Disclosed is a method of performing assay to a fluorite sample, which includes a first step for dissolving a fluorite sample, containing Ca and F, by use of a solvent, a second step for removing Ca and F from an obtained solution, and a third step for assaying, through ICP-MS, the solution having Ca and F removed therefrom. Also disclosed is a method of producing a fluorite crystal and an exposure apparatus using such fluorite crystal, and a device manufacturing method using such exposure apparatus. The assaying method of the present invention ensures assay and evaluation of a fluorite sample, of sensitivity several times higher than conventional methods.