| Full Reference | Locock, Andrew J.; Herd, Christopher D.K.; Ma, Chi; Steele-Macinnis, Matthew; Luth, Robert W. (2026) Ferropseudobrookite, armalcolite, pseudobrookite, and the pseudobrookite group. American Mineralogist. doi:10.2138/am-2026-10268 |
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| Plain Text | Locock, Andrew J.; Herd, Christopher D.K.; Ma, Chi; Steele-Macinnis, Matthew; Luth, Robert W. (2026) Ferropseudobrookite, armalcolite, pseudobrookite, and the pseudobrookite group. American Mineralogist. doi:10.2138/am-2026-10268 |
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| Abstract/Notes | Abstract The original definition of armalcolite, at the midpoint of a solid-solution series (MgTi4+2O5 – Fe2+Ti4+2O5), is not in accord with current IMA guidelines. The Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA-CNMNC) has approved a proposal (IMA 25-A) to validate ferropseudobrookite as a mineral species, to revise the definition of armalcolite following IMA recommendations, and to establish the pseudobrookite group. Ferropseudobrookite has been approved as a mineral species with the end-member formula Fe2+Ti4+2O5 (symbol Fpbk), on the basis of both a review of the literature, and new data acquired for lunar samples (from Apollo missions 11 and 17) and samples from Disko Island, Greenland. The terrestrial neotype for ferropseudobrookite is sample 176486 from Disko Island, Greenland, accessioned and stored by the Natural History Museum of Denmark, and the lunar cotypes for ferropseudobrookite include the samples: 10022,37; 10071,28; 70017,125; 70215,152; 71569,54; and 74275,91; these are accessioned and stored in the Apollo lunar sample collection of the Lunar Sample Laboratory Facility at the NASA Johnson Space Center. Armalcolite is redefined with the end-member formula MgTi4+2O5 (symbol Arm), and the terrestrial neotype for armalcolite is sample 176411 from Disko Island, Greenland, accessioned and stored by the Natural History Museum of Denmark. The neotype for pseudobrookite, with end-member formula Fe3+2Ti4+O5 (symbol Pbrk), is sample Á.59.6103 from the original locality of Măgura Uroiului, near the town of Simeria, Romania, accessioned and stored by the Hungarian Natural History Museum. The cotype for pseudobrookite is sample CMNMC 93855 (preliminary label BTL) from the same locality, accessioned and stored by the Canadian Museum of Nature. The pseudobrookite group, approved by the IMA-CNMNC, consists of orthorhombic oxides with general formula M3O5, and includes the five species: pseudobrookite, Fe3+2Ti4+O5; armalcolite, MgTi4+2O5; ferropseudobrookite, Fe2+Ti4+2O5; griffinite, Al2Ti4+O5 (symbol Gfn), and sassite, Ti3+2Ti4+O5 (symbol Ssi). The formal recognition of the pseudobrookite group and its five species should facilitate investigations and discussions of the physical and thermodynamic properties of solid solutions within this group, and their conditions of formation. |
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