Northwest Africa 12522 (NWA 12522)

Algeria

Purchased: 2018

Classification: Martian meteorite (Shergottite)

History: Two complete stones purchased by Jay Piatek from Abdelhadi Aithiba in Morocco, November 2018. The two stones were found together in the Algerian Desert near Ouargla, reportedly as part of a find of several stones with total mass of ~9 kg.

Physical characteristics: The two stones, 1071 g and 57 g, are both covered in fusion crust. The larger stone has smooth, wind-polished fusion crust on about 10% of its surface. The rest of the stone appears to have been buried in the sand and not wind-polished, but has instead extremely fresh and shiny black fusion crust. Flow lines and roll-over edges are present in this fusion crust. The smaller stone may have been completely buried in the sand as it has only very fresh-appearing fusion crust and one small chipped area which exposes the interior. Broken surfaces on both stones reveal shiny maskelynite patches that are visible with the naked eye. A piece of the fusion crust was imaged using BSE, showing it to be highly vesicular with average thickness ~450 μm.

Petrography: (C. Agee, UNM) The two major phases in this meteorite are clinopyroxene and maskelynite. Ubiquitous minor phases are merrillite, apatite, titanomagnetite, ilmenite, and troilite. The clinopyroxene has a modal abundance of approximately 60%, with significant core to rim zoning observed in backscatter electron images, indicating an igneous crystallization trend with Mg-rich pigeonite cores, mantled by augite, and rimmed with ferropigeonite. Clinopyroxene average grain sizes are approximately 300-500 μm. Maskelynite has modal abundances of approximately 30%, and most grains are thin and elongate with maximum length ~1 mm. Merrillite is about five times more abundant than apatite in this sample.

Geochemistry: (C. Agee, UNM) Clinopyroxene Fs_43.8±19.1Wo_21.8±6.7, core to rim range Fs_30.2Wo_13.6 (Mg-pigeonite) - Fs_22.6Wo_38.7 (augite) - Fs_78.4Wo_4.6 (ferropigeonite), Fe/Mn=33±5, n=48; maskelynite An_50.7±2.7Ab_47.6±2.2Or_1.7±0.6, n=17; fusion crust (20 μm defocused electron beam) SiO₂=45.4±1.0, TiO₂=1.2±0.3, Al₂O₃=7.3±2.1, Cr₂O₃=0.10±0.10, MgO=7.0±3.9, FeO=21.0±1.4, MnO=0.52±0.04, CaO=9.9±0.0, Na₂O=1.5±0.5 (all wt%), n=11; merrillite CaO=46.4±0.4, P₂O₅=44.4±0.3, FeO=5.2±0.4, MgO=0.7±0.3, Na₂O=1.5±0.1, (all wt%), n=19; apatite CaO=53.3±0.3, P₂O₅=40.5±0.1, FeO=1.3±0.1, MgO=0.2±0.2, Na₂O=0.12±0.04, SiO₂=0.87±0.06, F=1.2±0.1, Cl=2.3±0.2, (all wt%), n=4; titanomagnetite FeO=54.0±3.0, Fe₂O₃=15.1±6.4, TiO₂=26.6±5.0, Al₂O₃=1.8±1.8±0.4, MnO=0.57±0.06, (all wt%), n=27; ilmenite FeO=49.4±0.7, TiO₂=48.5±1.4, MnO=0.77±0.03, (all wt%), n=4. Oxygen isotopes (K. Ziegler, UNM): acid-washed fragment analyzed by laser fluorination gave δ¹⁸O= 4.426; δ¹⁷O= 2.567; Δ¹⁷O= 0.230 (linearized, per mil, TFL slope=0.528).

Classification: Geochemically evolved pyroxene-phyric basalt, clinopyroxene compositional zoning trends are similar to QUE 94201, maskelynite composition is similar to Los Angeles.

Specimens: 21 g including a probe mount on deposit at UNM, Jay Piatek holds the main mass.