Northwest Africa 13998 (NWA 13998)

(Northwest Africa)

Purchased: 2009 Jun

Classification: Carbonaceous chondrite (CK5)

History: Purchased from a Moroccan mineral dealer at the meteorite show in Ensisheim, France

Petrography: (K. Metzler, IfP) Chondrules, chondrule fragments, and CAIs are embedded in a recrystallized dark gray matrix, which is interspersed with magnetite, troilite, and pentlandite grains. The range of apparent sizes of most chondrules is 300-1300 µm (up to 2.5 mm).

Geochemistry: Mineral compositions and geochemistry: The mean composition of randomly chosen olivine is Fa_27.9±0.8 (Fa_26.5-29.0; n=13) with mean Ni concentration of 0.3 wt%. Random measurements of pyroxene grains revealed Fs_8.0±0.6Wo_46.4±0.8 (Fs_7.3-9.1Wo_45.1-47.8); n=12. The mean composition of feldspar is An_39.5±4.7Or_3.1±0.7 (An_35.9-47.7Or_2.1-3.9); n=5. Magnetite is the most abundant opaque phase and shows significant concentrations of elements other than Fe: MgO 0.2-0.5 wt%; Al₂O₃ 2.7-3.0 wt%; TiO₂ 0.5-0.7 wt%; Cr₂O₃ 6.0-6.2 wt%; NiO 0.1-0.3 wt% (n=3).

Classification: CK chondrite based on mineral chemistry. Petrologic type 5 based on the visibility of chondrules, but equilibrated state of olivine and pyroxene.