White epsomite needles growing down from the roof of Les Ferres mine, Catalona, Spain. Field of view is 25 cm across. (Photo courtesy Joan Rosell; unauthorized reproduction is prohibited.)

Formula: MgSO4.7H2O Orthorhombic


Epsomite usually forms as powdery, fibrous or botryoidal crusts growing as efflorescences on magnesium-rich rocks or as deposits around mineral springs. It is highly water soluble, hence will not survive long under unprotected conditions in Wisconsin’s climate.

LAFAYETTE COUNTY: Epsomite occurs as silky white tufts intermixed with melanterite, copiapite, gypsum and goslarite in numerous places in the Upper Mississippi Valley zinc lead district. These minerals form due to the alteration of iron sulfides in dolostone matrix. Some specific described localities include the Helena-Roachdale Mine in the center of sec. 7 and the Galena Level Mine in the SW sec. 4, both in T.1N. R.2E. near Shullsburg. (Heyl, et al., 1959).