Under ordinary conditions fluorine is a gas a little heavier than air, with a pale yellow colour; inhalation except in very low concentrations is dangerous. Upon cooling, fluorine becomes a yellow liquid. combined in the widely distributed mineral fluorite (calcium fluoride , fluorspar), its chief source, in the minerals cryolite and fluorapatite, and in small amounts in seawater, bones, and teeth. Not a rare element, it makes up about 0.065 percent of the Earth's crust. Only one isotope occurs Read more [...]