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Plagioclase; dark minerals. 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 ...
Granite. Granite (/ ˈɡrænɪt / GRAN-it) is a coarse-grained (phaneritic) 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.
Feldspar (/ ˈfɛl (d) ˌspɑːr / FEL (D)-spar; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. [3] The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium ...
A QAPF diagram is a doubled-triangle plot diagram used to classify intrusive igneous rocks based on their mineralogy. The acronym QAPF stands for " Quartz, Alkali feldspar, Plagioclase, Feldspathoid (Foid) ", which are the four mineral groups used for classification in a QAPF diagram. The percentages (ratios) of the Q, A, P and F groups are ...
The most common mineral assemblage of granulite facies consists of antiperthitic plagioclase, alkali feldspar containing up to 50% albite and Al 2 O 3-rich pyroxenes. Transition between amphibolite and granulite facies is defined by these reaction isograds: amphibole → pyroxene + H 2 O biotite → K-feldspar + garnet + orthopyroxene + H 2 O.
Trachyte. Trachyte (/ ˈtreɪkaɪt, ˈtræk -/) is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, [1] and is formed by the rapid cooling of lava (or shallow intrusions) enriched with silica and alkali metals. [2][3][4] It is the ...
Color index, or the modal abundance of minerals other than quartz, plagioclase and alkali feldspar (e.g., mafic silicates, oxides, sulfides, phosphates, etc.), can be used to infer the maturity of a granite. Juvenile I-type granites have a higher color index. Amphibole, biotite, sphene, allanite, and oxides are typically more abundant. In ...
Like all granites, the modal mineralogy of S-type granites are dominated by alkali - and plagioclase feldspars and quartz. Thus, S-type granites are silica over-saturated (contain quartz), and do not contain feldspathoids. An interesting feature of S-type granites, at the hand sample scale, is that alkali-feldspars are typically white in color ...