Bararite

Bararite is a natural form of ammonium fluorosilicate (also known as hexafluorosilicate or fluosilicate). It has chemical formula (NH₄)₂SiF₆ and trigonal crystal structure. This mineral was once classified as part of cryptohalite. Bararite is named after the place where it was first described, Barari, India. It is found at the fumaroles of volcanoes (Vesuvius, Italy), over burning coal seams (Barari, India), and in burning piles of anthracite (Pennsylvania, U.S.). It is a sublimation product that forms with cryptohalite, sal ammoniac, and native sulfur.