University of Colorado

Mineral Structure Data

Corundum Group

The corundum group is composed of the sesqui-oxide minerals of Aluminum (corundum), iron (hematite), chromium (eskolaite), and vanadium (karelianite). Also synthetic Ti2O3 has this structure but has recently (2009) been observed to occur in nature as the mineral tistarite in a chodrule in the Allende meteorite.

The crystal structure of corundum with c vertical is very dense and has face-sharing octahedra.

Corundum Group Unit Cells

                Corundum    Hematite    Eskolaite   Karelianite
                Al2O3        Fe2O3       Cr2O3        V2O3       


Form.Wt.        101.961     159.692     151.990     149.882    
Z               6           6           6           6          
CrystalSystem   Trig        Trig        Trig        Trig       
PointGroup      3m          3m          3m          3m         
SpaceGroup      R-3c        R-3c        R-3c        R-3c       

UnitCell
a(Å)            4.7589      5.038       4.9607      4.952    
c(Å)            12.9912     13.772      13.599      14.002   
Vol(Å3)         254.80      302.72      289.92      297.36  

MolarVol        25.577      30.388      29.093      29.850     
Density         3.986       5.255       5.224       5.021     

Thermal Expansion(Volumetric)
alpha           23.0        23.8        18.6        
a0              0.2276      0.1238      0.2146              
a1              0.4198      3.8014      0.1154               
a2              -0.0897     0.0000      -0.2904               

Elastic Properties
Ks(GPa)         253.5       206.6       234.0     195.
G(Gpa)          163.2       91.0        123.2

Corundum Group Cation Sites


EndMember        Corundum        Hematite        Eskolaite        Karelianite

C.N.             6               6               6                6
Occupant         Al              Fe              Cr               V

Point Sym.       3               3               3                3
Wyckoff Not.     12c             12c             12c              12c

Frac.Coord.
x                0               0               0                0
y                0               0               0                0
z                .3520           .3553           .3475            .3463

Distances
O1(3)            1.969           2.115           2.016            2.062
O1(3)            1.856           1.945           1.965            1.963

Mean             1.913           2.030           1.990            2.012
sigma             .062            .093            .028             .054

Poly.Vol.        9.066           10.754          10.312           10.719
Q.E.             1.0200          1.0264          1.0131           1.0098
Ang. Var.        66.6            85.0            45.2             32.7

Site Energy      2529.           2401.           2416.            2309.

Mineral Data Base Index

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