At temperatures above 73°C, the solubility of magnesium sulfate decreases with increasing temperature. This solubility behavior up to 140°C is described very well by the Extended UNIQUAC model as shown in the figure to the right.
In the phase diagram, the solid phase at temperatures between the eutectic point and 2°C is marked as MgSO4·12H2O. New research shows that this solid is actually Meridianiite, MgSO4·11H2O. This mineral was found recently on a frozen pond in British Colombia, Canada by Peterson et al. (R.C. Peterson, W. Nelson, B. Madu, and H.F. Shurvell, Meridianiite: A new mineral species observed on Earth and predicted to exist on Mars, American Mineralogist; October 2007; v. 92; no. 10; p. 1756-1759; DOI: 10.2138/am.2007.2668).
The other solid phases marked in the phase diagram are: