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Department of Geology, University of Kuwait, P.O. Box 5969, Kuwait

A significant occurrence of the metastable mineral bassanite (CaSO₄. ½H₂O) is reported here from the continental sabkha zone pans and gypsum dune complexes of Al-Khiran, Kuwait. This is the first known occurrence in the Arabian Gulf of this evaporite mineral outside the Abu Dhabi sabkha complex. The bassanite is probably partially topotactic after gypsum and occurs as a dissolution-reprecipitation product after gypsum. Scanning electron microscope (SEM) investigations show that the bassanite crystallites are approximately 5-30 µm in length, with a clearly identifiable hexagonal crystal morphology (illustrated here for the first time) which is only rarely observed in nature. The surficial layers of bassanite from Al-Khiran prevail only during the hot, dry summer season (April-October); during the wet winter months it reverts to gypsum fairly rapidly and hence a very significant climatic control is suggested for its genesis.