Alkaline Rocks and Carbonatites of the World

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Um Risha (Gabal Um Risha)

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Occurrence number: 
049-00-035
Country: 
Egypt
Location: 
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.

References: 
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.
Location: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith