Abstract
Magnetite in dacite from Haruna Volcano, Central Japan has been studied in detail with the electron probe microanalyser. It is found that the magnetite shows a distinct compositional variation before and after the eruption of magma; ΣFeO, Al2O3 and MgO decreased, while TiO2, V2O3 and MnO increased. Magnetite inclusions in the other crystallizing phases also show the same compositional change. By correlating the chemical compositions of discrete magnetites with those of the inclusion magnetites, the relative stage of crystallization of the minerals enclosing the magnetite inclusion can be estimated.
