Jebel Haraza

The complex forms a mountainous plateau 300 m above the Northern Kordofan plain. Nubian Sandstone, which previously buried the intrusion, lies to the west and south and still caps the northern summits, while Precambrian gneisses outcrop to the southwest. The main mass comprises flow-banded, brecciated and sometimes columnar jointed rhyolitic lavas with some tuffs and agglomerates. Rare phenocrysts of quartz and orthoclase lie in a devitrified base; riebeckite has been identified in some tuffs. Peralkaline granite forms a 15 km long intrusion southeast of the volcanic rocks and a number of small inliers within Nubian Sandstone to the west. The principal mafic mineral in the granite is aegirine with a sodic amphibole also present. Porphyry and felsite dykes in which aegirine may occur cut the volcanics and granite. A gabbro body is known to exist on the western flank of the hill but was not observed by Delaney (1958).