Sikhote-Alin

The Sikhote-Alin meteorite represents one of the most significant fall events of the twentieth century. On February 12, 1947, a celestial body of approximately 100 tons penetrated Earth's atmosphere and fragmented into thousands of pieces, creating a strewn field exceeding 2 km² across the Sikhote-Alin mountain range in the Russian Far East. The composition is typical of iron meteorites (siderites), with a natural alloy of iron and nickel that reflects the structure of the planetary core from which it originated.

The cubic crystal structure of Sikhote-Alin generates the celebrated Widmanstätten figures when the meteorite is polished and subjected to acid etching: these geometric patterns of diamond shapes and parallel lines result from the slow cooling of the Fe-Ni alloy in space, with the formation of kamacite crystals (Fe-Ni with low nickel content) and taenite (Fe-Ni with high nickel content). The hardness of 4-5 on the Mohs scale is typical of iron meteorites and reflects the pure metallic composition. From a collector's perspective, Sikhote-Alin remains one of the most sought-after meteorites in the world, with specimens ranging from fragments of a few grams to masses of tens of kilograms.

Classification: Octahedrite iron meteorite (group IIIAB according to Wasson classification). Chemical composition: Fe (87–90%), Ni (8–10%), Co (0.5–0.8%), traces of P, S, C. Crystal system: cubic (space group Im-3m). Structure: kamacite (cubic, a ≈ 2.87 Å) and taenite (cubic, a ≈ 3.58 Å). Hardness: 4–5 Mohs. Density: 7.8–7.9 g/cm³. Widmanstätten figure: mean width of kamacite bands 1–2 mm (estimated cooling rate: 5–10 °C/million years). Radiometric age (Ar-Ar): 4.53 ± 0.05 Ga (age of the Solar System). Nickel content in kamacite: 5.5–6.5% (EPMA analysis). Mössbauer spectroscopy: Fe²⁺/Fe³⁺ ratio consistent with a reduced environment. Traces of troilite (FeS) and schreibersite (Fe,Ni)₃P as minor phases. Magnetic properties: ferromagnetic, saturation magnetization ~220 A·m²/kg.