Noyon        43°13’11.8"N, 102°39’56.7"E

Omnogovi, Mongolia

Find: 2018 Aug 25

Classification: Ordinary chondrite (LL(L)3)

History: Meteorite (one sample - 745.47 g) was found 25 August 2018 by the UrFU - IAG-MAS meteorite expedition-2018 in southern Gobi (Pastukhovich A.Yu., Kolunin R.N., Larionov M.Yu., Muraviev L.A., Petrova E.V., Yakovlev G.A., Naasa Ochir) in 45 km East of Noyon, the Ömnögovi aimag (province), Mongolia.

Physical characteristics: Size is 10x5x5 cm. The meteorite has roughly rounded shape. Exterior of the stone is desert polished. The surface and interior of the meteorite are gray to dark brown in color due to Fe-hydroxides. Fusion crust is locally present.

Petrography: Classification (Victor V. Sharygin, SIGM and UrFU). The meteorite shows a chondritic texture. The amount of chondrules and their fragments is more than 90 vol.%. Chondrules are well delineated. Average chondrule apparent diameter 1008±442 μm (n=20). Chondrule apparent diameter up to 2 mm. Chondrules are represented by BO, PO, POP, RP and CC textural types. Chondrules mainly consist of olivine, low-Ca-pyroxene and glassy-like (cryptocrystalline) matrix, diopside, ±chromite and blebs of troilite and FeNi-metal. In all chondrules the mesostasis does not contain fresh glass, and is a finely devitrified aggregate of clinopyroxene and feldspar or nepheline-like phase. BSE images for some POP and PO chondrules show strong zonation for olivine and sometimes low-Ca-pyroxene, which can form skeletal/dendritic crystals. RP chondrules may contain SiO₂ polymorph. All these indicate the high rate of quenching. Olivine and low-Ca-pyroxene are main minerals in fine-grained matrix; plagioclase was not observed. All petrographic features indicate a petrological type of 3 for the meteorite. Undulatory extinction and irregular fractures in olivine reveal a shock stage of S2. Majority of grains of FeNi-metal (30-400 µm) are mainly represented by kamacite, taenite and tetrataenite; but individual grains of kamacite also occur. Weathering products (hematite, goethite and other Fe-Ni-hydroxides, gypsum) are locally abundant and mainly occur as in situ partial alteration of FeNi-metal and troilite, and fill microfractures in all minerals (weathering grade – W2-3). The appearance of Ni-rich pyrrhotite and smythite maybe related to troilite alteration. Clinopyroxene, chromite, ilmenite, merrillite and chlorapatite (100-300 µm) occur locally in the matrix. Merrillite was also as rounded inclusions (up to 5 µm) in FeNi-metal and troilite. The abundances of FeNi-metal and sulfides are 3.5 and 4.3 vol.%, respectively (by point counting over 670 mm², Pastukhovich A.Yu.).

Geochemistry: Mineral composition and Geochemistry: EDS-WDS analyses (V.V. Sharygin, SIGM and UrFU). The primary chondrite paragenesis includes olivine, low-Ca-pyroxene, Cr-bearing clinopyroxene (Cr₂O₃ - up to 2.6 wt.%), plagioclase, spinel-supergroup minerals, ilmenite, chlorapatite, merrillite, FeNi-metal, SiO₂ polymorph, troilite and maybe pyrrhotite. The main minerals drastically vary in composition. The averaged olivine is Fa_21.47±7.10 (N=100). The olivine grains from matrix have homogeneous composition – Fa_26.78±0.95 (N=30), max – Fa_28.83. However zoned olivine crystals in chondrules show a wider range: Fa_19.31±7.50 (n=70). The same situation exists with low-Ca-pyroxene: average - Fs_13.51±7.98Wo_2.04±2.45 (N=63); matrix – Fs_{18.53±6.5.13}Wo_2.04±2.55 (N=19), max – Fs_24.6; chondrules (N=44): average - Fs_11.38±8.09Wo_2.05±2.43 (N=63); core (min) – Fs_2.87, rim (max) – Fs_36.85. The maximal values of Fa and Fs in olivine and low-Ca pyroxene outline the LL group, whereas high standard deviations for these minerals in chondrules may indicate subtype 3.0-3.3. Plagioclase is rare and found only in matrix of some POP chondrules: anorthite An_76.6Ab_21.7Or_1.7 (N=4) occurs in the POP chondrules with zoned olivine, whereas albite Ab_89.6An_5.1Or_5.4 (N=8) is common of other POP chondrules. Spinel-supergroup minerals are represented by chromite Crt_89.6Spl_4.5 (N=10, common in matrix and chondrules) and zoned Cr-rich spinel (in some chondrules) with composition from Spl_58.6Crt_39.9 (core) to Spl_82.0Crt_16.1 (rim). Ilmenite is Ilm_87.3 (N=7). Composition of metals (in wt.%): kamacite (N=25) – Fe 93.62±0.85, Ni – 5.63±0.86, Co – 0.82±0.13; taenite (N=10) – Fe 60.76, Ni 38.93, Co 0.22; tetrataenite (N=12) – Fe 49.52, Ni 50.33, Co 0.16. Nepheline-normative glassy-like aggregate (or nepheline ?) in a POP chondrule with zoned olivine has following composition (in wt.%, N=12): SiO₂ 48.58, Al₂O₃ 28.42, TiO₂ 1.18, Cr₂O₃ 0.62, FeO 2.52, MgO 0.69, CaO 0.57, Na₂O 14.97, K₂O 2.28.

Classification: Ordinary chondrite. LL(L)3, S2, W2-3. In variations of Fa in olivine and Fs in low-Ca pyroxene in chondrules it seems to be related to 3.0-3.3 subtype. Chondrule size points to LL, but the metal content points to L, hence the LL(L) designation.

Specimens: 636 g sample – IAG-MAS; 102.72 g sample – UrFU; 6.75 g cut-off and thin section – SIGM.