Fluorine is an extremely reactive chemical element with atomic number 9. At standard conditions, pure fluorine is a toxic pale yellow diatomic gas. Fluorite, the element's primary mineral source, was first described in 1529, and fluorine was proposed as an element in 1810. As the lightest halogen and most electronegative reactive element, it is difficult to separate from its compounds, and several early experimenters died or were injured in the attempt. French chemist Henri Moissan finally succeeded in 1886 using low-temperature electrolysis, a process still used today. Global fluorochemical sales amount to more than US$15 billion a year, including in toothpaste and water fluoridation, refrigerants, Teflon for electrical insulation and cookware, pharmaceuticals, aluminium refining and steelmaking. Fluorocarbon gases are generally greenhouse gases. Fluorine has no known metabolic role in mammals, but a few plants and sea sponges synthesize poisonous fluorocarbons to deter predators. (Full article...)