Northwest Africa 11616 (NWA 11616)

(Northwest Africa)

Purchased: 2017 Mar

Classification: Lunar meteorite

History: Purchased by DPitt in March 2017 from a Mauritanian dealer.

Physical characteristics: A single very fresh specimen (2550.8 g) containing separate olivine gabbro and olivine-free basaltic clasts in a fragmental matrix.

Petrography: (A. Irving and S. Kuehner, UWS; S. Valencia and P. Carpenter, WUSL) Polymict breccia with two different clast types. Olivine gabbro clasts (mean grainsize 1.1 mm) consist of equant grains of olivine, zoned clinopyroxene (pigeonite, ferroan pigeonite, subcalcic augite) and maskelynite with accessory chromite, ilmenite, troilite, fayalite, taenite and baddeleyite. A basalt clast has porphyritic texture and is composed mainly of larger prismatic grains (up to 2.5 mm long) of zoned clinopyroxene and smaller lath-like grains of maskelynite with accessory ilmenite, chromite, troilite, silica polymorph, rare baddeleyite, rare K-feldspar and rare Ni-poor kamacite. The remainder of the breccia consists of related crystalline debris.

Geochemistry: Olivine gabbro clasts: olivine (Fa_34.6-59.8, FeO/MnO = 83-108, N = 9), pigeonite (Fs_26.4-39.4Wo_9.7-11.7, FeO/MnO = 51-70, N = 6), ferroan pigeonite (Fs_43.4-71.4Wo_15.4-25.0, FeO/MnO = 57-94, N =3), subcalcic augite (Fs_17.6-28.4Wo_27.2-35.6, FeO/MnO = 51-59, N = 5), maskelynite (85.2-95.6Or_2.2-0.1, N = 10). Basalt clast: pigeonite (Fs_26.2-26.3Wo_6.4-6.5; Fs_29.1Wo_11.7; Fs_49.8Wo_19.1; FeO/MnO = 55-73; N = 4), augite (Fs_21.9-25.6Wo_34.7-35.2, FeO/MnO = 49-50, N = 2), ferropigeonite rims (Fs_78.0-78.2Wo_18.9-20.3, FeO/MnO = 83-86, N = 2), maskelynite (An_84.4-86.2Or_3.6-2.0, N = 2). Bulk composition (R. Korotev, WUSL) INAA of breccia subsamples gave (in wt.%) FeO 19.1, Na₂O 0.25 (in ppm) Sc 42.0, Cr 3230, La 13.6, Nd 22.9, Sm 6.73, Eu 0.578, Tb 1.37, Yb 1.37, Lu 0.66, Hf 5.1, Th 2.0.

Classification: Lunar meteorite (polymict breccia with olivine gabbro and basalt clasts). The olivine gabbro lithology is paired with other magnesian gabbro material present in breccia stones such as NWA 773, NWA 2727 and NWA 3333 and also as discrete meteorites such as NWA 2977, NWA 6950 and NWA 8127. The olivine-free basalt lithology differs from the olivine-phyric basalt lithology represented by NWA 3160, and is a new member of the complex NWA 773 clan of lunar meteorites.

Specimens: 20.9 g including a polished thin section and polished endcut at UWB; remainder with DPitt.