Rapakivi

rapakivi

[¦rä·pə′kē·vē]
(petrology)
Granite or quartz monzonite characterized by orthoclase phenocrysts mantled with plagioclase. Also known as wiborgite.

Rapakivi

 

a granite of porphyroid structure with round phe-nocrysts of pink orthoclase surrounded by a white or light green shell of oligoclase. The granite consists of orthoclase (about 40 percent), oligoclase (about 20 percent), black mica (about 8 percent), idiomorphic quartz (about 30 percent), and secondary minerals (about 2 percent, including amphibole, orthite, sphene, diopside, magnetite, and apatite). Rapakivi is usually brownish pink or reddish; occasionally it is greenish or almost black.

The granite is common in Finland and Sweden. In the USSR it is found in the Karelian ASSR, in Leningrad Oblast (near the city of Vyborg), and in the Ukraine (near the village of Goro-dishche in Cherkassy Oblast). Rapakivi is a valuable building and facing stone. In Leningrad the columns of St. Isaac’s Cathedral are made of the granite, as is the facing of the banks of the Neva River.

References in periodicals archive ?
Fyffe (1998) noted that the Jake Lee Mountain pluton has a core of medium-to coarse-grained, equigranlar riebeckite-bearing granite enveloped by a fine-gained rim of rapakivi granite porphyry.
Further evidence for Proterozoic crustal residence age was provided by Sm-Nd analyses of rapakivi granites (Ramo et al.
Structurally, the anorogenic rock bodies belong to the Fennoscandian Palaeo-Mesoproterozoic Rapakivi Province (Ramo & Haapala 1995; Koistinen 1996; Puura & Floden 1999).
The Mesoproterozoic (Koistinen 1996) or Palaeo-proterozoic (Ogg 2008) rapakivi granite intrusion at Maardu (Maardu Pluton) is 1.
Malic pillow mounds (comparable to pillow basalts), granitic pipes intruding upwards into overlying mafic material, development of hybrid magmas of intermediate composition (that gave rise to enclaves), abundant disequilibrium textures (quartz ocelli and rapakivi feldspar), and large-scale compositional layering are common in the MASLI.
It is interesting as well that strong negative anomalies prevail in the Gulf of Riga, most likely caused by the large Riga rapakivi granite massif (see, e.
Rapakivi textures, pegmatitic sweats, a convex exfoliation and lack of a penetrative fabric suggest they are part of the adjacent Siluro-Devonian Saint George Batholith rather than the Rocky Lakes suite.
Even more detailed special surveys were performed in some spots of geological interest, such as Kardla meteorite crater, Marjamaa rapakivi pluton, Uljaste uplift, Valgej6e buried valley, etc.
Paavo Harma and Olavi Selonen (Geological Survey of Finland and Abo Akademi University) studied implications of surface weathering of rapakivi granite for natural stone evaluation.