Néma 001        16.650°N, 7.247°W

Hodh ech Chargui, Mauritania

Find: 2021 Sep 08

Classification: Ungrouped achondrite

History: Found in the Mauritanian Sahara.

Physical characteristics: A single 68.1 g stone mostly covered with thin glassy fusion crust. One face is devoid of fusion crust and has a pale orange color due to terrestrial weathering. A few pale orange fragments from the same stones were also found in the immediate vicinity, amounting to 7.7 g. The cut face show white and greenish crystals several mm in size

Petrography: (J. Gattacceca, CEREGE) Fractured unbrecciated coarse igneous rock with 5 mm grain size and subophitic texture. Main mineral are albitic plagioclase, orthopyroxene and Ca-pyroxene. Approximate modal abundances (from the polished section, likely not representative of the bulk stone in view of the grain size) are orthopyroxene 57 vol%, plagioclase 30 vol%, olivine 3 vol%. Accessory minerals: ilmenite (to 100 μm), chromite (to 60 μm, often associated with Fe-Mg-Ti spinels), kamacite (to 100 μm rounded grains and as small µm-sized blebs in silicates), troilite. Kamacite and troilite are often associated. One 50 × 10 μm euhedral K-feldspar grain was observed, set in plagioclase.

Geochemistry: Orthopyroxene Fs_19.5±0.1Wo_1.9±0.3, FeO/MnO = 14.9±0.7 (n=5). Ca-pyroxene Fs_7.1±0.2Wo_46.2±0.3, Cr₂O₃ 1.3±0.1 wt%, FeO/MnO = 11.4±0.7 (n=3). Plagioclase An_7.8±1.1Ab_86.4±0.6Or_5.8±0.5 (n=5). Sanidine An_1.5Ab_42.9Or_55.6 (n=1). Olivine Fa23.3±0.3, FeO/MnO = 24.8±1.4 (n=21). Chromite Cr# = 0.90 (n=2). Oxygen isotopic composition (J. Gattacceca, C. Sonzogni, CEREGE) from analysis of one acid-washed 1.9 mg aliquot of a powdered 7 mg bulk sample is δ¹⁷O=0.624‰, δ¹⁸O=3.257‰ , Δ¹⁷O=-1.070‰ (slope 0.52, analytical uncertainties 0.08‰, 0.12‰, 0.03‰ respectively). Magnetic susceptibility measured on the 68.1 g main mass is log χ (× 10^-9 m³/kg) = 3.03.

Classification: Achondrite, ungrouped. Ungrouped based on mineral chemistry and texture. Oxygen isotopic composition suggests a possible genetic link with acapulcoites and lodranites.

Specimens: Type specimen at CEREGE. The main mass is with Isselmou Kaye (Nouakchott, Mauritania); 5 g of fragments with Labenne.