Alkali feldspar granite
| Igneous rock | |
.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]
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]
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]- ^ "The Chief Commercial Granites of MA, NH and RI (see, for example, pp. 179-180)" (PDF). US Geological Survey.
- ^ "FAQ - What is Granite?". US Geological Survey.
- ^ a b "Granite: Characteristics, Uses and Problems". US General Services Administration. Archived from the original on 2015-12-09. Retrieved 2015-12-11.
- ^ "Field Classification and Description of Soils and Rock" (PDF). US Environmental Protection Agency.
- ^ 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.
- ^ "Granite and Granodiorite". US National Park Service.
External links
[edit]
Media related to Alkali feldspar granite at Wikimedia Commons