Abstract: Armalcolite and pseudobrookite have been crystallized from synthetic melts of basaltic composition with variable amounts of added TiO₂. It was found that the composition of the armalcolite and pseudobrookite are dependent on the TiO₂ content of the melt and the conditions (particularly oxygen fugacity, but also temperature and quenching rate) of formation. The maximum Al₂O₃ content of pseudobrookite appears to be ∼14–15 wt.% Al₂O₃, a spinel-like phase being exsolved at higher Al₂O₃ concentrations. Generally armalcolite is formed at low pO₂ and pseudobrookite at higher oxygen fugacities.