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Granite (/ ˈ ɡ r æ n ɪ t / GRAN-it) is a coarse-grained intrusive igneous rock composed mostly of quartz, alkali feldspar, 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 ...
Because volcanic rocks are mostly fine-grained or glassy, it is much more difficult to distinguish between the different types of extrusive igneous rocks than between different types of intrusive igneous rocks. Generally, the mineral constituents of fine-grained extrusive igneous rocks can only be determined by examination of thin sections of ...
Dunite – Ultramafic and ultrabasic rock from Earth's mantle which is made of the mineral olivine; Essexite – Igneous rock type; Foidolite – Igneous rock rich in feldspathoid minerals; Gabbro – Coarse-grained mafic intrusive rock; Granite – Type of igneous rock; Granodiorite – Type of coarse grained intrusive igneous rock
The minerals in a phaneritic igneous rock are sufficiently large to see each individual crystal with the naked eye. Examples of phaneritic igneous rocks are gabbro , diorite , and granite . Porphyritic textures develop when conditions during the cooling of magma change relatively quickly.
For phaneritic felsic rocks, the QAPF diagram should be used, and a name given according to the granite nomenclature. Often the species of mafic minerals is included in the name, for instance, hornblende-bearing granite, pyroxene tonalite or augite megacrystic monzonite, because the term "granite" already assumes content with feldspar and quartz.
Gneiss (pronounced nise) is a metamorphic rock. When granite is heated all the minerals melt down and make new crystals. Obviously, when the crystals are changed gneiss is formed. People crush this rock to make roads as this is very hard and a foliated rock.
Silica content is thus the most important chemical criterion for classifying igneous rock. [7] The content of alkali metal oxides is next in importance. [11] About 65% of the Earth's crust by volume consists of igneous rocks. Of these, 66% are basalt and gabbro, 16% are granite, and 17% granodiorite and diorite.
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]
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