This mineral has been known since ancient times as a flux for smelting ion. The name fluorite is derived from the latin root fluo, meaning "to flow", which eventually ended up in the name of the element fluorine. It also game its name to fluorescence, which the crystal emits when it contains certain impurities. The current main use of fluorite is dissolving it in sulphuric acid to produce HF.
The structure of fluorite is a ccp array of calcium ions with (smaller) fluorine ions inside every tetrahedral hole. Reversing the locations of the cations and ions creates an antifluorite structure.
The calcium ions are the ones in dark green. This is also a good way of learning the tetrahedral hole locations in a ccp unit cell, since here they are all filled by fluoride ions. The plan view below will help make the structure clear:
In the plan view, you should add (1,0) to the corner atoms.
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