Northwest Africa 13087 (NWA 13087)

(Northwest Africa)

Purchased: March 2018

Classification: HED achondrite (Eucrite, polymict)

History: The main mass was purchased in March 2018 in Arfoud, Morocco, from the Bouhayek brothers by Société Astronomique de France (SAF) member Pascal Maugein, who was given the type specimen in November 2018.

Physical characteristics: Main mass fully covered by black, regmaglypted fusion crust

Petrography: (E. Jacquet, B. Doisneau, MNHNP). Breccia with ophitic/subophitic and more blocky textured pyroxene/plagioclase clasts, along with mineral clasts of same. Pyroxene is frequently zoned in the former, and otherwise often presents augite lamellae, sometimes folded. The clasts may also contain silica and ilmenite-troilite-silica-pyroxene symplectites. Opaque clasts,whether with cryptocrystalline (plagioclase-pyroxene, <10 µm) or glassy (eucritic major element composition) groundmasses, are likely impact melts (with olivine a common minor mineral). Ferroan hedenbergite-fayalite-silica (or K-feldspar) clasts such as those described by Barrat et al. (2012) in howardites occur. One curious 0.6 mm anorthite clast with round <60 µm nodules of equant <10 µm euhedral pyroxene, silica, plagioclase crystals.

Geochemistry: Mineral compositions and geochemistry: Pyroxene Fe/Mn=34±4. Plagioclase is An_85.2±6.6Ab_13.4±6.0Or_1±0.9 (An_72.2-97.5Ab_1.1-19.2Or_0.1-2.5, N=19). One coarse chromite (Al₂O₃ = 17-21 wt%, Cr₂O₃ = 43-46 wt%; N=3). Olivine Fa_79.6±20.4 (Fa_51.9-90.0, N=4).

Classification: Eucrite (polymict). Clasts correspond to eucrite mineralogy but are variable in texture, mineral chemistry and metamorphism, hence the polymict nature of the breccia. Pyroxene Fe/Mn is consistent with HED.

Specimens: 320 g (main mass, plus one thin section, with P. Maugein); 30 g (type specimen, plus one thin section)