Northwest Africa 14146 (NWA 14146)

(Northwest Africa)

Purchased: 2020 Dec

Classification: Eucrite-mmict-an

History: Purchased by Shun-Chung Yang and Juan Chen in December 2020 from dealer in Tindouf, Algeria.

Petrography: (A. Irving, UWS and P. Carpenter, WUSL) Fresh monomict breccia composed of ophitic-textured diabasic eucrite clasts (mean grainsize ~1 mm) plus related crystalline debris. The major phases are unexsolved pigeonite (compositionally-zoned to ferroan subcalcic augite rims) and calcic plagioclase accompanied by accessory augite, fayalite, silica polymorph and ilmenite. One ferropigeonite grain with exsolution lamellae of subcalcic augite was observed in the studied thin section.

Geochemistry: Pigeonite cores (Fs_33.4-38.2Wo_6.1-7.8, FeO/MnO = 26-28, N = 3), subcalcic augite rims (Fs_53.0-68.2Wo_21.9-22.7, FeO/MnO = 32-34, N = 3), augite (Fs_29.0Wo_45.1, FeO/MnO = 34), ferropigeonite host (Fs_70.2Wo_7.5, FeO/MnO = 36), subcalcic augite exsolution lamella (Fs_46.4Wo_25.2, FeO/MnO = 31), fayalite (Fa_85.4-86.2, FeO/MnO = 42-43, N = 2), plagioclase (An_88.7-92.9Or_0.4-0.2, N = 4).

Classification: Eucrite (monomict diabasic breccia, anomalous). Despite being a breccia, this specimen shares many attributes with unbrecciated eucrite NWA 7035, especially the notable rarity of exsolution in the strongly-zoned clinopyroxenes coupled with the prominent presence of accessory fayalite. Such pyroxene zoning (reminiscent of that observed in shergottites) is very rare in eucrites and thus is an anomalous feature.

Specimens: 28.6 g including one polished thin section at UWB; remainder with Mr. S.-C. Yang and Mr. J. Chen.