Northwest Africa 033 (NWA 033)

Bechar, Algeria

Find: 1999

Classification: Carbonaceous chondrite (CL4)

Revised classification and description.

Physical characteristics: : Carbonaceous chondrite with high chondrule abundance (72 vol%) and low amount of fine-grained matrix (21 vol%). Composed of irregularly formed Type-I chondrules, few Type-II chondrules, refractory inclusions (CAIs, AOAs), inter-chondrule metal and sulfide grains and matrix. Contains high amounts of (partly terrestrially oxidized) metal (magnetic susceptibility log χ (× 10^-9 m³/kg) = 4.69). Mean chondrule size: 455±349 µm (65-2070 µm; n=274). Fragments of chondrules and refractory inclusions occur, but macroscopically this sample is unbrecciated. It is of shock stage C-S2 and has a weathering grade of W2.

Petrography: Olivine is equilibrated with a mean value of Fa_13.5±0.6. The mean composition of low-Ca pyroxene is Fs_7.9±3.1Wo_0.9±0.2. Bulk oxygen isotopic composition: δ¹⁷O = -3.911±0.164; δ¹⁸O = 0.102±0.228; Δ¹⁷O = -3.964±0.046 per mil. Bulk Ti and Cr isotopic composition: ε⁵⁰Ti ± 2σ = 2.35±0.05; ε⁵⁴Cr ± 2σ = 0.64±0.12.

Geochemistry: Due to its characteristically low amount of matrix, highly depleted concentrations of volatile elements, high magnetic susceptibility, low Fa values of equilibrated olivine, and unique position in the ε⁵⁰Ti-ε⁵⁴Cr diagram, this sample was reclassified as a CL4 chondrite by Metzler et al. (2021).