Kieserite is a magnesium sulfate mineral (MgSO4ĚH2O). It has a vitreous luster and it is colourless, greyish-white or yellowish. Its hardness is 3.5 and it has a monoclinic crystal system. It is used in the production of Epsom salt and is named after Dietrich Georg von Kieser (Jena, Germany 1862).
In early 2005, Mars Express, a European Space Agency orbiter, discovered evidence of kieserite in patches of Valles Marineris (the largest canyon on Mars), along with gypsum and polyhydrated sulfates. This is direct evidence of Mars's watery past and augments similar discoveries made by the Mars Exploration Rover Opportunity in 2004.