الملخص

Jabal Sanam is a salt plug, with cap rocks characterized by the presence of evaporitic sequence, where gypsum forms large part of this sequence. The field observations showed that gypsum occurs in form of massive beds and veins, In addition four petrological types of gypsum are recognized; alabastrine, selenite, fibrous, and rocky gypsum. The examination of (61) thin sections besides the X-ray analyses proved that the available gypsum represents the dominant mineral with few to trace amount of anhydrite, dolomite and quartz. Petrographically, four types of gypsum textures are also identified; alabastrine, porphyroblastic, fibrous and granular. All these textures suggest a secondary origin of Jabal Sanam gypsum due to the hydration of pre-existing anhydrite. The hydration occurs when the cap rocks approach the ground surface. The connate and groundwater form the main source of hydration water. ــــــــــــــــــــــــــــــــــــــــــــــــــــــ