Northwest Africa 6711 (NWA 6711)

(Northwest Africa)

Purchased: Sept 2009

Classification: HED achondrite (Eucrite)

History: Sample donated to Cascadia by Mr. Fred Olsen.

Physical characteristics: Oriented, shiny, vesicular, fusion-crusted individual with flow lines. Many grains from the interior are exposed at the surface in low spots between flow lines and along sharper edges of the specimen. Small patches of orange staining. Interior has basaltic texture. Specimen traversed by 0.3-0.5 mm wide, fine-grained, pinkish vein.

Petrography: (A. Ruzicka, Cascadia) Four holocrystalline lithologies. Lithology A predominates, subophitic basalt (grains ~0.2-2 mm) rich in heavily fractured pigeonite showing strong mosaic extinction, and twinned plagioclase showing undulatory extinction. Variable but not pervasive clouding by precipitates in pigeonite and plagioclase; augite occurs as lamellae in pigeonite and as discrete grains. Lithology A grades into dominantly granular areas (lithologies C, D) composed of a higher proportion of silica, augite, and ilmenite. Lithology C contains fine-grained silica, lithology D contains silica laths (to 2 mm) with undulatory extinction. The veins (Lithology B) consist of fine-grained (<0.3 mm), granular-textured basalt (relatively clear plagioclase, pigeonite, augite, ilmenite, silica mineral), which cross-cuts lithology A and occurs at the edge of lithology D.

Geochemistry: (A. Ruzicka and M. Hutson, Cascadia) Major minerals have relatively uniform compositions: plagioclase (Ab_9.6±1.0An_90.0±0.9Or_0.5±0.3, n=30), low-Ca pyroxene (Wo_6.2±0.3En_35.6±0.6Fs_58.3±0.6, Fe/Mn=31.7, n=21), augite (Wo_40.4±1.1En_29.7±0.5Fs_29.9±1.0, Fe/Mn = 32.5, n = 13).

Classification: Achondrite (eucrite). Equilibrated, moderately deformed, contains late-stage veining.

Specimens: A total of 20.5 g and 1 thin section are on deposit at Cascadia. Mr. McKenzie holds the main mass.