Granite (geology)

Granite (geology)
Name	Granite
Category	Igneous rock
Composition	Quartz, Feldspar, Mica (mineral)
Texture	Phaneritic
Color	Light-colored
Hardness	Mohs 6–7
Density	2.63–2.75 g/cm³

Granite (geology) Granite is a coarse-grained, felsic intrusive igneous rock widely studied in Geology and exposed in many orogenic belts such as the Himalayas, Alps, and Andes. It commonly hosts large batholiths like the Sierra Nevada (United States) plutons and shields such as the Canadian Shield, and it has been central to investigations by institutions including the Smithsonian Institution and the United States Geological Survey.

Definition and Characteristics

Granite is defined as a phaneritic intrusive rock dominated by quartz and alkali feldspar with subordinate plagioclase and mica; classical granitic bodies include the Sierra Nevada (United States), the Batholith of the Coast Mountains, and the Mojave Desert exposures examined by researchers from University of Cambridge, Harvard University, and University of California, Berkeley. Texturally, granites display large interlocking crystals comparable to plutonic suites studied by the Geological Society of America, and field mapping campaigns by agencies like the British Geological Survey and Geological Survey of Canada document typical exposures. Petrographic description standards are set by organizations such as the International Union of Geological Sciences and incorporated into curricula at institutions like the University of Oxford and Massachusetts Institute of Technology.

Petrography and Mineralogy

Typical mineral assemblages include quartz, K-feldspar (orthoclase, microcline), sodic and calcic plagioclase, biotite, muscovite, and accessory minerals such as zircon, apatite, titanite and magnetite; these assemblages are often characterized in samples from the Scandinavian Caledonides, the Karelian Province, and the Bandeira Mountains by teams at Uppsala University, University of Helsinki, and Universidade de São Paulo. Geochemical classification employs trace element and isotopic data measured at facilities like the Lamont–Doherty Earth Observatory, Geological Survey of Japan, and ETH Zurich laboratories. Mineral zoning and exsolution textures have been documented in classic localities such as the Grampian Mountains, the Aran Islands, and the Cornwall tin provinces studied by researchers from Truro College and University of Exeter.

Formation and Petrogenesis

Granite petrogenesis involves fractional crystallization, partial melting (anatexis) of continental crust, and magma mixing in settings like continental arcs exemplified by the Andean orogeny, the Caledonian orogeny, and the Variscan orogeny; major studies by researchers at Stanford University, University of Tokyo, and Australian National University address these processes. Geochronology using U–Pb zircon dating from localities such as the Western Ghats, the Baltic Shield, and the Athabasca Basin has tied granite emplacement to tectonic events recorded by organizations like the European Geosciences Union and the American Geophysical Union. Experimental petrology performed at facilities such as Caltech, Max Planck Institute for Chemistry, and CNRS laboratories constrains temperatures, pressures, and water contents required for crustal melting in terrains including the Sierra de Córdoba and the Namib Desert.

Textures and Classification

Granitic textures range from equigranular to porphyritic, with hyaline or sericitic alteration produced in hydrothermal systems studied at the Los Alamos National Laboratory and the Lawrence Berkeley National Laboratory. Classification schemes (e.g., IUGS QAPF) used by the International Geological Congress and taught at institutions like University of Vienna and University of Michigan distinguish true granites from granodiorites, monzogranites, and syenogranites in regions such as the Scottish Highlands, the Bavarian Alps, and the Sierra de Guadarrama. Microtextures such as myrmekite and perthite occur in samples from the Cornish and Massif Central provinces documented in monographs by the Royal Society.

Distribution and Tectonic Settings

Granite occurs in continental crust settings including cratons, orogenic belts, rifted margins, and post-collisional terrains; major occurrences include the Canadian Shield, the Fennoscandian Shield, the Yilgarn Craton, and the Amazonian Craton, mapped by bodies such as the Geological Survey of India and the Brazilian Geological Service (CPRM). Batholith-scale exposures such as the Sierra Nevada (United States), the Coast Mountains, and the Patagonian Batholith are associated with subduction zones studied by groups from University of British Columbia, Universidad de Chile, and Oregon State University. Post-orogenic and anorogenic granites appear in provinces like the Mesozoic North China Craton and the Aegean Arc, where research collaborations involve Peking University and National and Kapodistrian University of Athens.

Economic Uses and Quarrying

Granite has long been quarried for dimension stone and aggregate in famous sites such as the Shinagawa and Aberdeen quarries, and commercial operations are managed by companies profiled by the London Stock Exchange and the New York Stock Exchange. Historical uses in monuments and construction include projects like the Ellis Island structures, the New York Stock Exchange Building, and the Great Pyramid adjacent constructions referenced in studies by the Metropolitan Museum of Art and the Royal Ontario Museum. Modern extraction methods are regulated by agencies including the Environmental Protection Agency (United States), the European Commission, and national ministries like the Ministry of Mines (India) with engineering input from firms such as Vulcan Materials Company and Buzzi Unicem. Granite-hosted mineralization (tin, tungsten, rare earths) is economically significant in districts like Cornwall, the Bosnian Massif, and the Malkhan district investigated by geological surveys including the USGS and Geoscience Australia.

Weathering, Soil Formation, and Environmental Impact

Chemical and physical weathering of granite produces regolith and saprolite that develop into soils in landscapes such as the Loess Plateau, the Deccan Plateau, and the New England highlands; pedological studies are conducted by departments at Iowa State University, Wageningen University, and University of Pretoria. Weathering processes influence sediment supply to basins like the Ganges Delta, Amazon Basin, and Murray–Darling Basin and affect water chemistry monitored by institutions such as the World Meteorological Organization and UNEP. Quarrying impacts on habitats and heritage sites have prompted mitigation programs supported by organizations like ICOMOS and legislation influenced by the European Union and national heritage agencies.

Category:Igneous rocks