Meteoritical Bulletin: Entry for Northwest Africa 8154

Writeup from MB 102:

Northwest Africa 8154 (NWA 8154)

(Northwest Africa)

Purchased: 2005

Classification: Iron meteorite (ungrouped)

History: The iron was purchased from Greg Hupé in 2005.

Petrography: Compositionally anomalous iron with an anomalous structure. Weathering is minor. Metal consists of tiny crystals, ~0.2 × 0.05 mm in size. There is no recognizable octahedral structure. A striking feature are the grape-like clusters of graphite ellipsoids ("graphite flowers") with long axes of 1.0 to 0.4 mm. In the ~13 cm² section are two circular troilites (0.8 and 1.0 mm long axis), a schreibersite needle 1.8 × 0.25 mm surrounded by thin kamacite and schreibersite around a cavity, probably originally filled with troilite.

Geochemistry: (J. T. Wasson, UCLA) Composition by INAA (Mean of two analyses): 4.74 mg/g Co, 133 mg/g Ni, 52.7 μg/g Ga, 218 μg/g Ge, 16.2 μg/g As, 24.4 μg/g Ir, and 1.57 μg/g Au. Has high Cu (559 μg/g) and Sb (604 ng/g).

Classification: This iron has no close relatives. The seven ungrouped irons with Ga in the range 46 to 57 μg/g have very different Ni and, with two exceptions, very different Co contents. The 15 ungrouped irons with Co contents in the range 4.52 to 4.94 mg/g all have very different Ni contents and, with the exception of Etosha, very different Ga contents.

Specimens: 113 g at UCLA.

NWA 8154, reclassification

(J.T. Wasson, UCLA): Based on their high contents of Au, As and Sb, NWA 8154, NWA 8155, and their paired siblings (e.g., NWA 8539) are reclassified as ungrouped members of the IAB complex; non-IAB ungrouped irons have lower contents of these elements (especially Sb). They are ungrouped members of the IAB complex because they do not consistently plot in the Ni-Au, As-Au, Co-Au and Ga-Au fields of the IAB main group or of the five IAB subgroups