On the Geochemical Cycle of Fluorine

Abstract

The average concentration of fluorine in the earth's crust is about 800 gm. per ton. In basalts and gabbros it is present as apatite; in granites, gneisses, and metamorphic rocks it is contained in mica, hornblende, and fluorspar. Much fluorine enters into the magmatic gas phase, which has an acid reaction. Great amounts of fluorine are therefore exhaled by volcanic eruptions. If the magmatic gas phase has opportunity to react with the wall rock, it turns alkalic, and fluorine is extracted (as phosphate?) before it reaches the surface; alkaline hot springs carry no magmatic fluorine. Of the fluorine dissolved by the weathering processes, only 0.2 per cent is found in the ocean. Fluorine is extracted from inland waters and from the sea, forming mineral deposits with a composition resembling fluorapatite.