An Al-rich intercalation in garnetiferous migmatites near Vikeså, southwestern Norway, consists of sapphirine, bronzite, cordierite, phlogopite, hercynite, plagioclase (about 32 % An), K-feldspar, and magnetite. Optical properties and chemical compositions of the dominant minerals were determined in a rock specimen, for which the whole-rock analysis is given. There is evidence that sapphirine + bronzite + SiO₂ react into cordierite + hercynite. Phlogopite formed as a reaction product where there was metasomatism of potassium. The relict assemblage sapphirine + bronzite (9.2 wt% Al₂O₃) represents a high stage of granulite facies metamorphism with the estimated petrogenetic conditions of total pressure 3-6 kb and temperature of 900°C.