『Abstract
　The deterioration of buildings and monuments by gypsum is the result of crystallization cycles of this salt. Although gypsum can dehydrate to a hemihydrate, the mineral bassanite, and to an anhydrate, the mineral anhydrite, this reaction occurs in nature on a geological time scale and therefore it is unlikely to occur when gypsum is found on and in building materials. The CaSO4-H2O system appears deceptively simple, however there are still discrepancies between the experimental and thermodynamically calculated data. The reason for the latter can be attributed to the slow crystallization kinetics of anhydrite. Apart from this, the large numbers of studies carried out on this system have focused on industrially important metastable phases, such as the hemihydrate and soluble anhydrite. The paper presents a review of the studies dealing with the phase equilibria of the CaSO4-H2O system as well as the influence of other salts on the solubility of gypsum. It tries to glean out the relevant information that will serve to explain the deterioration observed on building materials by the crystallization of gypsum and thus allows developing improved conservation methods.

Keywords: Gypsum; Solubility; Deterioration action; Phases; Crystallization kinetics』

Introduction
Background information
　Geological background
　Mineralogy
　Industrial phases
Phase equilibria: a chronological review
　The CaSO4-H2O phase diagram and the gypsum-anhydrite equilibrium
　Solubilities of gypsum and anhydrite in the presence of other salts
Gypsum in the deterioration of monuments
　Crystallization of gypsum
　Deterioration mechanism for gypsum crystallization
Conclusions
Acknowledgments
References