Northwest Africa 8671 (NWA 8671)

(Northwest Africa)

Purchased: 2014 May

Classification: HED achondrite (Eucrite)

History: Purchased in Morocco by Ali and Mohammed Hmani in May 2014 and said to have been found near Foum El Hisn, Morocco.

Physical characteristics: Single stone (164.2 g) lacking fusion crust. The fresh interior is relatively coarse grained and composed of subequal amounts of dark gray pyroxene and beige plagioclase.

Petrography: (A. Irving and S. Kuehner, UWS) This is a very unusual specimen consisting of dispersed, angular domains of coarse, polygranular, birefringent, calcic plagioclase separated by regions of recystallized clinopyroxene. The plagioclase domains have irregular geometric shapes with re-entrant angles, and exhibit marginal reaction zones against clinopyroxene composed of ferropigeonite plus fayalitic olivine. The main regions of clinopyroxene contain numerous irregularly distributed, small patches with two distinctly different compositions: one low in Ca and the other higher in Ca. No high-Ca augite was found. Accessory minerals are silica polymorph, Al-bearing chromite and troilite.

Geochemistry: Low-Ca pyroxene (Fs_47.9-49.1Wo_5.5-4.4, FeO/MnO = 28-29, N = 3), pigeonite (Fs_36.3-34.7Wo_10.8-7.6, FeO/MnO = 26-28, N = 3), ferropigeonite rims (Fs_52.5-55.5Wo_21.6-16.5, FeO/MnO = 30, N = 2), fayalite (Fa_82.2-82.9, FeO/MnO = 39), plagioclase (An_91.4-93.0Or_0.1, N = 2). Oxygen isotopes (K. Ziegler, UNM): acid-washed subsamples analyzed by laser fluorination gave δ¹⁷O = 1.736, 1.642, 1.694; δ¹⁸O = 3.847, 3.688, 3.776; Δ¹⁷O = -0.295, -0.305, -0.300 per mil

Classification: Eucrite (unbrecciated, partially melted). The overall texture and reaction zones on plagioclase aggregates are unique among eucrites, and indicate that this specimen underwent a partial melting event subsequent to its igneous crystallization.

Specimens: 20.1 g including one polished thin section at UWB. The remainder is held by Hmani Inc.