–10^-5 bar) 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.

¹James P. Greenwood,¹Kenichi Abe,^1,2Benjamin McKeeby
American Mineralogist 105, 255–261 Link to Article [https://doi.org/10.2138/am-2020-7180]
¹Department of Earth and Environmental Sciences, Wesleyan University, Middletown, Connecticut 06459, U.S.A.
²Department of Geology and Environmental Science, University of Pittsburgh, Pittsburgh, PA 15260, U.S.A.
Copyright: The Mineralogical Society of America

We report the occurrence of a previously unidentified mineral in lunar samples: a Cl-,F-,REE-rich silico-phosphate identified as Cl-bearing fluorcalciobritholite. This mineral is found in late-stage crystallization assemblages of slowly cooled high-Ti basalts 10044, 10047, 75035, and 75055. It occurs as rims on fluorapatite or as a solid-solution between fluorapatite and Cl-fluorcalciobritholite. The Cl-fluorcalciobritholite appears to be nominally anhydrous. The Cl and Fe²⁺ of the lunar Cl fluorcalciobritholite distinguishes it from its terrestrial analog. The textures and chemistry of the Clfluorcalciobritholite argue for growth during the last stages of igneous crystallization, rather than by later alteration/replacement by Cl-, REE-bearing metasomatic agents in the lunar crust. The igneous growth of this Cl- and F-bearing and OH-poor mineral after apatite in the samples we have studied suggests that the Lunar Apatite Paradox model (Boyce et al. 2014) may be inapplicable for high-Ti lunar magmas. This new volatile-bearing mineral has important potential as a geochemical tool for understanding Cl isotopes and REE chemistry of lunar samples.

^1,2Péter Németh,^2,3Laurence A.J. Garvie
American Mineralogist 105, 276–281 Link to Article [https://doi.org/10.2138/am-2020-7305]
¹Institute of Materials and Environmental Chemistry, Research Center for Natural Sciences, Hungarian Academy of Sciences, H-1117 Budapest, Magyar Tudósok Körútja 2, Hungary
²School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287-6004, U.S.A.
³Center for Meteorite Studies, Arizona State University, Tempe, Arizona 85287-6004, U.S.A.
Copyright: The Mineralogical Society of America

Shock caused by impacts can convert carbonaceous material to diamond. During this transition, new materials can form that depend on the structure of the starting carbonaceous materials and the shock conditions. Here we report the discovery of cage-like nanostructured carbonaceous materials, including carbon nano-onions and bucky-diamonds, formed through extraterrestrial impacts in the Gujba (CB_a) meteorite. The nano-onions are fullerene-type materials and range from 5 to 20 nm; the majority shows a graphitic core-shell structure, and some are characterized by fully curved, onion-like graphitic shells. The core is either filled with carbonaceous material or empty. We show the first, natural, 4 nm sized bucky-diamond, which is a type of carbon nano-onion consisting of multilayer graphitic shells surrounding a diamond core. We propose that the nano-onions formed during shock metamorphism, either the shock or the release wave, of the pre-existing primitive carbonaceous material that included nanodiamonds, poorly ordered graphitic material, and amorphous carbonaceous nanospheres. Bucky-diamonds could have formed either through the high-pressure transformation of nano-onions, or as an intermediate material in the high-temperature transformation of nanodiamond to nano-onion. Impact processing of planetary materials was and is a common process in our solar system, and by extension, throughout extrasolar planetary bodies. Together with our previous discovery of interstratified graphite-diamond in Gujba, our new findings extend the range of nano-structured carbonaceous materials formed in nature. Shock-formed nano-onions and bucky-diamonds are fullerene-type structures, and as such they could contribute to the astronomical 217.5 nm absorption feature.

