Northwest Africa 1862 (NWA 1862)

(Northwest Africa)

Purchased: 2019

Classification: Ureilite

History: The meteorite was exported from Morocco for purchase by N. Gessler.

Physical characteristics: A subround single stone, 40% covered by relict, grainy, non-crazed, brown, lightly stained fusion crust, the other faces showing the texture of the individual crystals. Cut face shows "medium dark gray N4" overall appearance with laminar crystals <2 mm.

Petrography: The meteorite is a typical ureilite in terms of both texture and mode: mostly olivine, roughly 20% pigeonite, with a large component of interstitial opaque matter (presumably graphitic carbon). Olivine is anhedral-subequant and typically 1-2 mm, up to 3 mm across; pigeonite up to 2 mm. Olivine orientations show moderate (at least) lineation.

Geochemistry: Olivine core compositions (6 analyses) cluster tightly at Fa_17.8, with FeO/MnO (wt ratio) = 42.9 and minor element contents of 0.66 wt% Cr₂O₃, 0.39 wt% MnO, 0.32 wt% CaO. Two practically identical pigeonite analyses are Fs_15.4Wo_7.5, with minor element contents of (wt%) Cr₂O₃ 1.1, Al₂O₃ 0.62, MnO 0.43.

Classification: Ureilite

Specimens: Main mass with Gessler, type specimen, including multiple thin sections, at UCLA.