ENNORE INDIA CHEMICALS Hexafluorosilicic acid is an inorganic compound with the chemical formula (H3O)2SiF6 (also written as (H3O)2[SiF6]). It is a colorless liquid rarely encountered undiluted. Hexafluorosilicic acid has a distinctive sour taste and pungent smell. It is produced naturally on a large scale in volcanoes. It is manufactured as a precursor to aluminum trifluoride and synthetic cryolite. It is commonly used as a source of fluoride for water fluoridation. Salts derived from hexafluorosilicic acid are called hexafluorosilicates.