Northwest Africa 16895 (NWA 16895)

Algeria

Purchased: 2023 Feb

Classification: Martian meteorite (augite basalt)

History: Purchased jointly by Ahmed Salek and Omar Bourki in February 2023 from a meteorite dealer in Ouargla.

Physical characteristics: The single mass has a dark-gray fusion crust and medium grey interior. No alteration is evident.

Petrography: (C. Herd, UAb) Optical and microprobe examination of a polished thin section shows an ophitic texture with compositionally zoned augite intergrown with euhedral plagioclase and ilmenite. Pyroxene grain size is up to 500 μm in longest dimension; plagioclase is typically 100 μm wide and up to 1000 μm long. Ilmenite is typically 100 μm wide and up to 2000 μm long. Areas of mesostasis on the order of 200-400 μm across are present adjacent to ferroan augite; mesostasis minerals include fayalitic olivine, silica, hedenbergite, sulfide, apatite, ilmenite and baddeleyite. Shock features include plagioclase partially converted to diaplectic glass (maskelynite), mosaicism in pyroxene, melt pockets, and thin melt veins. There is no obvious terrestrial alteration.

Geochemistry: (C. Herd and A. Locock, UAb) Data obtained by EPMA of carbon-coated thin section: all pyroxene Fs_40±16Wo_30±7, FeO/MnO=63±7 (n=25), augite cores Fs_25±2Wo_36±5 (n=8), rims adjacent to mesostasis Fs_71±2Wo_21.6±0.8 (n=3), plagioclase Ab_19±3An_80±4Or_0.8±0.4, range An_75.3-86.5 (n=10). Ilmenite contains up to 1.2 wt% Fe₂O₃ by charge balance.

Classification: Martian (augite basalt). Pyroxene compositions directly overlap with those from other augite basalts such as NWA 7635 and NWA 8159, although plagioclase is more anorthitic and no magnetite was found.

Specimens: Type specimen of 24.7 g plus thin section at UAb, main mass with Ahmed Salek and Omar Bourki.