Northwest Africa 13854 (NWA 13854)

(Northwest Africa)

Purchased: 2021

Classification: Mesosiderite

History: The meteorite was purchased from a dealer in Morocco.

Physical characteristics: Dark brownish fragment without fusion crust.

Petrography: The meteorite displays a light brownish interior and consists of silicate (about 60 vol%) and metallic (about 40 vol%) portions. The silicate fraction is largely composed of low-Ca pyroxene up to 8 mm (sometimes weakly compositionally zoned) and angular calcic plagioclase grains up to 1 mm. Ca-pyroxene is present as blebby and lamellar exsolutions in low-Ca pyroxene. Plagioclase often poikilitically encloses smaller pyroxene grains. Sparse olivine show reaction coronas with pyroxene and contain symplectitic orthopyroxene-chromite inclusions. Minor phases are silica, Ti-chromite, ilmenite, FeS, and Mg-merrillite. Kamacite and taenite constitute the metallic portion and are present as up to 6 mm sized irregular shaped aggregates dispersed throughout the rock.

Geochemistry: low-Ca pyroxene: Fs_29.3±0.6Wo_4.5±0.2 (Fs_28.6-30.3Wo_4.2-5.0, FeO/MnO=24-27, n=10); augite exsolutions: Fs_16.5±0.6Wo_39.0±0.9 (Fs_15.9-17.6Wo_37.1-39.8, FeO/MnO=19-21, n=9); olivine: Fa_32.4±0.4 (Fa_31.7-33.1, FeO/MnO=41±2, n=11); calcic plagioclase: An_86.5±3.4 (An_83.3-92.8, n=11)