An occurrence of ultrapotassic dikes in the

A brief description is presented here of a group of highly potassic, highly magnesian dikes, originally called kersantites but better-named as lamproites. These rocks may contain phenocrysts of forsteritic olivine, diopside, phlogopite, amphibole (a unique potassic magnesioarfvedsonite) and pseudoleucite set in a groundmass rich in phlogopite, amphibole and carbonate. A K-Ar date on phlogopite indicates an age of ca. 1200 m.y. which is similar to that of a number of other alkaline rocks in the North Atlantic region