Rapakivi granite
2007201
208861131
2008-04-28T22:25:21Z
Smalljim
100426
Fixing [[Wikipedia:Disambiguation pages with links|links to disambiguation pages]] using [[Project:AutoWikiBrowser|AWB]]
[[Image:Rapakivigranite ss.jpg|thumb|right|Rapakivi granite.]]
[[Image:Rapakiwi-Geschiebe.jpg|thumb|right|Rapakivi from a moraine in Northern Germany.]]
[[Image:Eroded rapakivi granite.JPG|thumb|left|Eroded rapakivi granite in Finland]]
{{Unreferenced|date=February 2008}}'''Rapakivi granite''' is a [[hornblende]]-[[biotite]] [[granite]] containing large rounded crystals of [[orthoclase]] mantled with [[oligoclase]]. The name has come to be used most frequently as a textural term where it implies [[plagioclase]] rims around [[orthoclase]] in [[plutonic]] rocks. Rapakivi is [[Finnish language|Finnish]] for "crumbly rock", because the different heat expansion coefficients of the component minerals make exposed rapakivi crumbly.
==Occurrence==
Rapakivi is a fairly uncommon type of granite, but has been described from localities in [[North America|North]] and [[South America]], parts of the [[Baltic Shield]], southern [[Greenland]], southern [[Africa]], [[India]] and [[China]]. Most of these examples are found within [[Proterozoic]] [[metamorphic]] belts, although both [[Archaen]] and [[Phanerozoic]] examples are known.
==Formation==
Rapakivi granites are often found associated with intrusions of [[Anorthosite]], [[Norite]], [[Charnockite]] and [[Mangerite]]. It has been suggested that the entire suite results from the [[Fractional crystallization (geology)|fractional crystallization]] of a single parental magma <ref> Zhang,S-H., Liu,S-W., Zhao,Y., Yang,J-H. Song,B. and Liu,X-M. The 1.75–1.68 Ga anorthosite-mangerite-alkali granitoid-rapakivi granite suite from the northern North China Craton: Magmatism related to a Paleoproterozoic orogen. Precambrian Research, 155, 287-312.</ref>
==Use as a building material==
Rapakivi is the material used in [[Åland]]'s [[Middle Age]] stone [[Church (building)|churches]].
==References==
<references />
[[Category:Igneous rocks]]
{{petrology-stub}}
[[de:Rapakiwi]]
[[et:Rabakivi]]
[[eu:Rapakivi granito]]
[[fr:Granite rapakivi]]
[[nl:Rapakivi]]
[[pl:Granit rapakiwi]]
[[fi:Rapakivi]]
[[sv:Rapakivi]]
[[uk:Рапаківі]]