Northwest Africa 13745 (NWA 13745)

(Northwest Africa)

Purchased: 2020 Nov

Classification: HED achondrite (Eucrite, monomict)

History: Purchased from a group of Saharawi meteorite hunters in Nouadhibou, Mauritania.

Physical characteristics: Many meteorite fragments (main mass 469 g) without fusion crust.

Petrography: (K. Metzler, IfP) Monomict breccia consisting of basaltic lithic clasts with ophitic to subophitic textures and monomineralic fragments (pyroxene, plagioclase) set in a fine-grained clastic matrix of related debris. The lithic clasts are recrystallized, with frequent 120° triple junctions between mineral grains. Augite exsolution lamellae in low-Ca pyroxene and vice versa. Accessories are a silica polymorph, ilmenite, chromite, and traces of troilite and Ni-poor metal. One Fe-rich olivine grain was observed in a basalt clast. The sample is heavily shocked; all plagioclase has been transformed into maskelynite.

Geochemistry: Mineral compositions and geochemistry: Low-Ca pyroxene: Fs_69.7±0.5 Wo_2.3±0.3 (Fs_68.7-70.4 Wo_1.9-2.8); mean Fe/Mn (at.): 32; n=12. Ca-rich pyroxene: Fs_33.4±1.1 Wo_42.0±0.6 (Fs_31.8-35.2 Wo_40.7-42.8); n=12. Plagioclase (maskelynite): An_81.7±2.3 Or_0.5±0.4 (An_77.7-86.3 Or_0.0-0.9); n=12. Olivine: Fa₈₅; Fe/Mn (at.): 43.

Classification: Monomictly brecciated eucrite with highly ferroan pyroxene. Heavily shocked, with plagioclase completely transformed into diaplectic glass (maskelynite).