¹Wataru Fujiya,¹Yuto Aoki,²Takayuki Ushikubo,¹Ko Hashizume,³Akira Yamaguchi
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.02.003]
¹Faculty of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, 310-8512 Ibaraki, Japan
²Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 200 Monobe-otsu, Nankoku, Kochi 783-8502, Japan
³National Institute for Polar Research, Midoricho10-3, Tachikawa, Tokyo 190-8518, Japan
Copyright Elsevier

We report the variability in carbon and oxygen isotopic compositions, chemical compositions, and cathodoluminescence intensities within calcite grains in the Yamato-791198 CM chondrite measured by secondary ion mass spectrometry. To understand the change in carbon isotopic compositions during calcite formation, the carbon isotope-analyses were performed on a series of crystal growth bands of each calcite grain. The crystal growth of calcite grains was inferred from comprehensive analyses of oxygen isotopes, chemical compositions, and cathodoluminescence characteristics.

The observed δ¹⁸O variations within individual grains are as large as 13‰. The oxygen-isotope data plot on a single straight line with a slope of 0.61 ± 0.06 (2σ) in an oxygen three-isotope diagram. This slope steeper than that of the terrestrial fractionation line indicates that the oxygen isotopic compositions of aqueous fluids evolved from higher δ¹⁸O and Δ¹⁷O to lower δ¹⁸O and Δ¹⁷O compositions due to the oxygen-isotope exchange between water and anhydrous silicates in the parent body. Thus, calcite crystals grew from higher Δ¹⁷O to lower Δ¹⁷O areas. The crystal growth inferred from oxygen isotopic compositions is corroborated by the morphology and cathodoluminescence characteristics of the calcite grains. The minor element concentrations of the calcite grains did not increase/decrease monotonically during calcite formation.

The δ¹³C variations within individual grains are no more than 4‰ except for one grain. The intra-grain δ¹³C variations observed here are much smaller than inter-grain δ¹³C variations of ∼80‰ previously reported. These observations indicate that the carbon isotopic compositions of dissolved carbon species did not change during calcite formation and that they were locally heterogeneous which reflects variable proportions of carbon reservoirs with different isotopic compositions.

¹Eniko R.Toth,¹Manuela A.Fehr,¹Matthias Friebel,¹Maria Schönbächler
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.01.059]
¹Institute of Geochemistry and Petrology, ETH Zürich, Clausiusstrasse 25, 8092 Zürich, Switzerland
Copyright Elsevier

Nucleosynthetic isotope variations are well documented for refractory elements in meteorites and the Earth, while moderately volatile elements generally display homogeneous compositions. Cadmium is a moderately volatile element with eight stable isotopes generated by a variety of nucleosynthetic processes. To address the extent of the nucleosynthetic variability in moderately volatile elements, new high precision Cd isotope data are presented for bulk samples of six carbonaceous and one enstatite chondrite. In addition, we report the first Cd isotope results of sequential acid leachates for the CM2 chondrite Jbilet Winselwan. Our new Cd data displays nucleosynthetic homogeneity for bulk chondrites and acid leachates within analytical uncertainties, in agreement with results for other moderately volatile elements. This implies that Cd isotopes were efficiently homogenised prior to incorporation into planetary bodies. We propose that Cd never significantly condensed into dust in stellar environments, or alternatively that such Cd-bearing dust was efficiently destroyed and recycled in the interstellar medium. Our leachate data provides evidence for further homogenisation during thermal processing in the protoplanetary disk including parent body processing. The data shows that Cd in carbonaceous chondrites mainly resides in the more easily dissolved phases, most likely sulphides that were affected by aqueous alteration. Less than 1% of the total Cd was recovered in the final leach fractions that employed HF and mainly dissolve silicates and refractory oxides.

Cadmium is susceptible to thermal neutron-capture effects due to the large neutron capture cross-section of ¹¹³Cd (∼20,000 barns). We report variations of up to −0.6 ± 0.3 for ε¹¹³Cd (internally normalised to ¹¹⁶Cd/¹¹¹Cd) in bulk chondrites, which renders Cd a potential thermal neutron-capture monitor. Most neutron dosimeters, such as Pt, Os and Hf, are sensitive to neutron capture in the epithermal energy range and have applications mainly limited to lunar samples or iron and stony-iron meteorites. The additional use of Cd, susceptible to neutron capture in the thermal energy range, therefore provides a new tool to determine the exposure histories of stony meteorites in more detail. Our study demonstrates that thermal neutron-capture effects in carbonaceous and enstatite chondrites can produce resolvable effects and require attention when assessing nucleosynthetic isotope variations.

^1,2Jianqing Feng,^1,2Matthew A. Siegler,³Paul O. Hayne
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2019JE006130]
¹Planetary Science Institute, Tucson, AZ, USA
²Roy M. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, TX, USA
³Department of Astrophysical and Planetary Sciences and Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA
Published by arrangement with John Wiley & Sons

We derive a new constraint on the thermal and dielectric properties of the lunar regolith layer by reconciling data from the Lunar Reconnaissance Orbiter (LRO) Diviner infrared radiometer and Chang’E‐2 (CE‐2) microwave radiometer (MRM). The bolometric Bond albedo of the lunar surface, which characterizes the ability of the lunar surface to reflect visible radiation, is a function of incidence angle. We determined the Bond albedo by using the Lunar Orbiter Laser Altimeter 1,064‐nm normal albedo and the surface temperature at noon as a function of latitude. The results suggest a modification to existing regolith thermal conductivity models based on a fit to the diurnal variation of Diviner data. Based on the thermal model, a 1‐D radiative transfer and dielectric properties model is developed to fit MRM data for the global Moon. With a new dielectric loss tangent equation for highland regolith applied, our model matches MRM data well at 19.35 and 37 GHz, which are generally accepted to be well calibrated. A global map of loss tangent of the Moon at these frequencies is also obtained by fitting the diurnal amplitude of microwave brightness temperature (TB) of each location on the Moon. We find that the loss tangent of highlands regolith has a slight frequency dependence and is larger than previous studies. We also identify a large discrepancy between our theoretical model and TB obtained by CE‐2 MRM at low frequencies, which is attributed to issues caused by contamination on calibration horn.

