Northwest Africa 8287 (NWA 8287)

(Northwest Africa)

Purchased: 2013

Classification: Primitive achondrite (Acapulcoite)

History: Purchased by Brahim Tahiri from a Moroccan meteorite hunter and sent to his partner Sean Tutorow for classification, 2013.

Physical characteristics: Single stone, weathered exterior with dark brown patina. Saw cut reveals abundant metal and sulfide set in a fine-grained silicate groundmass.

Petrography: (C. Agee, UNM) Microprobe examination of a polished mount. Silicates: ~95% orthopyroxene, ~3% plagioclase, ~2% diopside. Silicate grains 50-200 μm, polygonal texture with 120° triple-junction grain boundaries. Numerous kamacite and troilite domains up to 1000 μm which constitute ~25% of this meteorite. Metal/sulfide veinlets throughout, many on grain boundaries.

Geochemistry: (C. Agee and H. Miley, UNM) Orthopyroxene Fs_10.6±0.1Wo_1.7±0.3, Fe/Mn=14±1, n=7; diopside Fs_4.9±0.1Wo_44.0±0.3, Fe/Mn=10±1, Cr₂O₃=1.06±0.02 wt%, n=6; plagioclase Ab_73.5±0.7An_23.6±0.6Or_2.9±0.2, n=8; kamacite Ni=10.8 wt%. Oxygen isotopes (K. Ziegler, UNM) Oxygen isotope values of 4 acid-washed aliquots of bulk sample, 1.5, 1.2, 1.5, 1.0 mg, gave δ¹⁷O = 0.121, 0.236, 0.356, 0.500, δ¹⁸O = 2.330, 2.585, 2.944, 3.200, Δ¹⁷O = -1.109, -1.129, -1.198, -1.190 (linearized, all permil).

Classification: Primitive achondrite (Acapulcoite) based on oxygen isotopes which are coincident with the acapulcoite/lodranite field, distinguished from lodranite type by the modal abundance of plagioclase and the relatively small silicate grain size. This acapulcoite is a highly equilibrated orthopyroxenite and is unique in that olivine is absent.

Specimens: 20.03 g including a probe mount on deposit at UNM, Sean Tutorow holds the main mass.