Notes on the Egersund anorthosite, Norway

Abstract

Located in the extreme southern part of Norway, the region has been described in part by F. K. Kolderup, and is now under investigation by Professor Tom. F. W. Barth of Oslo. Among the outstanding features of the rock are straight, sharp dikes of massive medium‐grained anorthosite, the rocks of which are indistinguishable from their wall‐rocks, but they cut the foliation of the wall‐rocks at high angles. Equally remarkable are discordant dikes, up to three feet thick, of coarse, pegmatitic texture, composed megascopically of plagioclase (probably calcic andesine), pyroxene, and ilmenite. Preliminary examination by Barth and the writer in the field failed to reveal any hydroxyl‐bearing minerals or quartz. Some dikes are so rich in ilmenite that they constitute commercial ore. These dikes raise the question as to what volatiles are capable of precipitating the above mineral associations.