¹Maree McGregor,²Erin L.Walton,³Christopher R.M.McFarlane,¹John G.Spray
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.01.052]
¹Planetary and Space Science Centre, University of New Brunswick, Fredericton, NB E3B 5A3, Canada
²Department of Physical Sciences, MacEwan University, Edmonton, AB, T5J 4S2, Canada
³Department of Earth Sciences, University of New Brunswick, Fredericton, NB E3B 5A3, Canada
Copyright Elsevier

In situ U-Pb geochronology has been conducted using laser ablation inductively coupled mass spectrometry (LA-ICP-MS) on shocked and thermally metamorphosed apatite, titanite, and zircon grains from the Steen River impact structure, Canada. The dated relict mineral phases occur within impact melt-bearing breccias that underwent post-deposition sintering at 450°C > T < 850°C. Apatite yields a refined lower intercept age of 141 ± 4 Ma, which we interpret as the best estimate for the Steen River impact event. Titanite was only partially reset; yielding a lower intercept age of 113 ± 41 Ma. Zircon yields a lower intercept impact age of 120 ± 14 Ma, which is considered a minimum best-estimate impact age. The most reset zircon ages that control this lower intercept are complicated by combinations of common-Pb incorporation and evidence for recent Pb loss associated with granularized and radiation-damaged domains. All three phases preserve Paleoproterozoic crystalline basement ages, with a single concordant ²⁰⁶Pb/²³⁸U age of 1914 ± 39 Ma from apatite, an upper intercept age of 1882 ± 11 Ma from zircon, and an upper intercept age of 1842 ± 9 Ma from titanite. For apatite, the degree of isotopic resetting is largely thermally controlled, with the extent of reset closely associated with textural setting (degree of grain armouring, melt proximity and sample temperature) and, to a lesser extent, by shock/thermally generated microstructures (i.e., planar fractures, micro-vesicles, and recrystallized domains). While titanite records an impact age that falls within error of apatite and zircon, the majority of grains experienced only partial isotopic resetting, which we attribute to incomplete Pb loss associated with rapid cooling and post-depositional sintering of the breccia matrix below the titanite closure temperature (∼800°C). In zircon, ancient (impact) Pb-loss was facilitated along defect-related, fast-diffusion pathways within pre-impact metamict domains, shock defects, and via recrystallization. These same domains were also subject to recent (post-impact) Pb loss and common Pb contamination, significantly compromising the reliability of zircon ages. The distribution of U-Pb ratios in apatite and titanite is unlike those obtained in crystalline targets, a feature we interpret to be characteristic of impact structures developed in mixed (sedimentary – crystalline) targets, such as Steen River. In this case disaggregated melt systems create thermal regimes distinct from those derived from predominantly igneous/metamorphic targets. With an age of 141 ± 4 Ma, Steen River joins the Dellen (Sweden), Gosses Bluff (Australia), Mjølnir (Barents Sea), and Morokweng (South Africa) impact structures in being formed at, or close to, the Jurassic-Cretaceous boundary.

¹Eleanor C.McIntosh,¹James M.D.Day,²Yang Liu,¹Courtney Jiskoot
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.01.051]
¹Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
Copyright Elsevier

