Mirabilite

Mirabilite, also known as Glauber's salt, is a hydrous sodium sulfate mineral with the formula Na2SO4·10H2O. It is a vitreous, colourless to white monoclinic mineral that forms as an evaporite from sodium sulfate-bearing brines, and is found around saline springs and along saline playa lakes. Associated minerals include gypsum, halite, thenardite, trona, glauberite and epsomite. It is unstable and quickly dehydrates in dry air, the prismatic crystals turning into a white powder of thenardite, which can absorb water and turn back into mirabilite. In traditional Chinese medicine it is used as a purgative and anti-inflammatory remedy, and is called máng xiāo. Its name comes from the phrase sal mirabilis, Latin for wonderful salt, used by Johann Rudolph Glauber, who made it by accident. Late Archaic and Early Woodland peoples probably mined it in Mammoth Cave for use as a laxative.