¹Chi Ma, ²Chaney Lin, ³Luca Bindi, ^2,4Paul J. Steinhardt
American Mineralogist 102, 3 Link to Article [https://doi.org/10.2138/am-2017-5991]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
²Department of Physics, Princeton University, Princeton, New Jersey 08544, U.S.A.
³Dipartimento di Scienze della Terra, Università di Firenze, Via La Pira 4, I-50121 Florence, Italy
⁴Princeton Center for Theoretical Science, Princeton University, Princeton, New Jersey 08544, U.S.A.
Copyright: The Mineralogical Society of America

Our nanomineralogy investigation of the Khatyrka CV3 carbonaceous chondrite has revealed three new alloy minerals—hollisterite (IMA 2016-034; Al3Fe), kryachkoite [IMA 2016-062; (Al,Cu)6(Fe,Cu)], and stolperite (IMA 2016-033; AlCu)—in section 126A of USNM 7908. Hollisterite occurs only as one crystal with stolperite, icosahedrite, and khatyrkite, showing an empirical formula of Al2.89Fe0.77Cu0.32Si0.02 and a monoclinic C2/m structure with a = 15.60 Å, b = 7.94 Å, c = 12.51 Å, b = 108.1°, V = 1472.9 Å3, Z = 24. Kryachkoite occurs with khatyrkite and aluminum, having an empirical formula of Al5.45Cu0.97Fe0.55Cr0.02Si0.01 and an orthorhombic Cmc21 structure with a = 7.460 Å, b = 6.434 Å, c = 8.777 Å, V = 421.3 Å3, Z = 4. Stolperite occurs within khatyrkite, or along with icosahedrite and/or hollisterite and khatyrkite, having an empirical formula of Al1.15Cu0.81Fe0.04 and a cubic Embedded Image structure with a = 2.9 Å, V = 24.4 Å3, Z = 1. Specific features of the three new minerals, and their relationships with the meteorite matrix material, add significant new evidence for the extraterrestrial origin of the Al-Cu-Fe metal phases in the Khatyrka meteorite. Hollisterite is named in honor of Lincoln S. Hollister at Princeton University for his extraordinary contributions to earth science. Kryachkoite is named in honor of Valery Kryachko who discovered the original samples of the Khatyrka meteorite in 1979. Stolperite is named in honor of Edward M. Stolper at California Institute of Technology for his fundamental contributions to petrology and meteorite research.

¹Shijie Li, ²Shijie Wang, ³Ingo Leya, ¹Yang Li, ¹Xiongyao Li, ³Thomas Smith
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12842]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
²State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
³Physikalisches Institut, Universität Bern, Switzerland
Published by arrangement with John Wiley&Sons

A meteorite fall was heard and collected on July 13, 2010 at about 18:00 (local time) in the Shibanjing village of the Huaxi district of Guiyang, Guizhou province, China. The total mass of the fall is estimated to be at least 1.6 kg; some fragments are missing. The meteorite consists mainly of olivine, low-Ca pyroxene, high-Ca pyroxene, plagioclase, kamacite, taenite, and troilite. Minor phases include chromite and apatite. Various textural types of chondrules exist in this meteorite: most chondrule textures can be easily defined. The grain sizes of secondary plagioclase in this meteorite range from 2 to 50 μm. The chemical composition of olivine and low-Ca pyroxene are uniform; Fa in olivine and Fs in low-Ca pyroxene are, respectively, 19.6 ± 0.2 and 17.0 ± 0.3 (mole%). Huaxi has been classified as an H5 ordinary chondrite, with a shock grade S2, and weathering W0. The weak shock features, rare fractures, and the high porosity (17.6%) indicates that Huaxi is a less compacted meteorite. The preatmospheric radius of Huaxi is ~11 cm, corresponding to ~21 kg. The meteorite experienced a relatively short cosmic-ray exposure of about 1.6 ± 0.1 Ma. The 4He and 40Ar retention ages are older than 4.6 Ga implying that Huaxi did not degas after thermal metamorphism on its parent body.