Impactors striking the Moon since the formation of its crust have left an indelible imprint on the lunar surface, in the guise of craters and associated impact rocks. The lunar crust has low intrinsic abundances of the highly siderophile elements (HSE: Re, Os, Ir, Ru, Pt, Rh, Pd, Au), at greater than 3000 times lower than in chondrite meteorites. Consequently, during impact, bolides with chondritic or differentiated iron-rich compositions should impart elevated HSE signatures to the lunar crust. Here we examine glassy lunar impact melt coats (IMC) from the outside rims of Apollo 16 cataclastic anorthosites (60015, 65325) and breccias (65035), as well as both fragments and powders of Antarctic anorthositic regolith breccia (ARB) meteorites (Miller Range 090034/36/70/75 and MacAlpine Hills 88105) for their petrography, mineral chemistry and bulk-rock compositions. The HSE concentrations for IMC range from ∼0.001 to 0.1 × CI chondrite, with measured ¹⁸⁷Os/¹⁸⁸Os between 0.1189 and 0.1366. Anorthositic regolith breccia meteorites, which have components with 2.6-4.1 Ga ages, have similar HSE concentrations to IMC, but typically have lower ¹⁸⁷Os/¹⁸⁸Os (0.1164-0.1284). These latter Os ratios are generally less radiogenic than those measured in ∼3.8-3.9 Ga Apollo impact melt breccias. The Apollo 16 IMC are not well-dated, but their KREEPy trace-element signatures and associated ages of 3.7 to 3.8 Ga for Apollo 16 glasses might imply, at least in part, an origin from the Imbrium or Serenitatis basin-forming impacts. Within the IMC, metal-schreibersite-troilite assemblages record significant inter-element HSE fractionation which is also reflected in bulk HSE patterns for both IMC and ARB meteorites. Variations in relative and absolute HSE compositions directly reflect the control of metal and sulfide segregation within and between impact melt and breccia lithologies. Collectively, IMC and ARB meteorites exhibit approximately 50% of the variation in Ru/Ir and ¹⁸⁷Os/¹⁸⁸Os observed in lunar impact melt breccias. These results imply that significant variations in inter-element compositions can occur during impact brecciation and melting and so some impact melt rock HSE compositions may not record the compositions of impactors that struck the Moon with fidelity. Nonetheless, the generally low ¹⁸⁷Re/¹⁸⁸Os of lunar impact melt rocks means that osmium isotope ratios provide evidence for impact composition, and a change from ordinary to carbonaceous-like impactors either with time – or location – striking the Moon.

¹Hidetomo HONGU,¹Akira YOSHIASA,¹Tsubasa TOBASE ,²Maki OKUBE,²Kazumasa SUGIYAMA,³Tsutomu SATO
Journal of Mineralogical and Petrological Sciences 114, 224-230 Link to Article [DOI https://doi.org/10.2465/jmps.180927]
¹Graduate School of Science and Technology, Kumamoto University
²Institute for Materials Research, Tohoku University
³Graduate School of Engineering, Hokkaido University

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Masami KANZAKI
Journal of Mineralogical and Petrological Sciences 114, 214-218 Link to Article [DOI https://doi.org/10.2465/jmps.190414]
¹Institute for Planetary Materials, Okayama University

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

^1,2Emily C. First,^1,3Tanis C. Leonhardi,¹Julia E. Hammer
Contributions to Mineralogy and Petrology 175, 13 Link to Article [DOI
https://doi.org/10.1007/s00410-019-1638-7]
¹Department of Geology and GeophysicsUniversity of Hawai‘i at Mānoa, Honolulu,USA
²Department of Earth, Environmental and Planetary Sciences Brown University, Providence,USA
³Department of Earth and Planetary Science University of California, Berkeley,Berkeley,USA

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Martin Ferus et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113670]
¹J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, CZ18223 Prague 8, Czech Republic
Copyright Elsevier

The main objective of this study is to provide data on the bulk elemental composition, mineralogy and the possible origin of the Porangaba meteorite, whose fall was observed at 17:35 UT on 9 January 2015 on several sites of the state of São Paulo in Brazil. The surface of the meteorite was mapped by Scanning Electron Microscopy (SEM) and optical microscopy. The mineralogy and the bulk elemental composition of the meteorite were studied using Energy-Dispersive and Wavelength-Dispersive X-ray Spectroscopy (EDS/WDS) together with Electron BackScatter Diffraction (EBSD). The bulk elemental composition was also independently analysed by Atomic Absorption Spectrometry (AAS), Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Laser Ablation ICP MS (LA ICP-MS) and Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS). Based on the available visual camera records of the Porangaba meteorite fall, its orbit was tentatively calculated, and possible candidates for the source bodies in the Solar system were proposed. We also present a laboratory simulation of a Porangaba-like (L4 Ordinary Chondrite) meteor emission spectra. These can be used as benchmark spectra for the identification of meteor rock types through their comparison with meteor spectra recorded by high-speed video-cameras equipped with simple grating spectrographs.