Sunday, July 17, 2011
Rockall is made of a type of peralkaline granite that is relatively rich in sodium and potassium. Within this granite are darker bands richer in the alkali pyroxene mineral aegirine and the alkali amphibole mineral riebeckite. The dark bands are a type of granite that geologists have named "rockallite", although use of this term is now discouraged. In 1975, a new mineral was discovered on Rockall. The mineral is called bazirite, (chemical composition BaZrSi3O9), named after the elements barium and zirconium. Rockall forms part of the deeply eroded Rockall Igneous Centre that was formed as part of the North Atlantic Igneous Province, approximately 55 million years ago, when the ancient continent of Laurasia was split apart by plate tectonics. Greenland and Europe separated and the north-east Atlantic Ocean was formed between them.