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Blue Pearl Granite (larvikite, Larvik Batholith, 292-298 Ma, Early Permian; near Larvik, southern Norway) | by James St. John
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Blue Pearl Granite (larvikite, Larvik Batholith, 292-298 Ma, Early Permian; near Larvik, southern Norway)

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

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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.

 

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Taken on August 2, 2014