Mineralogy of the oxidation products of the Sputnik 4 fragment and of iron meteorites

The melted and oxidized products on the Sputnik 4 fragment make up 10 to 15 per cent of the total mass and consist of droplets of a iron, coated with the iron oxides wüstite (Fe1−xO), magnetite (FeFe2O4), and akaganéite (β FeO(OH)), and the magnesium oxide periclase (MgO). This assemblage of minerals reflects nonequilibrium conditions of rapid cooling from above 1535°C, the melting point of iron, to below 80°C, the temperature region in which akaganéite can form as a rnetastable variety of iron oxy hydroxide. A re-examination of the crust during the fifth month after recovery showed that the akaganéite and some of the wüstite had been oxidized to hematite (α Fe2O3). Wüstite and akaganéite are metastable at surface temperatures and are therefore virtually unknown in terrestrial rocks and in meteorites. Their discovery on the Sputnik 4 fragment, however, led to the investigation, by X-ray diffraction procedures, of the crusts of numerous iron meteorites. Wüstite was identified in association with magnetite in the fusion crust of the Bogou iron that fell in Upper Volta in August 1962, and of several older irons including the Braunau, Czechoslovakia, hexahedrite that fell in 1847. Akaganéite was found among the alteration products of weathered iron meteorites.