Interesting informations are including in attached file. Old, but efficient paper..:-)

I found this paper by Serafeimidis and Anagnostou in 2015 very useful.  Here is the link to it:

http://link.springer.com/article/10.1007/s00603-014-0557-1

Here is the citation if the link doesn't work:

K. Serafeimidis, G. Anagnostou, The solubilities and thermodynamic equilibrium of anhydrite and gypsum, Rock Mechanics and Rock Engineering, 48 (2015) 15-31.

Dear Erhan,

Have a look at these papers.

Kind Regards,

Masoud Ovissi

Testa, G., and S. Lugli. "Gypsum–anhydrite transformations in Messinian evaporites of central Tuscany (Italy)." Sedimentary Geology 130.3 (2000): 249-268.

Azimi, Ghazal, and Vladimiros G. Papangelakis. "Mechanism and kinetics of gypsum–anhydrite transformation in aqueous electrolyte solutions." Hydrometallurgy 108.1 (2011): 122-129.

Ossorio, M., et al. "The gypsum–anhydrite paradox revisited." Chemical Geology 386 (2014): 16-21.