A detailed mineralogical, petrographic, and geochemical study of the highly reduced chondrite, Acfer 370

1,2Giovanni Pratesi,3Stefano Caporali,4Richard C. Greenwood,5Vanni Moggi Cecchi,1Ian A. Franchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13409]
1Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via Giorgio La Pira, 4, 50121 Firenze, Italy
2INAF‐IAPS, Via Fosso del Cavaliere 100, 00133 Rome, Italy
3Dipartimento di Ingegneria Industriale, Università degli Studi di Firenze, Via Santa Marta 3, 50139 Firenze, Italy
4Planetary and Space Sciences, The Open University, Milton Keynes, MK7 6AA UK
5Museo di Storia Naturale, Università degli Studi di Firenze, Via Giorgio La Pira, 4, 50121 Firenze, Italy
Published by arrangement with John Wiley & Sons

Among the many ungrouped meteorites, Acfer 370, NWA 7135, and El Médano 301—probably along with the chondritic inclusion in Cumberland Falls and ALHA 78113—represent a homogeneous grouplet of strongly reduced forsterite‐rich chondrites characterized by common textural, chemical, mineralogical, and isotopic features. All of these meteorites are much more reduced than OCs, with a low iron content in olivine and low‐Ca pyroxene. In particular, Acfer 370 is a type 4 chondrite that has olivine and low‐Ca pyroxene compositional ranges of Fa 5.2–5.8 and Fs 9.4–33.4, respectively. The dominant phase is low‐Ca pyroxene (36.3 vol%), followed by Fe‐Ni metal (16.3 vol%) and olivine (15.5 vol%); nevertheless, considering the Fe‐oxyhydroxide (due to terrestrial weathering), the original metal content was around 29.6 vol%. Finally, the mean oxygen isotopic composition Δ17O = +0.68‰ along with the occurrence of a silica phase, troilite, Ni‐rich phosphides, chromite, and oldhamite confirms that these ungrouped meteorites have been affected by strong reduction and are different from any other group recognized so far.

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