Structural and compositional studies on selected phases of iron and stony-iron meteorites

Abstract

On the basis of new data for the frequency of band width distributions in a collection of 63 octahedrites, a revised classification into coarse, medium and fine octahedrites has been proposed. A study of the nickel contents and structures of iron meteorites would suggest that the following relationships hold: hexahedrites and nickel-poor ataxites, 5.5-6.0% nickel; coarse octahedrites, 6.0-7.2% nickel; medium octahedrites, 7.0-10.2% nickel; fine octahedrites 7.7-14% nickel; nickel-rich ataxites, 14.23(?)% nickel. New data on the metal phase of iron meteorites indicate that the gallium and germanium contents are distributed between three distinct levels, confirming a previous observation by Goldberg, Uchiyama and Brown (1951) with regard to gallium. Cobalt and copper values are shown to vary more or less sympathetically with the nickel content. The distribution of chromium would appear to be complicated by the presence of troilite either close to, or contaminating, the sample analysed. Similar data for the metal phase of nine stony-iron meteorites suggest a similarity in nickel content and trace element content of all the samples analysed. Semi-quantitative determinations have been made of cobalt, chromium, copper, germanium, manganese, nickel, lead, tin, vanadium and zinc in troilite from fourteen iron and two stony-iron meteorites. Similar determinations have been made on schreibersite from two iron meteorites. Semi-quantitative analyses of barium, cobalt, chromium, copper, gallium, germanium, manganese, nickel, tin, titanium, vanadium and zirconium in olivine from four pallasites, together with macro-analyses and optical data, suggest that the olivine has a constant composition. The data have been used to calculate new abundances for these elements in meteorites and new data on the geochemical behavior of these elements.