Akwanga, updated information and classification.

History: "The Akwanga meteorite fell on July 2, 1959, 2 miles from the village of Gaji, Akwanga Division of the Plateau Province, Nigeria. It weighs approximately 3 kg and made a hole about 18 inches deep at the point of impact. The noise of descent and impact was heard up to a distance of 3 miles.” [Geophysical Abstracts 189, April-June 1962, and taken from Macleod, W.N. and Jefford, G. (1961) The Akwanga meteorite. Records of the Geological Survey of Nigeria. for 1959, p 15-20.]

Physical characteristics: Fusion crusted stone with a few broad regmaglypts. Description based on a 5 × 7 cm slice. Sawn surface shows rounded light-colored clasts to 3 cm in a dark matrix. Even distribution of <1-mm-sized metal grains. Few thin shock veins. One chondrule to 3 mm, though most <0.8 mm diameter. Fusion crust to 0.5 mm thick.

Petrography: (L. Garvie, ASU) Thin section dominated by chondrules, most with moderately diffuse chondrule-matrix boundary, and metal grains with holly-leaf-shaped outlines in a fine-grained recrystallized matrix. Recognizable chondrules dominated by PO and BO types. Metal dominated by single-crystal kamacite some bearing diffuse Neumann bands. Less common rounded <0.4 mm metal grains with Ni-rich rims of tetrataenite and cores of kamacite. Native Cu common (15 grains recognized in one thin section) as small, <50 μm, grains associated with a composite grain composed of troilite, Ni-rich metal, and dark-etch plessite. Troilite grains typically <0.5 mm and single crystal lacking shock lamellae. Two petrographic types of chromite: anhedral grains to 0.2 mm, and regions to 0.4 mm composed of fine-grained (to 30 μm) chromite in feldspathic matrix. Feldspar abundant and typically in regions <25 μm across. A few scattered Ca-Cl and Ca-Na-Mg phosphates to 0.5 mm found.

Geochemistry: (L. Garvie, ASU) Olivine Fa_18.8±0.4, Fe/Mn=36.1±1.9 wt%, n=15. Low-Ca pyroxene Fs_16.4±0.2Wo_1.3±0.1, Fe/Mn=22.6±1.3 wt%, n=13. High-Ca pyroxene Fs_5.9±0.3Wo_46.3±0.2, n=2, and Fs_8.5Wo_39.8, n=1.

Classification: H5, S2, W0

Specimens: 42.5 g slice and one thin section at ASU.