rapakivi texture

rapakivi texture

[¦rä·pə′kē·vē ′teks·chər]
(petrology)
An igneous and metamorphic rock texture in which spherical potassium feldspar crystals are surrounded by a rim of sodium feldspar, both within a finer-grained matrix.
References in periodicals archive ?
The Churio granite is pinkish, apparently fresh, leucocratic with rapakivi texture.
Rapakivi granites are defined as A-type granites characterized by the presence, at least in the larger batholiths, of granite varieties showing rapakivi texture (Haapala & Rama 1992).
These stones are coarse-grained rocks with a typical rapakivi texture of large round K-feldspar ovoids, with or without a plagioclase rim.
Sederholm (1891) noted that the typical rapakivi texture is more prone to breakdown of mineral grains than, e.g.
Typical shallow-crustal granites with rapakivi texture are found in the central part (Bogatikov & Birkis 1973), while subvolcanic granophyres occupy large areas in its northern part--on the basement of Ruhnu Island in the Gulf of Riga and in the southwestern part of Saaremaa Island (Kuuspalu 1975; Puura et al.
Plagioclase-mantled alkali feldspar ovoids (the rapakivi texture) are lacking; this texture is found only in the granites of the Riga batholith.
The MWG contains feldspars of various textures and composition, including abundant plagioclase-mantled K-feldspar (rapakivi texture), boxy and spongy cellular plagioclase, and plagioclase that show An spikes and/or central cures of higher Ca content.
The pressure quench formation of rapakivi texture. Contributions to Mineralogy and Petrology, 68, pp.
In addition to the K-feldspar (which includes minor amounts of microcline) + plagioclase assemblage there is a range of disequilibrium feldspar textures, including plagioclase mantles on K-feldspar (rapakivi textures), boxy and spongy cellular plagioclase, complexly zoned plagioclase grains commonly displaying an An "spike", and plagioclase displaying central cored zones.
Some samples contain oligoclase mantles around perthite (rapakivi texture) or vice versa.