Northwest Africa 12688 (NWA 12688)

(Northwest Africa)

Purchased: 20 Apr 2017

Classification: Ureilite

History: The meteorite was purchased from Mr. Aziz Habibi in Agadir (Morocco) in April 20, 2017.

Physical characteristics: Single stone of 140 g total weight has angular shape and dark brownish surface. Fusion crust is not preserved.

Petrography: (Lorenz C. A., Vernad) The rock has coarse grained (0.5-1 cm) metamorphic texture with triple junctions of mineral grains and composes of clino and orthopyroxene and olivine. Clinopyroxene contains rare large inclusions of olivine, orthopyroxene and glass. Accessory metal Fe and sulfide form thin linear veinlets along the silicate grains borders and are mostly replaced by Fe-hydroxides. Rare rounded inclusions of intergrown metal Fe, troilite and shreibersite occur within the silicate grains. Olivine has undulatory optical extinction, irregular and planar fractures. Some olivine grains are rich in fine-grained vermicular aggregates of troilite associated with the veinlets. Graphite was not found.

Geochemistry: Mineral compositions and geochemistry: (N. N. Kononkova, EMP, Vernad) Pyroxene: Fs_10.6±0.2Wo_4.7±0.3 (in wt%: Al₂O₃ = 1.23±0.19; Cr₂O₃ = 1.09±0.07; Fe/Mn = 12.0±1.6; N = 18); Ca-pyroxene Fs_6.4±0.3Wo_38.5±2.1 (in wt%: Al₂O₃ = 2.59±1.66; Cr₂O₃ = 1.29±0.17; TiO₂ = 0.4 ± 0.2; Fe/Mn = 12.0±1.6; N = 7); Glass, in wt%: SiO₂ = 60.0; Al₂O₃ = 23.5; Na₂O = 4.81; CaO = 8.78; FeO = 2.41; MgO = 2.13; metal Fe (in wt%): Ni = 1.7; P = 1.2; Si < 0.04; Ni/Co=7.7; troilite Cr = 2.0 wt%. Mineral norms from bulk analysis (T. G. Kuzmina, XRF, Vernad), in wt% Ol 54.2; Hyp 23.3; Di 18.9; Fsp 3.4; Oxygen isotopes (I. A. Franchi, OU, laser fluorination): δ¹⁷O = 3.13 δ¹⁸O = 7.78 Δ¹⁷O = -0.916; δ¹⁷O = 3.095 δ¹⁸O = 7.791 Δ¹⁷O = -0.956.

Classification: Based on a texture, mineral chemistry and oxygen isotopic composition the meteorite is classified as ureilite.

Specimens: Cutted piece and three sub-samples of 27.7 g in total, and thin polished section are on deposit in Vernad.