Northwest Africa 13943 (NWA 13943)

Algeria

Find: 2020

Classification: Carbonaceous chondrite (CK4/5)

History: Purchased by Bo Zhang in April 2021 from an anonymous dealer in NWA.

Physical characteristics: A single cone-shaped stone with a complete fusion crust and visible contraction cracks.

Petrography: Petrographic examination of a thick section shows this meteorite is composed of about 78 vol.% of olivine, 9 vol.% of pyroxene, 3 vol.% of plagioclase, and abundant Cr-bearing magnetite ( 9 vol.%) with minor Ca,Mg carbonates which mainly occur along the cracks. Most olivine grains are free of NiO, but a few with NiO up to 0.22 wt.%. Relatively well-formed chondrules are mainly PO and POP with a size range of 0.21-1.45 mm. Matrix consists of fine-grained olivine, pyroxene, plagioclase, magnetite and minor Ca,Mg carbonates. Both albitic (Ab_74±10.7, n=22) and calcic feldspar (An_82.6±12.8, n=10) are present. The size of plagioclase ranges from a few µm to 45 µm with a peak at 16.9±6.7 µm (n=206). Metallic Fe-Ni are essentially absent and sulfides are rare.

Geochemistry: Both Na-rich plagioclase (An_23.5±11.1Ab_74±10.7,n=22 ) and Ca-rich plagioclase(An_82.6±12.8Ab_17.4±12.8?n=10) are present, olivine (Fa_30.3±1.6, FeO/MnO=77-110, n=59), low-Ca pyroxene (Fs_27±6.3Wo_1.9±3.8, FeO/MnO=52-76, n=79), Ca-rich pyroxene (Fs_16.4±4.5Wo_29.9±1.8, FeO/MnO=37.4, n=3), Cr-bearing magnetite (Cr₂O₃ 2.4-3.2wt%)).

Classification: The texture and mineral composition are consistent with CK4/5 chondrites.