Where do inorganic fluorides come from?
The Earth’s crust contains about one tenth of a percent of fluorine, making fluorine its thirteenth most common element. Fluorine is widely found in minerals and sedimentary rocks formed by compaction of particles in lakes and oceans. The main fluorine-containing minerals are calcium fluoride, fluoroapatite and cryolite. All compounds that contain fluorine are called fluorides; inorganic fluorides are a subset, referring to those that do not contain carbon. Inorganic fluorides are released slowly from rocks and minerals as they erode under normal weather conditions. Other natural sources for inorganic fluorides are active volcanoes and marine aerosols. Human activities such as mining, phosphate fertilizer production, and aluminium smelting cause unnaturally high levels of inorganic fluorides to be released into air, onto land, or into water.
