Northwest Africa 2727

Morocco or Algeria

Find: June/July 2005

Achondrite (lunar, mare basalt/gabbro breccia)

History: Four stones of 30.6 g, 11.6 g, 64 g, and 85 g were purchased from Moroccan dealers in Erfoud for a consortium of North American collectors in June and July of 2005.

Petrography and Geochemistry: (T. Bunch and J. Wittke, NAU; A. Irving and S. Kuehner, UWS; R. Korotev, WUSL) All stones are very similar and consist of clast-dominated polymict breccias composed of >80 vol% olivine-phyric basalt and gabbroic/diabasic clasts (0.2 cm to several cm across) within a finer breccia matrix. The basalt clasts show a wide range in mineral compositions, but all contain phenocrysts of olivine (Fa_28–99; FeO/MnO = 98.9) and some also have phenocrysts of pyroxferroite or chromite all in a fine-grained matrix consisting of intergrown pigeonite, pyroxferroite, K-Ba feldspar, ilmenite, merrillite, baddeleyite, troilite, silica, and glass. The gabbroic clasts range in texture from coarser-grained (>3 mm) hypidiomorphic gabbro to finer-grained (~1 mm) diabasic clasts. Both types of gabbroic lithologies consist mainly of pigeonite (Fs_23.3–31.3Wo_8.7–11.5; FeO/MnO = 60–69) and subhedral to anhedral olivine (Fa_34.1–41; FeO/MnO = 85– 99) with less abundant augite (Fs_24.1–47.5Wo_24.4–32.1) and partly maskelynite, blocky to tabular plagioclase (An_81–94). The breccia matrix consists mainly of gabbroic debris with fragments of basalt, silica polymorph, symplectites, subparallel intergrowths of anorthite + pyroxferroite + ilmenite and shock-melted material. Bulk compositions: (R. Korotev, WUSL) INAA of 11 subsamples show that they vary considerably in bulk composition, with the most Fe-rich subsample nearly indistinguishable from NWA 3160 basalt. All other subsamples are compositionally equivalent to mixtures of NWA 3160 basalt and the regolith breccia lithology of NWA 773, but with slightly lower concentrations of incompatible elements. Note: Based on petrography, mineral compositions, and bulk compositions, these stones are paired with NWA 3160 and may be paired with NWA 773.

Classification: Achondrite (lunar, mare basalt/gabbro breccia).

Specimens: A 20.2 g type specimen and two polished thin sections are on deposit at NAU. A 0.5 g type specimen is on deposit at WUSL. Oakes, Reed, Boswell, and Turecki hold the main masses.