Northwest Africa 8402 (NWA 8402)

(Northwest Africa)

Purchased: 2014

Classification: Mesosiderite (group A3)

History: Purchased from S. Haddany in March 2014

Physical characteristics: Single stone with irregular dark gray-brown exterior. Saw cut reveals numerous spherical metal domains >1 mm, but also abundant fine-grained metal distributed uniformly throughout. Silicate clasts >1 mm, some fragmental, others rounded or texturally equilibrated. Abundant fine-grained silicate groundmass.

Petrography: (C. Agee, UNM) Microprobe examination of a polished mount shows pyroxene making up approximately 75% of the silicate portion of this meteorite, ~25% plagioclase, ~5% silica. Pyroxene grains in section up to 1 mm, some poikiloblastic; plagioclase up to 500 μm, but also finer-grained intergranular; numerous intersertal silica laths up to 200 μm in length and ~10 μm thick; no olivine detected. Metal makes up approximately 40% of this meteorite and is primarily segregated into domains >1 mm, although there are scattered smaller (~10 μm) grains throughout the silicate domains. No brecciation observed. Minor oxidation of metal and a few weathering veinlets.

Geochemistry: (C. Agee and N. Muttik, UNM) Low-Ca pyroxene Fs_37.4±0.3Wo_3.2±0.1, Fe/Mn=22±1, n=3; high-Ca pyroxene Fs_18.6±0.1Wo_39.9±0.0, Fe/Mn=18±0, n=2; plagioclase An_90.2±1.8Ab_9.2±1.8Or_0.6±0.1, n=6; kamacite Fe=93.7±0.1, Ni=6.2±0.0 (wt%), n=2; taenite Fe=62.0±5.8, Ni=37.9±5.8 (wt%), n=2.

Classification: Mesosiderite-A3. Relatively high abundance of plagioclase and silica consistent with group A. Segregated metal, presence of some texturally and chemically equilibrated silicates, and absence of brecciation consistent with type 3.

Specimens: 29.7 g including a probe mount on deposit at UNM, DPitt holds the main mass.