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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 for "crumbly rock", because the different heat expansion coefficients of the component minerals make exposed rapakivi crumbly.〔(Tietoaineistot - maaperäkartan käyttöopas - rapautuminen - GTK )〕 Rapakivi was first described by Finnish petrologist Jakob Sederholm in 1891.〔"Ueber die finnländischen Rapakiwigesteine〕 Since then, southern Finland's rapakivi granite intrusions have been the type locality of this variety of granite.〔"(3000 miljoonaa vuotta, Suomen Kallioperä )" Finnish geological society, 1998, chapter 9, ISBN 952-90-9260-1 . Language: Finnish. 〕 ==Occurrence== Rapakivi is a fairly uncommon type of granite, but has been described from localities in 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 Archaean and Phanerozoic examples are known. Best known occurrence range is from Ukraine, through Finland and Scandinavia, southern Greenland to the Labrador peninsula and on through the North American continent to California. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rapakivi granite」の詳細全文を読む スポンサード リンク
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