Northwest Africa 6232: Visible–near infrared reflectance spectra variability of an olivine diogenite

1Christian Carli,2,3Giovanni Pratesi,3Vanni Moggi-Cecchi,1Francesca Zambon,1Fabrizio Capaccioni,2Simone Santoro
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13056]
1IAPS-INAF, Rome, Italy
2Department of Earth Science, University of Florence, Florence, Italy
3Natural History Museum of University of Florence, Florence, Italy
Published by arrangement with John Wiley & Sons

Visible and near-infrared (VNIR) reflectance is an important spectroscopic technique to identify minerals, and their associations, on planetary body surfaces. Howardites, eucrites, and diogenites (HED) are a class of igneous-like meteorites whose genetic connection with asteroid 4 Vesta has since long been inferred and recently confirmed by Dawn mission results. Pyroxene and olivine are the two major mafic minerals present in HED which can be identified with VNIR reflectance measurements. Thus, studying the compositional variability of those phases and their mixtures by means of laboratory spectroscopic measurements on different diogenitic or eucritic samples is one of the prime methods to better understand the evolution of 4 Vesta’s crust. Here, we report the VNIR reflectance spectral analysis of a harzburgitic olivine diogenite, Northwest Africa 6232 (probably paired with Northwest Africa 5480), containing variable amounts of olivine as small grains or aggregates. We found that the olivine diogenite spectral parameters (e.g., band position) of powdered samples and polished slabs are in agreement. Moreover, the olivine diogenite band position shifts from synthetic orthopyroxene in accordance with the presence of olivine and chromite. In particular, the presence of a large olivine clast permits us to determine a linear variation of the band position from synthetic orthopyroxene and olivine, but underestimates the presence of olivine in the olivine diogenite spot.

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