Northwest Africa 8614 (NWA 8614)

(Northwest Africa)

Purchased: 2002 Feb

Classification: Primitive achondrite (Winonaite)

History: Purchased February 2002 at the Gem and Mineral show in Tucson by Edwin Thompson from a Moroccan trader. Donated to Cascadia on May 24, 2002.

Physical characteristics: Small rounded specimen, has fusion coat on two flat faces. Elsewhere a dark colored exterior with abundant metal and a few chondrules visible.

Petrography: (K. Farley, A. Ruzicka, K. Armstrong, Cascadia) Dominantly granoblastic texture with over a dozen indistinct chondrules visible in two small thin sections. Apparent chondrule diameter is 0.48±0.27 mm (N=13). Mineralogy determined by EDS mapping suggests the following mode (area%): 44.3 low-Ca pyroxene, 12.3 olivine, 10.1 feldspar, 4.6 high-Ca pyroxene, 6.9 troilite, 10.6 kamacite, 1.4 taenite, 0.2 schreibersite, 0.4 chromite, 0.7 phosphate, 0.2 daubreelite, 8.4 weathering product. Roughly 40% of the metal has been weathered.

Geochemistry: (K. Farley and A. Ruzicka, Cascadia) Olivine (Fa _6.5±0.5, Fe/Mn = 13±2 at., N=18), low-Ca pyroxene (Fs _7.8±0.3Wo _1.4±0.2En _90.9±0.5, Fe/Mn = 8.8±0.8 at., N=28), high-Ca pyroxene (Fs_3.5±0.5Wo_45.5±0.3En _50.9±0.5, N=19), feldspar (Ab_79.9±2.0Or_6.4±1.2An_13.6±1.2, N=23). Oxygen isotope compositions (acid-treated samples to remove weathering product, K. Ziegler, UNM) of six subsamples spread along a mass fractionation line with average δ¹⁷O = 1.416±0.166, δ¹⁸O = 3.543±0.297, Δ¹⁷O = -0.455±0.046 (linearized values).

Classification: Winonaite. Oxygen Δ¹⁷O values lie on an extension of the Clayton and Mayeda (1996) winonaite line and are distinct from acapulcoites and lodranites. Mineralogy and phase compositions are consistent with winonaites. The sample is unusual among winonaites in containing many identifiable chondrules.

Specimens: Cascadia holds the entire sample which includes 21.6 g, 3 polished thin sections, and 2 butts.