magnésium fluoride

It is soluble in nitric acid, slightly soluble in diluted acid, insoluble in water and alcohol. It appears a weak violet fluorescence when heated under electric arc light, its crystal has upstanding polarization, and so it is fairly suitable for ultraviolet spectrum and infrared spectrum. It is toxic. 
[Fampiasana]  It is used as flux of smelting magnesium, as additive of electrolysis aluminium, in coating optical lenses and filter, in coating agent of titanium pigment, in fluorescent agent of cathode ray screen. It is also used in ceramic and glass industry.