The crystal structures of two natural magnetites were refined. Both turned out to have equipoints 8a and 16d (Fd3m) fully occupied and hence different from type I and type II defect structures investigated by Fleet (1981, 1982). It was possible to improve the cation radii for Fe2+ ad Fe3+ in octahedral and tetrahedral coordinations for pure and almost pure magnetites obtaining very good agreement between observed and calculated values of the two independent geometric structure parameters, i.e. cell edge and oxygen coordinate. The present results lead to an estimate of inversion parameter i in (Fe 1–i 2+ Fe i 3+ )(Fe i 2+ Fe 2t-i 3+ )O4, of about 0.90, equal for all the four pure magnetites, independently of type of structure and also of cooling history.
Crystal structure and cation distribution in some natural magnetites
PRINCIVALLE, FRANCESCO;
1987-01-01
Abstract
The crystal structures of two natural magnetites were refined. Both turned out to have equipoints 8a and 16d (Fd3m) fully occupied and hence different from type I and type II defect structures investigated by Fleet (1981, 1982). It was possible to improve the cation radii for Fe2+ ad Fe3+ in octahedral and tetrahedral coordinations for pure and almost pure magnetites obtaining very good agreement between observed and calculated values of the two independent geometric structure parameters, i.e. cell edge and oxygen coordinate. The present results lead to an estimate of inversion parameter i in (Fe 1–i 2+ Fe i 3+ )(Fe i 2+ Fe 2t-i 3+ )O4, of about 0.90, equal for all the four pure magnetites, independently of type of structure and also of cooling history.Pubblicazioni consigliate
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