NWA 12241 Shergottite
Northwest Africa 12241 (NWA 12241)
Purchased: 2018 Aug
Classification: Martian meteorite (Shergottite)
History: Purportedly found in Algeria and purchased by Mohamed Brahim Sueilem in August 2018 from a dealer in Bordj Badji Mokhtar, Algeria.
Physical characteristics: The material (total weight 1150 g) comprises multiple broken fragments, some with adhering black fusion crust. The friable pieces are pale green in color and contain white plagioclase but no evident maskelynite.
Petrography: (A. Irving and S. Kuehner, UWS) This fresh specimen has an orthocumulate texture with ~15 vol.% lath-like, birefringent plagioclase occurring interstitially to more abundant and coarser grained (0.2-1.6 mm, mean 0.7 mm) mafic silicate grains (unzoned olivine and patchily zoned low-Ca and high-Ca clinopyroxene with very limited compositional variation). Accessory phases include Mg-merrillite, chlorapatite, ilmenite, Ti-rich chromite, Cr-rich chromite and pyrrhotite (some associated with minor pentlandite). Levels of shock are judged to be low, based on the absence of optical effects in plagioclase and the complete lack of any conversion to maskelynite; the presence of widespread microcracks in mafic silicates is the only clear evidence of shock.
Geochemistry: Olivine (Fa32.7-34.3, FeO/MnO = 47-48, N = 4), pigeonite (Fs25.0-30.4Wo5.5-10.0, FeO/MnO = 28-30, N = 4), subcalcic augite (Fs17.1-18.1Wo32.7-32.4, FeO/MnO = 23-25, N = 2), aluminous augite inclusion in olivine (Fs17.1Wo39.5, FeO/MnO = 28, TiO2 = 1.1 wt.%, Al2O3 = 6.2 wt.%), plagioclase (An43.0-57.8Or2.4-1.3, N = 3). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed subsamples by laser fluorination gave, respectively, δ17O 2.907, 2.635, 2.808; δ18O 5.092, 4.620, 4.875; Δ17O 0.218, 0.195, 0.234 per mil.
Classification: Martian (shergottite, olivine gabbroic, orthocumulate, low shock).
Specimens: 22.4 g including one polished thin section at UWB; remainder held jointly by Naji Ben Faraji and Mohamed Brahim Sueilem.
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