Northwest Africa 8656 (NWA 8656)

Northwest Africa

Purchased: 2014 Jan

Classification: Martian meteorite (Shergottite)

History: Purchased by Darryl Pitt in January and February 2014 from a group of dealers in Mauritania.

Physical characteristics: Exterior mostly wind-ablated with a few remnant patches of dull black fusion crust. Cut interior surfaces are overall greenish-gray with clear, glassy maskelynite evident, and sporadically-distributed dark glass pockets and veinlets.

Petrography: (A. Irving and S. Kuehner, UWS) Diabasic texture. Complexly zoned, prismatically-twinned clinopyroxene (up to 3.5 mm long) and maskelynite laths (up to 1.6 mm long) are the major constitutents along with accessory ilmenite, ulvöspinel, pyrrhotite, merrillite and vesicular glass, plus very minor barite.

Geochemistry: Subcalcic augite (Fs_22.6-26.9Wo_34.3-26.0, FeO/MnO = 28-29, N = 4), ferroan subcalcic augite (Fs_40.7-42.6Wo_29.4-30.6, FeO/MnO = 33-36, N = 2; Fs_58.5Wo_23.6, FeO/MnO = 37), pigeonite (Fs_38.1-45.8Wo_13.8-15.5, FeO/MnO = 31-37, N = 2), ferropigeonite rims (Fs_63.2-65.9Wo_14.0-17.2, FeO/MnO = 35-40, N = 4), plagioclase (maskelynite) (An_50.3-56.6Or_2.9-1.5, N = 4). Oxygen isotopes (K. Ziegler, UNM): analyses of four acid-washed subsamples by laser fluorination gave, respectively, δ¹⁷O 2.772, 2.534, 2.623, 2.480; δ¹⁸O 4.692, 4.276, 4.417, 4.075; Δ¹⁷O 0.295, 0.276, 0.291, 0.328 (all values in per mil).

Classification: Martian (shergottite, diabasic). Likely paired with NWA 8657.

Specimens: 41.3g including two polished thin sections at UWB. The remaining material is held by DPitt.