Mineralogy and Genesis of Zeolites of Gedarif Area, Eastern Sudan

Abstract

Amygdaloidal, cavity- and vein-filling zeolites in basaltic rocks from the Gedarif area in the eastern Sudan have been studied in some detail by optical microscope and XRD techniques combined with field observations. This show that basalt experienced two paragenetic stages with respect to their texture and mineralogy. Stage 1 alteration, which occurred in response to the burial of basaltic rocks and their interaction with heated groundwater, is characterized by the formation of low-temperature zeolite facies minerals in vesicles (amygdales) containing mainly fine-grained zeolite minerals (natrolite, stilbite, chabazite, analcime and thomsonite). Stage 2 mineralization occurred due to an activity of hydrothermal solutions that formed large crystals of natrolite, stilbite, chabazite, analcime and mesolite, associated frequently with quartz (Geodes quartz), calcite and semi gemstones.