Description
Northwest Africa 7397 (NWA 7397)
Northwest Africa
Purchased: 2012 Jun
Classification: Martian meteorite (Shergottite)
History: Found near Smara, Morocco and purchased by Darryl Pitt and David Gheesling from a dealer in Zagora, Morocco in 2012 June.
Physical characteristics: A 2130 g, partially covered in fusion crust. Interior larger ovoid crystals in a finer grained matrix.
Petrography: (A. Irving and S. Kuehner, UWS) Large oikocrysts (up to 1.5 cm across) of low-Ca pyroxene enclose multiple chadacrysts of olivine and Cr-rich chromite. Relatively equigranular domains between oikocrysts are composed of low-Ca and high-Ca pyroxene (showing very limited compositional zoning), maskleynite and olivine with accessory merrillite, Ti-chromite, pyrrhotite and ilmenite (with associated grains of baddeleyite up to 10 μm across). Olivine contains sparse melt inclusions composed of K-Na-Al-Si-rich glass surrounded by characteristic post-shock radial expansion microfractures.
Geochemistry: Olivine (Fa38.9-40.7; FeO/MnO = 47-54), orthopyroxene (Fs30.3Wo3.3; FeO/MnO = 36), pigeonite (Fs25.1-27.6Wo6.6-10.0; FeO/MnO = 28-33), subcalcic augite (Fs17.0-19.0Wo35.1-35.4; FeO/MnO = 22-25). Bulk trace element composition (G. Chen, UAb): analysis by ICP-MS of clean wire-saw cutting dust gave (in ppm) La 1.66, Ce 4.48, Nd 2.93, Sm 1.13, Eu 0.3, Gd 1.59, Dy 1.95, Yb 1.02, Lu 0.14, Hf 1.66, Th 1.15, Rb 2.89, Sr 33.6.
Classification: Martian (shergottite, poikilitic).
Specimens: A total of 20 g of type material and one large polished thin section are on deposit at UWB. The main mass is held jointly by DPitt and D. Gheesling.
