Northwest Africa 13272 (NWA 13272)

(Northwest Africa)

Purchased: 2019 Dec

Classification: Ungrouped achondrite

History: Found in Mauritania and purchased by Rachid and Jaouad Chaoui in December 2019 from a dealer in Zouerat, Mauritania.

Physical characteristics: The specimen lacks fusion crust and is coated by a shiny brown desert patina. Polished interior surfaces reveal the presence of rare tiny specks of partially altered metal.

Petrography: (A. Irving, UWS and P. Carpenter, WUSL) The specimen has a fine grained, poikilitic igneous texture. Composed predominantly of polysynthetically-twinned, compositionally-zoned pyroxene oikocrysts (with domains of orthopyroxene, pigeonite and subcalcic augite) enclosing chadacrysts of olivine, together with interstitial devitrified silicic glass (pale pink in thin section) plus accessory troilite (some Cr-bearing), Ti-poor chromite and very rare kamacite (some altered to Fe hydroxides). Olivine is preferentially stained pale orange in thin section, and there are some cross-cutting dilation veins filled with comminuted olivine and orthopyroxene. Minor secondary calcite and anhydrite are present.

Geochemistry: Olivine (Fa_24.0-29.5, N = 8), orthopyroxene (Fs_17.9-19.0Wo_2.0-3.8, N = 5), pigeonite (Fs_18.9-19.0Wo_7.2-9.0, N = 2), subcalcic augite (Fs_12.2-12.6Wo_33.7-37.1, N = 4). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed bulk subsamples by laser fluorination gave, respectively, δ¹⁷O 4.120, 4.159, 4.045; δ¹⁸O 5.908, 6.096, 5.717; Δ¹⁷O 1.001, 0.940, 1.026 per mil.

Classification: Achondrite (ungrouped, igneous, with oxygen isotopic affinity to L chondrites).

Specimens: 22.1 g including one polished thin section at UWB; remainder held by Mr. R. Chaoui and Mr. J. Chaoui.