Northwest Africa 16682 (NWA 16682)

Mali

Purchased: 2022 Jan

Classification: HED achondrite (Eucrite, unbrecciated)

History: Purchased jointly by Ahmed Salek and Omar Bourki from a nomad in Sebkhat el Maleh in January 2022.

Petrography: (C. Herd, UAb) Optical and electron backscattered investigation of a polished thin section reveals an ophitic to subophitic texture of pyroxene and plagioclase. Pyroxene and plagioclase are 0.5-2 mm in longest dimension. Nearly all low-Ca pyroxene contains high-Ca exsolution lamellae. Accessory minerals include silica polymorph, ilmenite and chromite. Areas of plagioclase consist of sub-micron domains, and grain boundaries with pyroxene show contact melting of pyroxene. Pyroxene is recrystallized and shows low pleochroism. Melt veins and pockets are pervasive. Only very minor iron staining is present along grain boundaries.

Geochemistry: (C. Herd, A. Locock, and D. Poon-Matsune, UAb) Data obtained by EMP examination of carbon-coated thin section: low-Ca pyroxene: Fs_61.6±0.8Wo_2.8±0.7 (Fe/Mn = 30.4±0.8; n=13); high-Ca pyroxene lamellae: range Fs₅₁Wo_{15 -} Fs₃₅Wo₃₄ (Fe/Mn ~ 30); plagioclase: An_89±2Or_0.3±0.2 (n=16). Chromite contains 3-18 wt% TiO₂.

Classification: HED achondrite, unbrecciated. Equilibrated non-cumulate basaltic eucrite.

Specimens: Type specimen of 25.2 g at UAb, main mass with Ahmed Salek and Omar Bourki.