Meteoritical Bulletin: Entry for Northwest Africa 5782

Writeup from MB 97:

Northwest Africa 5782

Morocco

Found: Purchased: September 2008

Classification: Achondrite (acapulcoite/lodranite)

History and physical characteristics: Purchased by Blaine Reed at the Denver Mineral Show. Two pieces with a total mass of 130 g were found in a batch of meteorites. The stones experienced moderate terrestrial weathering, but some fusion crust is still visible.

Petrography: (T. Bunch and J. Wittke, NAU; A. Irving, UWS; P. Sipiera, PSF): A polymict breccia of subrounded to subangular clasts (exhibiting some preferred orientation) set in a cataclastic matrix with minor glass and secondary Fe hydroxide veinlets (Fig. 3). The most abundant clasts (45 vol%) are recrystallized acapulcoites with polygonal texture (mean grain size is 0.225 mm). Coarser grained, protogranular to polygonal textured clasts (25 vol%) are various types of lodranites (mean grain size is 0.745). The matrix (30 vol%) contains debris from both types of lithology, and additionally rare, small xenolithic fragments of augite with exsolution lamellae of Ca-poor pyroxene.

Mineral compositions and geochemistry: Acapulcoites Olivine Fa_8.7–13.3(FeO⁄MnO = 17–27); low-Ca pyroxene Fs_9.0–4.1, Wo_2.1–3.0; clinopyroxene Fs_4.8–7.5, Wo_45.7–47.9.Lodranites Olivine Fa_8.6–13.7(FeO⁄MnO = 16–18); low-Ca pyroxene Fs_12.7–13.7, Wo_2.8; clinopyroxene Fs_4.6, Wo_46.7(Al₂O₃ 1.10 wt%, Cr₂O₃ 1.83 wt%, TiO₂ 0.63 wt%). Xenolithic fragment clinopyroxene Fs_19.5, Wo_42.8(FeO⁄MnO = 24); orthopyroxene Fs_40.7Wo_4.1(FeO⁄MnO = 32). Oxygen isotopes (D. Rumble, CIW): acid-washed material analyzed in duplicate by laser fluorination gave, respectively δ¹⁷O = 0.53, 0.66; δ¹⁸O = 3.24, 3.03; Δ¹⁷O = -1.172, -0.936 per mil.

Classification: Achondrite (acapulcoite, anomalous). This specimen is unusual among acapulcoites in that it is a breccia and contains a significant component of lodranite clasts.

Specimens: A total of 20.8 g of material and one polished thin section are on deposit at FMNH in the PSF collection; another thin section is on deposit at NAU. The main mass is held by B. Reed.