^1,2Jennika Greer,²Surya. S. Rout,^3,4Dieter Isheim,^3,4David N. Seidman,⁵Rainer Wieler,^1,2Philipp R. Heck
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13443]
¹Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois, 60637 USA
²Robert A. Pritzker Center for Meteoritics and Polar Studies, Field Museum of Natural History, Chicago, Illinois, 60605 USA
³Northwestern Center for Atom Probe Tomography (NUCAPT), Northwestern University, Evanston, Illinois 60208, USA
⁴Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois, 60208 USA
⁵Institute of Geochemistry and Petrology, ETH Zürich, Zürich, Switzerland
Published by arrangement with John Wiley & Sons

The surfaces of airless bodies, such as the Moon and asteroids, are subject to space weathering, which alters the mineralogy of the upper tens of nanometers of grain surfaces. Atom probe tomography (APT) has the appropriate 3‐D spatial resolution and analytical sensitivity to investigate such features at the nanometer scale. Here, we demonstrate that APT can be successfully used to characterize the composition and texture of space weathering products in ilmenite from Apollo 17 sample 71501 at near‐atomic resolution. Two of the studied nanotips sampled the top surface of the space‐weathered grain, while another nanotip sampled the ilmenite at about 50 nm below the surface. These nanotips contain small nanophase Fe particles (~3 to 10 nm diameter), with these particles becoming less frequent with depth. One of the nanotips contains a sequence of space weathering products, compositional zoning, and a void space (~15 nm in diameter) which we interpret as a vesicle generated by solar wind irradiation. No noble gases were detected in this vesicle, although there is evidence for ⁴He elsewhere in the nanotip. This lunar soil grain exhibits the same space weathering features that have been well documented in transmission electron microscope studies of lunar and Itokawa asteroidal regolith grains.

¹Johnson, D.,²Tyldesley, J.
Mummies, magic and medicine in ancient Egypt (Book Chapter) Link to Article [ISBN: 978-178499750-2;978-178499243-9]
¹The Department of Physical Sciences, The Open University, United Kingdom
²The University of Manchester, United Kingdom

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^1,2Louisa J. Preston,^2,3Rebeca Barcenilla,³Lewis R. Dartnell,⁴Ezgi Kucukkilic-Stephens,⁴Karen Olsson-Francis
Astrobiology 20, Link to Article [https://doi.org/10.1089/ast.2019.2106]
¹Department of Earth Sciences, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK
²Department of Earth and Planetary Sciences, Birkbeck College, University of London, London, UK.
³Department of Life Sciences, University of Westminster, London, UK.
⁴Department of EEES, The Open University, Walton Hall, Milton Keynes, UK.

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^1,2Lidia Pittarello,^3,4Joerg Fritz,¹Julia Roszjar,⁵Christoph Lenz,⁵Chutimun Chanmuang N.,^1,2Christian Koeberl
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13445]
¹Natural History Museum Vienna, Burgring 7, A‐1010 Vienna, Austria
²Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A‐1090 Vienna, Austria
³Saalbau Weltraum Projekt, Liebigstrasse 6, D‐64646 Heppenheim, Germany
⁴Zentrum für Rieskrater‐ und Impaktforschung Nördlingen (ZERIN), Vordere Gerbergasse 3, D‐86720 Nördlingen, Germany
⁵Institut für Mineralogie und Kristallographie, University of Vienna, Althanstrasse 14, A‐1090 Vienna, Austria
Published by arrangement with John Wiley & Sons

Shock amorphization of plagioclase, from partial to complete, has been used to evaluate the degree of shock in meteorites. Important information on the shock amplitude can be derived from the measurement of the refractive index in plagioclase, either from mineral separates or in petrographic thin sections. However, this technique is time‐consuming, and associated sample preparations are considered destructive and are not always possible for precious and rare meteorite samples. In addition, plagioclase amorphization is commonly inhomogeneous at the sample scale and a statistically meaningful number of grains must be considered. Here, we apply several nondestructive spectroscopic techniques, such as Raman spectroscopy, photoluminescence, and cathodoluminescence, to plagioclase experimentally shocked at 28 GPa, and thus in the transition regime between crystalline plagioclase and fully amorphous material. Most of the plagioclase was transformed into diaplectic glass at 28 GPa, yet some grains exhibit heterogeneously distributed crystalline domains. This confirms that intrinsic and extrinsic factors lead to local variations in the intensity of the shock pressure within individual plagioclase crystals of homogeneous composition. The amorphization of plagioclase can qualitatively (and potentially also quantitatively) be investigated by spectroscopic techniques, highlighting such local variations in the shock efficiency.

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

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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.