Northwest Africa 4964 (NWA 4964)

(Northwest Africa)

Purchased: 2007

Classification: Carbonaceous chondrite (CK3)

Petrography: (K. Metzler, IfP) Chondrules and CAIs are embedded into a fine-grained brownish matrix. The matrix consists mostly of equilibrated Fe-rich olivine grains, interspersed with magnetite nodules. The mean apparent chondrule diameter is 1.13±0.69 mm (0.47-3.83 mm; n=31). Chondrules with igneous rims occur and CAIs up to 1.3 cm are observed.

Geochemistry: The composition of matrix olivine is Fa_33.8±0.6 (Fa_32-35; n=16), while olivine in chondrule cores retained its original Mg-rich composition. Random olivine measurements revealed Fa_30.7±5.9 (Fa_13-35; n=22). Low-Ca pyroxene (En_95-98Fs_1-4 Wo₁; n=5) mainly occurs in chondrules. Most pyroxene grains outside of chondrules are Ca-rich (En_36-42Fs_7-14 Wo_49-51; n=7). The compositional range of feldspar (n=4) is An_21-31. Magnetite is the most abundant opaque phase and shows significant concentrations of elements other than Fe (n=3): MgO 0.8-0.9 wt%; Al₂O₃ 3.2-3.6 wt%; TiO₂ 0.8-0.9 wt%; Cr₂O₃ 2.6-3.7 wt%; NiO 0.3-0.4 wt%.

Classification: CK chondrite based on mineral chemistry. Petrologic type 3 based on the chemical variation of olivine and pyroxene.