Ngare Sero        2°37.845’S, 35°53.353’E

Arusha, Tanzania

Find: 9 Sept 2017

Classification: Ordinary chondrite (L5)

History: Meteorite (2233 g) was found 9 Sept 2017 by Kirill Vlasov and Artyom Akshintsev while returning to the field camp from Ngare Sero village. The date of fall is unknown.

Physical characteristics: Total mass is 2233 g. Meteorite has roughly rounded shape. The surface and interior is light with dark brown crust up to 2 mm due to desert weathering. Cracks (up to 0.1 mm in thickness) occur in external part of meteorite.

Petrography: Classified by P. Yu. Plechov, FMMR. Petrographic observation of a polished section shows clearly delineated chondrules in a coarse recrystallized matrix. Chondrules are relatively rare and their sizes vary from 500 to 1200 µm. They have quenched or porphyritic texture, rarely cryptocrystalline, and consist of Ol+Pl, Opx+Pl, Ol+Opx+Cpx+Pl or Opx+Cpx+Pl. Olivine, low-Ca-pyroxene and plagioclase are main minerals in matrix. Plagioclase grains are larger than 50 µm. This indicates a petrological type of 5 for the meteorite. Olivine has no undulatory extinction, as well as the absence of opaque shock veins and melt pockets indicates a shock stage of S1. Fresh FeNi metals and troilite (up to 200 µm) occurs in recrystallized matrix. Some taenite-kamacite aggregates have thin rims of Fe-hydroxide. Kamacite-taenite-troilite aggregates (up to 20 µm) are observed in some cryptocrystalline chondrules. Weathering products (goethite, "hydrogoethite") occur as veins and in situ alteration of FeNi-metals and troilite near meteorite surface. Olivine, pyroxene, chromite and troilite are fresh and not weathered (weathering grade – W1). Clinopyroxene, chromite, chlorapatite and merrillite (up to 200 µm) occur locally in the matrix.

Geochemistry: EDS-WDS analyses (P. Yu. Plechov, FMMR). The primary chondrite paragenesis includes olivine Fa_25.24±0.6 (N=28), orthopyroxene Fs_22.8±0.53Wo_1.66±0.35 (N=19), plagioclase Ab_80.2An_10.6Or_6.3 (N=11), Cr-bearing clinopyroxene En_47.8Fs_8.1Wo_43.9 (N=6), chromite Crt_76.6±4.5Spl_10.5±1.3 (N=14), chlorapatite and merrillite. Chlorapatite contains Cl – 5.26 wt.% (N=5). Merrillite has wide range in FeO content (0.54-2.92 wt.%, N=13). Composition of kamacite (in wt.%, N=8): Fe 92.3±0.67, Ni – 6.3±0.7, Co – 1.45±0.17. Troilite is close to ideal FeS. Rare goethite contains 4.2-6.8 wt.% NiO and up to 1.12 wt.% CoO.

Classification: Ordinary chondrite. L5, S1, W1

Specimens: 2127 g – Kirill Vlasov; 106 g cut-offs and thin section – FMMR.