An ionic crystal structure shown by compounds of the type AB2O4. There is a face-centred cubic arrangement of O2− ions. The A cations occupy one eighth of the tetrahedral holes and the B cations occupy the octahedral holes. Example of the spinel structure are MgAl2O4, Fe3O4, and Mn3O4.
http://cst-www.nrl.navy.mil/lattice/struk/h1_1.html An interactive version of the structure