Alkaline Rocks and Carbonatites of the World

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Um Risha (Gabal Um Risha)


Occurrence number: 
Longitude: 33.3, Latitude: 23.3

The exposed part of the Um Risha complex measures 12 km east-west but an unknown area is concealed beneath Nubian sandstone. The intrusive rocks are peralkaline syenites and granites of varying grain size. The principal mafic minerals are aegirine-augite and a range of amphiboles including riebeckitic types. What are taken to be remnants of a volcanic cone include pyroclastic rocks, trachyte and trachybasalt, the trachyte containing aegirine-augite, amphibole and sanidine. There are a few bostonite dykes within the complex.

EL RAMLY, M.F., ARMANIOUS, L.K. and HUSSEIN, A.A.A. 1979. The two ring complexes of Hadayib and Umm Risha, SE. Desert. Annals of the Geological Survey of Egypt, 9: 61-9.
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