¹Fred Jourdan, ^1,2Ela Eroglu
Meteoritics & Planetary Science (in Press)  Link to Article [DOI: 10.1111/maps.12838]
¹Western Australian Argon Isotope Facility, JdL Center & Department of Applied Geology, Curtin University, Perth, Western Australia, Australia
²Department of Chemical Engineering, Curtin University, Perth, Western Australia, Australia
Published by arrangement with John Wiley&Sons

No meteorites from Mercury and Venus have been conclusively identified so far. In this study, we develop an original approach based on extensive Monte Carlo simulations and diffusion models to explore the radiogenic argon (40Ar*) and helium (4He*) loss behavior and the range of 40Ar/39Ar and (U-Th)/He age signatures expected for a range of crystals if meteorites from these planets were ever to be found. We show that we can accurately date the crystallization age of a meteorite from both Mercury and Venus using the 40Ar/39Ar technique on clinopyroxene (± orthopyroxene) and that its 40Ar/39Ar age should match the Pb-Pb age. At the surface of Mercury, phases like albite and anorthite will exhibit a complete range of 40Ar* loss ranging from 0% to 100%, whereas merrillite and apatite will show 100% 4He* loss. By measuring the crystal size and diffusion parameters of a series of plagioclase crystals, one can inverse the 40Ar* loss value to estimate the maximum temperature experienced by a rock, and narrow down the possible pre-ejection location of the meteorite at the surface of Mercury. At the surface of Venus, plagioclase and phosphate phases will only record the age of ejection. The (U-Th)/He systematics of merrillite and apatite will be, respectively, moderately and strongly affected by 4He* loss during the transit of the meteorite from its host planet to Earth. Finally, meteorites from Mercury or Venus will each have their own 40Ar/39Ar and (U-Th)/He isotopic age and 38Arc cosmic ray exposure age signatures over a series of different crystal types, allowing to unambiguously recognize a meteorite for any of these two planets using radiogenic and cosmogenic noble gases.

¹M.J. Burchell, ¹K.M. Harriss, ¹M.C. Price,^1,2L. Yolland
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2017.02.028]
¹Centre for Astrophysics and Planetary Science, School of Physical Sciences, Univ. of Kent, Canterbury, Kent CT2 7NH, United Kingdom.
²Now at: Computational Life and Medical Sciences Network, University College London, 20 Gordon Street, London WC1H, United Kingdom.
Copyright Elsevier

Previously it has been shown that diatom fossils embedded in ice could survive impacts at speeds of up to 5 km s−1 and peak shock pressures up to 12 GPa. Here we confirm these results using a different technique, with diatoms carried in liquid water suspensions at impact speeds of 2 to 6 km s−1. These correspond to peak shock pressures of 3.8 to 19.8 GPa. We also report on the results of similar experiments using forams, at impact speeds of 4.67 km s−1 (when carried in water) and 4.73 km s−1 (when carried in ice), corresponding to peak shock pressures of 11.6 and 13.1 GPa respectively. In all cases we again find survival of recognisable fragments, with mean fragment size of order 20 – 25 µm. We compare our results to the peak shock pressures that ejecta from giant impacts on the Earth would experience if it subsequently impacted the Moon. We find that 98% of impacts of terrestrial ejecta on the Moon would have experienced peak pressures less than 20 GPa if the ejecta were a soft rock (sandstone). This falls to 82% of meteorites if the ejecta were a hard rock (granite). This assumes impacts on a solid lunar surface. If we approximate the surface as a loose regolith, over 99% of the impacts involve peak shock pressures below 20 GPa. Either way, the results show that a significant fraction of terrestrial meteorites impacting the Moon will do so with peak shock pressures which in our experiments permit the survival of recognisable fossil fragments.