Castanheiras        11°29’11’’S, 61°48’41’’W

Rondonia, Brazil

Find: 2017 Oct 15

Classification: Iron meteorite (ungrouped)

History: The meteorite was found in the afternoon of October 15, 2017, on a rural property in the municipality of Castanheira, Rondônia, Brazil, by the farmer Ademilson Vieira da Luz, while he was plowing the land for the end of year planting. He discovered the iron mass when the tractor passed over a resistance, causing a different noise than when the plow cuts through the soil. He stopped the machine to see what had happened and identified a black mass about 20 cm long with a density much higher than any other stone he had ever seen. Almost a year later, in September 2018, the mass was presented to geologist Paulo Afonso Ribeiro Barbosa, an Exploration Manager who was developing a research project in the finding area. Due to its high density and apparent nickel content, measured by a portable X-ray spectrometer, it was quickly assumed that the mass could be an iron meteorite and Prof. César Ferreira Filho at the University of Brasilia was contacted to liaise with a specialist to obtain a scientific classification of the material. After some negotiations, the finder of the mass, Mr. Ademilson, finally agreed to donate the entire material to the Geological Museum, University of Brasilia, Brazil. In 2020, a small sample of the iron was send to Dr. Ansgar Greshake at the MNB for classification.

Physical characteristics: Individual with black to brownish regmaglypted exterior.

Petrography: Etching of a polished section reveals a hexaedrite texture with several sets of Neumann lines and abundant rhabdites. Terrestrial alteration occurs along fractures.

Geochemistry: µXRF data (MNB): Ni = 4.68 wt%. ICP-MS data (H. Pourkhorsandi and V. Debaille, ULB): Ni = 4.78, Co = 0.37, P = 0.18 (all wt%); Cr = 64.1, Cu = 84.5, Ge = 100.7, Ga = 39.1, As = 2.67, Mo = 4.06, Pd = 1.31, Sb = 0.03, W = 2.03, Ir = 15.0, Au = 0.28 (all ppm)

Classification: Iron meteorite, ungrouped. The meteorite shows a hexahedrite structure with Neumann bands. IIG can be excluded based on the Ge/Ga ratio and high Ir concentration. Elemental concentrations also do not fit the IIAB trends (Wasson et al., 2007)