SYNTHETIC ARMALCOLITE AND PSEUDOBROOKITE

Abstract

Armalcolite and pseudobrookite have been crystallized from synthetic melts of basaltic composition with variable amounts of added TiO 2. It was found that the composition of the armalcolite and pseudobrookite are dependent on the TiO 2 content of the melt and the conditions (particularly oxygen fugacity, but also temperature and quenching rate) of formation. The maximum Al 2O 3 content of pseudobrookite appears to be ∼14-15 wt.% Al 2O 3, a spinel-like phase being exsolved at higher Al 2O 3 concentrations. Generally armalcolite is formed at low pO 2 and pseudobrookite at higher oxygen fugacities.