Northwest Africa 13446 (NWA 13446)

Algeria

Purchased: 2020 Jun

Classification: Ungrouped achondrite

History: Purportedly found in Algeria and purchased by Habib Naji in June 2020 from a dealer in Adrar, Algeria.

Petrography: (A. Irving, UWS and P. Carpenter, WUSL) The specimen has an igneous cumulate texture and consists predominantly of zoned olivine (~90 vol.%) with intercumulus assemblages composed of low-Ca pyroxene (mostly pigeonite), subcalcic augite and sodic plagioclase-like glass with accessory chromite, troilite and very rare spherical grains of metal (kamacite and taenite).

Geochemistry: Olivine (Fa_19.8±3.7, range Fa_15.8-27.9, FeO/MnO = 47-54, N = 11), low-Ca pyroxene (Fs_28.8Wo_4.6, FeO/MnO = 26), pigeonite (Fs_26.6±4.4Wo_10.4±4.7, range Fs_18.3-30.6Wo_6.5-18.9, FeO/MnO = 26-30, N = 6), subcalcic augite (Fs_34.2±6.7Wo_27.2±5.0, range Fs_27.3-43.3Wo_23.0-34.2, FeO/MnO = 27-35, N = 4), plagioclase-like glass (Ab_65.4-86.0An_15.7-5.8Or_18.9-8.2, N = 4), kamacite (Ni = 1.6 wt.%), taenite (Ni = 36.4 wt.%). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed subsamples by laser fluorination gave, respectively, δ¹⁷O 3.638. 3.614, 3.623; δ¹⁸O 4.887, 4.859, 4.947; Δ¹⁷O 1.058, 1.049, 1.012 per mil (all data linearized).

Classification: Achondrite (igneous, ultramafic, ungrouped). This specimen is an almost metal-free, olivine-dominated igneous achondrite with oxygen isotope affinities to L chondrites. Olivine exhibits compositional zoning from core values typical of H chondrites to rim values more typical of L chondrites, and intercumulus pyroxene also exhibits zoning from pigeonite cores to subcalcic augite rims.

Specimens: 54 g including one polished thin section at UWB; remainder with Mr. H. Naji.