Northwest Africa 7475 (NWA 7475)

(Northwest Africa)

Purchased: 2012 Sep

Classification: Martian meteorite (basaltic breccia)

History: Purportedly recovered at the find site for NWA 7034 near Bir Anzarane, southern Morocco in 2012 and purchased by Luc Labenne from a Moroccan dealer in September 2012.

Physical characteristics: Black, partly fusion-crusted stone (80.2 g) consisting of black and white angular clasts plus dark spheroidal objects in a black matrix.

Petrography: (A. Wittmann, R. Korotev, P. Carpenter and B. Jolliff, WUSL; A. Irving and S. Kuehner, UWS; D. Moser and I. Barker, UWO) Complex breccia composed of angular to rounded mineral clasts, lithic fragments, and spheroidal objects (up to 5 mm in diameter), in a fine grained, dark matrix rich in magnetite. Minerals present include a variety of pyroxenes (orthopyroxene, pigeonite, subcalcic augite, augite and hedenbergite), sodic to intermediate plagioclase, Ti-bearing magnetite, chlorapatite, ilmenite, pyrite, maghemite, hematite, alkali feldspar, anorthoclase, rutile, and monazite. Many clasts exhibit 50 μm-thick mantles of concentrically aligned, accreted debris >5 μm in size. Clast types range from monomineralic feldspar and pyroxene fragments <1 mm size to polymineralic clasts that are aphanitic-glassy (some with igneous contacts to the host matrix). Crystallized melt clasts have textures ranging from sub-ophitic to ophitic, granular and poikilitic with grain sizes of plagioclase and pyroxene <0.5 mm. Some spheroidal objects are composed of glass or fine grained quench assemblages, whereas others consist of concentrically zoned grain aggregates with radial shrinkage fractures.

Geochemistry: (A. Wittmann, WUSL; S. Kuehner, UWS) Orthopyroxene (Fs_19-48Wo_1-5, FeO/MnO = 27-45; n = 38), pigeonite (Fs_25-44Wo_5-19, FeO/MnO = 23-45; n = 9), subcalcic augite (Fs_17-30Wo_29-41, FeO/MnO = 17-41; n = 18), augite (Fs_9-18Wo_45-49, FeO/MnO = 18-61; n = 5), hedenbergite (Fs_37-44Wo_43-48, FeO/MnO = 40-65; n = 2), plagioclase (An_10-58Or_1.9-6.8; n = 35), alkali feldspar (An_0.8-13Or_53-90Cn1-6; n = 10), anorthoclase (An_22-26Or_10-20; n = 2), magnetite (0.3-16.1 wt.% Cr₂O₃, 0.25-0.38 wt.% NiO; n = 15), ilmenite (3-5 wt.% MgO; n = 8), pyrite (up to 2.8 wt.% Ni; n = 7).

Classification: Martian (basaltic breccia). This specimen is essentially identical in texture and mineralogy to NWA 7034 and NWA 7533, and is evidently paired with those distinctive stones.

Specimens: 16.1 g of type material and one polished thin section are on deposit at UWB. The remaining material is held by Labenne.