Blue Pearl Granite (larvikite) Larvik Batholith Norway

Larvikite is an

igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma o ...

, specifically a variety of

monzonite Monzonite is an igneous intrusive rock, formed by slow cooling of underground magma that has a moderate silica content and is enriched in alkali metal oxides. Monzonite is composed mostly of plagioclase and alkali feldspar. Syenodiorite is an o ...

, notable for the presence of thumbnail-sized

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...

s of

feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) felds ...

. These feldspars are known as ''ternary'' because they contain significant components of all three endmember feldspars. The feldspar has partly unmixed on the micro-scale to form a

perthite Perthite is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar (near K-feldspar, KAlSi3O8, in composition) includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar (near albite, ...

, and the presence of the alternating

alkali feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldspa ...

and

plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more p ...

layers give its characteristic silver-blue

schiller Johann Christoph Friedrich von Schiller (, short: ; 10 November 17599 May 1805) was a German playwright, poet, and philosopher. During the last seventeen years of his life (1788–1805), Schiller developed a productive, if complicated, friends ...

effect (called labradorescence) on polished surfaces.

Olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...

can be present along with

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common ...

, and locally

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical f ...

. Larvikite is usually rich in

titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion i ...

, with titanaugite and/or

titanomagnetite Titanomagnetite is a mineral containing oxides of titanium and iron, with the formula Fe2+(Fe3+,Ti)2O4. It is also known as titaniferous magnetite, mogensenite, Ti-magnetite, or titanian magnetite. It is part of the spinel group of minerals. The Cu ...

present. Larvikite occurs in the Larvik

Batholith A batholith () is a large mass of intrusive igneous rock (also called plutonic rock), larger than in area, that forms from cooled magma deep in Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, s ...

(also called the Larvik Plutonic Complex), a suite of ten igneous

pluton In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s emplaced in the Oslo Rift (Oslo Graben) surrounded by ~1.1 billion year old Sveconorwegian

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures a ...

es. The Larvik Batholith is of

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleo ...

age, about 292–298 million years old. Larvikite is also found in the Killala Lake Alkalic Rock Complex near

Thunder Bay Thunder Bay is a city in and the seat of Thunder Bay District, Ontario, Canada. It is the most populous municipality in Northwestern Ontario and the second most populous (after Greater Sudbury) municipality in Northern Ontario; its populati ...

Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...

, Canada. The name originates from the town of

Larvik Larvik () is a town and municipality in Vestfold in Vestfold og Telemark county, Norway. The administrative centre of the municipality is the city of Larvik. The municipality of Larvik has about 46,364 inhabitants. The municipality has a 110 ...

Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of ...

, where this type of igneous rock is found. Many quarries exploit larvikite in the vicinity of Larvik.

Formation

Intrusions of larvikite in Norway form part of the suite of

s that were emplaced during the Permian period, associated with the formation of the Oslo Rift. The crystallisation of a ternary feldspar indicates that this rock began to crystallise under lower crustal conditions.

Uses

Larvikite is prized for its high polish and the labradorescence of its feldspar crystals, and is used as

dimension stone Dimension stone is natural stone or rock that has been selected and finished (e.g., trimmed, cut, drilled, ground, or other) to specific sizes or shapes. Color, texture and pattern, and surface finish of the stone are also normal requirements. ...

, often cladding the facades of commercial buildings and corporate headquarters. It is known informally as ''Blue Pearl

Granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...

'', although this is not an accurate description. Larvikite has been designated by the

International Union of Geological Sciences The International Union of Geological Sciences (IUGS) is an international non-governmental organization devoted to international cooperation in the field of geology. About The IUGS was founded in 1961 and is a Scientific Union member of the Int ...

as a Global Heritage Stone Resource.

References

External links

Petrogenesis of the Oslo Region Larvikites and Associated Rocks (abstract)
Journal of Petrology, 1980, volume 21, Number 3, pages 499-531
Structure of the larvikite-lardalite complex, Oslo-region, Norway, and its evolution (abstract)
International Journal of Earth Sciences, 1978, volume 67, number 1, pages 330-342
Plutonic rocks Geology of Norway Larvik Building stone {{petrology-stub