| Igneous rock | |
 Larvikite fromLarvik, Norway | |
| Composition | |
|---|---|
| Plagioclase,alkali feldspar,amphibole |
_Larvik_Batholith_Norway.jpg)
Larvikite is anigneous rock, specifically a variety ofmonzonite,[1] notable for the presence of thumbnail-sizedcrystals offeldspar. These feldspars are known asternary because they contain significant components of all threeendmember feldspars.[1] The feldspar has partly unmixed on the micro-scale to form aperthite, and the presence of the alternatingalkali feldspar andplagioclase layers give its characteristic silver-blueschiller effect (calledlabradorescence) on polished surfaces.Olivine can be present along withapatite, and locallyquartz. Larvikite is usually rich intitanium, withtitanaugite and/ortitanomagnetite present.
Larvikite occurs in the LarvikBatholith (also called the Larvik Plutonic Complex), a suite of ten igneousplutons emplaced in theOslo Rift (Oslo Graben) surrounded by ~1.1 billion year oldSveconorwegiangneisses. The Larvik Batholith is ofPermian age, about 292–298 million years old.[2] Larvikite is also found in the Killala Lake Alkalic Rock Complex nearThunder Bay inOntario, Canada.[3]
The name originates from the town ofLarvik inNorway, where this type of igneous rock is found. Many quarries exploit larvikite in the vicinity of Larvik.
Intrusions of larvikite in Norway form part of the suite ofigneous rocks that were emplaced during the Permianperiod, 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.[1]
Larvikite is prized for its high polish and the labradorescence of its feldspar crystals, and is used asdimension stone, often cladding the facades of commercial buildings and corporate headquarters.[1] It is known informally asBlue PearlGranite, although this is not an accurate description. Larvikite has been designated by theInternational Union of Geological Sciences as aGlobal Heritage Stone Resource.[4]
