This fluoride typically occurs in the earths crusts as fluorspar(CaF2), rock phosphate, cryolite (Na3AlF6), apatite(Ca5(PO4)3F), mica, and hornblende.[2] Fluorine is the most electronegative element and is extremely reactive, rarely found outside of its ionic form, fluoride.[2]The fluoride then leaches off of these minerals and into the groundwater.