¹Atencio, D.,¹Cunha, D.,²Ribeiro Moutinho, A.L.,³Zucolotto, M.E.,¹Tosi, A.A.,³Nassif Villaça, C.V.
Brazilian Journal of Geology 50, 2020 Link to Article [DOI: 10.1590/2317-4889202020190085]
¹Universidade de São Paulo, São Paulo (SP), Brazil
²International Meteorite Collector Association, Jacareí (SP), Brazil
³Universidade Federal do Rio de Janeiro, Rio de Janeiro (RJ), Brazil

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¹Maximilian P.Reitze,¹Iris Weber,¹Andreas Morlok,¹Harald Hiesinger,¹Karin E.Bauch,¹Aleksandra N.Stojic,²Jörn Helbert
Earth and Planetary Science Letters 554, 116697 Link to Article [https://doi.org/10.1016/j.epsl.2020.116697]
¹Institut für Planetologie, Westfälische Wilhelms-Universität (WWU) Münster, 48149 Münster, Germany
²Deutsches Zentrum für Luft- und Raumfahrt (DLR), Rutherfordstr. 2, 12489 Berlin, Germany
Copyright Elsevier

We analyzed plagioclase feldspar samples that were well-characterized in terms of chemical composition as well as degree of Al,Si order in mid-infrared reflection spectra between 7 μm and 14 μm (1429 cm−1 and 714 cm−1). The chemical compositions were derived with an electron microprobe analyzer. To determine the degree of Al,Si order, powder X-ray diffraction methods were applied. For the interpretation of the infrared spectra, we used the wavelength of the Christiansen feature (CF) and the autocorrelation function for a specific wavelength region. The CF shifts from around 7.72 μm (1296 cm−1) in Na-richest samples to 8.10 μm (1234 cm−1) in the Ca-richest sample. Combining the CF position and the autocorrelation-derived value allowed to determine the degree of Al,Si order of the samples based on reflection spectra. The wavelength of the Transparency feature (TF) in the finest analyzed grain size fraction also depends on the chemical composition and the degree of Al,Si order. Our results are helpful for the interpretation of data returned by the MERTIS experiment onboard BepiColombo. The data help to distinguish between space weathering, shock effects, and ordering effects in plagioclase samples.

¹Zachary A. Torrano,^1,2Jemma Davidson,¹Meenakshi Wadhwa
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13587]
¹School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, 85287 USA
²Center for Meteorite Studies, Arizona State University, Tempe, Arizona, 85287 USA
Published by arrangement with John Wiley & Sons

The similarities between CV and CK chondrites are so substantial that some studies have argued for a common parent body origin. These similarities also mean that they are susceptible to misclassification as one another. It is, therefore, important to accurately classify CV and CK chondrites to properly compare the properties of the two groups and evaluate the single parent body hypothesis. In this study, we re‐evaluate the current classification of Northwest Africa (NWA) 2900 as a CV3 chondrite. Based on chondrule abundance (~13%), average chondrule diameter (1.11 ± 0.67 mm), iron content in chondrule olivine (Fa1 to Fa35 with a peak near ~Fa31) and matrix olivine (Fa33 to Fa36), magnetite abundance (~4 vol%), elemental abundances in olivine (Cr2O3, Al2O3, TiO2, MnO, NiO, and CaO) and magnetite (Cr2O3, Al2O3, TiO2, and NiO), and comparison with previously reported data for CV and CK chondrites, we propose that the classification of NWA 2900 be changed from CV3 chondrite to CK3 chondrite, with characteristics most similar to those of the CK3.8 subtype. We additionally suggest minor modifications to the compositional criteria used to distinguish between CV and CK chondrites and demonstrate that NWA 2900 extends the range of bulk oxygen isotope compositions of CK chondrites.