Northwest Africa 12445 (NWA 12445)

(Northwest Africa)

Purchased: 2018 Aug

Classification: HED achondrite (Eucrite, anomalous)

History: A total of 21 similar stones (total 797 g) were recovered ~70 m apart at a location in Algeria, and were purchased by Mbark Arjdal in August 2018 from an Algerian dealer.

Petrography: (A. Irving and S. Kuehner, UWS) Breccia composed of some lithic eucrite clasts plus a lot of related, angular crystalline debris in a finer grained matrix. Lithic clasts have microgabbroic to subophitic textures. Minerals are exsolved pigeonite (pale orange in thin section), anorthite (exhibiting undulose extinction), silica polymorph, fayalite, ilmenite, troilite and minor Ni-free metal.

Geochemistry: Low-Ca pyroxene host (Fs_67.7±1.6Wo_3.1±1.3, range Fs_66.0-70.6Wo_1.7-5.3, FeO/MnO = 29-31, N = 6; Fs_59.7Wo_2.4, FeO/MnO = 28), high-Ca pyroxene exsolution lamellae (Fs_32.1±2.0Wo_42.8±0.7, range 29.2-34.4Wo_42.0-43.7, FeO/MnO = 30-33, N = 6; Fs_24.7-25.9Wo_44.5-42.9, FeO/MnO = 29-30, N = 2), fayalitic olivine (Fa_73.8±6.5, range Fa_69.3-78.4, FeO/MnO = 46, N = 2), anorthite (An_91.9-93.3Or_0.6-0.3, N = 2).

Classification: Eucrite (breccia, anomalous). The predominance of highly ferroan low-Ca and high-Ca pyroxenes in this specimen is an anomalous feature; these now-exsolved highly ferroan pigeonites are reminiscent of similar pyroxenes in anomalous ferroan eucrite NWA 11729.

Specimens: 38.2 g including one polished thin section at UWB; remainder with Mr. M. Arjdal.