Gypsum and anhydrite have been found extensively in evaporite beds. Gypsum is the low-temperature, hydrous form of calcium sulfate, while anhydrite is the high-temperature, anhydrous form. The temperature of gypsum-anhydrite transition has been fixed, by both solubility measurements and thermodynamic calculations, in the range of 38 to 42°c in pure water; and at lower values with increasing NaCl content in the solutions. However, the precipitation of anhydrite has never been obtained experimentally in its own stability field, gypsum is always metastably formed instead.
Many investigators believe that the primary precipitation of anhydrite from solutions is improbable. It is usually converted from gypsum by the diagenesis due to the effects of burial, anhydrite is always secondary.
The present work is to study the precipitation of calcium sulfate by mixing CaCl2, with Na4SO4 in various ways to evaluate the possibility of direct precipitation of anhydrite.
It has been found that anhydrite can be formed in concentrated CaCl2 solution, or H2SO4 solution, because the kinetics of nucleation is favored by increased super saturation.
Earth and Planetary Sciences
Level of Degree
Department of Earth and Planetary Sciences
First Committee Member (Chair)
Edgar F. Cruft
Second Committee Member
Albert Masakiyo Kudo
Third Committee Member
Roger Yates Anderson
Fourth Committee Member
Vincent Cooper Kelley
Chao, Pao-Chin. "Effect Of Supersaturation On The Kinetics Of The Gypsum-Anhydrite Transition.." (1969). https://digitalrepository.unm.edu/eps_etds/311