Titanomagnetites from a differentiation sequence, analcime-olivine theralite to analcime-tinguaite

Abstract

Summary: Six titanomagnetites from a differentiated alkaline intrusion have been studied using microscopie, chemical, and X-ray techniques. The titanomagnetites are homogeneous; with differentiation their FeO and TiO₂contents decrease, and Fe₂O₃increases. The titanomagnetite course of crystallization extends from close to the ulvöspinel-magnetite join, near to ulvöspinel, towards magnetite. The recalculated normative compositions of three titanomagnetites indicate that they are essentially Fe₃O₄-(γ-FeTiO₃)-(γ-Fe₂O₃)solid solutions. The changing chemistry of the titanomagnetites is ascribed primarily to variations in the chemistry of the magma during differentiation.