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]]