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GRANITE ( /ˈɡrænᵻt/ ) is a common type of felsic intrusive igneous rock that is granular and phaneritic in texture. Granites can be predominantly white, pink, or gray in color, depending on their mineralogy. The word "granite" comes from the Latin
Latin
_granum_, a grain, in reference to the coarse-grained structure of such a holocrystalline rock. Strictly speaking, granite is an igneous rock with between 20% and 60% quartz by volume, and at least 35% of the total feldspar consisting of alkali feldspar , although commonly the term "granite" is used to refer to a wider range of coarse grained igneous rocks containing quartz and feldspar.

The term "granitic" means granite-like and is applied to granite and a group of intrusive igneous rocks with similar textures and slight variations in composition and origin. These rocks mainly consist of feldspar , quartz, mica , and amphibole minerals , which form an interlocking, somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende ) peppering the lighter color minerals. Occasionally some individual crystals (phenocrysts ) are larger than the groundmass , in which case the texture is known as porphyritic . A granitic rock with a porphyritic texture is known as a granite porphyry . Granitoid is a general, descriptive field term for lighter-colored, coarse-grained igneous rocks. Petrographic examination is required for identification of specific types of granitoids. The extrusive igneous rock equivalent of granite is rhyolite .

Granite
Granite
is nearly always massive (lacking any internal structures), hard and tough, and therefore it has gained widespread use throughout human history as a construction stone. The average density of granite is between 2.65 and 2.75 g/cm3 (165.4 - 171.7 lb/ft3), its compressive strength usually lies above 200 MPa, and its viscosity near STP is 3–6 • 1019 Pa·s.

The melting temperature of dry granite at ambient pressure is 1215–1260 °C (2219–2300 °F); it is strongly reduced in the presence of water, down to 650 °C at a few kBar pressure.

Granite
Granite
has poor primary permeability , but strong secondary permeability.

CONTENTS

* 1 Mineralogy

* 1.1 Chemical composition

* 2 Occurrence

* 3 Origin

* 3.1 Geochemical origins * 3.2 Chappell "> QAPF diagram for classification of plutonic rocks Mineral
Mineral
assemblage of igneous rocks

Granite
Granite
is classified according to the QAPF diagram for coarse grained plutonic rocks and is named according to the percentage of quartz , alkali feldspar (orthoclase , sanidine , or microcline ) and plagioclase feldspar on the A-Q-P half of the diagram. True granite according to modern petrologic convention contains both plagioclase and alkali feldspars. When a granitoid is devoid or nearly devoid of plagioclase, the rock is referred to as alkali feldspar granite . When a granitoid contains less than 10% orthoclase, it is called tonalite ; pyroxene and amphibole are common in tonalite. A granite containing both muscovite and biotite micas is called a binary or _two-mica_ granite. Two-mica granites are typically high in potassium and low in plagioclase, and are usually S-type granites or A-type granites.

CHEMICAL COMPOSITION

A worldwide average of the chemical composition of granite, by weight percent, based on 2485 analyses:

SiO2 72.04% (silica) 72.04

Al2O3 14.42% (alumina) 14.42

K2O 4.12% 4.12

Na2O 3.69% 3.69

CaO 1.82% 1.82

FeO 1.68% 1.68

Fe2O3 1.22% 1.22

MgO 0.71% 0.71

TiO2 0.30% 0.3

P2O5 0.12% 0.12

MnO 0.05% 0.05

OCCURRENCE

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The Cheesewring , a granite tor A granite peak at Huangshan
Huangshan
, China

Granite
Granite
containing rock is widely distributed throughout the continental crust . Much of it was intruded during the Precambrian age; it is the most abundant basement rock that underlies the relatively thin sedimentary veneer of the continents. Outcrops of granite tend to form tors and rounded massifs . Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels . Granite
Granite
often occurs as relatively small, less than 100 km² stock masses (stocks ) and in batholiths that are often associated with orogenic mountain ranges. Small dikes of granitic composition called aplites are often associated with the margins of granitic intrusions . In some locations, very coarse-grained pegmatite masses occur with granite.

