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

Pratesi, Giovanni; Caporali, Stefano; Greenwood, Richard; Moggi Cecchi, Vanni and Franchi, Ian (2019). A detailed mineralogical, petrographic, and geochemical study of the highly reduced chondrite, Acfer 370. Meteoritics and Planetary Science, 54(12) pp. 2996–3017.

DOI: https://doi.org/10.1111/maps.13409

Abstract

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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