22274 - Top Rare NWA 10023 Anomalous Plessitic Pallasite Meteorite PMG-an 1.128 g

Northwest Africa 10023 (NWA 10023)

(Northwest Africa)

Purchased: 2014

Classification: Pallasite (Main group, anomalous)

History: Purchased from Rachid Chaoui in December 2014, reportedly found near the Moroccan/Algerian border.

Physical characteristics: One piece. Polished saw cuts show angular, orange-brown-green, translucent olivine; some grains up to ~2 cm in size. Metal makes up approximately 30-40% of this meteorite. There is only minor oxidation present.

Petrography: (C. Agee, UNM) The etched surface of this pallasite shows approximately 98% of the metal consisting of very fine-grained (<1 μm) plessite, whereas kamacite occurs only as a thin mantling around olivine crystals. Olivine is the only silicate phase present. Accessory schreibersite, chromite, Ni-rich sulfide, and Ca-Mg phosphates were observed.

Geochemistry: (C. Agee and N. Muttik, UNM) Olivine Fa_12.7±0.6, Fe/Mn=47±3, n=8; plessite Fe=84.0±1.2, Ni=15.4±0.7, Co=0.55±0.08 (all wt%), n=4; kamacite Fe=93.1±3.0, Ni=5.9±0.2, Co=0.88±0.13 (all wt%), n=4; schreibersite Fe=58.8±5.1, Ni=27.9±2.1, Co=0.22±0.00, P=14.8±0.08 (all wt%), n=2; Fe-Ni sulfide Fe=49.9, Ni=16.1, Co=0.24, S=33.9 (all wt%), n=1. Likely farringtonite Mg₃(PO₄)₂ and stanfieldite Ca₃Mg₃(PO₄)₄ detected in EDS. Oxygen isotopes (K. Ziegler, UNM): 7 acid-washed fragments analyzed by laser fluorination gave, respectively δ¹⁸O= 3.667, 3.554, 3.167, 3.143,3.608, 3.887, 3.368; δ¹⁷O= 1.693, 1.630, 1.440, 1.458, 1.668, 1.753, 1.572; Δ¹⁷O= -0.243, -0.247, -0.232, -0.202, -0.237, -0.299, -0.206 (linearized, all per mil), mean value δ¹⁸O=3.485±0.273, δ¹⁷O=1.602±0.118, Δ¹⁷O=-0.238±.032 (TFL slope=0.528).

Classification: Pallasite, PMG-an. An unusually high amount of the metal is in the form of plessite. Oxygen isotopes indicate an affinity to the pallasite main group.

Specimens: 20.3 g including a probe mount on deposit at UNM, DPitt holds the main mass.