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

GEOL 3010 Syllabus

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