Ammonium fluorosilicate
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Ammonium fluorosilicate (also known as ammonium hexafluorosilicate, ammonium fluosilicate or ammonium silicofluoride) has the formula (NH4)2SiF6. It is a toxic chemical, like all salts of fluorosilicic acid. It is made of white crystals, which have at least three polymorphs and appears in nature as rare minerals cryptohalite or bararite.