CHEMISTRY AND MINERALOGY OF OXIDATION-PRODUCTS ON THE SURFACE OF THE HOBA NICKEL-IRON METEORITE

An oxide layer adjacent to the surface of the Hoba Ni-Fe meteorite was analyzed chemically and mineralogically. Maghemite, magnetite, goethi te and lepidocrocite were the main Fe minerals found in the oxide laye r surrounding Hoba. Most of the Ni from the unweathered original meteo rite was distributed among the above minerals with spinel-type oxides (maghemite and magnetite) having the largest Ni fraction. Some Ni migr ated to the limestone in which the meteorite is embedded. No evidence for zaratite or akaganeite was found in the oxide layer. Sulfate deriv ed from the oxidation of troilite precipitated as gypsum. Phosphate ac cumulation in limestone in contact with the meteorite is probably due to phosphate adsorbed on Fe-oxides. Maghemite with some magnetite was the oxidation product immediately next to the meteorite metal surface, which accommodated most of the Ni and Fe from the meteorite into its structure. Upon oxidation, some of the Ni, which was incorporated into calcite, was released. Cobalt associated with the oxides stayed withi n the oxide structure regardless of the oxidation state and did not mi grate to the limestone. This suggests that Co may be a good tracer for oxides of meteoritic origin.