Rapakivi Granite

Rapakivi granite

Rapakivi granite is an igneous intrusive rock and variant of alkali feldspar granite. It is characterized by large, rounded crystals of orthoclase each with a rim of oligoclase. Common mineral components include hornblende and biotite. The name has come to be used most frequently as a textural term where it implies plagioclase rims around orthoclase in plutonic (intrusive) rocks. Rapakivi is a Finnish compound of "rapa" and "kivi", because the different heat expansion coefficients of the component minerals make exposed rapakivi crumble easily into sand.

Granite

Granite is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, mica and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies underground. It is common in the continental crust of Earth, where it is found in igneous intrusions. These range in size from dikes only a few centimeters across to batholiths exposed over hundreds of square kilometers.

rapakivi

Noun

1. A form of granite found in southeastern Finland.

granite

Noun

1. A group of igneous and plutonic rocks composed primarily of feldspar and quartz. Usually contains one or more dark minerals, which may be mica, pyroxene, or amphibole. Granite is quarried for building stone, road gravel, decorative stone, and tombstones. Common colors are gray, white, pink, and yellow-brown.
2. Toughness; the quality of having a thick skin or being rough.