The
spinels are any of a class of
minerals of general formulation A
2+B
3+2O
2-4 which
crystallise in the
cubic (isometric) crystal system, with the oxide anions arranged in a cubic
close-packed lattice and the cations A and B occupying some or all of the
octahedral and
tetrahedral sites in the lattice. Although the charges of A and B in the prototypical spinel structure are +2 and +3, respectively, other combinations incorporating
divalent, trivalent, or tetravalent
cations, including
magnesium,
zinc,
iron,
manganese,
aluminium,
chromium,
titanium, and
silicon, are also possible. The anion is normally oxygen; when other
chalcogenides constitute the anion sublattice the structure is referred to as a
thiospinel.