Larvikite (“Blue Pearl Granite”) from the Larvik Batholith (Early Permian) near Larvik, southern Norway.

Larvikite is one of my favorite rocks. It’s a variety of monzonite, though it’s sometimes misperceived as a variety of syenite. Larvikite is dominated by large crystals of spectacularly bluish-iridescent (schillerescent) perthitic feldspar (closely intergrown potassium feldspar and plagioclase feldspar). The play of colors is the result of light being dispersed along the plagioclase and K-feldspar crystal boundaries. The smaller black crystals are pyroxene.