Northwest Africa 11115 (NWA 11115)

Morocco

Find: 2016

Classification: Martian meteorite (Shergottite)

History: Purchased by Terry Boudreaux.

Physical characteristics: Completely covered with smooth fusion crust; rounded shape with no regmaglypts.

Petrography: (M. Melwani Daswani, UChi) SEM/EDS analyses of a polished epoxy mount revealed basalt with large (up to 2 mm) olivine phenocrysts. Shock stage is high: all plagioclase has been converted to maskelynite, and some pyroxene + maskelynite melt pockets are visible. Fractures and voids are abundant throughout the sample, especially across olivine grains and along olivine grain boundaries, where spaces are filled by abundant secondary calcite.

Geochemistry: Mineral compositions and geochemistry: SEM/EDS mineral mode (UChicago and FMNH): ~ 9 % olivine, ~ 32 % pyroxene, ~ 56 % maskelynite. Remaining minerals are spinel (mainly chromite), phosphate, silica, and secondary calcite infilling cracks. Mineral composition: olivine Fa_51.5±14.2, Fe/Mn=53.2±6.3 (N=56) shows strong zonation from core (Fa_29.2) to rim (Fa_54.7) in large grains and also compositional differences between large grains and smaller grains. Pyroxenes: low-Ca Wo_4.4±0.2Fs_25.8±0.3, Fe/Mn=28.8±2.8 (N=8); pigeonite Wo_11.1±2.9Fs_34.5±6.2, Fe/Mn=30.4±2.8 (N=24); augite Wo_24±5.5Fs_28.4±3.4, Fe/Mn=28.5±3.2 (N=2); maskelynite An_49.3±4.4Ab_48.7±3.9Or_2.0±0.6 (N=74). LA-ICP-MS whole rock chemistry: four measurements of one glass bead revealed very low K/Th (K/Th=746.6±69.7) compared to other martian meteorites, but bulk Fe/Mn=44.7±0.6 and Rb/K=0.0057±0.0016 are consistent with other shergottites. Oxygen isotopes, laser fluorination (R. Greenwood, OU): analyses on 2 aliquots gave values of δ¹⁷O=2.829, 2.817, δ¹⁸O=4.821, 4.770, Δ¹⁷O=0.322, 0.337 (given), Δ¹⁷O=0.302, 0.316 (linearized, all permil).

Classification: Achondrite (Martian basalt), basaltic shergottite with olivine phenocrysts. Large olivine grains show core to rim iron-enrichment trend.

Specimens: 34.2g at FMNH.