Fluorine is found in the minerals fluorapatite, cryolite and fluorspar in the Earth's crust. It is not found as a free element in nature because it is too reactive.
Fluorine is classified as a nonmetal and is a halogen. It is the most reactive and electronegative element, meaning that it attracts electrons toward itself. It appears pale yellow as a gas and is corrosive. Fluorine reacts with most organic and inorganic substances. It is unusual for fluorine to be used in its pure form, but compounds of fluorine are used in toothpaste, pharmaceuticals and tap water and to prevent tooth decay.