Sierra Gorda 012        22°30.198’S, 69°08.703’W

Antofagasta, Chile

Find: 2018 Apr 6

Classification: Ordinary chondrite (H4)

History: The meteorite was found on 6 April 2018 by Ilya Chaplygin during an expedition organized by Timur Kryachko.

Physical characteristics: The meteorite is covered by a thin film of weathered material. Fusion crust has been totally sand-blasted. The interior of the meteorite is gray to dark brown whereas the surface is dark brown.

Petrography: (Pavel Yu. Plechov, FMMR) Petrographic observation of a polished section shows chondrules with clear borders. Chondrules size up to 1200 µm. Porphyric olivine and olivine-pyroxene chondrules as well as nonporphyric pyroxene and barred olivine chondrules are present. POP chondrules consist of large homogeneous Ol crystals whereas Low-Ca Px occupies peripheral parts. Low-Ca Px often has clear zoning from very high-Mg relict parts (Fs_1.8) to more ferrous rims (Fs_14.8) in these chondrules. Matrix consists of tiny olivine and low-Ca pyroxene grains (near 1 µm) with Fe-Ni metal and troilite. Metal consists of kamacite and taenite (with 23-34 wt% Ni). Very rare Plagioclase grains (An_1.9-3.5) are about 1 µm and only few are up to 3-5 µm. These features indicate a petrological type of 4 for the meteorite. Olivine shows no undulatory extinction. No shock veins or melt were found. Weathering products (goethite, "hydrogoethite") occur as veins and in situ alteration of FeNi metal.

Geochemistry: Mineral composition and Geochemistry: EDS-WDS analyses (Pavel Yu. Plechov, FMMR). Olivine Fa_15.8±1.2 (N=48), orthopyroxene Fs_11.2±3.1Wo_0.8±0.6 (N=24), plagioclase Ab_91.7An_2.6Or_5.1 (N=5), Cr-bearing clinopyroxene En_49.9Fs_15.4Wo_34.2 (N=5), chromite Crt76.8Spl5.5 (N=6). Phosphates are both Cl-apatite and merrillite. Composition of kamacite (in wt%, N=5): Fe 92.4, Ni 7.1, Co 0.56 (measured by WDS). Taenite (N=3): 27.1 wt% Ni, 0.26 wt% Co. Troilite is close to ideal FeS.

Classification: Ordinary chondrite (H4).

Specimens: Ilya Chaplygin holds main mass. 61 g and thin section, FMMR.