Exclusivo ERG ATOUILA 001 Desagrupado Meteorito de acondrita - 0.36 g - (1)

Erg Atouila 001 (EA 001) 22.489944, -4.551744

Gao, Mali

Find: 2020

Classification: Ungrouped achondrite

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 Ab91.8±0.7Or6.3±1.1An1.9±0.4, n=4; K-feldspar Ab10.2±2.3Or89.3±2.4An0.5±0.1, n=3; high-Ca pyroxene Fs10.0±0.6Wo44.0±0.4, Fe/Mn=9±1, n=10; olivine Fa29.3±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.