ORIGIN

Granite
Granite
has a felsic composition and is more common in recent geologic time in contrast to Earth's ultramafic ancient igneous history. Felsic rocks are less dense than mafic and ultramafic rocks, and thus they tend to escape subduction , whereas basaltic or gabbroic rocks tend to sink into the mantle beneath the granitic rocks of the continental cratons . Therefore, granitic rocks form the basement of all land continents .

GEOCHEMICAL ORIGINS

Granitoids have crystallized from magmas that have compositions at or near a eutectic point (or a temperature minimum on a cotectic curve). Magmas will evolve to the eutectic because of igneous differentiation , or because they represent low degrees of partial melting. Fractional crystallisation serves to reduce a melt in iron , magnesium , titanium , calcium and sodium , and enrich the melt in potassium and silicon – alkali feldspar (rich in potassium) and quartz (SiO2), are two of the defining constituents of granite.

This process operates regardless of the origin of the parental magma to the granite, and regardless of its chemistry. However, the composition and origin of the magma that differentiates into granite leaves certain geochemical and mineral evidence as to what the granite's parental rock was. The final mineralogy, texture and chemical composition of a granite is often distinctive as to its origin. For instance, a granite that is formed from melted sediments may have more alkali feldspar , whereas a granite derived from melted basalt may be richer in plagioclase feldspar . It is on this basis that the modern "alphabet" classification schemes are based. Granite has a slow cooling process which forms larger crystals.

CHAPPELL & WHITE CLASSIFICATION SYSTEM

The letter-based Chappell "> Grus sand and granitoid it derived from

Physical weathering occurs on a large scale in the form of exfoliation joints , which are the result of granite's expanding and fracturing as pressure is relieved when overlying material is removed by erosion or other processes.

Chemical weathering of granite occurs when dilute carbonic acid , and other acids present in rain and soil waters, alter feldspar in a process called hydrolysis . As demonstrated in the following reaction, this causes potassium feldspar to form kaolinite , with potassium ions, bicarbonate, and silica in solution as byproducts. An end product of granite weathering is grus , which is often made up of coarse-grained fragments of disintegrated granite. 2 KAlSi3O8 + 2 H2CO3 + 9 H2O → Al2Si2O5(OH)4 + 4 H4SiO4 + 2 K+ + 2 HCO3−

Climatic variations also influence the weathering rate of granites. For about two thousand years, the relief engravings on Cleopatra\'s Needle obelisk had survived the arid conditions of its origin before its transfer to London. Within two hundred years, the red granite has drastically deteriorated in the damp and polluted air there.

NATURAL RADIATION

Granite
Granite
is a natural source of radiation , like most natural stones. However, some granites have been reported to have higher radioactivity, thereby raising some concerns about their safety.

Potassium-40 is a radioactive isotope of weak emission, and a constituent of alkali feldspar , which in turn is a common component of granitic rocks, more abundant in alkali feldspar granite and syenites . Naturally, a geiger counter should register this low effect.

Some granites contain around 10 to 20 parts per million (ppm) of uranium . By contrast, more mafic rocks, such as tonalite, gabbro and diorite , have 1 to 5 ppm uranium, and limestones and sedimentary rocks usually have equally low amounts. Many large granite plutons are sources for palaeochannel -hosted or roll front uranium ore deposits , where the uranium washes into the sediments from the granite uplands and associated, often highly radioactive pegmatites. Cellars and basements built into soils over granite can become a trap for radon gas, which is formed by the decay of uranium. Radon
Radon
gas poses significant health concerns and is the number two cause of lung cancer in the US behind smoking.

Thorium
Thorium
occurs in all granites as well. Conway granite has been noted for its relatively high thorium concentration of 56±6 ppm.

