Definition and range of composition of naturally occurring minerals with the pseudobrookite structure

Pseudobrookite, armalcolite, Ti₃O₅, and “kennedyite” all have the pseudobrookite structure and, besides Ti, Fe, and oxygen, can contain appreciably concentrations of additional elements (Cr, Al, V, Mn, Ca, Zr, etc.). The compositional range of these minerals has never been adequately defined, and there is some confusion in the literature that leaves room for further misunderstanding. A survey of the principal analyses of pseudobrookite, armalcolite, “anosovite” (Ti₃O₅), and “kennedyite” leads, in this paper, to a definition of the range of composition of these minerals, based on established practice and chemically defined boundaries.

“Kennedyite” is an unnecessary name that is now discarded. Pseudobrookite is defined as having an ideal formula of Fe₂TiO₅ with a composition limited by FeTi₂O₅, Fe-Mg_0.5Ti_1.5O₅, and intermediate compositions. Armalcolite has an ideal formula Fe_0.5Mg_0.5Ti_2.5O₅ with a compositional range limited by MgTi₂O₅, FeTi₂O₅, FeMg_0.5Ti_1.5O₅, and Mg_0.5Ti_2.5O₅ and including intermediate compositions.

These proposals have been submitted to the IMA Commission on New Minerals and Mineral Names, and the commission has given its approval.