Structural and Mineralogical Changes of the Kaalijarv Iron Meteorite Substance Under Terrestrial Conditions

Abstract: The article presents detailed study of the structural, mineralogical and chemical changes in the Kaalijarv iron meteorite sample occurred as a result of the prolonged terrestrial weathering under the natural conditions in Estonia. The changes in the meteoritic matter manifested themselves as the widespread kamacite corrosion, moderate taenite and phosphide corrosion, and the terrestrial contamination by quartz. The priority terrestrial weathering of the α-(Fe,Ni) phase occurred at the boundary with the phosphide grain inclusions; in (α + γ)-(Fe,Ni) phase in the zonal taenite plate; as well as in the form of extensive replacement of kamacite over the area. The minor oxidation of the taenite occurred in: a) the light taenite zone in the zonal plate at the boundary with the weathered kamacite matrix; b) the edge of the taenite plate at the boundary with the shreibersite grains and limonite in the taenite + shreibersite + kamacite aggregate. Fractured rhabdite and shreibersite grains were subjected to moderate corrosion. A single pseudomorphic replacement of the rhabdite grain was located in unaltered kamacite matrix. The weathering of meteoritic material was accompanied by the moisture migration, the ion migration, removal of Fe, Ni, P from iron-nickel alloy and phosphides, the introduction of water molecules, Si, Mg, Al, Ca, Na, S, K, Cl from the environment. It is unlikely to find the aggressive component of akaganéite, β-FeO(OH, Cl) due to the constantly low content of Cl– ions in the terrestrial weathering products, which ensures long-term storage of the Kaalijarv iron meteorite sample in the laboratory and meteorite collection.