Peralkaline rock
Peralkaline rocks include those igneous rocks which have a deficiency of aluminium such that sodium and potassium are in excess of that needed for feldspar. The presence of aegerine and riebeckite are indicative of peralkaline conditions. An example is the peralkaline granite that forms the islet of Rockall in the North Atlantic Ocean.
Peralkaline rocks are indicative of continental rift basin-related volcanicity, for example the peralkaline rhyolite lavas of the East African Rift in central Kenya.
