Fluorine, chemical element, symbol F; for physical constants see Periodic Table. Fluorine was discovered in 1886 by Henri Moisson. It occurs chiefly in the form of the minerals fluorspar (calcium fluoride) and cryolite (sodium aluminum fluoride). It is obtained by electrolyzing a solution of potassium hydrogen fluoride in anhydrous hydrogen fluoride. Compounds of fluorine were used for years before the element was finally isolated. Fluorine is a member of the halogen family of elements. Fluorine is a pale yellow, corrosive, and poisonous gas and is the most electronegative and reactive of all elements. Commercial production of the element began only after World War II for preparing uranium hexafluoride. Fluorine and its compounds are used for glass etching, production of fluorocarbons, and in drinking water to prevent dental cavities. Fluorine and the fluoride ion are highly toxic.