Erg Atouila 001 (EA 001)        22.489944, -4.551744

Gao, Mali

Find: 2020

Classification: Ungrouped achondrite

History: The first piece of 553 g was found by a nomad in August 2020. A second piece of 240 g was found less than a km from the first piece location in September 2020. Both pieces were purchased by Mohamed Aid.

Physical characteristics: Two similar appearing pieces, 553 and 240 g. Exterior is dominated by a pink to light orange color with some dark gray patches with oxidation halos, and some small green patches are scattered throughout. No fusion crust is present. Several dark-colored shock melt veinlets are visible.

Petrography: (M. Spilde, A. Ross, C. Agee, UNM) Microprobe examination and an SEM survey show that albitic alkali feldspar makes up 95% of the modal abundance of this meteorite. Clinopyroxene makes up approximately 3% of the mode, phases with less than 1% modal abundance include olivine, K-feldspar, fluorapatite, troilite, Fe-metal, ilmenite, and oxidized iron. Small poikiolitic inclusions of olivine and lamellae of K-spar are ubiquitous within the host albite. Clinopyroxene occurs primarily in centimeter-sized nodules along with olivine inclusions and other minor phases.

Geochemistry: (A. Ross, UNM) Albite Ab_91.8±0.7Or_6.3±1.1An_1.9±0.4, n=4; K-feldspar Ab_10.2±2.3Or_89.3±2.4An_0.5±0.1, n=3; high-Ca pyroxene Fs_10.0±0.6Wo_44.0±0.4, Fe/Mn=9±1, n=10; olivine Fa_29.3±0.8, Fe/Mn=20±1, n=3; apatite F=3.2 wt%, Cl=0.13 wt%, iron metal Ni=0.26±0.02 wt%, n=3. Oxygen isotopes (K. Ziegler, UNM): 3 acid-washed fragments analyzed by laser fluorination gave δ¹⁸O= 4.789, 4.744, 4.088; δ¹⁷O= 1.437, 1.423, 1.074; Δ¹⁷O= -1.091, -1.082, -1.084 (linearized, all per mil, TFL slope=0.528).

Classification: Ungrouped achondrite (albitite). This meteorite is an albitite with one of the highest modal feldspar contents ever reported in a meteorite – comparable modal abundance to lunar anorthosite meteorites, however its feldspar is an alkali feldspar solid solution. This albitite meteorite is also unlike other Na-feldspar-rich ungrouped achondrites such as GRA 06128/06129 (Shearer et al., 2008) and Almahata Sitta ALMA-A (Bischoff et al., 2014) which have feldspar as plagioclase solid solutions. When plotted on a total alkali-silica (TAS) diagram the bulk composition of this meteorite falls within the trachyte field. Given the relatively coarse grain size present, syenite or olivine syenite are alternative igneous rock names for this meteorite. The oxygen isotope values plot near the acapulcoite-lodranite field although there is no obvious petrologic link between this meteorite and acapulcoites/lodranites. 

Specimens: 20.5 g on deposit at UNM, Mohamed Aid holds the main mass.