There is some concern that some granite sold as countertops or building material may be hazardous to health. Dan Steck of St. Johns University has stated that approximately 5% of all granite is of concern, with the caveat that only a tiny percentage of the tens of thousands of granite slab types have been tested. Various resources from national geological survey organizations are accessible online to assist in assessing the risk factors in granite country and design rules relating, in particular, to preventing accumulation of radon gas in enclosed basements and dwellings.

A study of granite countertops was done (initiated and paid for by the Marble
Marble
Institute of America) in November 2008 by National Health and Engineering Inc. of USA. In this test, all of the 39 full-size granite slabs that were measured for the study showed radiation levels well below the European Union safety standards (section 4.1.1.1 of the National Health and Engineering study) and radon emission levels well below the average outdoor radon concentrations in the US.

INDUSTRY

Granite
Granite
and related marble industries are considered one of the oldest industries in the world; existing as far back as Ancient Egypt .

Major modern exporters of granite include China, India, Italy, Brazil, Canada, Germany, Sweden, Spain and the United States .

Indian granite quarries have been mired in controversy over child labor and slavery .

USES

ANTIQUITY

Cleopatra's Needle, London

The Red Pyramid
Red Pyramid
of Egypt (c. 26th century BC), named for the light crimson hue of its exposed limestone surfaces, is the third largest of Egyptian pyramids . Menkaure\'s Pyramid , likely dating to the same era, was constructed of limestone and granite blocks. The Great Pyramid of Giza (c. 2580 BC ) contains a huge granite sarcophagus fashioned of "Red Aswan
Aswan
Granite". The mostly ruined Black Pyramid dating from the reign of Amenemhat III
Amenemhat III
once had a polished granite pyramidion or capstone, which is now on display in the main hall of the Egyptian Museum in Cairo
Cairo
(see Dahshur
Dahshur
). Other uses in Ancient Egypt include columns , door lintels , sills , jambs , and wall and floor veneer. How the Egyptians worked the solid granite is still a matter of debate. Dr. Patrick Hunt has postulated that the Egyptians used emery , which has greater hardness on the Mohs scale .

Rajaraja Chola I of the Chola Dynasty in South India
India
built the world's first temple entirely of granite in the 11th century AD in Tanjore
Tanjore
, India
India
. The Brihadeeswarar Temple dedicated to Lord Shiva was built in 1010. The massive Gopuram (ornate, upper section of shrine) is believed to have a mass of around 81 tonnes. It was the tallest temple in south India.

Imperial Roman granite was quarried mainly in Egypt, and also in Turkey, and on the islands of Elba
Elba
and Giglio . Granite
Granite
became "an integral part of the Roman language of monumental architecture". The quarrying ceased around the third century CE. Beginning in Late Antiquity the granite was reused, which since at least the early 16th century became known as spoliation . Through the process of case-hardening , granite becomes harder with age. The technology required to make tempered steel chisels was largely forgotten during the Middle Ages. As a result, Medieval stoneworkers were forced to use saws or emery to shorten ancient columns or hack them into discs. Giorgio Vasari
Giorgio Vasari
noted in the 16th century that granite in quarries was "far softer and easier to work than after it has lain exposed" while ancient columns, because of their "hardness and solidity have nothing to fear from fire or sword, and time itself, that drives everything to ruin, not only has not destroyed them but has not even altered their colour."

MODERN

Sculpture And Memorials

Various granites (cut and polished surfaces)

In some areas, granite is used for gravestones and memorials. Granite is a hard stone and requires skill to carve by hand. Until the early 18th century, in the Western world, granite could be carved only by hand tools with generally poor results.

A key breakthrough was the invention of steam-powered cutting and dressing tools by Alexander MacDonald of Aberdeen
Aberdeen
, inspired by seeing ancient Egyptian granite carvings. In 1832, the first polished tombstone of Aberdeen
Aberdeen
granite to be erected in an English cemetery was installed at Kensal Green Cemetery
Kensal Green Cemetery
. It caused a sensation in the London monumental trade and for some years all polished granite ordered came from MacDonald's. As a result of the work of sculptor William Leslie, and later Sidney Field, granite memorials became a major status symbol in Victorian Britain. The royal sarcophagus at Frogmore was probably the pinnacle of its work, and at 30 tons one of the largest. It was not until the 1880s that rival machinery and works could compete with the MacDonald works.

