Fluorine is the ninth element on the periodic table. It is the first element in a group called the halogens (others include chlorine and bromine). Fluorine is a fairly common element, the thirteenth most common element found on Earth.
Elemental fluorine exists not as a monoatomic entity but a diatomic one. In other words, elemental fluorine exists as the yellowish gas F2 (two fluorine atoms connected through a single bond). F2 is a highly reactive species and as such does not exist in nature. Due to its extremely high electronegativity, fluorine likes to obtain an extra electron to exist as the fluoride anion (F-). As the fluoride anion, fluorine exists most commonly on Earth in the ground as inorganic salts and minerals. Fluorine is most commonly found in the form of fluorite (CaF2). Fluorite is found all over the planet. The most commercial mining of fluorite is in China and Mexico. Naturally occurring fluorine is also found in the form of fluorapatite [Ca5(PO4)3F] and cryolite (Na3AlF6). Elemental fluorine (F2) can be made from these precursors through a process called electrolysis, or introducing an electric current to a solution of fluoride ions to produce the electronically neutral gas.
Fluorine is found in nature in minerals such as fluorite. It is also common in the Earth's crust and is usually found as fluoride ions. We use Fluorine for steel, toothpaste, fluoridated water, coolants, and Teflon. Another place you can find it is as the mineral fluorapatite in bones and teeth.