1. Oxides Tetrahedral oxides – four-fold coordination
Octahedral oxides – six-fold coordination
Mixed octahedral and tetrahedral coordination
Cubic oxides – eight-fold coordination
Mixed cubic and cube-octahedral oxides –
twelve-fold coordination
Oxides with unusual coordination

2. Tetrahedral oxides The only common mineral is zincite, ZnO,
which has the wurtzite structure.

3. Periclase (MgO) has the halite structure.
Octahedral Oxides
Periclase (MgO) has the halite structure.

4. The hematite group Minerals in this group are based on the
general formula X2O3 with hexagonal close-
packed structure where 1/3 of the octahedral voids are vacant.

5. corundum
corundum
Al2O3

6. Hematite-type structure
corundum
corundum

7. Hematite, variety specularite, or specular hematite

9. Ilmenite (FeTiO3)

10. hematite
hematite
ilmenite

12. Rutile group
The rutile group is based on the general formula XO2 .

13. rutile
TiO2

14. Cassiterite (SnO2)
The rutile structure

15. Pyrolusite (MnO2)

16. columbite-tantalite, so-called “coltan”
(Fe,Mn)Nb2O6- (Fe,Mn)Ta2O6

17. Mixed octahedral and tetrahedral coordination
Spinel group XY2O4
X = 2+,Y = 3+
Inverse
Normal
XY2O4
Y[XY]O4
chromite
magnesiochromite
hercynite
galaxite
franklinite
magnetite
magnesioferrite
jacobsite
spinel
ulvospinel

18. Spinel (MgAl2O4)

19. Fe3+[Fe2+Fe3+]O4

20. chromite (FeCr2O4)

21. franklinite (ZnFe2O4)

22. chrysoberyl (BeAl2O4)

23. Cubic oxides
Uraninite UO2 has the flluorite structure.

24. uraninite (UO2)

26. Mixed Octahedral and Cuboctahedral Oxides
perovskite
CaTiO3

27. Ti in octahedral (6-fold) coordination
Ca in cuboctahedral (12-fold) coordination

28. Oxides with Unusual Coordination

29. cuprite (Cu2O)