Crystalline boron is chemically inert and resistant to attack by boiling hydrofluoric or hydrochloric acid. It also measured atmospheric chemicals including hydrochloric acid, hydrofluoric acid, bromine and iodine. It is slowly attacked by concentrated hydrofluoric acid and sulfuric acid. Different substrates need different etching solutions, such as hydrochloric, hydrofluoric, and sulfuric acids. Other inorganic fluorides prepared from hydrofluoric acid include sodium fluoride and uranium hexafluoride. These include mixtures of phosphoric and hydrofluoric acids as well as surfactants. The widespread use of sulfuric acid and hydrofluoric acid in refineries poses significant environmental risks. Potassium fluoride is prepared by dissolving potassium carbonate in hydrofluoric acid. Fluorine is used to fluorinate uranium tetrafluoride, itself formed from uranium dioxide and hydrofluoric acid. Industrially, the mineral is an important source of both phosphoric and hydrofluoric acids. It dissolves in warm alkali hydroxides and in hydrofluoric acid. Niobium is attacked by hydrofluoric acid and hydrofluoric/nitric acid mixtures. Fluoride salts and hydrofluoric acid are the main fluorides of industrial value. Aqueous solutions of HF are called hydrofluoric acid. The reaction of silicon fluoride with excess hydrofluoric acid produces the octahedral hexafluorosilicate anion .