Mineralogy of Gumbeyka L6 chondrite, a new meteorite in South Urals, Russia

[Marco E. Ciriotti]

Referenza:
▪ Dugushkina, K.A., Sharygin, V.V., Grokhovsky, V.I., Pastukhovich, A.Yu. (2023): Mineralogy of Gumbeyka L6 chondrite, a new meteorite in S.Urals, Russia. Meteoritics & Planetary Science, 58, 6009.

Abstract:
Meteorite Gumbeyka (one sample, 415 g) was found 29 April 2022 near the settlement of Pervomaisky (near the city of Magnitogorsk, Chelyabinskaya oblast’, S.Urals). The meteorite sample has roughly rounded shape. Its surface is totally covered by dark fusion crust; the interior is light colored and contains visible opaque shock veins. It was classified as ordinary chondrite L6S4W1 and approved 11 February 2023 in the Meteoritical Society (Meteoritical Bulletin Database). The Gumbeyka chondrite is fourth meteorite found in the Chelyabinsk territory (after Kunashak, L6, 1949, Chelyabinsk, LL5, 2013, Yaratkulova, H5, 2016). The meteorite contains a fine-grained to coarse recrystallized matrix, rare chondrules, shock veins and fusion crust (Fig. 1). The chondrules (POP, GOP and BO species) are very poorly defined; their sizes vary from 300 to 800 µm. The chondrite matrix consists of olivine (Fa25.04±0.41, n=88), low-Ca pyroxene (Fs21.51±0.39Wo1.59±0.28, n=63), Cr-bearing diopside (En45.7Fs8.0Wo46.3, Cr2O3 – 0.6-1.1 wt.%, n=16), albitic plagioclase (Ab81.9An9.6Or8.5, n=41, size - >50-100 µm), troilite, Fe-Ni-metals, chromite (Crt81.5Spl12.5, n=17), accessory chlorapatite contains (Cl – 5.2, F – 0.55 wt.%, Na2O – 0.5 wt.%, n=8) and merrillite (FeO – up to 1.1 wt.%, n=4). Metal-sulfide assemblages fill intergranular space between the key chondrite minerals. They consist of kamacite (Fe – 92.6±0.5, Ni – 6.8±0.64, Co – 0.62±0.07 wt.%, n=29), taenite (Fe – 69.2±2.4, Ni – 30.4±2.7, Co – 0.31±0.05 wt.%, n=15), troilite (close to FeS) and rarely pentlandite (Fe – 48.1, Ni – 18.0, Co – 0.2, S – 33.6 wt.% n=3). Troilite and Fe-Ni-metals sometimes contain rounded grains of olivine and low-Ca pyroxene. In addition to chondrules chromite-plagioclase assemblages (10–300 µm) occur in the recrystallized chondrite matrix. The opaque shock veins is up to 1 mm and contain metal-sulfide blebs (troilite + taenite + kamacite) in the fine-grained low-Ca pyroxene + glass matrix. The thickness of fusion crust is up to 100 µm. It is highly vesicular and zoned in texture: the outmost zone (up to 50 µm) is cryptocrystalline aggregate of new-formed skeletal and zoned crystals of olivine (core – Fa11.5-19.4, rim – Fa22.3-41.2) + magnetite + glass; the inner zone (in the contact with unaffected chondrite) is represented by larger skeletal crystals of new-formed olivine + glass + minor magnetite. Both zones contain rounded relics of primary olivine and chromite and new-formed Ni-rich metal-sulfide globules (up to 10 µm, mainly martensite/taenite + troilite ± pentlandite). Martensite from these blebs bears 10.4-21.0 wt.% Ni (n=9), taenite – 31-8-36.6 wt.% Ni (n=2). Weathering in the chondrite is fixed by presence of thin Fe-hydroxide rim around some metal and troilite grains. Goethite and hibbingite (Cl - up to 16.6 wt.%) were identified among Fe-hydroxides.