Modern methods of carving include using computer-controlled rotary bits and sandblasting over a rubber stencil. Leaving the letters, numbers, and emblems exposed on the stone, the blaster can create virtually any kind of artwork or epitaph.

The stone known as "black granite" is usually gabbro , which has a completely different chemical composition.

Buildings

Granite
Granite
has been extensively used as a dimension stone and as flooring tiles in public and commercial buildings and monuments. Aberdeen
Aberdeen
in Scotland, which is constructed principally from local granite, is known as "The Granite
Granite
City". Because of its abundance in New England
New England
, granite was commonly used to build foundations for homes there. The Granite Railway
Granite Railway
, America's first railroad, was built to haul granite from the quarries in Quincy, Massachusetts , to the Neponset River in the 1820s. With increasing amounts of acid rain in parts of the world, granite has begun to supplant marble as a monument material, since it is much more durable. Polished granite is also a popular choice for kitchen countertops due to its high durability and aesthetic qualities. In building and for countertops, the term "granite" is often applied to all igneous rocks with large crystals, and not specifically to those with a granitic composition.

Engineering

Engineers
Engineers
have traditionally used polished granite surface plates to establish a plane of reference, since they are relatively impervious and inflexible. Sandblasted concrete with a heavy aggregate content has an appearance similar to rough granite, and is often used as a substitute when use of real granite is impractical. A most unusual use of granite was as the material of the tracks of the Haytor Granite Tramway , Devon, England, in 1820. Granite
Granite
block is usually processed into slabs, which can be cut and shaped by a cutting center . Granite tables are used extensively as bases for optical instruments because of granite's rigidity, high dimensional stability, and excellent vibration characteristics. In military engineering, Finland planted granite boulders along its Mannerheim Line to block invasion by Russian tanks in the winter war of 1940.

Other Uses

Curling
Curling
stones are traditionally fashioned of Ailsa Craig granite. The first stones were made in the 1750s, the original source being Ailsa Craig in Scotland
Scotland
. Because of the rarity of this granite, the best stones can cost as much as US$1,500. Between 60 and 70 percent of the stones used today are made from Ailsa Craig granite, although the island is now a wildlife reserve and is still used for quarrying under license for Ailsa granite by Kays of Mauchline for curling stones.

ROCK CLIMBING

Granite
Granite
is one of the rocks most prized by climbers, for its steepness, soundness, crack systems, and friction. Well-known venues for granite climbing include Yosemite
Yosemite
, the Bugaboos , the Mont Blanc massif (and peaks such as the Aiguille du Dru , the Mountains of Mourne , the Adamello-Presanella Alps , the Aiguille du Midi and the Grandes Jorasses ), the Bregaglia , Corsica , parts of the Karakoram (especially the Trango Towers ), the Fitzroy Massif, Patagonia
Patagonia
, Baffin Island , Ogawayama , the Cornish coast , the Cairngorms , Sugarloaf Mountain
Mountain
in Rio de Janeiro, Brazil, and the Stawamus Chief , British Columbia, Canada.

Granite
Granite
rock climbing is so popular that many of the artificial rock climbing walls found in gyms and theme parks are made to look and feel like granite.

*

Life-size elephant and other creatures carved in granite, 7th–9th century A.D.; Mahabalipuram
Mahabalipuram
, India. *

Polished red granite tombstone *

Granite
Granite
was used for setts on the St. Louis riverfront and for the piers of the Eads Bridge (background) *

The granite peaks of the Torres del Paine
Torres del Paine
in the Chilean Patagonia
Patagonia
*

Half Dome , Yosemite
Yosemite
, a classic granite dome and popular rock climbing destination *

Rixö red granite quarry in Lysekil , Sweden

SEE ALSO

* Cold Spring Granite * Cheyenne Mountain
Mountain
Complex * Epoxy granite * Exfoliating granite * Falkenfelsen, or Falcon Rock * Fall River granite * Greisen * Hypersolvus * Igneous
Igneous
rock * List of rock types
List of rock types
* Luxullianite * Mourne Mountains
Mourne Mountains
* Orbicular granite * Pikes Peak granite , Colorado * Quartz
Quartz
monzonite * Rapakivi granite * Stone Mountain
Mountain
, Georgia * Subsolvus * Wicklow Mountains , Ireland
Ireland

REFERENCES

Notes

* ^ "Granitoids – Granite
Granite
and the Related Rocks Granodiorite, Diorite
Diorite
and Tonalite". Geology.about.com. 2010-02-06. Retrieved 2010-05-09. * ^ Haldar, S.K.; Tišljar, J. (2014). _Introduction to Mineralogy and Petrology_. Elsevier. p. 116. ISBN 978-0-12-408133-8 . * ^ "Basic Rock Mechanics". Webpages.sdsmt.edu. Retrieved 2010-05-09. * ^ Kumagai, Naoichi; Sadao Sasajima; Hidebumi Ito (1978). "Long-term Creep of Rocks: Results with Large Specimens Obtained in about 20 Years and Those with Small Specimens in about 3 Years". _Journal of the Society of Materials Science (Japan)_. 27 (293): 157–161. doi :10.2472/jsms.27.155 . * ^ Larsen, Esper S. (1929). "The temperatures of magmas". _American Mineralogist_. 14: 81–94. * ^ Holland, Tim; Powell, Roger (2001). "Calculation of phase relations involving haplogranitic melts using an internally consistent thermodynamic dataset". _Journal of Petrology_. 42 (4): 673–683. doi :10.1093/petrology/42.4.673 . * ^ Harvey Blatt & Robert J. Tracy (1997). _Petrology_ (2nd ed.). New York: Freeman. p. 66. ISBN 0-7167-2438-3 . * ^ Singh, G. (2009). _Earth Science Today_. Discovery Publishing House. ISBN 9788183564380 . * ^ Chappell, B. W.; White, A. J. R. (2001). "Two contrasting granite types: 25 years later". _Australian Journal of Earth Sciences_. 48 (4): 489–499. doi :10.1046/j.1440-0952.2001.00882.x . * ^ Boroughs, S.; Wolff, J.; Bonnichsen, B.; Godchaux, M.; Larson, P. (2005). "Large-volume, low-δ18O rhyolites of the central Snake River Plain, Idaho, USA". _Geology_. 33 (10): 821. doi :10.1130/G21723.1 . * ^ Frost, C.D. _et al_. (2005) " Extrusive A-type magmatism of the Yellowstone hot spot track". 15th Goldschmidt Conference Field Trip AC-4. Field Trip Guide, University of Wyoming. * ^ Weinberg, R. F.; Podladchikov, Y. (1994). "Diapiric ascent of magmas through power law crust and mantle". _Journal of Geophysical Research_. 99: 9543. Bibcode :1994JGR....99.9543W. doi :10.1029/93JB03461 . * ^ Clemens, John (1998). "Observations on the origins and ascent mechanisms of granitic magmas". _Journal of the Geological Society of London_. 155 (Part 5): 843–51. doi :10.1144/gsjgs.155.5.0843 . * ^ " Granite
Granite
". _ University College London
University College London
_. Retrieved 10 July 2014. * ^ "Hydrolysis". _ Geological Society of London
Geological Society of London
_. Retrieved 10 July 2014. * ^ Marsh, William M.; Kaufman, Martin M. (2012). _Physical Geography: Great Systems and Global Environments_. Cambridge University Press. p. 510. ISBN 9781107376649 . * ^ "Decay series of Uranium". Archived from the original on March 9, 2012. Retrieved 2008-10-19. * ^ " Radon
Radon
and Cancer: Questions and Answers". National Cancer Institute. Retrieved 2008-10-19. * ^ Hubbert, M. King (March 8, 1956) Nuclear Energy and the Fossil Fuels. American Petroleum Institute Conference. Energy Bulletin. * ^ Adams, J. A.; Kline, M. C.; Richardson, K. A.; Rogers, J. J. (1962). "The Conway Granite
Granite
of New Hampshire As a Major Low-Grade Thorium
Thorium
Resource" . _Proceedings of the National Academy of Sciences of the United States of America_. 48 (11): 1898–905. PMC 221093  _. PMID 16591014 . doi :10.1073/pnas.48.11.1898 . * ^ Steck, Daniel J. (2009). "Pre- and Post-Market Measurements of Gamma Radiation and Radon
Radon
Emanation from a Large Sample of Decorative Granites". Nineteenth International Radon
Radon
Symposium_ (PDF). pp. 28–51. * ^ Natural Stone Countertops and Radon
Radon
– Environmental Health and Engineering – Assessing Exposure to Radon
Radon
and Radiation from Granite
Granite
Countertops. * ^ Nelson L. Nemerow (27 January 2009). _Environmental Engineering: Environmental Health and Safety for Municipal Infrastructure, Land Use and Planning, and Industry_. John Wiley & Sons. p. 40. ISBN 978-0-470-08305-5 . * ^ Parmodh Alexander (15 January 2009). _A Handbook of Minerals, Crystals, Rocks and Ores_. New India
India
Publishing. p. 585. ISBN 978-81-907237-8-7 . * ^ "Modern slavery and child labour in Indian quarries - Stop Child Labour". _Stop Child Labour_. Retrieved 2016-03-09. * ^ "Modern slavery and child labour in Indian quarries". _www.indianet.nl_. Retrieved 2016-03-09. * ^ James A. Harrell. "Decorative Stones in the Pre-Ottoman Islamic Buildings of Cairo, Egypt". Retrieved 2008-01-06. * ^ "Egyptian Genius: Stoneworking for Eternity". Archived from the original on 2007-10-14. Retrieved 2008-01-06. * ^ Heitzman, James (1991). "Ritual Polity and Economy: The Transactional Network of an Imperial Temple in Medieval South India". _Journal of the Economic and Social History of the Orient_. BRILL. 34 (1/2): 23–54. JSTOR 3632277 . doi :10.1163/156852091x00157 . * ^ _A_ _B_ "Reviving Antiquity with Granite: Spolia and the Development of Roman Renaissance Architecture". _ARCHITECTURAL HISTORY_. 59: pp. 149–179. doi :10.1017/arh.2016.5 . CS1 maint: Extra text (link ) * ^ Friends of West Norwood Cemetery newsletter 71 Alexander MacDonald (1794–1860) – Stonemason, * ^ Robbins, Eleanora I. (2001). _Building Stones and Geomorphology of Washington, D.C.: The Jim O’Connor Memorial Field Trip_. CiteSeerX 10.1.1.124.7887  _. * ^ "Black granite and black marble". Trade Brochure_. Graniteland.com. Retrieved 21 May 2014. * ^ Roach, John (October 27, 2004). "National Geographic News — Puffins Return to Scottish Island Famous for Curling
Curling
Stones". National Geographic News.

FURTHER READING

* Blasik, Miroslava; Hanika, Bogdashka, eds. (2012). _Granite: Occurrence, Mineralogy and Origin_. Hauppauge, New York: Nova Science. ISBN 978-1-62081-566-3 . * Twidale, Charles Rowland (2005). _Landforms and Geology of Granite Terrains_. Leiden, Netherlands: A. A. Balkema. ISBN 978-0-415-36435-5 . * Marmo, Vladimir (1971). _ Granite
Granite
Petrology and the Granite Problem_. Amsterdam, Netherlands: Elsevier Scientific. ISBN 978-0-444-40852-5 .

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