Sodium fluorosilicate is a compound with the chemical formula Na<sub>2</sub>[SiF<sub>6</sub>]. Unlike other sodium salts, it has a low solubility in water.
Sodium hexafluorosilicate occurs naturally as the rare mineral malladrite found within some volcanic fumaroles.
Sodium fluorosilicate is made by neutralizing fluorosilicic acid with sodium chloride or sodium sulfate.
Sodium fluorosilicate is used in some countries as additives for water fluoridation, opal glass raw material, ore refining, or other fluoride chemical (like sodium fluoride, magnesium silicofluoride, cryolite, aluminum fluoride) production.
It is used for extraction of beryllium from beryl, by roasting the mineral with it at 700-750 ðC, leaching the soluble fluoride with water, and then precipitating it as Be(OH)<sub>2</sub> at about pH 13.
It also is an ingredient in some ceramic cements.