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
Tetrahedral oxides The only common mineral is zincite, ZnO, which has the wurtzite structure.
Periclase (MgO) has the halite structure. Octahedral Oxides Periclase (MgO) has the halite structure.
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.
corundum corundum Al2O3
Hematite-type structure corundum corundum
Hematite, variety specularite, or specular hematite
Ilmenite (FeTiO3)
hematite hematite ilmenite
Rutile group The rutile group is based on the general formula XO2 .
rutile TiO2
Cassiterite (SnO2) The rutile structure
Pyrolusite (MnO2)
columbite-tantalite, so-called “coltan” (Fe,Mn)Nb2O6- (Fe,Mn)Ta2O6
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
Spinel (MgAl2O4)
Fe3+[Fe2+Fe3+]O4
chromite (FeCr2O4)
franklinite (ZnFe2O4)
chrysoberyl (BeAl2O4)
Cubic oxides Uraninite UO2 has the flluorite structure.
uraninite (UO2)
Mixed Octahedral and Cuboctahedral Oxides perovskite CaTiO3
Ti in octahedral (6-fold) coordination Ca in cuboctahedral (12-fold) coordination
Oxides with Unusual Coordination
cuprite (Cu2O)