Northwest Africa 13955 (NWA 13955)

Algeria

Find: 2020

Classification: Ungrouped achondrite

History: A single 1760 g stone was recovered by a group of Saharawi meteorite hunters in the Algerian part of the Erg Chech region during the summer of 2020, and then purchased by Ali Salamu from a dealer in Nouadhibou, Mauritania.

Physical characteristics: The interior of the specimen has an overall light brown color with small orange patches, and contains sporadic smooth-walled vesicles.

Petrography: (A. Irving, UWS and P. Carpenter, WUSL) Cumulate texture. Composed of subhedral grains of olivine (~20 vol.%) and low-Ca pyroxene (~70 vol.%, zoned from small orthopyroxene cores to thick mantles of pigeonite) together with intercumulus calcic plagioclase (<10 vol.%) and accessory chromite (low-Ti to Ti-free), metal with (Fe/Ni ratios intermediate between those for typical typical kamacite and taenite), and Fe oxide (possibly representing altered sulfide). Sporadic vesicles or vugs are present.

Geochemistry: Olivine (Fa_33.8-34.8, FeO/MnO = 41-44, N = 4), orthopyroxene cores (Fs_19.1-20.5Wo_0.7-0.8, FeO/MnO = 29-30, N = 2), low-Ca pyroxene (Fs_26.8-27.6Wo_3.4-5.2, FeO/MnO = 26-28, N = 3), pigeonite (Fs_25.1-26.7Wo_7.7-7.8, FeO/MnO = 28-29, N = 2), plagioclase (An_79.9-86.3Or_1.1-0.5, N = 3). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed subsamples by laser fluorination gave, respectively, δ¹⁷O 1.716, 1.777, 1.725; δ¹⁸O 3.828, 3.873, 3.782; Δ¹⁷O -0.305, -0.268, -0.272 (all data linearized).

Classification: Ungrouped achondrite (ultramafic, vesicular). The meteorite is different from diogenites with orthopyroxene present as cores only, and predominance of pigeonite. The oxygen isotopic composition plots below the values for diogenites and typical eucrites.

Specimens: 20.7 g including one polished thin section at UWB; remainder with Mr. A. Salamu.