LARVIKITE
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.