Alkali feldspar granite

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Alkali feldspar granite
Igneous rock
Rocks - Alkali feldspar granite.JPG
Alkali feldspar granite. Holocrystalline texture, coarse-grained. Great amounts of potassium feldspar (orthoclase, pink-reddish in colour)
Composition
Primary Potassium feldspar, quartz
Secondary 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 amounts of black minerals.[2][3]

QAPF diagram for classification of plutonic rocks

Chemical composition[edit]

As shown in the QAPF diagram, alkali feldspar granite contains between 20% - 60% quartz. Less quartz content would lead to "quartz alkali feldspar syenite". More than 90% of the total feldspar content is in the form of alkali feldspar. Less than that amount would designate the rock as a granite.[4]

Mineral assemblage of igneous rocks

Other incorporated silicate minerals may include, very minor amounts of plagioclase feldspar, mica in the form of muscovite and/or biotite, and amphibole (often hornblende). Oxide minerals such as magnetite, ilmenite, or ulvospinel. Some sulfides and phosphates (mainly apatite) may also be present.

Occurrence[edit]

Alkali feldspar granites generally occur with other alkali-rich granitoids, such as monzogranite and syenogranite, forming part of the A-type granites. They are found in a wide range of tectonic settings and their origins remain uncertain.[5]

Uses[edit]

Granitic rocks in general are of interest to geologists, geochemists, etc., because they provide 'crystallized' telltale clues of their environment of formation.[6]

Alkali feldspar granite is used as construction material in the form of dimension stones, and polished slabs or tiles for building facades, pavements, and kitchen countertops.[3]

References[edit]

  1. ^ "The Chief Commercial Granites of MA, NH and RI (see, for example, pp. 179-180)" (PDF). US Geological Survey. 
  2. ^ "FAQ - What is Granite?". US Geological Survey. 
  3. ^ a b "Granite: Characteristics, Uses and Problems". US General Services Administration. 
  4. ^ "Field Classification and Description of Soils and Rock" (PDF). US Environmental Protection Agency. 
  5. ^ Bonin B. (2007). "A-type granites and related rocks: Evolution of a concept, problems and prospects" (PDF). Lithos. 97 (1-2): 1–29. doi:10.1016/j.lithos.2006.12.007. Archived from the original (PDF) on 2014-02-11. 
  6. ^ "Granite and Granodiorite". US National Park Service.