Mirabilite, also known as Glauber's salt, is a hydrous sodium sulfate mineral with the chemical formula Na₂SO₄·10H₂O. It is a vitreous, colorless to white monoclinic mineral that forms as an evaporite from sodium sulfate-bearing brines. It is found around saline springs and along saline playa lakes. Associated minerals include gypsum, halite, thenardite, trona, glauberite, and epsomite.