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-Mg0.5Ti1.5O5, and intermediate compositions. Armalcolite has an ideal formula Fe0.5Mg0.5Ti2.5O5 with a compositional range limited by MgTi2O5, FeTi2O5, FeMg0.5Ti1.5O5, and Mg0.5Ti2.5O5 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.

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