Northwest Africa 13917 (NWA 13917)

(Northwest Africa)

Purchased: 2020

Classification: Primitive achondrite (Winonaite)

History: Purchased from Morocco in September 2020 and January 2021.

Physical characteristics: Several identical appearing stones found together -- the largest of which are individuals weighing 1.6 kg, 1.4 kg, and 1.2 kg. Saw-cut surface shows abundant fine-grained metal and sulfide set in a mosaic of brown and gray silicate minerals. A prominent metal vein 2 mm thick and several cm in length crosscuts the deposit sample slice.

Petrography: (C. Agee, UNM) Microprobe examination of a polished mount shows a texturally equilibrated mosaic of enstatite and diopside with grain size in the range 100-300 μm, many triple junctions are present. Forsterite is ubiquitous but is significantly less abundant than the pyroxenes. Kamacite, taenite, and troilite make up approximately 10% of this meteorite, most grains are 100-300 μm in diameter. A phosphate phase was detected. No feldspar was observed in the microprobe mount.

Geochemistry: (C. Agee UNM) Forsterite Fa_4.0±0.0, Fe/Mn=16±0, n=2; enstatite Fs_4.7±0.2Wo_1.9±0.2, Fe/Mn=13±1, n=3; diopside Fs_1.3±0.4Wo_44.8±0.3, Fe/Mn=13±7, n=4. Oxygen isotopes (K. Ziegler, UNM): 3 acid-washed fragments analyzed by laser fluorination gave δ¹⁸O=4.959, 5.107, 5.236; δ¹⁷O=2.055, 2.179, 2.232; Δ17O=-0.563, -0.518, -0.533 (linearized, all per mil, TFL slope=0.528).

Classification: Primitive achondrite (Winonaite)

Specimens: 67.9 g on deposit at UNM. Mark Lyon holds the main masses.