Northwest Africa 13984 (NWA 13984)

(Northwest Africa)

Purchased: 2018 Oct

Classification: Carbonaceous chondrite (C3, ungrouped)

History: Purchased by Ziyao Wang in October 2018 from a dealer in Guelmim, Morocco.

Petrography: (A. Irving, UWS and P. Carpenter, WUSL; L. Garvie, ASU) Well-formed small chondrules (apparent diameter 290 ± 150 µm, N = 20) are set in a fine grained matrix (black in thin section). No CAI were observed; however, rare isolated grains of highly aluminous enstatite and diopside are present. Accessory phases identified by electron microprobe analysis are kamacite, tetrataenite (with Ni>Fe), Fe sulfide and a Cr-Fe metal or oxide phase (with a small V peak, but without Mg and Al). X-ray diffraction analysis found olivine (with a wide range of in Fa contents), enstatite, magnetite, possible maghemite, calcite, dolomite, pyrrhotite and pentlandite, but no phyllosilicates.

Geochemistry: Olivine (Fa_28.6±21.7, range Fa_0.6-80.0, N = 20; Cr₂O₃ in ferroan olivine 0.23-0.38 wt.%, N = 16), enstatite (Fs_1.5Wo_1.0), aluminous enstatite (Fs_1.1Wo_3.2, Al₂O₃ = 15.7 wt.%, TiO₂ = 0.5 wt.%), pigeonite (Fs_7.3Wo_7.9), diopside (Fs_1.3±0.7Wo_43.2±1.7, range Fs_0.7-2.1Wo_41.6-44.9, Al₂O₃ 2.2-13.9 wt.%, N = 3). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed subsamples by laser fluorination gave, respectively, δ¹⁷O -8.610, -5.847, -8.477; δ¹⁸O -4.172, -1.364, -4.177; Δ¹⁷O -6.407, -5.127, -6.272 per mil (all data linearized).

Classification: Carbonaceous chondrite (C3-ungrouped). Type 3 based on the absence of phyllosilicates. Ungrouped designation based on the oxygen isotopic composition that plot sbelow the CCAM trend, near results for ungrouped C3 chondrite NWA 13671.

Specimens: 8.5 g including one polished thin section at UWB; remainder with WangZ.