University of Colorado

Mineral Structure and Property Data

Armalcolite Group

The Pseudobrookite or armalcolite group is composed of minerals of the general formula X2YO5. Both X and Y sites are octahedral and so considerable substiutuion can take place between Fe2+, Fe3+, Mg, Al, and Ti. The principal end-members are pseudobrookite (Fe2TiO5), Ferropseudobrookite (FeTi2O5), and armalcolite (Mg.5Fe.5Ti2O5). Karooite and tialite are synthetic endmembers.

The crystal structure of armalcolite.

                Pseudobrookite  Tialite       Armalcolite 
Formula         Fe2TiO5        Al2TiO5        Mg.5Fe.5Ti2O5        

Form.Wt. 239.591 181.860 215.876 Z 4 4 4 CrystalSystem Orth Orth Orth PointGroup mmm mmm mmm SpaceGroup Bbmm Bbmm Bbmm UnitCell a(Å) 9.767 9.429 9.7762 b(Å) 9.947 9.636 10.0214 c(Å) 3.717 3.591 3.7485 Vol 361.12 326.27 367.25 MolarVol 54.375 49.128 55.298 Density 4.406 3.702 3.904 Thermal Expansion(Volumetric) alpha a0

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