¹Ebihara, M. et al. (>10)*
¹Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Hachioji, Tokyo, Japan
*Find the extensive, full author and affiliation list on the publishers website

Two silicate grains (RB-QD04-0049 and RA-QD02-0064, whose estimated masses are 0.050 μg and 0.048 μg, respectively) recovered from the asteroid Itokawa by the Hayabusa spacecraft were studied for their mineralogical characteristics by synchrotron X-ray diffraction and synchrotron X-ray microtomography and further analyzed for their bulk chemical compositions by instrumental neutron activation analysis (INAA). According to X-ray tomography, RB-QD004-0049 is composed of olivine, high-Ca pyroxene, plagioclase, Ca-phosphate, and troilite, whereas RA-QD002-0064 entirely consists of olivine. INAA data are consistent with these mineral compositions except for rare earth elements (REEs). Although the grain RB-QD004-0049 contains measurable REEs, which seems to be consistent with the presence of Ca-phosphate, their abundances are anomalously high. Very low abundance of Co implies less than 0.1 mass% of metals in these two grains by calculation, which is in contrast to the result for the previously analyzed grain RA-QD02-0049 (Ebihara et al., 2011). FeO/Sc ratios of the grains fall within the range of those for ordinary chondrite olivines, implying that these grains are extraterrestrial in origin. FeO/MnO ratios also confirm this conclusion and further suggest that the Hayabusa grains analyzed in this study are similar to material found in LL chondrites rather than CK chondrites although olivines from LL and CK chondrites have similar Fa# (molar% of Fe relative to [Fe+Mg] in olivine) (~30) to those of the Hayabusa grains including the two grains analyzed in this study.

Reference
Ebihara M et al. (2015) Chemical and mineralogical compositions of two grains recovered from asteroid Itokawa. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12418]

Publsihed by arrangement with John Wiley&Sons

^1,2Hezel, D. C. et al. (>10)*
¹Department of Mineralogy, Natural History Museum, London, UK
²Department of Geology and Mineralogy, University of Cologne, Köln, Germany
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Meteorite fusion crust formation is a brief event in a high-temperature (2000–12,000 K) and high-pressure (2–5 MPa) regime. We studied fusion crusts and bulk samples of 10 ordinary chondrite falls and 10 ordinary chondrite finds. The fusion crusts show a typical layering and most contain vesicles. All fusion crusts are enriched in heavy Fe isotopes, with δ56Fe values up to +0.35‰ relative to the solar system mean. On average, the δ56Fe of fusion crusts from finds is +0.23‰, which is 0.08‰ higher than the average from falls (+0.15‰). Higher δ56Fe in fusion crusts of finds correlate with bulk chondrite enrichments in mobile elements such as Ba and Sr. The δ56Fe signature of meteorite fusion crusts was produced by two processes (1) evaporation during atmospheric entry and (2) terrestrial weathering. Fusion crusts have either the same or higher δ18O (0.9–1.5‰) than their host chondrites, and the same is true for Δ17O. The differences in bulk chondrite and fusion crust oxygen isotope composition are explained by exchange of oxygen between the molten surface of the meteorites with the atmosphere and weathering. Meteorite fusion crust formation is qualitatively similar to conditions of chondrule formation. Therefore, fusion crusts may, at least to some extent, serve as a natural analogue to chondrule formation processes. Meteorite fusion crust and chondrules exhibit a similar extent of Fe isotope fractionation, supporting the idea that the Fe isotope signature of chondrules was established in a high-pressure environment that prevented large isotope fractionations. The exchange of O between a chondrule melt and an 16O-poor nebula as the cause for the observed nonmass dependent O isotope compositions in chondrules is supported by the same process, although to a much lower extent, in meteorite fusion crusts.

Reference
Hezel DC et al. (2015) Fe and O isotope composition of meteorite fusion crusts: possible natural analogues to chondrule formation? Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12414]
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¹Steven J. Jaret,¹William R. Woerner,¹Brian L. Phillips,^1,2Lars Ehm,¹Hanna Nekvasil,^3,4Shawn P. Wright,¹Timothy D. Glotch
¹Department of Geosciences, Stony Brook University, Stony Brook, NY
²Photon Sciences Directorate, Brookhaven National Laboratory, Upton, NY
³Department of Geosciences, Auburn University, Auburn, AL
⁴Planetary Science Institute, Tucson, AZ

We present the results of a combined study of shocked labradorite from the Lonar Crater, India, using optical microscopy, micro-Raman spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, high-energy X-ray total scattering experiments, and micro-Fourier transform infrared (micro-FTIR) spectroscopy. We show that maskelynite of shock class 2 is structurally more similar to fused glass than to crystalline plagioclase. However, there are slight but significant differences – preservation of original pre-impact igneous zoning, anisotropy at infrared wavelengths, X-ray anisotropy, and preservation of some intermediate range order – which are all consistent with a solid-state transformation from plagioclase to maskelynite.

Reference
Jaret SJ, Woerner WR, Phillips BL, Ehm L,Nekvasil H, Wright SP, Glotch TD (2015) Maskelynite Formation via Solid-State Transformation: Evidence of Infrared and X-Ray Anisotropy. Journal of Geophysical Research Planets (in Press)
Link to Article [10.1002/2014JE004764]

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¹Fumio Kitajima et al. (>10)*
¹Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University, Hakozaki 812-8581, Fukuoka, Japan
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We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Kitajima F et al. (2015) A micro-Raman and infrared study of several Hayabusa category 3 (organic) particles. Earth, Planets & Space 67:20

Link to Article [doi:10.1186/s40623-015-0182-6]

¹Abrar H. Quadery,¹Shaun Pacheco,¹Alan Au,¹Natalie Rizzacasa,¹Joshua Nichols,¹Timothy Le,¹Cameron Glasscock,^1,2Patrick K. Schelling
¹Department of Physics, University of Central Florida, Orlando, Florida, USA
²Advanced Material Processing and Analysis Center, University of Central Florida, Orlando, Florida, USA

Classical molecular dynamics was used to study the annealing of anion and cation Frenkel defects in olivine and orthopyroxene minerals. While it was found that for both minerals, reorganization of the Si-O bonds, often accompanied by large Si displacements, occurs to maintain the fourfold coordination of the SiO4 tetrahedra, important differences are observed in their annealing behavior. Specifically, cation defects are substantially more mobile in olivine than in orthopyroxene leading torapid annihilation of cation Frenkel defects and formation of extended defects in olivine. By contrast, the diffusion rate of anion defects in orthopyroxene is much higher than that in olivine, and also exhibits large anisotropy. Consequently, it was found that diffusion in orthopyroxene occurs without significant annihilation of anion Frenkel defects or trapping of anion interstitials or vacancies into clusters. The results obtained here are discussed in the context of space weathering of olivine and orthopyroxene. Specifically, two important observations are made which may explain previous experimental results. First, ion irradiation experiments that show reduced tolerance for radiation damage in orthopyroxene may be explained by the rapid, one-dimensional anion mobility which prevents healing of the lattice. Second, laser heating experiments which show that orthopyroxene has enhanced tolerance to reduction and the evolution of nanophase Fe inclusions could be due to the observed rapid anion diffusion in orthopyroxene, which might allow the bulk to act as a reservoir for the surface.

Reference
Quadery AH,Pacheco S,Au A, Rizzacasa N, Nichols J, Le T, Glasscock C, Schelling PK (2015) Atomic-scale simulation of space weathering in olivine and orthopyroxene. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004683]

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