Mineralogy and Stability of Soil Evaporites in North Dakota

Abstract

The evaporite mineralogy of 106 samples of salt efflorescence collected from throughout North Dakota was determined by x‐ray powder diffraction. The mineralogies of these efflorescences are dominated by sulfate salts of Na, Mg, and Ca. The evaporite minerals were mirabilite, thenardite, gypsum, epsomite, hexahydrite, konyaite, bloedite, burkeite, and tychite. Konyaite is the most frequently and widely occurring mineral identified. Efflorescences dominated by Na‐ and MgSO 4 minerals account for >90% of the observed mineralogies. The mineral assemblages dominated by Na 2 SO 4 minerals were evenly distributed across the state. The MgSO 4 ‐rich efflorescences were confined to the glaciated part of the state. Many of the observed minerals are labile with respect to temperature and water vapor pressure. Dissociation vapor pressure curves from the literature are used to describe the field stability relations of epsomite/hexahydrite and mirabilite/thenardite.