Fluorine is a chemical element (atomic number 9) that exists as a gas at normal temperatures and pressures. It is both toxic (more so than cyanide) and very reactive - it forms compounds with almost every other element, including some of the noble gases. Because it is so reactive, it is rarely found in its gaseous state and is almost always found in minerals. Most fluorine used for industrial purposes is from the mineral fluorite, a compound of fluorine and calcium.because extracting pure flourine from minerals is both expensive and dangerous.
The primary medical use of fluorine compounds is as an additive to toothpastes as fluorine both inhibits the growth of bacteria and combines with calcium in the teeth to make the enamel layer harder. However, it is also part of about 20% of all pharmaceutical compounds. Radioactive fluorine-18 is used in PET scans. Fluorocarbons are also being investigated as a blood substitute as they can hold large amounts of dissolved oxygen.
Although flourine is part of some organic tissues, it is not believed that it is an essential trace element.