Northwest Africa 16272 (NWA 16272)

(Northwest Africa)

Purchased: 2023

Classification: Martian (vesicular basalt)

History: Purchased by a northwest African meteorite dealer in 2022. Purchased by Jay Piatek in 2023.

Physical characteristics: Single stone 202.2 g. This sample appears to be a highly vesicular volcanic rock (appearance resembling terrestrial and lunar vesiculated basaltic lavas) with abundant large vesicles and vugs, many in the 2-5 mm size range, but some are as large as 1 cm. The exterior surface around the vesicles is brown and smooth with a red/orange tint. Some patches of unweathered black fusion crust are visible. Scattered green pyroxene grains are also exposed on the surface of this meteorite.

Petrography: (A. Ross. and C. Agee UNM) Microprobe examination and reflected light microscopy of two polished mounts shows an igneous rock with plumose or spinifex texture primarily of fine-grained pyroxene and plagioclase laths. Scattered pyroxene phenocrysts up to a few mm in size are present throughout. Pyroxenes show igneous differentiation trends from magnesian low Ca-pyroxene to intermediate composition pigeonite to ferro-pigeonite to ferro-subcalcic augite. Rare olivine was detected and one large ~5 mm plagioclase phenocryst was observed in the probe mounts. None of plagioclase appears to be maskelynitized. Many of the phenocrysts appear to have resorption rims. Accessory phases detected include magnetite, aluminous chromite, Fe-sulfide, and trace fine-grained low-Ni metal.

Geochemistry: Electron microprobe (A. Ross and M. Spilde, UNM) Phenocrystic pyroxene Fs_31.1±9.5Wo_5.2±3.4, Fe/Mn=33±3, n=7, range Fs21.1-Fs_49.4; groundmass pyroxene Fs_48.2±14.1Wo_16.8±7.6, Fe/Mn=35±4, n=23, range Fs29.4-Fs_76.4; groundmass plagioclase An_61.8±2.1Ab_37.6±2.0Or_0.5±0.1, n=8; plagioclase phenocryst An12.6Ab84.4Or3.0; olivine Fa 29.1±4.5, Fe/Mn=40±5, n=3. HR-ICP-MS (J.-A. Barrat, Université de Bretagne Occidentale) La 2.39, Ce 5.69, Pr 0.825, Nd 3.93, Sm 1.20, Eu 0.519, Gd 1.56, Tb 0.287, Dy 1.94, Ho 0.425, Er 1.25, Tm 0.190, Yb 1.24, Lu 0.182, Hf 1.07, Pb 1.01, Th 0.368, U 0.100, Ni 69.9, Co 10.6, Mn 3115, V 70.1, Cr 2667, K 1167, Rb 3.00, Sr 88.6 (all ppm). ICP-AES (J.-A. Barrat, IUEM) SiO₂ 50.1, TiO₂ 0.56, Al2O3 11.0, FeO 18.1, MnO 0.44, MgO 8.37, CaO 9.33, Na₂O 1.78, K₂O 0.12, P₂O₅ 0.23 (all wt%). Oxygen isotopes (K. Ziegler, UNM): 6 acid-washed bulk meteorite fragments analyzed by laser fluorination gave δ¹⁸O= 6.328, 6.477, 6.596, 6.417, 6.878, 6.274; δ¹⁷O= 3.943, 3.966, 4.102, 3.973, 4.222, 3.912; Δ¹⁷O= 0.602, 0.546, 0.619, 0.585, 0.590, 0.600; (linearized, all per mil, TFL slope=0.528).

Classification: This meteorite is an unbrecciated vesicular basalt. It has oxygen isotope values that plot exactly within the array of martian polymict breccia NWA 7034. The mean value for this meteorite is Δ¹⁷O=0.59±0.02 permil (n=6), compared to NWA 7034 mean value Δ¹⁷O=0.58±0.05 permil (n=13). It also possesses pyroxenes with Fe/Mn that are similar to NWA 7034 and other martian meteorites. The pyroxenes of this meteorite show an igneous differentiation trend similar to that seen in some NWA 7034 lithologies. Plagioclase compositions are slightly more anorthitic than those in NWA 7034 but are within the range observed in shergottites. Trace element abundances and ratios are similar to martian basaltic meteorites, for example Ni/Co and Ni/Mg. The REE pattern of this bulk meteorite is similar to those of enriched shergottites (i.e. Shergotty), but with a positive europium anomaly. Stable isotope and major and trace element values for this meteorite strongly suggest a martian origin and source similar to some lithologies within NWA 7034.

Specimens: 20 g on deposit at UNM, Jay Piatek holds the main mass.