Boussingaultite is a rare sulfate mineral of the chemical formula: (NH₄)₂Mg(SO₄)₂·6(H₂O). The formula of boussingaultite is that of Tutton's salts type. It was originally described from geothermal fields in Tuscany, Italy, where it occurs together with its iron analogue mohrite, but is more commonly found on burning coal dumps. The mineral possess monoclinic symmetry and forms clear, often rounded crystals.