Northwest Africa 10401 (NWA 10401)

(Northwest Africa)

Purchased: 2015

Classification: Lunar meteorite

History: Purchased by Steve Arnold from a dealer in Ouarzarete, Morocco in 2015.

Physical characteristics: Two stones totaling 354 g (218 and 136 g). A sawed piece from one of the stones reveals a very fine-grained, light-gray groundmass that is cross-cut by several shock melt veins. Larger white clasts within the groundmass are present.

Petrography: A. Hilton (CoW), J. Gross (Rut). This meteorite is an anorthositic troctolite with a granulitic texture. It contains plagioclase (59-65%), olivine (23-26%), orthopyroxene, and clinopyroxene (pyx total: 12-15%) as the main silicate phases. Accessory grains of spinel were observed. Microprobe examination shows two particularly large clasts (diameters 3.1-4.7 mm) surrounded by a light-gray, fine-grained matrix and many smaller clasts (0.1-0.8 mm). The sample is crosscut by an abundant number of thin shock melt veins. The veins show compositional variation as well as partial assimilation of surrounding grains in some areas and are homogeneous in others. Plagioclase grains (0.2-0.8 mm) are angular and sub-euhedral in shape, while mafic clasts rich in olivine and pyroxene (0.1-0.3 mm) are composed of small (<10-35 μm) anhedral olivine and pyroxene grains. Single anhedral grains of olivine and pyroxene are also present in the sample, including some that exhibit pyroxene exsolution lamellae. The matrix is composed of small, granular, anhedral grains of olivine and pyroxene that appear to outline grain boundaries of plagioclase fragments.

Geochemistry: J. Gross (Rut) and A. Hilton (CoW). Olivine Fa_18.6±2 (N=180), Fe/Mn=88.1±8.3; Orthopyroxene: Fs_15.5±2Wo_3.1±0.6En_81.4±4.7, Fe/Mn=49.3±6 (N=48); Clinopyroxene: Fs_9.0±1.4Wo_41.3±7.9En _49.7±6.8, Fe/Mn=37.2±4 (N = 20); Plagioclase An_96.6±0.3Ab_2.9±0.6Or_0.1±0.05 (N=254). The shock melt vein (defocused electron beam as proxy for bulk composition) has an average composition of: Na₂O = 0.27±0.1, MgO = 9.7±0.3, SiO₂ = 45±0.8, Al₂O₃ = 26±0.6, P₂O₅ = 0.02±0.04, K₂O = 0.01±0.01, CaO = 15±6, TiO₂ = 0.12±0.03, MnO = 0.06±0.04, FeO = 4.1±0.3, BaO = 0.01±0.03 Cr₂O₃ = 0.13±0.03, NiO = 0.02±0.02, N=74. Bulk composition (R. Korotev, WUSL): INAA on a 99 mg fragment gave FeO 6.1 wt%, Na₂O 0.24 wt%; Sc 8.7, Cr 1300, Ni 124, La 0.65, Sm 0.38, Eu 0.55, Yb 0.37, Th 0.07, all in ppm.

Classification: Lunar (anorthositic troctolitic breccia with granulitic texture)

Specimens: 20 g at TCU, thick section probe mount at RU; Peter Scherff holds the main mass.