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TITANOMAGHEMITE IN IGNEOUS ROCKS



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THE AMERICAN MINERALOGIST TITANOMAGHEMITE VOL 46 JANUARY FEBRUARY 1961 IN IGNEOUS ROCKS T qK sur Karsuna Toktto Insti tute of Technology o o Ixuo Kusnrno GeologicalInstitute Uniaersity of Tokyo Anstnacr olivine and hypersthene are partially or completely altered to chlorite and serpentine but it occurs also in some unaltered lava flows It is concluded that titanomagnetite crystallizing from magma is oxidized to produce titanomaghemite under a certain condition which may be easily obtained during the cooling process It is not necessary to consider the special solid solution series between 7 FeTiO3 and Feaor in order to explain the formation of titanomaghemite in igneous rocks The titanomaghemite possesses vacancies of two or three metal ions in a unit ceII The lattice parameters vary with the ratios Fe Fe Ti and 32 Fe Ti 0 and range from 8 359 to 8 419 A INtnonucuoN Titanomagnetites in igneous rocks are generally considered to have in the syscompositionswithin a triangular field TiFeOa TiFezOa Fe3Oa belonging as explained are Their compositions TiOz FeO FezOs tem solid to the oI solution solid TiFezO FesOa 7 TiFeOrFeaOr either to the However 1957 al et Vincent 1950 Chevallier Girard and solution some titanomagnetites have compositions outside of the triangular field Iying even near the TiFeOr FezOajoin Such compositionscannot be explained by the two simple solid solution series Recently Akimoto and Katsura 1959 discussedthe origin of the titanomagnetitesoutside the triangular field TiFeOs TiFezOa Feroaon the basis of their experiments Akimoto Katsura and Yoshida 1957 and concluded that they were formed by oxidation of the normal titanomagnetite belonging to the solid solution But they did not discuss the extent to TiFe O FeaOa which the spinel phase can exist as a single phase Basta 1953 1959 named the titanomagnetiteshaving compositionsclose to the TiFeOeFerO3join and the TiOz FezOajoin the titanomaghemites and also concluded that they were formed by oxidation of



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