Campo del Cielo

Campo del Cielo represents one of the most significant meteoritic events in recent geological history. The impact, which occurred in Chaco Province, Argentina, generated a vast dispersal field containing thousands of iron fragments, the largest of which weighs approximately 37 tonnes (Gancedo meteorite). The composition is characteristic of siderite (or iron meteorite) type meteorites, dominated by an Fe-Ni alloy with nickel percentages ranging between approximately 5 and 35%. The crystalline structure reveals Widmanstätten patterns, namely lamellar bands of kamacite (Fe-Ni with low Ni content) and taenite (Ni-rich Fe-Ni) that form during extremely slow cooling in the asteroidal mantle.

From a collecting standpoint, Campo del Cielo fragments are among the most accessible and sought-after iron meteorites worldwide. Their relative abundance, combined with the beauty of Widmanstätten figures after polishing and acid etching, makes them ideal for museums, private collections, and academic research. Radiometric dating places the fall event around 2737 BCE, although more recent estimates suggest a broader timeframe. The discovery site continues to be the subject of archaeological and geological investigations, as traces of the impact remain visible in the landscape.

Classification: Siderite (iron meteorite), subclass octahedrite based on Widmanstätten band widths (typically 0.5–2 mm). Approximate chemical composition: Fe 90–95%, Ni 5–10%, Co 0.5–1%, traces of P, S. Crystal structure: cubic, space group Im3m, lattice parameter a ≈ 2.87 Å. Density: 7.3–7.9 g/cm³. Mohs hardness: 4–5 (due to malleable Fe-Ni composition). Magnetic properties: ferromagnetic, with saturation magnetization around 220 A·m²/kg. Microstructure: constituted of kamacite phases (cubic, a ≈ 2.87 Å, Ni 5–8%) and taenite (face-centered cubic, a ≈ 3.58 Å, Ni 25–35%), with possible plessite (fine intergrowth of kamacite and taenite) in interstitial regions. Iron isotopic analysis indicates origin from a differentiated parent body in the primordial solar system. Radiometric age (Pb-Pb, Ar-Ar): approximately 4.56 Ga for crystallization in the parent body; fall age estimated around 4,700 years ago via cosmogenic dating (cosmic ray-produced radionuclides: ¹⁰Be, ²⁶Al). Polished section etched with dilute nitric acid (2–5%) reveals characteristic Widmanstätten pattern with well-defined parallel bands.