A type of ionic crystal structure in which the cations have an expanded face-centred cubic arrangement with the anions occupying both types of tetrahedral hole. The cations have a coordination number of 8 and the anions have a coordination number of 4. Examples of compounds with this structure are CaF2, BaCl2, and PbO2.
The antifluorite structure is the opposite arrangement, with anions in the f.c.c. array with coordination number 8 and cations in the tetrahedral holes with coordination number 4. Examples of the antifluorite structure are K2O, Li2O, Na2O, K2S, and Na2S.
http://www.chemtube3d.com/solidstate/_fluorite(final).htm An interactive version of the structure