Erg Atouila 003 (EA 003)        ~22.490°N, ~4.552°W

Gao, Mali

Purchased: 2022 Jan

Classification: Ungrouped primitive achondrite

History: Five stones were found by an anonymous prospector in Mali in August 2021 in close proximity to the first specimen of the Erg Atouila 001 ungrouped achondrite. Specific distances of the find sites relative to the Erg Atouila stone are 40, 100, 150, 700, and 900 m. The stones were purchased from the finder by Said Yousfi in January 2022.

Physical characteristics: The five stones (1152, 84.8, 72.9, 71.4, and 52.6 g: total 1442 g) are all visually similar, but different from the more pale colored Erg Atouila 001 material. Exterior surfaces are light brown with black patches, whereas broken interior surfaces are more beige in color and polycrystalline with a vitreous luster. No fusion crust is apparent.

Petrography: (A. Irving, UWS and P. Carpenter, WUSL) All five stones have triple grain junction metamorphic texture (mean grainsize ~250 µm). All are composed predominantly of albite (~50 vol.%) with subordinate low-Ca pyroxene, olivine and diopside plus accessory ilmenite (containing rare baddeleyite inclusions), chromite (with variable Ti content), merrillite, apatite (halogen-bearing), troilite, and ~5 vol% of metal (kamacite and taenite). Most apatite contains only F, whereas some contains minor Cl as well.

Geochemistry: Electron microprobe analyses were conducted on polished pieces of each of the five stones. Albite (Ab_90.4-91.7An_4.1-3.2Or_4.7-5.8, N = 6), olivine (Fa_23.6-27.3, FeO/MnO = 22-25, N = 7), low-Ca pyroxene (Fs_20.2-22.7Wo_1.4-1.8, FeO/MnO = 14-15, N = 5), diopside (Fs_7.1-8.2Wo_45.6-44.1, FeO/MnO = 9-12, N = 7). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed subsamples by laser fluorination gave, respectively, δ¹⁷O=2.420, 2.439, 1.864; δ¹⁸O=6.372, 6.313, 5.334; Δ¹⁷O=-0.944, -0.894, -0.952 ‰ (all data linearized, TFL slope = 0.528).

Classification: Primitive achondrite, ungrouped. This material is more feldspar-rich than acapulcoites and contains plagioclase that is much more sodic. Although found in close proximity to the Erg Atouila 001 stones and possessing some similarities to them, this material differs significantly in terms of its texture and mineralogy. In comparison to Erg Atouila 001 (see Meteoritical Bulletin entry and Irving A. et. al., 2022. Lunar Planet. Sci. LIII, #2059), the mineral assemblage has about half as much albitic plagioclase, and contains low-Ca pyroxene and more Ni-rich metal (both of which have not been reported in Erg Atouila 001). The mafic mineral compositions are also somewhat more magnesian than those in Erg Atouila 001 (e.g., olivine is more magnesian by up to 6 mole% Fa).

Specimens: 20.4 g including two polished mounts at UWB; remainder with Mr. S. Yousfi.