Abstract
Abstract A glacial boulder found at the village of Norsjovallen, 80 km WNW of the town of Skelleftea in Vasterbotten County, contains orbicules characterized by plagioclase (oligoclase) cores, which are surrounded by shells containing amphibole (actinolite), plagioclase and biotite. The grain size decreases outwards, accompanied by a greater degree of preferred orientation in the minerals. Amphibole, plagioclase and biotite are arranged so that their c-axes are aligned towards the centre of the orbicules. The matrix is much more granitic than the orbicules. In the matrix, microcline, plagioclase, quartz and biotite are the major phases. A deeply etched boulder of orbiculite from Smaland's Anneberg, 10 km NE of the town of Nassjo, also shows orbicules with plagioclase (oligoclase) cores, although in this case the cores have been affected by secondary microcline mineralization. Outer shells show contrasting proportions between plagioclase, hornblende and biotite. The outermost shells are characterized by an...
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