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A piece of tonalite on red granite gneiss from Tjörn, Sweden QAPF diagram with tonalite field highlighted. Tonalite is an igneous, plutonic rock, of felsic composition, with phaneritic (coarse-grained) texture.
Alkali feldspar granite, some varieties of which are called 'red granite', [1] is a felsic igneous rock and a type of granite rich in the mineral potassium feldspar (K-spar). It is a dense rock with a phaneritic texture. The abundance of K-spar gives the rock a predominant pink to reddish hue; peppered with minor amounts of black minerals. [2] [3]
[5] [6] A granite containing both muscovite and biotite micas is called a binary or two-mica granite. Two-mica granites are typically high in potassium and low in plagioclase, and are usually S-type granites or A-type granites, as described below. [7] [8] Another aspect of granite classification is the ratios of metals that potentially form ...
It characterizes one of the most well-preserved and oldest pieces of continental crust today by containing rocks in the Barberton Granite Greenstone Terrain (3.55–3.22 Ga). The BGB is a small, cusp-shaped succession of volcanic and sedimentary rocks, surrounded on all sides by granitoid plutons which range in age from >3547 to <3225 Ma. [1]
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 (a variety of plagioclase). Common mineral components include hornblende and biotite. The name has come to be used most frequently as a textural term where it implies ...
Granite rock hand-sized sample. A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. [1] Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quartz-poor monzonites to quartz-rich quartzolites. [2]
The grains best matched a group of sedimentary rocks known as Old Red Sandstone found in the Orcadian Basin in northeast Scotland, which differed completely from stones found in Wales.
Igneous rocks are divided into two main categories: Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earth's crust. A common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, forming minerals such as pumice or basalt. [5]