الملخص

Dissolution rate (K) of gypsum rocks of Fat'ha Formation (Middle Miocene) was determined at three different environments; closed system, that is still water and open system, that is flowing water and river water. In closed system, the dissolution rate is not a constant; it increases as the concentration (C) of the dissolving solution. In an open system, dissolution rate is a constant at constant flow velocity (V) and given temperature (T). It increases with an increase of either of them; however, the effect of (V) on (K) is much more pronounced than that of (T). Published data on the value of dissolution rate (K), based on laboratory experiments, are exaggerated by a factor of (4.1) to (4.6) compared with values of the present study. This is possibly due to the fact that these data represent dissolution through fissures in gypsum rocks and being far from natural environments for gypsum dissolution.