Northwest Africa 8417 (NWA 8417)

(Northwest Africa)

Purchased: 2014 Apr

Classification: Ordinary chondrite (LL7)

History: Purchased by Aras Jonikas in April 2014 from a Moroccan dealer.

Physical characteristics: Single stone (221.5 g) partly coated by brownish-black fusion crust. The interior is pale green with sparse black grains and visible specks of metal plus brown stained areas.

Petrography: (A. Irving and S. Kuehner, UWS) Very fresh, metal-poor specimen with a complex texture. Large (up to 5 mm across) oikocrysts of orthopyroxene enclose numerous small chadacrysts of olivine, but there also are regions of about equal size composed mostly of olivine and orthopyroxene exhibiting triple grain junctions. Chondrules are absent. Olivine and orthopyroxene of all textural types are highly equilibrated. Accessory minerals are clinopyroxene, Ti-free chromite, sodic plagioclase, K-feldspar, albite, stained kamacite (<1 vol.%), troilite and taenite.

Geochemistry: Olivine (Fa_26.5-26.6; FeO/MnO = 54-63), orthopyroxene (Fs_21.6-21.7Wo_2.8-3.2; FeO/MnO = 31-32), clinopyroxene (Fs_10.5-10.7Wo_40.4-39.6). Oxygen isotopes (K. Ziegler, UNM): acid-washed subsamples analyzed by laser fluorination gave the following results, respectively: δ¹⁷O 3.789, 3.862, 3.729; δ¹⁸O 4.937, 5.020, 4.890; Δ¹⁷O 1.182, 1.211, 1.147 (all per mil).

Classification: Ordinary chondrite (LL7). The very low metal content, the large size of the oikocrysts (presumably representing former chondrules), and the FeO/MnO ratios in olivine are features consistent with LL parentage (prior to thermal metamorphism). Oxygen isotope compositions plot within the overlapping fields for LL and L chondrites, and the olivine and pyroxene compositions fall within the gaps between the accepted ranges for L and LL chondrites, but if all the characteristics are considered together then this specimen is best classified as an LL7 chondrite.

Specimens: 21 g including one polished thin section at UWB. The main mass is held by A. Jonikas.