Northwest Africa 13777 (NWA 13777)

(Northwest Africa)

Purchased: 2021

Classification: CK6-an

History: The meteorite was purchased from a group of meteorites hunters in Nouadhibou, Mauritania, in early 2021.

Physical characteristics: Dark-grayish rock without fusion crust.

Petrography: The meteorite displays a dark-gray interior and is largely composed of fine-grained recrystallized matrix dominated by ferroan, Ni-bearing olivine. Chondrules are only rarely encountered. Less abundant phases include low-Ca pyroxene, intermediate plagioclase, and FeS. Cr-rich magnetite is abundant; metal was not detected. The meteorite contains shock melt veins.

Geochemistry: olivine: Fa_24.9±0.4, FeO/MnO= 85±8, NiO=0.48±0.05 wt%, n=14; low-Ca pyroxene: Fs_22.9±0.2Wo_0.8±0.1, FeO/MnO= 54±3, n=8; plagioclase: Ab_60.6±6.6An_35.9±7.6Or_3.5±1.0, n=5; Cr₂O₃ in magnetite is about 3.3 wt%.

Classification: Carbonaceous chondrite (CK6, anomalous). Anomalous designation from the unusually Fe-poor olivine. Out of 368 equilibrated CK chondrites with available olivine analyses (data from Meteoritical Bulletin Database as of March 2021), only six have similar or lower Fa content: Graves Nunataks 98102 (CK4 Fa₂₄); NWA 5580 (CK4 Fa_25.2); NWA 7615 (CK6 Fa_24.7) and NWA 11207 (CK5 Fa_24.9), NWA 11299 (CK5 Fa_24.6), and NWA 11338 (CK4 Fa_24.6-25.0).