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.
Varieties of larvikite are popular decorative/ornamental stones known commercially as “Blue Pearl Granite”, “Emerald Pearl Granite”, and other names. They are quarried from the Larvik Batholith (a.k.a. Larvik Pluton, Larvik Complex, Larvik Plutonic Complex), a suite of 10 igneous plutons emplaced in the Oslo Rift (Oslo Graben) surrounded by ~1.1 billion year old Sveconorwegian gneisses. The Larvik Batholith dates to about 292-298 million years old (early Early Permian). Many quarries exploit larvikite in the vicinity of the town of Larvik in southwestern Vestfold County, southern Norway.
Larvikite (“Blue Pearl Granite”) from the Larvik Batholith (Early Permian) near Larvik, southern Norway.
Larvikite (“Emerald Pearl Granite”) from the Larvik Batholith (Early Permian) near Larvik, southern Norway.