Northwest Africa 8276 (NWA 8276)

(Northwest Africa)

Purchased: 2013

Classification: Ordinary chondrite (L3.00)

History: Adam Bates identified this meteorite from images he received as a possible pairing to NWA 7731, even though they came from a different Moroccan meteorite dealer. Both pieces were then purchased within a few weeks of each other in October 2013. The meteorite dealer claimed both pieces originated in Mauritania.

Physical characteristics: A single stone, broken into two pieces (394 and 395 g) that fit together, >90% black fusion crust with polygonal cracks, light desert weathering, saw-cut reveals many densely packed chondrules of variable size.

Petrography: (C. Agee, UNM) Microprobe examination of a polished mount shows numerous unequilibrated chondrules, apparent mean diameter 496±296 μm (n=122), many with porphyritic, igneous-zoned olivines and pyroxenes, most with glass or mesostasis. Abundant fine-grained matrix throughout.

Geochemistry: (C. Agee, N. Muttik, H. Miley, UNM) All chondrule olivine Fa_12.2±9.3, range Fa_0.7-26.3, n=67; ferroan olivine Fa_17.8±5.9, Fe/Mn=47±11, Cr₂O₃=0.42±0.10 wt%, range Cr₂O₃=0.29-0.66 wt%, n=44; low-Ca pyroxene Fs_13.0±8.3Wo_1.9±2.7, Fe/Mn=26±14, n=41. Augite and aluminous diopside present. Mesostasis or glass (n=25) in 10 ferroan porphyritic chondrules Na₂O=6.27±3.20 wt%, K₂O=0.51±0.40 wt%, Na/Al=1.14, K/Al=0.95 (mean values, CI normalized). Fine-grained matrix S=1.7±1.6 wt%, n=17. Oxygen isotopes (Karen Ziegler, UNM) Oxygen isotope values of 3 acid-washed aliquots of bulk sample, 1.1, 1.3, 1.4 mg, gave δ¹⁷O = 3.589, 2.734, 2.839, δ¹⁸O = 5.511, 4.643, 4.201, Δ¹⁷O = 0.679, 0.282, 0.621 (linearized, all permil).

Classification: Ordinary chondrite (L3.00), type 3.00 based on ferroan olivine mean Cr₂O₃ content and sigma from Grossman and Brearley (2005) and by the presence of S-rich matrix. Comparison of Cr₂O₃ in ferroan olivines done using the same microprobe and conditions at UNM gave: NWA 7731 (L3.00) Cr₂O₃=0.43±0.11 wt%, n=98; Semarkona (LL3.00) Cr₂O₃=0.41±0.09 wt%, n=45. Oxygen isotopes appear to be relatively heterogeneous and fall within the same range of δ¹⁷O and δ¹⁸O as NWA 7731 (Ziegler et al., 2014). Apparent mean chondrule size similar to NWA 7731 (Agee et al., 2013). Weathering grade (W1). Possibly paired with NWA 7731.

Specimens: 20.1 g including a probe mount on deposit at UNM, Adam Bates, Mendy Ouzillou, and Darryl Pitt hold the main mass.