Northwest Africa 15236 (NWA 15236)

(Northwest Africa)

Purchased: 2022 Feb

Classification: HED achondrite (Eucrite, polymict)

History: Purchased by Wei Jiang from a Moroccan dealer in 2021 and subsequently acquired by Ziyao Wang and Jiachang Yu in February 2022.

Petrography: (A. Irving, UWS and P. Carpenter, WUSL) Complex breccia containing some lithic clasts but mostly crystalline debris derived from several different lithologies. Most of the lithic clasts are microgabbroic and composed of zoned, unexsolved pigeonite, subcalcic augite and calcic plagioclase together with fine grained symplectitic intergrowths of augite+fayalitic olivine+silica polymorph+troilite. Grains of orthopyroxene are present as a minor component (<5 vol.%) and have rims of exsolved ferroan pigeonite. Isolated angular grains of silica polymorph, ilmenite, troilite, Ni-poor Fe metal and rare zircon are also present.

Geochemistry: Basaltic clasts: low-Ca pyroxene (Fs_55.3-55.6Wo_2.4-5.0, FeO/MnO = 33-34, N = 2), pigeonite (Fs_31.2Wo_7.1, FeO/MnO = 28), subcalcic augite (Fs_34.8Wo_30.2; Fs_52.8Wo_25.4; FeO/MnO = 30; N = 2), fayalitic olivine in symplectites (Fa_82.1-84.0, FeO/MnO = 41-43, N = 2), plagioclase (An_85.2-89.3Or_1.2-0.3, N = 3). Orthopyroxene cores (Fs_27.8-28.1Wo_3.3-3.5, FeO/MnO = 29-31, N =2), low-Ca pyroxene in rims (Fs_49.9-54.3Wo_2.1-3.4, FeO/MnO = 33, N = 2). Orthopyroxene host (Fs_55.6Wo_1.6, FeO/MnO = 34), augite exsolution lamellae (Fs_26.4-27.6Wo_37.8-42.0, FeO/MnO =30-31, N = 2). Ferroan olivine in matrix (Fa_72.0, FeO/MnO = 48).

Classification: Eucrite (polymict breccia).

Specimens: 20.8 g including one polished thin section at UWB; remainder with Jiachang Yu.